A fundamental characteristic of biological systems is that their organisation and function are based on compartmentalisation. Biomineralisation processes, which lead to the generation of mineral-based structures such as bones, teeth and seashells are no exception to this, and it has long been recognised that biominerals form within the confines of “privileged environments” delineated from the organism, where spatial constraints and chemical conditions can be precisely controlled. Despite this, experiments aiming to mimic these processes are invariably carried out in bulk solution and usually employ soluble additives as a control strategy. Here, we adopt a different premise and demonstrate that nature may in fact use confinement as a significant route to controlling crystallisation. A series of systems including crossed cylinders, track-etch membrane pores and droplet arrays which offer confinement from the nanometer to the micron scale are used to demonstrate that confining the reaction volume can significantly affect crystal nucleation and growth processes, leading to control over features such as polymorph, morphology, orientation and single crystal/ polycrystalline structure. We also describe a novel “crystal hotel”, where this microfluidic device comprises a series of “rooms”, each of which offers an independent, structured reaction environment. Confinement therefore enables effective control over crystallization processes, and as such promises the ability to optimise the synthesis of crystalline materials such as nanostructures, to minimise undesirable processes such as scale deposition or kidney stone formation and to achieve repair over structures such as bones and teeth.

The biomineralization of living cells depends on proteins that ultimately nucleate inorganic minerals and direct their growth. This interaction of cells with extracellular matrix (ECM) proteins is essential to tissue development. However, the majority of the vital ECM proteins need surface interactions in order to begin nucleation. Fibronectin is a major ECM adhesive protein, which forms complex fibrillar structures in the presence of cells. When treated with a fibronectin solution, the high charge density surface (> 0.08 C/m²) of partially sulfonated polystyrene (SPS, 12.3% degree of sulfonation) is sufficient enough to initiate spontaneous fibronectin fibrillogenesis similar to the fibrillar networks seen to form in vivo [1]. Fibronectin, like all other ECM proteins, is polyampholytic and adsorbs to SPS after undergoing a conformation change from the electric field formed by the negative surface charge of SPS. The ability of SPS to mimic the natural fibrillogenesis process provides a suitable scaffold for tissue engineering. Dental pulp derived cells (DPCs) are highly proliferative and can be induced towards osteogenic-like differentiation, which offer potential application in orthodontic treatments. DPCs grown on 20 nm thick films of partially SPS (degree of sulfonation: 33%) were shown to have higher cell plating efficiency and enhanced differentiation than cells grown on tissue culture plastic (TCP), which is non-sulfonated polystyrene. The ECM proteins present in the serum and those secreted by the DPCs adsorbed to the SPS films similar to the aforementioned fibronectin model. Energy dispersive X-ray spectroscopy (EDXS) analysis confirmed the biomineralized deposits were crystalline calcium phosphate from the DPCs on the SPS films. Since the ECM proteins and cell membrane proteins are diamagnetic, we investigated the role of an external magnetic field on the interaction of the DPCs and the ECM. The moderate static magnetic field (SMF) of 173 mT displayed influences on early and late differentiation of the DPCs. After the first 24 hours of incubation, the DPCs on the SPS films exposed to the SMF accumulated towards the center of the scaffolds with elongated morphology. Thus forming multicellular layers and tissue-like layer at an earlier stage than the DPCs not exposed to SMF. The SMF exposed cultures on the SPS films also deposited inorganic mineral more rapidly than the DPCs on SPS and TCP without SMF exposure. These results propose how understanding the scaffold surface interactions with the cell membrane and ECM proteins will advance the design of synthetic substrates for tissue engineering.
This work was supported by the NSF INSPIRE Program.
[1] Pernodet, N., Rafailovich, M., Sokolov, J., Xu, D., Yang, N.-L. and McLeod, K. (2003), Fibronectin fibrillogenesis on sulfonated polystyrene surfaces. J. Biomed. Mater. Res., 64A: 684-692.

Biominerals exhibit morphologies, hierarchical ordering and properties that excel those of their synthetic counterparts. A key feature of biominerals, which discriminates them from simple minerals or synthetic crystals, is their nanocomposite structure resulting from an intimate association of biopolymers with the mineral host. The occlusion of non-adapted proteins may induce dramatic changes to the mechanical properties of synthetic minerals and lead to quasi-elastic behavior, whereas the natural counterparts with occlusions of adapted proteins show brittle failure. To understand and potentially apply nature&’s biomineralization strategies for a bottom-up synthesis of nanostructures, simple synthetic mimics are currently being studied. We have investigated calcium carbonate crystals grown in the presence of functionalized spherical Au or asymmetric Janus-type Au@ZnO@SiO₂ nanocrystals. CaCO₃ crystals were grown from supersaturated calcium bicarbonate solutions, containing the functionalized spherical or Janus-type nanocrystals as additive at various concentrations. The formed polymorph was in all cases calcite with a morphologies derived from rhombohedral crystals to elongated and faceted crystals with increasing particle concentrations. Most notably, during mineralization the spherical particles become included in the crystals, which could be traced by confocal fluorescence light microscopy due to the plasmon resonance of the Au component. In general, the effect on the crystallization was shown to depend on the morphology and functionalization of the nanoparticles. Wheras charged and isotropic particles are easily occluded in domain boundaries of the host crystal, anisotropic Au@ZnO@SiO₂ nanorods only induce a surface modification due to particle-particle interactions. Au@ZnO@SiO₂ nanorods show an amphiphilic behavior by forming micellar or layer-like aggregates, which could be demonstrated by light scattering. In contrast, spherical nanoparticles act as zero-dimensional templates or inclusions. The integration of the particles strongly depends on their functionalization, as demonstrated by polymer- or protein-functionalized nanocrystals. We demonstrate that the synthetic minerals are single crystals of calcite occluding spherical particles, which act as #8222;micelles“ or #8222;pseudo-proteins“. The synthetic crystals exhibit analogous texture and defect structures to biogenic calcite crystals and are harder than pure calcite.
In contrast, amphiphilic rod-like Au@ZnO@SiO₂ nanocrystals are specifically adsorbed on crystal faces and induced a change in the morphology of the host crystal. This system provides a unique model for understanding biomineral formation, giving insight into both the mechanism of the occlusion of nanoparticles and macromolecules within single crystals, and the relationship between the macroscopic mechanical properties of a crystal and its microscopic structure.

Biogenic calcite is known to be harder than pure geologic calcite and synthetic analogs have been used to investigate the effects of inclusions ranging from magnesium substitutions for calcium to large occluded polymer particles. Small molecules, such as amino acids, are intermediate, mezzo-scale inclusions that are larger than solid solution species, yet still too small to be counted as second phase particles. To investigate the effect of these intermediate scale inclusions, calcite samples containing Aspartic Acid (Asp) and Glycine (Gly) up to 7 mol% were prepared and their mechanical properties determined using nanoindentation. Samples with low amino acid concentrations were rhombohedral, but became increasingly rounded as amino acid content increased. Hardness increased with the square root of the amino acid volume density suggesting that interactions between dislocations and individual molecules determined the hardness. Indeed, a detailed analysis suggests that the force needed for dislocations to cut through the amino acid molecules determines the hardness. Furthermore the onset of surface morphology changes is correlated with the average spacing between the molecules in the crystal, suggesting that growth step pinning by the molecules causes the morphology change.

Bone and teeth are two major hard tissues in human body. These hard tissues are formed by a natural process of mineral deposition called biomineralization, which generally provides toughness to hard tissues. In extracellular matrix of hard tissues, collagen acts as an organic template to guide mineral deposition. Carbonic apatite is naturally occurring calcium apatite which acts as inorganic phase in humans. In bone and teeth, these organic and inorganic phases interact at molecular level forming hierarchical nanocomposites. However, most of the materials currently being used are just physical blends of organic and inorganic phases. Thus, there is need to fabricate materials which mimic structural hierarchy of natural tissues at nano/microscale to promote regeneration of damaged tissues.
We developed hierarchical fibrous hydrogels mimicking collagen at nano- to microscale (fibrils to fibers to fiber bundles) and studied their potential for biomineralization. In order to study role of amount of charge and charge imparting groups in biomineralization, we chose three different pairs, each with two oppositely charged polymers, for preparing hydrogel scaffolds. Hierarchical structure of hydrogels and chemical composition of deposited minerals was studied along with their chemical composition using scanning and transmission electron microscopy, X-ray diffraction and Fourier transform infrared spectroscopy (FTIR). Morphology and nature of mineral deposits also varied among the scaffolds. Mineral deposition on the surface was also found to be aligned along the length of hydrogel fibers in scaffolds. Mineral deposition, both on surface and inside the scaffolds, was orderly.
Scaffolds showed ability to sequester minerals after three days incubation in simulated body fluid. Electrostatic charges of constituent polymers of these fibrous hydrogels played important role in dictating mineral size and structure. These differences further led to different mineral deposition behavior on the surface and inside the scaffold. Interestingly, mineral deposition was orderly rather than random. These studies collectively prove collagen-mimicking ability of aligned fibrous hydrogels to guide mineral deposition in vitro. They also suggest potential of these scaffolds for promoting mineralization.

Biominerals possess shapes, structures and properties not found in synthetic minerals. The dream of exploiting the biological principles of controlled mineral formation in materials chemistry inspires a large community to investigate the underlying mechanisms through biomimetic mineralization experiments.¹ The defining characteristics of biominerals arise from the interplay of the mineral with a macromolecular matrix, which directs crystal nucleation and growth. Within this three dimensional biomolecular assembly, the developing mineral interacts with acidic macromolecules, either dissolved in the crystallization medium or associated with an insoluble templating structure.² Although acidic macromolecules are known to affect growth habits and phase selection or even to completely inhibit precipitation in solution, little is known on the mechanisms by which they alter the pathways of mineralization.
CryoTEM has proven to be a powerful tool to investigate - with great detail - organic-inorganic interactions in calcium carbonate and calcium phosphate based systems.^3-5 We now explore the formation mechanisms of magnetite (Fe₃O₄) in bio-inspired crystallization experiments and show how precursor phases can be used to control crystal nucleation and growth.⁶ Using time resolved cryoTEM were able to demonstrate how multistep nucleation pathways are altered through the influence of polypeptide based additives, which helps us to understand the underlying mechnismsm and ultimately to control the size, shape and orientation of the crystals and optimize them for specific technological applications.
However, the plunge frozen samples used in cryoTEM do not provide information on the dynamics of the organic-inorganic interactions during the crystallization process. To investigate this aspect we use in situ liquid phase transmission electron microscopy (LP-TEM) mimicking the organic matrix inside a liquid cell with two electron transparent silicon nitride (SiN) membranes. With this LP-TEM set up we were able to visualize the nucleation and growth of CaCO₃ in a matrix of polystyrene sulfonate (PSS).⁷ We observed that PSS alters the nucleation pathway through a previously suggested but not well understood mechanism. By extracting kinetic data from the recorded time-lapse series we were able to demonstrate that the PSS alters polymorph selection by acting as an ion-sponge that locally increases supersaturation, thereby effectively changing the kinetic barrier for nucleation, independent of any controls over the free energy barriers that are considered in most heterogeneous nucleation studies.
^[1] Nudelman and Sommerdijk, Angewandte Chemie-International Edition2012, 51, 6582.
^[2]Chem. Rev.2008, 108, 4329.
^[3] Pouget, et al., Science2009, 323, 1455.
^[4] Dey, et al., Nat. Mater.2010, 9, 1010.
^[5] Nudelman, et al., Nature Materials2010, 9, 1004.
^[6] Lenders, et al., Adv. Funct. Mater.2015, 25, 711.
^[7] Smeets, et al., Nat. Mater.2015, 14, 394.

Hydroxyapatite and other calcium phosphates are of particular interest as biomaterials due to their compatibility with bones and teeth. Calcium phosphate materials have been prepared and studied in a multi-stream microfluidic laminar flow device that achieves a liquid-liquid interface for controlled precursor mixing. The microfluidic device has been integrated with microscopy analysis with and without quartz crystal microbalance (QCM) to compare mass analysis with morphology of forming mineral. The instrument has been evaluated for analysis performance in a variety of conditions, demonstrating it to be a widely applicable technique and has been useful in the evaluation of biomimetic mineralization templates, including unique DNA aptamers. Analysis has revealed that rheological effects can have a significant impact on mineral formation, DNA templates enhance the kinetics of mineral formation, and DNA templates show distinct differences in heterogeneous and homogeneous biomimetic template activity.

Studying the early and intermediate stages of crystallization provides an important route to gaining mechanistic understanding but can be extremely challenging due to the rapid growth of small particles. This work addresses this challenge and describes an investigation into the effects of solution supersaturation and diffusion and flow of ingredients on crystal growth in small volume.
We introduce a microfluidic device termed a “Crystal Hotel” which was constructed from poly(dimethyl siloxane) (PDMS), the crystal Hotel comprises a series of “rooms”, each of which offers an independent closed(batch) or open(continuous feeding) reaction environment. Effects of diffusion of ingredients and impurities are also investigated by building an array of round nanoobstacles within individual room. The crystals on a substrate in the array were examined using POM, SEM and raman microscope. Addition of the soluble additives in the confined system allowed us to observe the early and intermediate stages of crystal growth more in details, showing interesting sequences of morphological evolution influenced by the additives with time. Examination of crystallization in the patterned arrays with time revealed that due to limited ingredients and diffusion, CaCO₃ crystallization proceeded significantly more slowly, and limited nucleation events occurred creating large single crystal patch within a room.
This approach could provide a unique opportunity to study heterogeneous nucleation and crystal growth on directly on desired substrate in environments where the volume and reservoir was controlled. The results are significant for biomineralization processes, where mineral formation occurs both within compartments and in association with organic matrices, showing that the environment in which a crystal forms can have a significant effect not only on its morphology and orientation but also on the rate of crystallization.

Calcite (CaCO3) of biological origin, such as the shells of mollusks, has been shown to exhibit higher hardness and toughness, compared to that of geologic origin. This strengthening is likely due to the synergistic effect of multiple mechanisms, and efforts are being made to evaluate possible strengthening mechanisms using synthetic analogues. One possible explanation for the observed strengthening in biogenic calcite is defects left behind by growth via an amorphous calcium carbonate precursor (ACC growth), rather than by traditional ion-by-ion growth. ACC growth is known to be favored at higher supersaturations and faster growth rates. We have designed a synthetic system in which the growth rate is systematically varied and measured in-situ via optical microscopy. The mechanical properties of the resulting crystals are evaluated by a nanoindentation technique that accounts for the small size and irregular shapes of the crystals. The connection between growth mechanism and hardness, including the role that ACC growth plays in the strengthening of single crystals of calcite, will be discussed.

Calcium carbonate is known to form through an amorphous precursor, previously thought to be unstable and now considered a critical stage before it reaches its final crystalline form. Many organisms in nature are able to stabilize this amorphous precursor and crystallize it at-will to form highly ordered and functional structures. The interactions between the organic polymer matrices in these organisms are believed to play a major role in exerting control over the stabilization of the amorphous phase, as well as the morphology and functionality of the final crystalline phase. Deciphering these polymer-mineral interactions is of great interest for the development of smart biomimetic materials.
Previous light-scattering measurements of calcium carbonate&’s precipitation have been limited by the overlapping turbidity, sedimentation and crystallization of calcium carbonate. A Transmission Interferometric Adsorption Sensor (TInAS) is an efficient technique that provides real-time measurements of surface-adsorbate interactions.¹ However, traditional TInAS measurements do not perform well under conditions of varying light intensity and surface roughness, through crystallization, for example. A modified, yet simple, TInAS setup is proposed to study the formation/sedimentation of calcium carbonate at a surface with different chemistries tuned with biomimetic polymers. The total absorbance is recorded during ACC formation, growth, sedimentation and crystallization. These novel measurements provide a fast and simple way of determining the kinetics involved in calcium carbonate formation under different conditions and varying surface chemistries.
1. Heuberger, M.; Balmer, T. E., The transmission interferometric adsorption sensor. Journal of Physics D: Applied Physics 2007,40 (23), 7245

Hard and soft structural composites found in biology provide inspiration for the design of advanced synthetic materials. This talk focuses on the development of hard/soft engineering composites in 2D and 3D configurations that can be (1) tailored precisely to match the non-linear mechanical properties of biological tissues, with application opportunities that range from soft biomedical devices to constructs for tissue engineering and (2) designed into extended, open 3D topologies, reminiscent of neural networks in the brain, with potential use in neuroscience research.

Nature has provided us with exemplary models of self-healing materials including our own bodies which produce scar tissue at injured areas, plants which demonstrate harmonized cellular growth to renew damaged sites, and even some animals that completely regrow lost appendages. In this study, we emulate nature by synthesizing a novel, cement-based porous nanoparticle loaded with sealant material which, upon exposure to mechanical stress, heat, or other stimuli, releases into the surrounding space to ‘heal&’ the material. We demonstrate, for the first time ever, a new type of programmable nanomaterial that can act as both a self-healing filler and strength reinforcement. The self-healing efficiency of a number of different sealant materials and nanoparticle compositions on a variety of bulk materials and their properties (strength, permeation, etc.) are investigated. Our preliminary results reveal a promising nanomaterial that opens up a new phase space of multifunctional, self-healing structural materials.

Self-assembly of proteins and inorganic nanoparticles driven by weak interactions opens the door for engineering organic-inorganic analogs of cellular organelles comprised of diverse components and with integrated functionalities. Such systems are fundamentally and technologically attractive due to their uniformity, versatility and simplicity of preparation. To demonstrate such assemblies, we combine ~3.4 nm FeS₂ nanoparticles with ~5 nm protease protein and observe spontaneous formation of spherical supraparticles with a narrow size distribution containing both components. Assembly was originated from the competition between electrostatic repulsion and non-covalent attractive interactions. Non-covalent interactions between protease and like-charged NPs lead to drastically different self-assembly behavior previously unseen for each component individually, and which mimics the cooperative assemblies of proteins. We also demonstrate remarkable that the catalytic curve profile has changed, but the catalytic activity is retained in a determinate temperature and pH.
Examination by scanning electron microscopy (SEM) and transmission electron microscopy (TEM) of 1:3 FeS₂ NPs-protease assembly reveals the formation of uniformly sized, spherical SPs with a TEM diameter of 112 ± 13nm which matches the diameter determined from Dynamic light scattering (DLS). Image of individual NP inside a SP can be distinguished by its crystal lattice with periodicity of 0.26nm. Besides the SPs were investigated by tomography 3D and the overall attractive potential between the similarly charged FeS₂ NPs and Protease is investigated by theoretical calculations. Further were examined the effect of ionic strength and temperature of assembly on the diameter of the SPs. Various spectroscopy data were performed which shows the positions of all peaks in the UV-Visible / Circular Dichroism spectra remain unchanged, indicating that the electronic state and conformation of the protease molecules in the SPs are preserved.
Catalytic activity of FeS₂-protease SPs using casein as substrate at pH 11 and at 4°C and 20°C showed a huge catalytic curve profile change, demonstrating that Superstructures display complex internal organization and can incorporate biological component which retains its functionality.

Polymers are susceptible to damage in the form of small cracks, which are often difficult to detect. In coatings, corrosion and other forms of environmental degradation initiate at the damage site, compromising the underlying substrate material. In fiber reinforced polymer composites, barely visible impact damage can lead to significant degradation in mechanical performance. Here we introduce a microcapsule-based scheme for autonomous detection of damage in polymers and polymer composites. The concept is first demonstrated for an epoxy coating which incorporates an encapsulated reporting agent, 2&’,7&’-dichlorofluorescein (DCF). Upon damage, the DCF is released into the crack plane. An intense, highly localized color change is triggered by reaction of the DCF with residual amines in the epoxy coating. The color change is highly stable and the intensity depends on the size and concentration of reporter capsules, as well as the size of the damage. Cracks as small as 10 mu;m are successfully detected. The introduction of a second type of microcapsule filled with amine enables autonomous damage indication in a range of polymeric coating materials. Work is in progress to combine the ability to detect virgin damage with an additional indicating repsonse to reveal crack healing events.

Bone is a composite material, comprised of collagen protein as the main organic component and hydroxyapatite (Ca₁₀(PO₄)₆(OH)₂, HAP) as the inorganic, mineral phase.¹ Collagen molecules self-assemble to form fibrils, in which the individual molecules are arranged in three-dimensions to form a pseudo-hexagonal array. The fibrils provide the organic matrix and serve as the scaffold within which mineralization occurs.² This structure offers outstanding biomechanical properties to bone. Thus, the mechanism of bone structure formation has attracted many attentions in different fields from chemistry and biology to biomaterial sciences and bioinspired engineering. Several non-collagenous proteins, which are present in the extracellular matrix, may regulate biomineralization, but their specific functions are not known. Some proposed roles in the literature include aiding collagen fibrillogenesis, as well as the nucleation and growth of HAP crystals.³ Here we examined the role of a non-collagenous protein, osteocalcin (OCN, 5.8 kDa), on collagen fibrillogenesis and HAP formation. Collagen molecules were reconstituted in the presence of OCN. It was shown by transmission electron microscopy that collagen fibrils formed in the presence of low OCN concentration (0.25 mg/ml) had a diameter of ~ 150 nm and the characteristic periodic, pseudo-hexagonal structure. However, fibril formation was disrupted in the presence of high OCN concentration (1 mg/ml). Fibrillogenesis was also monitored by turbidity measurement and quantified by hydroxyproline assay, and the results were consistent. We hypothesized that OCN can enter the collagen fibrils during self-assembly, and, thus, inhibit the fibril formation, since its size is small enough to fit in the intrafibrillar space in the collagen matrix. To support this hypothesis, immunocytochemistry was used to localize OCN molecules. Furthermore, mineralization within collagen matrix in the presence of OCN was conducted in a solution supersaturated with HAP in the absence and presence of fetuin, a 48 kDa protein, which is known as an inhibitor for mineralization. Fetuin inhibited extrafibrillar mineralization, suggesting that it was too large thus excluded from collagen fibrils.⁴ The results showed that HAP grew exclusively within the collagen fibrils in the presence of fetuin and OCN. In conclusion, the study proved that OCN may disrupt collagen fibrillogenesis and may also have a potential role in intrafibrillar mineralization. This knowledge of biomineralization process will benefit the design of bioinspired structural materials, such as self-assembled biomimetic peptides, and the biomimetic control for HAP formation in bone tissue engineering.
References
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Biomimetics is the study of biological systems in order to find out smart solutions for complex technological challenges [1]. The cutting edge application of biomimetics regards the micro- and nanoscale, since inherent limitations of fabrication techniques often prevent the replication of complex hierarchical microstructures, as found in nature. We present here some examples of artificial bioinspired functional surfaces, having peculiar properties such as self-cleaning, water harvesting, air retention, dry adhesion, antifouling, water drag reduction and structural coloration. The fabrication approach is direct laser lithography (DLL), based on two-photon absorption, allowing the three-dimensional fabrication in the microscale with nanometric resolution [2].
The first type of artificial surface, is inspired by the leaves of Salvinia Molesta leaves, an aquatic floating fern. These leaves show the ability of self-cleaning, due to super-hydrophobicity, and air retention when submerged by water [3]. These features are due to the presence on the leaf surface of hairs capped with a crown-like head of about 500 µm in height. Arrays of salvinia hairs were reproduced with DLL about 100 times smaller than in the biological model. Nevertheless such surfaces showed not only the same properties of the salvinia leaves in terms of air retention and hydrophobicity, but also the capability of promoting the condensation of the water present in the atmosphere (fog harvesting). Similar fog-collecting properties, were also tested with artificial surfaces, inspired by the exoskeleton of Stenocara, a desert beetle characterized by a randomly distributed array of circular bumps on top of a smooth surface.
Structures for dry adhesion were fabricated taking the gecko foot skin as inspiration. The multilevel hierarchical conformal structure of the artificial gecko setae can enhance, thanks to nanometric features, short range interactions, producing attractive Van der Waals forces.
DLL has been used also for the fabrication of patterned surfaces for water drag reduction, inspired by the shark skin which is covered by minute dermal micrometric denticles, aligned parallel to the flow direction of the water. The reduction of hydrodynamic drag is a feature that can potentially be exploited in different fields, such as microfluidics or bioengineering.
[1] B. Bhushan. Biomimetics: Lessons from Nature - an Overview. Philos. Trans. R. Soc. Math. Phys. Eng. Sci. 367: 1445-1486 (2009).
[2] A. Marino et al. Biomimicry at the nanoscale: Current research and perspectives of two-photon polymerization. Nanoscale, 7: 2841-2850 (2015).
[3] W. Barthlott. The Salvinia Paradox: Superhydrophobic Surfaces with Hydrophilic Pins for Air Retention Under Water. Advanced Materials 22: 2325-2328 (2010).

With increasing amounts of CO₂ in the atmosphere linked to potentially catastrophic climate change, it is critical that we find methods to permanently sequester and store CO₂. Inspired by the natural biomineralization of calcium carbonate (CaCO₃), one future goal of this project is to understand the mechanisms of CaCO₃ mineralization in order to ultimately optimize a bioinspired hydrogel system, which produces high value industrial powders that consume CO₂ as a feedstock. Along the way, we are developing a rheological technique to study mineral nucleation and growth events by measuring the modulations in mechanical properties of a hydrogel system during mineralization. Our initial system consists of a gelatin hydrogel matrix, which is preloaded with calcium ions, and an aqueous solution of carbonate ions, which are allowed to diffuse through the gel to initiate the mineralization process. In order to monitor how the growth of minerals affects the mechanical properties of the gel network, we measure the storage (G&’) and loss (G”) moduli of the system in situ. Future work will focus on modifying the properties of the minerals formed by changing the polymer used in the hydrogel network and adding other organic molecules into the system. Thus, we will eventually be able to tailor hydrogel systems to produce a wide variety of CaCO₃ powders with different polymorphs and morphology, which can be used for industries such as plastics, paper, cosmetics, paints, and pharmaceuticals.

Among minerals on Earth, calcite, the most stable polymorph of calcium carbonate, is one of the most abundant species. Elucidating the interfacial properties of calcite in nanoconfinement help understand better the critical mechanisms underlying biomineralization in confined spaces, such as in cells and pores in scaffolds.
In this work, direct force measurements have been conducted on a calcite substrate in i) water, ii) saturated calcium carbonate solution, and iii) in a mixture of MgCl₂ and CaCl₂ solutions by Atomic Force Microscopy (AFM). DLVO and non-DLVO forces are identified and modeled, and they provide a unique insight into the properties of nanoconfined calcite interfaces in aqueous systems.
The Poisson-Boltzmann (PB) equation is applied to model the diffuse layer of a system comprised of dissimilar surfaces in the presence of divalent ions which provides the surface potential, and surface charge at the selected conditions as the two interfaces are in close proximity. Time-dependent force isotherms reveal how changes take place in surface properties during calcite dissolution and re-precipitation. Besides, these kinetic studies also show a perturbation of the electric double layer upon nanoconfinement, and the time required to re-equilibrate; both ion condensation and pressure-solution upon nanoconfinement help to explain the observed phenomena. At surface separations smaller than ~2 nm a hydration force is observed as a stronger repulsion with superposed steps that result from the squeezing out of surface-adsorbed layering species. We identify both the layering species from the size of the steps, and the energy required for the film-thickness transition to happen, which is related to the surface dehydration at the investigated aqueous conditions. The experimental observations are further supported by Quantum Chemistry calculation of calcium carbonate hydration.
Our study of nanoconfined calcite interfacial structure by AFM provides a new means to investigate molecular-scale phenomena underlying biomineralization.

The hydration shell of calcium carbonate is believed to play a significant role during its early stages of formation and growth. Ab-initio computational techniques are a powerful tool that can probe the energetics and optimal conformations of calcium carbonate hydrated clusters. Ab-initio studies of the hydration of calcium carbonate have been rather limited, especially in the conditions in which calcium carbonate&’s amorphous precursor can form.
Conformational searches for equilibrium structures of large hydrated clusters are challenging and computationally expensive due to the existence of multiple local energy minima. Extensive conformational searches of gas-phase hydrated calcium carbonate clusters were performed using an efficient multi-level optimization approach. Low energy candidates were identified by Monte Carlo searches, which were further optimized with Density-Functional based Tight Binding (DFTB+) and DFT software at the B3LYP/6-311G(d,p) levels. Selected structures were also reoptimized using Moller-Plesset perturbation theory (MP2) to independently verify the relative energies of the hydrated clusters. Structural and energetics analysis allow for determination of the first hydration shell of calcium carbonate and its corresponding binding energies. Besides, the solvation of calcium carbonate in bulk water was also investigated using a hybrid approach in which the microsolvated calcium carbonate clusters are reoptimized in a polarizable continuum model (PCM).

Achieving tight integration of semiconductor-based biomedical devices with biological components is challenging, but is central to signal transduction in electrical sensing and stimulation. Current approaches include conjugation of adhesive biomolecules on device surfaces, and implementation of advanced device geometry and mechanics designs. Natural skeletal elements or extracellular matrices have mesoscale features that are known to promote cellular interactions. Synthesis, however, of semiconductors with well-defined three dimensional mesostructures that can replicate the complexity of natural biomaterials still remains a daunting challenge. Advances in this area require a new synthetic concept and possibly new molecular or even atomic scale components to enable interfacial organization. Herein we utilize biomineralization as a guide, and develop a modular deposition-diffusion-incorporation approach for direct chemical synthesis of mesostructured skeleton-like spicules made of silicon. Electron tomography shows that silicon spicules have three-dimensional tectonic motifs, reduced symmetries, and curvilinear open frameworks with gradient. Atom probe tomography and other quantitative measurements indicate the existence individual gold atoms in controlling patterned interfaces and spicule morphogenesis. We demonstrated that silicon spicules form robust and flexible interfaces with cellular protrusions. When interfacing with collagen hydrogels, synthetically enabled mesostructures in silicon lead to enhanced detachment force and work, suggesting enhanced bio-interfaces.

Magnetotactic bacteria represent a fascinating model organism for the controlled mineralization and organization of magnetic nanoparticles. These microorganisms form a structure, which is called magnetosome and consists of magnetite, and/or greigite nanoparticles, proteins and a membrane. The magnetosomes are aligned by a bundle of filaments along the long axis of the bacteria to form the magnetosome chain and act as miniature compass needles. Such magnetosome chains were shown to have e.g. superior contrast properties in MRI ¹.
We performed biomimetic synthesis in the presence of biological determinants, related to organic compounds of the MTB, to control the dimension and structure of magnetite nanoparticles. The synthetic route leads to the formation of colloidaly stable magnetite nanoparticles forming a “chain-like” structure. Magnetite particles within this structure are highly monodisperse and XRD measurements confirm that the diameter of these particles is similar to that of magnetosomes in magnetotactic bacteria.
However, electron microscopy images show that these nanoparticles are built from aggregated individual subunits in a consensus crystallographic orientation. We therefore studied the magnetic properties of magnetite nanoparticles, known to be essentially size-dependent. Magnetite particles with diameter le; 25 nm are superparamagnetic. In this case, magnetite nanoparticles have to be placed in an external magnetic field to exhibit measurable magnetic properties. Particles whose diameter lies between 25 nm to 80 nm fall under the category of stable single domain. A ferrimagnet in which the magnetization does not shift across the magnet has this SSD behavior.
Our magnetite particles exhibit a mixture of SP and SSD behavior, suggesting a structure made of a mixture of particles in different size ranges. The entire particle itself provides a SSD behavior due to a mean grain size of ~40 nm. However, smaller individual subunits within one single particle exhibit SP behavior due to their sizes, less than 10 nm in diameter.
1 E. Alphandéry, S. Faure, O. Seksek, F. Guyot and I. Chebbi, ACS Nano, 2011, 5, 6279.

The nature of disorder characterising the metastable vaterite polymorph of CaCO₃ has been debated in the literature for many years. This phase is extremely important as it is naturally produced on the surface of many living organisms to form a ‘semi-amorphous&’ nanoparticle interface between the exterior of the organism and specific active biomolecules. Furthermore, recent computational and synthetic studies have suggested that CaCO₃ polymorphs can grow under both biogenic and abiotic conditions, and this has challenged the models of classical nucleation theory that have underpinned the conventional understanding of the formation of CaCO₃.^1-4
The biggest problem confronting our understanding of vaterite structure is the clear lack of agreement between the structures proposed by characterisation techniques (such as X-ray diffraction, transmission electron microscopy and Raman spectroscopy) and those predicted as energetically favourable by ab initio computational methods.
This stark lack of agreement has motivated research into complex models for vaterite extending beyond the notion of vaterite as a unique crystallographic structure. These propose the existence of at least two different crystallographic forms in domains that co-exist within a pseudo-single crystal⁵ or higher order superstructure involving various possible stacking&’s of the carbonate layers. Such stacking models comprise of isolated vaterite structures that fall within one of three approximately isoenergetic superbasins.⁶
Short range information provided by solid state NMR provides sufficient information to distinguish between these basins. We report 1D and 2D ¹⁷O and ¹³C MAS NMR measurements, in combination with GIPAW DFT calculations (atomistic scale) and a statistical stacking model to elucidate the average nature of the vaterite structure on larger length scales. By this combined approach, we present evidence that synthetic vaterite consists of stacking consistent with only one of the low energy superbasins.
¹ B. Hasse, H. Ehrenberg, J. C. Marxen, W. Becker and M. Epple, Chem.-Eur. J., 2000, 6, 3679.
² T. Ogino, T. Suzuki and K. Sawada, Geochim. Cosmochim. Acta, 1987, 51, 2757.
³ J. D. Rodriguez-Blanco, S. Shaw and L. G. Benning, Nanoscale, 2011, 3, 265.
⁴ D. Gebauer, P. N. Gunawidjaja, J. Y. P. Ko, Z. Bacsik, B. Aziz, L. J. Liu, Y. F. Hu, L. Bergstrom, C. W. Tai, T. K. Sham, M. Eden and N. Hedin, Angew. Chem., Int. Ed., 2010, 49, 8889.
⁵. L. Kabalah-Amitai, B. Mayzel, Y. Kauffmann, A.N. Fitch, L. Bloch, P.U.P.A. Gilbert, B. Pokroy, Science 340 ,2013, 454-457
⁶. R. Demichelis, , P. Raiteri, J. D. Gale, R. Dovesi, Crystal Growth & Design ,2013,13(6): 2247-2251

Many surfaces in nature have superhydrophobic self-cleaning properties, such as the lotus plant and water strider legs [1, 2]. On those surfaces, water forms marble-like shapes and rolls off and picks up dirt, viruses and bacteria. To achieve superhydrophobicity, the surfaces are usually textured combined with low water affinity. However, such surfaces will lose self-cleaning ability when exposed to oil or mechanically abraded. Although superamphiphobic surfaces could stop oil contamination [3], it is still not applicable to lubricating components such as bearings and gears. Here, we have developed a paint-like suspension of perfluorosilane-coated TiO₂ nanoparticles that can be applied on both hard and soft substrates to create a self-cleaning surface. Self-cleaning properties function even after oil lubrication because the treated surfaces had gained a slippery state [4]. Surface robustness can be dramatically promoted by bonding the paint with commercial or industrial adhesives; the idea is to use more sophisticated adhesive techniques to overcome weak robustness of superhydrophobic surfaces. The surfaces remain water repellence after finger wipe, knife scratch and even multi-cycles of sandpaper abrasion. The formulations developed can be used on glass, metal, wood, clothes and paper for a myriad of self-cleaning applications.
For details please refer to Y. Lu et al., Science 347, 1132 (2015).
References
[1] W. Barthlott, C. Neinhuis, Planta202, 1(1997)
[2] X. Gao, L. Jiang, Nature432, 36 (2004)
[3] A. Tuteja et al., Science318, 1618 (2007)
[4] A. Grinthal, J. Aizenberg, Chem. Mater. 26, 698 (2014)

The materials properties of bulk metal-ligand coordinate polymer gels have been actively studied in the field, with increased understanding and control of their self-healing, mechanical, and optical properties. It is less clear, however, how metal-ligand coordinate polymer networks would behave at a soft interface or in thin-film form. We present a thin-film synthesis method for metal-ligand coordinate polymer systems inspired by the adhesive chemistry and structural characteristics of mussel byssal threads. The materials properties of our model system are compared to those of the bulk gels. By studying these systems, we can design unique soft interfacial materials for biomedical applications such as sealants, coatings, and biosensors.

The lossless and controllable manipulation of liquid droplets with different volume has great promising applications in the fields of localized chemical reaction and biochemical separation. In recent years, extreme wettability surface has been verified as an effective solid surface to realize the lossless transfer of liquid droplets. However, most of the methods using extreme wettability surface is hard to realize the reversible and volume-controllable lossless manipulation. Here, we developed a new pressure-driven method to lossless manipulate underwater oil droplets with controllable volume. First, electrochemically anodic etching and boiling water immersion were used together to obtain underwater superoleophobic Al rod with long time stable superhydrophilicity in air (more than 1 year). A hole with diameter of 1 mm was bored in the middle part of superoleophobic Al rod to install pressure soft tube. Under the pressure driving, oil droplets with different volume from 1µL to 30µL were easily and precisely manipulated from one place to another several places. The largest volume of the oil droplet was not depended on adhesive force of the surface but depended on the penetration pressure of micro/nanometer-scale structures of the surface. This volume was simulated according to the cross-sectional view of SEM images. The main composition of the micro/nanometer-scale structures was characterized by XRD to analyze the reason of the long time stable superhydrophilicity in air and superoleophobicity under water. The strategy shows better potential application than other methods.

Combining unique mechanisms of different species in nature within a single material/coating has been rarely pursued in the fields of biomimicry and bio-inspired engineering.^[1] A recent notable example of cross-species inspiration is a reversible wet/dry adhesive inspired by the adhesion mechanisms of geckos and mussels.^[2] The functionality of the bio-inspired adhesive outperforms many of the existing adhesive systems. Combining multiple natural mechanisms within a single material would lead to new bio-inspired interfacial materials with novel functions that would not have been achieved by mimicking a single biological species alone. Inspired by the wax regeneration ability of plant leaves ^[3] and the slippery surfaces of the Nepenthes pitcher plants ^[4,5], we have developed robust omniphobic coatings that can self-repair under thermal stimulation even under large area physical and chemical damage. We have studied and characterized the performance and underlying mechanism of the thermal-healing property in detail. These thermally self-healing omniphobic coatings can be applied onto a broad range of metals, plastics, glass, and ceramics of any shapes, and show excellent repellency towards aqueous and organic liquids.
References
[1] Tak-Sing Wong, Taolei Sun, Lin Feng & Joanna Aizenberg, Interfacial materials with special wettability, MRS Bulletin. 38, 366 - 371 (2013).
[2] Lee, H., Lee, B. P. & Messersmith, P. B. A reversible wet/dry adhesive inspired by mussels and geckos. Nature448, 338-41 (2007).
[3] Koch, K., Dommisse, & Barthlott, W. Chemistry and Crystal Growth of Plant Wax Tubules of Lotus (Nelumbo nucifera) and Nasturtium (Tropaeolum majus) Leaves on Technical Substrates. Cryst. Growth Des.6, 2571-2578 (2006).
[4] Bohn, H. F. & Federle, W. Insect aquaplaning: Nepenthes pitcher plants capture prey with the peristome, a fully wettable water-lubricated anisotropic surface. Proc. Natl. Acad. Sci. U. S. A.101, 14138-14143 (2004).
[5] Tak-Sing Wong, Sung Hoon Kang, Sindy K. Y. Tang, Elizabeth J. Smythe, Benjamin D. Hatton, Alison Grinthal & Joanna Aizenberg, Bioinspired self-repairing slippery surfaces with pressure-stable omniphobicity. Nature477, (2011).

The catecholic amino acid 3, 4-dihydroxyphenylalanine (DOPA) is known to play an important role in strong and enduring wet adhesion for underwater attachment systems of e.g. mussels and sandcastle worms. Much effort has been taken to mimic the adhesion properties by synthesizing polymers functionalized with catechol groups. A common synthesis method is free radical polymerization of vinyl monomers bearing an un-protected catechol group. However, catechol groups are known to be radical scavengers. This scavenging ability may trigger the catechol to react with the propagating radicals and consequently result in the formation of branched polymer chains. In previous work, the structure of the obtained polymer is presented as a linear polymer chain and little discussion was presented on possible side reactions. In our work, catechol-functionalized polymers are synthesized by free radical polymerization of dopamine methacrylamide (DMA) and 2-methoxyethyl methacrylate (MEA) at 60 °C in DMF. By varying the DMA content in the polymer, it is found that during free radical polymerization, the catechol groups in DMA react with the propagating radicals, resulting in the formation of a crosslinked structure. We systematically study the effect of DMA content and crosslinking on the adhesion properties of the polymer. Under both dry and wet conditions, maximum adhesion is obtained for a polymer composed of 5 mol% DMA. This polymer exhibits an optimum balance between catechol content to strengthen the interface, compliance to ensure good contact formation and cohesive strength to resist separation. An increase in the crosslinking degree of the polymer resulted in reduced dry adhesion.

The development of biomaterials with antibacterial surfaces which suppress bacterial colonization and proliferation is of profound importance for biomaterial applications. The bacterial growth may result in formation of biofilmswhich protect the microorganisms against host defensemechanisms and also make the antibiotic treatments difficult.Recently,an interesting example of an antibacterial effect based solely on a special nanostructured patternwasdiscovered in the wing of Clanger cicada(Psaltodaclaripennis)¹.The wing surfaceis covered by a hexagonal array of nanopillars. This nanostructured surface destroysthe gram-negative bacteria by a physical-mechanical effect due to the nanopillars pattern.The aim of this study was to implementthisphysico-mechanical antibacterial effect to metallic thin-film biomaterials. Titanium (Ti)nanocolumnar surfaces (~ 400 nm thick) were fabricatedby glancing angle sputter deposition (GLAD) on silicon substrates. Usingthe GLAD technique, an obliquelyincident particle flux β (usually β ge; 80^°, with respect to the substrate normal) leads to the growth of a highly porous, columnarfilm as a result of strong influence of self-shadowing mechanism.A dense and smooth Ti thin film (~ 100 nm thick) was also fabricated as a reference sample by a confocal magnetron sputtering technique. Two different types of bacteria, i.e. S. aureus as well as E. coli, were cultured with nanostructured or reference Ti thin-film samples for one and three hours under cell culture conditions at 37°C. Bacterial adherence, morphology, and viability were analyzed by fluorescence staining (BacLight) and scanning electron microscopy (SEM).Furthermore, the viability and proliferation of the human mesenchymal stem cells (hMSCs) as well as the human peripheral blood mononuclear cells (PBMCs) were investigated. In contrast to S. aureus the viability of E. coli was significantly decreased after 3 h of the cell culture on the nanostructured film compared to the dense film. An irregular morphology of the E. coli bacteriaaccompanied by a cell wall rupture was detected on the Ti nanostructured surfaces. Interestingly, the cell adherence, spreading and viability of hMSCs and PBMCswere not affected on the nanostructured surface. This study demonstrates that the selective antibacterial effect of the cicada wing could be transferred to a nanostructured metallic thin-film biomaterial by mimicking the natural nanocolumnar topography².
References
¹Ivanova EP, Hasan J, Webb HK, Truong VK, Watson GS, Watson JA, Baulin VA, Pogodin S, Wang JY, Tobin MJ, Lobbe C, Crawford RJ. Natural bactericidal surfaces: mechanical rupture of pseudomonas aeruginosa cells by cicada wings. Small 2012; 8: 2489-94
²Sengstock C, Lopian M, Motemani Y, Borgmann A, Khare C, Buenconsejo PJS, Schildhauer TA, Ludwig A, Köller M. Structure-related antibacterial activity of a titanium nanostructured surface fabricated by glancing angle sputter deposition. Nanotechnology 2014; 25, 195101.

The brilliant iridescent blue of the Morpho Rhetenor butterfly is a result of structural color created by complex nanostructures found on the surface of its wings. The cross section of this nanostructure resembles arrays of “pine trees” with their branches (lamella) and surrounding medium forming a multilayer stack. The Morpho butterfly exhibits strong short wavelength reflection and a unique two lobe optical signature in the incident (theta;) and reflected (phi;) space. These 3D photonic structures have proven difficult to replicate. Here, we report the large area fabrication of a Morpho like structure and its replication in Perfluoropolyether (PFPE). Polymer replicas display wavelength select reflection akin to the butterfly&’s, determined by the fabricated dimensions of the structure. Reflection comparisons of periodic and semi random polymer artificial butterfly nanostructures show similar spectrums but differ in the angular theta;-phi; dependence. The semi random sample is shown to produce a two lobe angular reflection with minimal specular refection, in close proximity to the actual butterfly optical behavior. FDTD simulations confirm this is a result of the quasi-random periodicity and shows the significance of the inherent randomness in the Morpho&’s photonic structure.

Second-degree burns often cause dehydration, blisters, scarring and pain. If not directly treated, there is a high risk of infection and other possible complications. Current methods for the treatment of superficial to second-degree burns rely on the use of wound dressings such as bandages, hydrogels, foams, sponges, etc. However, none of the conventional dressings has the capability of dissolution when it is changed, reducing the pain often felt with conventional dressings. We have developed a hydrogel-based burn dressing for the treatment of second-degree burn wounds that will provide a barrier to infection and promote wound healing. Its controlled dissolution into safe by-products will allow for on-demand dressing removal and re-exposure of the wound without the need for mechanical debridement and cutting. The burn dressing will absorb wound exudates, maintain a highly moist environment for faster healing, possess elasticity to accommodate movement, lessen trauma to the wound during dressing changes, and protect it from infections. Most importantly, unlike every burn dressings in use today, it will be removed painlessly from the burn site by dissolution via exposure to an aqueous cysteine solution (a thiol-thiolester exchange mechanism). The studies are motivated by our preliminary data demonstrating the synthesis and characterization of an on-demand dissolvable burn dressing and its successful performance in a pilot in vivo study.

Many geometric patterns are seen in the natural world, including patterns that take form spontaneously by self-assembly. Among these, the“wrinkle”structure is very commonly seen on the surface of a leaf, on skin and brain. In this study, we tried to prepare various wrinkle structure using original 3D-streching method based on bioinspired surface buckling: additional mechanical factors in the outer layer of our cells play a large role in the formation and the morphogenetic process of our bodies and tissues. It found that surfaces with different properties—an ultra-water-repellent and high-adsorption area and an ultra-water-repellent area—can be generated on the basis of two different pattern structures by applying water-repellent coating to the wrinkle film. Moreover, we succeeded fabrication of film with highly adhesive superhydrophobic surface and SERS activity. The results of this study will not only contribute to resolving issues of
conventional top-down lithography techniques but will also be applicable to environmental, water-saving, medical and many other fields.

Inspired by natural fauna and flora, scientists have used a wide variety of methods to fabricate artificial superhydrophobic surfaces. Natural superhydrophobic surfaces are not very robust; they are easily oxidized, lose their properties under abrasion, and transition to the Wenzel state in heavy rain. A wide variety of techniques have been reported to fabricate superhydrophobic surfaces, however there are few reports that discuss their durability. By forming synthetic materials with low surface energy and high chemical/mechanical stability into a hierarchical texture, superhydrophobic surfaces could be fabricated that are sufficiently stable for industrial applications. Thus, it should be possible to create synthetic superhydrophobic materials with mechanical, chemical and morphological properties that are far beyond those of natural superhydrophobic surfaces.
In this paper, we will present a novel method for fabricating superhydrophobic surfaces with a significant degree of hierarchical roughness that imparts excellent mechanical stability. The properties of surfaces fabricated with different roughness values are quantified with respect to frictional abrasion, rain erosion, water immersion and chemical exposure tests. Due to the lack of standards, testing superhydrophobic surfaces is often application specific. We detail the development of a rain erosion test, quantifying drop diameter and drop velocity distribution using a high-speed camera and comparing experimentally generated results to those of natural rainfall. The precipitation rate of the accelerated rain test is 200 mm/min so 7 minutes of exposure is equivalent to approximate one year of rainfall in New York City (1267 mm/year). Similarly we detail an anti-icing test to simulate resistance of superhydrophobic surfaces to ice accretion from super-cooled water droplets at different tilt angles and substrate temperatures. In addition, we use a Taber mechanical abraser to quantify abrasion resistance. The degradation mechanisms of the surfaces of these surfaces under these accelerated test conditions will be discussed.

The recent advances in the preparation technique of superhydrophobic surfaces have brought new functionalities to various polymers for future applications. However, still versatile and cost-effective preparation methods are needed for their commercialization. In this study, we explored the possibility of crystallization-based methods to prepare superhydrophobic surfaces of various polymers. Directional melt crystallization (DMC), a relatively new method for porous materials preparation, was modified to treat polymer surfaces. Various polymers such as polystyrene, polyvinyl alcohol, polycarbonate and polyurethane were successfully processed into materials having highly porous surfaces by DMC. We first dissolved polymer surfaces by proper solvents and then rapidly crystallized the solvents under a directional temperature gradient. In the crystallization step, the cooling rate of polymer surfaces was found to be an important parameter, so we controlled freezing rate by pre-cooling polymer surface method. The key achievement of our study is that we successfully prepared treated polymer surfaces of porous and rough surfaces. In addition, we pretty confirmed changing modified surface morphology as for changing freezing rate and polymers. We also confirmed that the hydrophobicity of treated surfaces increased. For example, PS contact angle degree was increased to about 140#730; from 80#730;. With this versatile method, various polymer surfaces can be treated conveniently without complex and delicate processing steps.

Forces generated by living cells are key to structure formation in cellular environments. To investigate such forces, hydrogel-based traction force microscopy (TFM) and soft substrates such as PDMS micropillars are often used.^1,2,3 However, these methods are of limited accuracy in the measurement of cell traction forces. The resolution of TFM depends on the elasticity of the substrate, and its optical resolution is deeply influenced by the position of fluorescent nanoparticles used as indicators for substrate deformation. Finally, the analysis of 3D deformation measurements is extremly time consuming. On the other hand, micropillar substrates can be used for in-plane deformation measurements only. Furthermore, the substrates used for the above-mentioned techniques might also influence cell behavior due to their surface elasticity and structure.
For the generation of a comprehensive model of cell traction forces based on precise and high-throughput data analysis, 2D NiTi cantilever arrays on the micrometer scale are designed based on finite element analysis (FEA) and fabricated by thin film technology⁴. Within the simulations, stress forces in the nanonewton region and cantilever deformations were analyzed. In this way, cell traction forces affecting the inner contact point of the cantilevers were mimicked.
For the measurement of normal and shear traction forces generated by cells, the x-, y- and z-deflection of elastic cantilevers of a specifically defined shape will be detected.
In this work, first design results of the FEA are presented.
1 J. L. Tan et al., Cells lying on a Bed of Microneedles: An Approach to isolate Mechanical Force, Proc. Natl., Acad. Sci. USA (2003), 100, 1484.
2 K. A. Beningo et al., Nascent Focal Adhesion are responsible for the Generation of Traction Forces, J. Cell Biol. (2001), 153, 4.
3 M. L. Gardel et al., Traction Stress in Focal Adhesions correlates biphysically with actin retrograde flow Speed, J. Cell Biol. (2008), 183, 6.
4 R. Lima de Miranda et al., Micropatterned Freestanding Superelastic TiNi Films, Adv. Eng. Mater., (2013),15, 1-2.

The natural sequence specificity of DNA base pairing can be exploited for rational design of DNA strands that self-assemble to form two- and three-dimensional nanostructures. These nanostructures can then act as “breadboards” for precise arrangement of molecules and nanoparticles at nanometer-scale separations. DNA has also emerged as a powerful tool for stabilizing small metal clusters, most notably few-atom fluorescent silver clusters with rod-like geometries (Ag-DNAs). Ag-DNAs have fluorescence colors ranging from ~500 nm into the near-infrared that are selected by DNA sequence, which selects the cluster&’s size and therefore its color. We show that silver clusters with atomically precise sizes can be arrayed at nanoscale separations on a prototypical DNA nanostructure: a DNA nanotube with protrusions that bind single Ag-DNAs at programmed sites along the nanotube [1]. Both the nanotube protrusions and the DNA strands that host the silver clusters are designed using large experimental data sets and tools borrowed from bioinformatics. These fluorescent arrays illustrate the power of DNA for assembly across multiple length scales: single atom differences in the sizes of silver clusters, nanometer-scale spacing between Ag-DNAs on a DNA breadboard, and the micron-scale breadboard itself. Such atomically precise metal cluster arrays offer new coupling-based sensing possibilities due to the unique combination of molecular and metallic attributes in the cluster regime and the high sensitivity of Ag-DNAs to DNA environment.
[1] S. M. Copp, D. Schultz, S. Swasey, and E. Gwinn. ACS Nano 9, 2303 (2015).

The non-covalent interaction of biomolecules at the aqueous materials interface, including nanoparticles, is of great interest due to potential applications such as material synthesis, biosensing and nano-medicine.[1] These applications have prompted interest in the development of peptides that can: (i) selectively adsorb to the aqueous graphene interface[2,3], and (ii) once adsorbed, self-assemble into supra-molecular overlayer structures.[3] However, to fully exploit peptide-graphene interactions, a deeper understanding of the molecular level processes occurring at the interface is required. Molecular dynamics (MD) simulations, with the ability to predict and reveal interactions at the atomic level, can contribute to the elucidation of the structure/property relationships of such systems.[4,5]
Using advanced sampling techniques[6,7] in combination with a polarizable force-field specifically developed to model the interaction of biomolecules with graphitic nanostructures[8], we predict the conformational ensemble of peptides adsorbed at the aqueous graphene interface. The adsorption behavior of a peptide, known to have a strong affinity for the basal plane of graphene, as well as a number of mutant analogues, is characterized. We also investigate the aggregation and self-assembly properties of the peptide at the graphene interface. Our findings provide valuable information regarding the links between a peptide sequence and its interfacial binding properties, moving us closer to the ultimate goal of de novo design of materials-selective peptides.
[1] Evans, J.S., et al., Molecuar Deisgn of Inorganic-Binding Polypeptides MRS Bull., 2008, 33, 514-518.
[2] Kim, S.N., et al., Preferential Binding of Peptides to Graphene Edges and Planes, J. Am. Chem. Soc., 2011, 133, 14480-14483.
[3] So, C.R., et al., Controlling Self-Assembly of Engineered Peptides on Graphite by Rational Mutation,ACS Nano, 2012, 5, 1648-1656.
[4] Hughes., Z.E. and Walsh, T.R., What makes a good graphene-binding peptide? Adsorption of amino acids and peptides and aqueous graphene interfaces, J. Mater. Chem. B, 2015, 3, 3211-3221.
[5] Hughes, Z.E. and Walsh, T.R., Computational Chemistry for Graphene-based Energy Applications: Progress and Challenges, Nanoscale, 2015, 7, 6883-6908.
[6] Terakawa, T., et al.; On easy implementation of a varient of the replica exchange with solute tempering in GROMACS, J. Comput. Chem., 2010, 32, 1228-1234.
[7] Wright, L.B. and Walsh, T.R.; Efficient conformational sampling of peptides adsorbed onto inorganic surfaces: insights from a quartz binding peptide, Phys. Chem. Chem. Phys., 2013, 15, 4715-4726.
[8] Hughes, Z.E., Tomásio, S.M. and Walsh, T.R., Efficient simulations of the aqueous bio-interface of graphitic nanostructures with a polarisable model, Nanoscale, 2014, 6, 5438-5448.

The exoskeleton of the armored fish, Polypterus senegalus, uses both material and morphometric design rules to provide biomechanical flexibility alongside protection from predatory biting attacks. Bioinspired flexible, composite armor prototypes based on the ganoid squamation of P. senegalus were generated and tested through a series of steps. X-ray micro-computed tomography was used to generate 3D reconstructions of the mineralized fish scales, and landmark-based geometric morphometric analysis was used to quantify the spatial variation of fish scale geometry. Geometric abstraction and 3D associative modeling were used to computationally design assemblies of rigid scales integrated with compliant, tissue-like connective elements on a flexible substrate. Multi-material 3D printing was used to fabricate the macroscale composite prototypes. The mechanical behavior of the prototypes was analyzed with displacement-controlled bending experiments and further characterized through finite element simulations. The scale assemblies exhibited global anisotropic (orientation-dependent) bending stiffness resulting from scale morphometry, arrangement, and interlocking joints that control the local, inter-scale mobility mechanisms, in addition to the material properties of the constituent materials. Synthetic models that replicate the complex architecture and biomechanics of actinopterygian fish armor give insight into developing flexible, human-fit protection that maintains both full-body coverage and user mobility.

The progress of a wide range of strategic fields from aerospace, construction, transportation or medicine depends on our ability to develop new light weight composites with outstanding mechanical properties. In this respect, natural materials such as bone, silk or nacre offer clear examples of how enhanced mechanical performance can be reached in low density materials through structural manipulation. Much attention has been paid to the idea of applying the design principles observed in nature to the fabrication of synthetic composites. One of the common design features in natural composites seems to be the use of layered and brick-and-mortar structures in which stiff layers or bricks are joined by thin soft interlayers. An interesting possibility is the replication of these designs using technical ceramics as the stiff phase and metallic alloys as the mortar. However, the challenge still remains on how to effectively translate natural principles to synthetic metal-ceramic materials and how to develop effective fabrication technologies to implement them in practical dimensions.
In this project we have used a combination of freeze-casting and reactive presureless infiltration to fabricate layered alumina/Al4Mg composites. By using ceramic particles with different aspect ratios it is possible to manipulate the layer thickness at the microscopic scale between few microns up to 50 µm and to control the structure of the ceramic layer (grain size and porosity). The resulting composites are lightweight, strong and tough. We have characterized their mechanical response as a function of their architecture. The composites can exhibit high flexural strengths and initiation fracture toughness (up to 800 MPa and 16 MPa.m^1/2). More interestingly, these materials exhibit several toughening mechanisms that result in a unique R-curve behaviour with fracture resistance values that can reach up 100 MPa.m^1/2. Crack propagation has been investigated with different techniques (optical microscope, in-situ SEM and x-ray tomography) to analyse the key toughening mechanisms. The observations have served to identify the role of phenomena such as crack propagation or bridging and to propose strategies to enhance their contribution. In this presentation we will also discuss the best approaches towards the characterization of the mechanical response of this kind of bio-inspired materials.

I discuss recent results from our research group on designing responsive polymer and biopolymer based soft nanocomposite materials for microcapsules with tunable permeability, cell protection, and ultra-strong and conductive bionanocomposites.[1]^{, [2]} Ultrathin silk fibroin shells are assembled in order to conduct surface modification and protection of microparticles, cells and cell assemblies and form permeable microcapsules. Biocompatible, compliant and permeable LbL shells are formed from silk fibroins, their ionomers, and pegylated derivatives and transferred onto various yeast and bacterial cells.[3]^, Organized multiplexed arrays of ink-jet printed silk templates have been utilized for cell encapsulation with high viability and their long-term storage for biosensing arrays.[4]^,[5] On the other hand, ultra strong laminated bionanocomposites from silk and graphene oxide components with unique interphase morphology were found to possess extremely high elastic modulus and toughness [6] as well as ability gotconductive patterning with localized electrochemical reduction.[7]
[1] I. Drachuk, V. V. Tsukruk, Biomimetic coatings to control cellular function through cell surface engineering, Adv. Funct. Mater.,2013, 23, 4437.
[2] K. Hu, et al., Graphene-Polymer Nanocomposites for Structural and Functional Applications, Prog. Polym. Sci., 2014, 39, 1934
[3] Drachuk, R. et al.^, Silk Macromolecules With Amino Acid-Peg Grafts For Controlling LbL Encapsulation And Aggregation Of Recombinant Bacterial Cells, ACS Nano,2015, 9, 1219.
[4] R. Suntivich, et al. Inkjet printing of silk nest arrays for cell hosting, Biomacromolecules, 2014, 15, 1428
[5] Drachuk, et al. Printed “Red-Green” Dual Silk Cell Arrays for Multiplexed Sensing, ACS Biomat. Sci.&Eng., 2015, in print
[6] K. Hu, et al. Ultra-Robust Graphene Oxide-Silk Fibroin Nanocomposite Membranes, Adv. Mater., 2013, 25, 2301.
[7] Hu, K. et al. Written-in Conductive Patterns on Robust Graphene Oxide Biopaper by Electrochemical Microstamping. Angew. Chem. Int. Ed.,2013, 52, 1378

Diatoms algae are a class of photosynthetic microorganisms which produce nanostructured silica shells (frustules) whose size and morphology are highly species-specific. The regular shapes with symmetrical and hierarchical nano-sized porosity of the frustules make diatoms&’ biosilica attractive for applications in materials science and nanotechnology. In addition, diatoms&’ biosilica can be chemically modified with functional molecules both by in vivo incorporation and by in vitro covalent grafting on the biosilica structures after removing the biological matter by acidic/oxidative treatment. The lecture will discuss two examples, the first relevant to the use of diatoms' biosilica as a multifunctional material for bone tissue regeneration, and the second dealing with the assembly of luminescent hybrid nanostructures with photonic properties.
In the first study, nanostructured silica from Thalassiosira weissflogii diatoms is covalently functionalized with the radical scavenger 2,6,6-tetramethylpiperidine-N-oxyl (TEMPO), and then tested as a drug delivery vehicle for ciprofloxacin, an antibiotic widely used in orthopedic and dental implant infections. The TEMPO-biosilica, combining drug delivery with anti-oxidant properties able to prevent inflammatory effects, is finally demonstrated to be a suitable substrate for bone cells growth.¹
The second part of the lecture will present luminescent biosilica nanostructures from Thalassiosira weissflogii or Coscinodiscus wailesii diatoms. In vivo integration of organic fluorophores or phosphorescent organometallic complexes into diatoms&’ silica shells followed by removal of the biological matter via acidic/oxidative treatment affords new luminescent nanostructures with light emission and other intriguing photonic properties.
More in general, this lecture will emphasize the enormous potentialities arising from the combination of biotechnological production and chemical modification as a convenient approach to the synthesis of functional nanostructured materials.
References
[1] S. R. Cicco, D. Vona, E. De Giglio, S. Cometa, M. Mattioli-Belmonte, F. Palumbo, R. Ragni, G. M. Farinola, ChemPlusChem2015 (DOI: 10.1002/cplu.201402398).

Many high-performance natural composite materials found in nature such as bones or shells, contain nanocrystalline inorganic components that are formed or stabilized by the presence of peptides and proteins. Many of these biomineral-associated peptides/proteins exhibit the ability to carry out function in the absence of a well-defined secondary, a property of intrinsically disordered peptides/proteins (IDPs). [1] Furthermore a subset of these IDPs also display the ability to reversibly switch conformations from random-coil to a well-defined structure in the presence of an external stimulus.
Molecular simulations have been utilized to study the conformational properties of IDP sequences associated with the nucleation of natural composites [2], offering new complementary, in-depth molecular-level insights into these challenging systems. However molecular simulations face serious challenges in capturing the conformational switching abilities that are thought to allow some IDPs to control their conformation and, in turn, their function.
Hydroxyapatite (HAP)-binding sequences such as osteocalcin and the de novo designed JAK1 peptide display disordered native states in aqueous solution, however the presence of calcium is thought to induce helical folding which in turn facilitates binding to hydroxyapatite. The interaction between Ca²⁺ and key post-translationally-modified γ-carboxylate glutamic acid (Gla) residues is thought to be responsible for triggering helical folding and binding functionality. Mutations of these sequences where Gla → Glu display a loss of helical folding and are thought to abrogate the ability to bind to HAP. [3,4]
To investigate this conformational switching, we study the JAK1, and osteocalcin sequences in NaCl and CaCl₂ solutions using large-scale Replica Exchange with Solute Tempering (REST) molecular dynamics simulations. [5] We analyse the frequency and length of secondary structure motifs using Ramachandran plots, cluster analysis to explore the dominant conformations and residue-residue contact maps to determine key intra-peptide interactions to provide molecular level insights into the conformational switching mechanisms. We also utilize metadynamics[6] simulations to explore the strength of the Ca²⁺ interactions with the Glu and Gla side-chains and suggest new force field parameters to improve the representation of these interactions. Our work provides insight into the molecular level structure/property relationships of these peptides, and highlights some of the challenges that simulations face when studying complex IDP systems.
[1] Uversky, V. N. Int. J. Biochem. 2011, 43, 1090
[2] Brown, A. H. et al. Biomacromolecules, 2014, 15, 4467
[3] Cristiani A. et al. Front Biosci, 2014, 19, 1105
[4] Capriotti, L. A. et al. J. Am. Chem. Soc. 2007, 129, 5281
[5] Terakawa, T. et al. J. Comp. Chem. 2010 32, 1228
[6] Barducci, A. et al. Phys. Rev. Lett., 2008, 100, 020603

Biologiclal systems routinely produce nanoscopic molecular structures with considerably less dispersion in size and shape than encountered in most manufactured materials. Indeed, Biological structures are frequently and essentially monodisperse. An example of this uniformity, combined with an intriguing geometry, is the nanometer-scale protein nanorings produced by interaction of the protein tubulin with certain hydrophobic tri-, tetra- and pentapeptides originally extracted from marine natural products. Different peptides produce different sized nanorings, but we focus on those produced by binding to tubulin of the cyclic depsipeptide cryptophycin. The nanorings that form upon binding of this ligand show a sharp mass distribution indicating that the naorings are made of 8 tubulin dimers of 100 kDa.
In this submission, we demonstrate how a combination of fluorescence correlation spectroscopy, dynamic light scattering, electron microscopy, analytical ultracentrifugation, small-angle neutron scattering, and modeling is applied to reveal interactions of tubulin and cryptophycin in solution and to characterize their nanostructures. We find that the cryptophycin-tubulin nanorings (~25 nm diameter) are single-walled, appear rigid, are composed of 8 tubulin dimers in a single closed ring, and are stable upon dilution to nanomolar concentrations.
Similar studies with a different peptide, the linear pentapeptide dolastatin 10, demonstrates that binding of this peptide to tubulin produces larger nanorings (14 tubulin dimers, ~45 nm diameter rings), with slightly different properties. The ability to adjust the ring size with different peptides, and produce uniform nanorings with properties that differ slightly between size classes, makes the tubulin-peptide ring structures an appealing structural system.

Fabrication of well-ordered and defect-free two-dimensional (2D) structures on the nanoscale is of technological importance in energy storage and electronic devices.¹ The Ff class of inoviruses (filamentous phages) has been the subject of intensive studies due to their self-assembling nature.² In this study, wild-type (WT) filamentous phages, denoted M13, were deposited from a viral solution on amorphous carbon (a-C) and silicon dioxide (SiO₂) films. Using scanning electron microscopy (SEM) and transmission electron microscopy (TEM), we show that the a-C surface induces the assembly of M13 phages into parallel arrays. When the phages were immobilized on the SiO₂ surface, the trend of the system was toward the formation of an isotropic phase. However, viral particles show a high degree of alignment along a common axis on a-C surface as per nematic liquid crystalline model. The M13 phage particles were found to have a high affinity for incorporation into a closely-ordered pattern onto a-C surface.³ Such patterns can further function as templates to nucleate highly uniform and smooth inorganic layers. To study defects in the ordering of filamentous particles, we present a phenomenological model using an experimental approach in order to elucidate the surface action and anchoring contribution on the WT M13 phages, with extremely high aspect ratio (i.e., having diameter of 6.7 nm and length of 880 nm),³ in irregular confined spaces. Using TEM, the M13 phage bending and the competitive anchoring forces of the adjacent confining geometries was investigated on the many-particle levels, which conforms to the theoretical arguments for very long rods. On the basis of the bending energy, properties of individual wormlike macromolecules such as DNA and unfolded proteins have been extracted from two-dimensional atomic force and scanning tunneling microscopy images.⁴ However, the deposition method under consideration organizes M13 phages into dense two-dimensional bundles where individual phages are almost as close as they can be to one another. Here we provide a simple expression for the total bending energy of such a two-dimensional bundle consisting of N phages and we show that the width and topology of the surface microstrands compete to dictate the spatial arrangement of uniaxial liquid crystals. The particular orientation of the colloidal particles in the surface layer is shown to incline towards the curvatures with lower local radius in boundary conditions.
References
1. L. Shen, N. Bao, Z. Zhou, P. E. Prevelige and A. Gupta, Journal of Materials Chemistry, 2011, 21, 18868-18876.
2. A. S. Khalil, J. M. Ferrer, R. R. Brau, S. T. Kottmann, C. J. Noren, M. J. Lang, M. Belcher, Proceedings of the National Academy of Sciences, 2007, 104, 4892-4897.
3. P. Moghimian, V. Srot, D. Rothenstein, S. J. Facey, L. Harnau, B. Hauer, J. Bill and P. A. van Aken, Langmuir, 2014, 30, 11428-11432.
4. Deng et al., Nano Lett., 2012, 12, 2452-2458.

3D cell assemblies are being utilized to a great extent for in vivo replacement for damaged tissues and organs and also have a significant role in vitro drug screening. Theses tissues mimics are likely to provide a crucial complement to model human biology, which now predominantly based on well-established 2D culture technique of human cell and other models tissue and organ function. It is believed that the seemingly random cells combination(including several cell types) in tissue and organs is hierarchal and tightly controlled organization of various cell types and has the capability to appropriately self-organize over time. However, the assembly and fabrication of three-dimensional multi-cell co-culture mode is still challenging. We here present a new method based on microfluidic technology of a micro-three-dimensional cell culture system. We use a triggered ionic crosslink formation to generate highly monodisperse and structurally homogeneous alginate micro-beads as the synthetic extracellular matrix. This hydrogel network can be transferred into an aqueous environment without losing its structural integrity. Furthermore, we design multiphase micro-device to form multi-compartment microgels with desired features by one-step and continuous process. The proposed multicompartment hydrogel offer a new platform for the construction of tissues in natural organisms. To our best knowledge, such microgels have not previously been reported. For the initial result, we also encapsulate individual mesenchymal stem cells (MSCs) with different cell into the microbeads which show the aspired cell growth and cell-cell interaction.

We build branched DNA species that can be joined using Watson-Crick base pairing to produce N-connected objects and lattices. We have used ligation to construct DNA topological targets, such as knots, polyhedral catenanes, Borromean rings and, using L-nucleotides, a Solomon's knot.
Nanorobotics is a key area of application. We have made robust 2-state and 3-state sequence-dependent devices and bipedal walkers. We have constructed a molecular assembly line using a DNA origami layer and three 2-state devices, so that there are eight different states represented by their arrangements. We have demonstrated that all eight products can be built from this system.
One of the major aims of DNA-based materials research is to construct complex material patterns that can be reproduced. We have built such a system from DNA motifs, which can reach 2 generations of replication. We have achieved exponential growth in an origami-based system.
We have self-assembled a 3D crystalline array and reported its crystal structure to 4 Å resolution. We can use crystals with two molecules in the crystallographic repeat to control the color of the crystals. Rational design of intermolecular contacts has enabled us to improve crystal resolution to better than 3 Å. We can change the color of the crystals by doing strand displacement in 3D to change the color of crystals. We are using the crystals to attempt to control the structure of other materials in 3D.

Neuronal cells form complex networks that can receive, send, and store information. Neurons form these networks by sending out long processes called axons that can sense their environment and connect to other cells. Understanding what physical processes govern network assembly is essential for the development of new biomaterials used for guiding network formation for regenerative treatments and nerve repair applications. We demonstrate that substrate stiffness, texture, and topography heavily influence axonal growth and can be controlled accurately by using polymer susbstrates (PDMS, silk, nano-ppx) . Using fluorescent and atomic force microscopy we explore neuronal growth on micropatterned surfaces with highly periodic surface topographies. We analyze the axons&’ angular distributions on these surfaces and show that their growth dynamics are described by stochastic equations. Our results demonstrate high degree of control over the axonal directionality on these substrates.

Microtubules (MTs) are biopolymeric cytoskeletal filaments that are important in a number of cellular functions, including maintaining cell structure, driving chromosome separation during mitosis and providing platforms for intracellular transport. Such cytoskeletal filaments are being explored as nanostructure templates (i.e., for nanowire synthesis) due to their dimensions and self-assembly dynamics. MTs have intriguing and unique self-assembly processes that scale from polymerization of tubulin dimer units at the nanometer scale, to the head-to-tail micron-scale assembly of mature MT filaments, forming segmented nano-arrays. Being able to deliberately control the assembly of these MT nano-arrays, however, requires characterization of the properties driving MT self-assembly. Here, we demonstrate that biophysical features of MTs, including electrostatics, persistence length (stiffness), and temperature regulate the directed assembly of MT nano-arrays. Due to the overall negative surface charge of MT filaments, electrostatic shielding of the MTs using monovalent salts resulted in an increased rate of assembly. Furthermore, increasing the persistence length resulted in a decreased rate of nano-array assembly, likely caused by reduced rate of diffusion and thus lower probability of head-to-tail interactions. Finally, preliminary data exploring the role of temperature suggests that as the temperature increases, MT filaments likely have a phase transition resulting in a discontinuous Arrhenius behavior. Together, these results provide detailed insight into the tunable parameters driving the self-assembly of MT nano-arrays. Adjusting these parameters to optimize nano-array assembly will greatly aid in the direct application of biopolymeric templates for use in nanomaterials applications.
Sandia National Laboratories is a multi-program laboratory managed and operated by Sandia Corporation, a wholly owned subsidiary of Lockheed Martin Corporation, for the U.S. Department of Energy&’s National Nuclear Security Administration under contract DE-AC04-94AL85000

In nature, assembly of functional molecules (e.g. proteins) into molecular machines that carry out the vast array of functions is a commonplace phenomenon. Inspired by nature, self-assembly process has been widely used for self-assembly of proteins and peptides into functional materials. However, proteins and peptides exhibit so complex folding capabilities due to the formation of both intra- and inter- sequence hydrogen bonds, the prediction of their structures and assembly is still extremely difficult. Furthermore, the application of protein- and peptide-based materials is limited because of their poor stabilities against thermal and chemical degradation. To address these challenges, we recently focused our research on developing sequence-specific peptoids to mimic peptides and proteins for functions.
In this presentation, I will report my group&’s recent progress in exploiting lipid-like peptoids to self-assemble biomimetic membranes both in solution and on substrate surfaces. In aqueous solution, these peptoids self-assemble into highly-crystalline and free-floating membranes through a solvent-driven crystallization process. X-ray diffraction data indicate that peptoids are highly packed to form membranes through π-π stacking and side-chain hydrogen bonding. These membranes are highly chemically and thermally stable, no significant changes were observed after they were exposed to 10× PBS, 1.0 M Tris-HCl buffer, or even pure organic solvents (e.g. ethanol and acetonitrile). Overnight heating of membrane-water suspensions at 600C shows no disruption of peptoid membranes. Upon exposure to external stimuli, these peptoid membranes exhibit cell-membrane-like thickness changes, varying from 3.5 nm to 5.6 nm. We further demonstrate that single-layer of peptoid membranes can be formed on various substrate surfaces, and peptoid membranes with defects created by mechanical damages can be self-repaired. Displaying functional groups at the different location of membrane-forming peptoids produces membranes with similar structures, indicating that they can be used as a robust platform for a wide range of applications, such as integrating synthetic water channels and protein complexes for selective water or oxygen transport and separation. Multi-scale simulations were used to successfully predict the favored peptoid membrane structures.

DNA origami is a class of self-assembled nanostructures whose geometry can be designed with a few nanometer precision via sequence design. Dynamic DNA origami structures that can change conformations in response to environmental cues or external signals are of great interest for their promise in sensing and actuation at the nanoscale. While most DNA origami structures are static, several examples of dynamic DNA origami structures have been demonstrated largely based on single-stranded hinge mechanism. As a result, dynamics of DNA origami are initiated by DNA hybridization and/or strand displacement. Here, we demonstrate a different actuation mechanism and show that DNA-binding molecules such as ethidium bromide (EB), tetra-(N-methyl-4-pyridyl)porphyrin (TMPyP4), and photochromic spiropyran can be used to modulate the global curvature of DNA origami structures. These molecules unwind DNA double helices upon binding, therefore increase the helical pitch of the duplexes, change the stress in the structure, and ultimately change the overall conformation of the whole DNA origami. As model systems, we demonstrate (1) the switching of a DNA origami nanoribbon between different twisted (left-handed vs. right-handed) and flat states, and (2) the cis-trans switching of a DNA origami shaft. From absorption titration studies, the binding isotherms of DNA origami with these molecules are studied, yielding the dissociation constant and the maximum binding capacity. By monitoring the cyclization efficiency of a DNA origami rectangle as a function of adduct concentration, the stiffening effect of the DNA-binding molecules on the mechanical property of DNA origami is demonstrated. Finally, with the knowledge gained from this study, we demonstrate reversible photo-control of DNA origami conformation by utilizing water-soluble spiropyran molecules that possess photo-switchable DNA-binding properties. Our method provides a clean, rapid and reversible way to remotely control DNA origami conformation and should be valuable for applying DNA origami for various functionalities. This work demonstrates efficient DNA origami reconfiguration, advances our understanding of the dynamics and mechanical properties of self-assembled DNA structures, and should be valuable to the field of DNA nanotechnology.

A promising route to protein-mimetic materials capable of complex functions, such as molecular recognition and catalysis, is provided by sequence-defined peptoid polymers, structural relatives of polypeptides. Peptoids, which are relatively non-toxic and resistant to degradation, can fold into defined structures through a combination of sequence-dependent interactions. However, the range of possible structures accessible to peptoids and other biomimetics is unknown, and our ability to design hierarchical protein-like architectures from these polymer classes is limited. I will describe our use of molecular dynamics simulations, together with scattering and microscopy data, to determine the atomic-resolution structure of the recently-discovered peptoid nanosheet, an ordered supramolecular assembly that extends macroscopically in only two dimensions. Our simulations show that nanosheets are structurally and dynamically heterogeneous, can be formed only from peptoids of certain lengths, and are potentially water- and ion-porous. Moreover, their formation is enabled by peptoids&’ adoption of a secondary structure not seen in the natural world. This structure, a zig-zag pattern that we call a Sigma-strand, results from the ability of adjacent backbone monomers to adopt opposed rotational states, thereby allowing the backbone to remain linear and untwisted. Such a binary rotational state motif is not seen in protein regular structures, which are built generally from one type of rotational state. Linear backbones tiled in a brick-like way form an extended two-dimensional nanostructure.

Control of polymer-inorganic hybrid structures from nano- to mesoscopic length scales remains a grand challenge. For example, bone and teeth are both composites comprised primarily of inorganic nanocrystals of hydroxylapatite (Ca₁₀(PO₄)₆(OH)₂), and an organic polymer, collagen. The differences between the tissues are the ratio of inorganic to organic material and the ordering of inorganic crystals in different hierarchical structures, which results in different mechanical properties. Within the field of self-assembled nanostructures, block copolymers and peptide block copolymers offer new ways to direct the crystallization of calcium phosphate. We demonstrate the evaporation-induced self-assembly of composites with tunable nanostructures from ultra-small, organosilicate-modified amorphous calcium phosphate nanoparticles (osm-ACP-NPs) and poly(isoprene)-block-poly(styrene)-block-poly(2-(dimethylamino)ethyl methacrylate) block copolymers. The osm-ACP-NPs are synthesized via a two-step sol-gel process in which (3-glycidyloxypropyl)trimethoxysilane quenches the reaction and functionalizes the NP surfaces. Moving from all-synthetic to synthetic-peptide block copolymers significantly increases the information content in the organic structure-directing agents relative to past efforts. We will present initial results on how such synthetic-peptide block copolymers can direct the assembly of inorganic materials. This work will impact multiple fields where highly crystalline materials are desired, such as biomaterials, catalysis and electronics.

Peptoids are a promising class of bioinspired polymers with several unique properties bridging the gap between proteins and bulk polymers, such as sequence specificity, thermal stability, and resistance to protease digestion. Studies show certain sequences can form 1D fibers and 2D sheets, thus they are promising candidates to develop self-assembling protein-like materials. Here we investigated the mechanisms and controls on peptoid self-assembly and related them to the underlying sequence. Several peptoids with sequences of hydrophilic and hydrophobic side chains were synthesized and shown to self-assemble into 2D or 3D structures ranging from bi-layer sheets to 2D fiber arrays to 3D porous networks. Their assembly pathways on mica surfaces were characterized in real time using in situ AFM and related to solution species observed through dynamic light scattering and TEM. While some sequences exhibited typical Langmuir adsorption kinetics and classical nucleation pathways, slight changes in sequence led to hierarchical pathways involving disordered precursors that transformed into ordered nuclei before growing, or aggregates that deposited and spread laterally into single bilayers creating a series of growth pulses. During hierarchical assembly of the porous fibril-based networks, 3nm-high “proto-fibers” were found to be the basic building blocks. These extended laterally to create an initial 3-fold symmetric array of fibers one molecule in width, and grew outward in 3nm increments to create a 3-fold symmetric array of one-molecule wide fins and, ultimately, a 3D porous network. However, the proto-fibers formed via transformation of 5Å-high clusters with no apparent order. The kinetics of assembly was also investigated. We found the nucleation rate of 3 nm proto-fibers dramatically increased after an incubation time that increased with peptoid concentration and decreased with calcium concentration. In contrast, appearance of 5Å clusters was initially constant and rapid by comparison, but their number reached a maximum before rapidly decreasing due to their conversion into 3 nm proto-fibers. Based on these results and XRD analysis of peptoid fibers and sheets, we propose a model to describe this self-process. Small peptoid clusters form rapidly in solution and adsorb onto the mica surface to form 5Å-high clusters in which peptoids are randomly arranged and “lying down”. Over time, these undergo a transformation in which the molecules “stand up” and are joined by others to form 3nm-high bi-layer particles. The bi-layer particles then grow in length by addition of molecules to the fiber ends (x direction) and nucleation of new bilayers on the top (z direction). We constructed a kinetic model that considers the competing rates of the various deposition, nucleation, and transformation processes. The predictions agree qualitatively with the observations and place bounds on the magnitude of kinetic terms controlling the assembly pathway.

The self-assembly of peptides into 1-, 2-, and 3-dimensional supramolecular arrangements represents a bioinspired route to creating complex functional nanostructures. Understanding the complex relationship between the peptide sequence and the ability to form well-defined arrangements will help better facilitate their application as functional biological nanostructures. The rational design and assembly of proteins and peptides are central to understanding structure-propert relationships in biomaterials. Changes in a single amino acid can often lead to changes in supramolecular assembly or disrupt assembly. Even with the advances in computer software predicting the supramolecular assembly based on a peptide sequence can be difficult. More experimental exploration is needed to better understand how de novo peptides assemble into homogeneous oligomers, which will allow better control of their molecular properties. The design of new interaction motifs, therefore, opens new areas for study in peptide self-assembly. Inspired by conductive bacterial pili fibers, we developed a novel synthetic peptide incorporating aromatic residues that assembles into an antiparallel coiled-coil hexamer of alpha-helices, ACC-hex. Our results show that the ACC-Hex peptide self-assembles to form discrete hexamers at low concentrations in buffered solutions and can associate further to form conductive fibers and gels at higher concentrations. We will discuss here the structural and electrical and mechanical property characterization of these novel peptide fibers. The ACC-hex structure is unprecedented in both synthetic and natural supramolecular peptide assemblies and exhibits structural characteristics and properties which suggest it is an ideal platform for functional biological nanostructures.

Mechanisms of morphogenesis and adaptability in artificial systems can guide us to discoveyr of mechanisms of morphogenesis in biological systems as well. Here we look at several mechanisms of symmetry breaking, some of which have parallels in biological systems, and some that don't yet. We expect parallels for the novel mechanisms will be found in biology, and out understanding of these systems will be improved. We show how liquid crystal arrangements could result in force generation in liquids, dynamic rearrangements of particle shapes, as well as simplification of chemical syntheses of artificial muscles. We discuss the principles of multistability found in these systems.

Learning from nature and based on lotus leaves and fish scale, we developed super-wettability system: superhydrophobic, superoleophobic, superhydrophilic, superoleophilic surfaces in air and superoleophobic, superareophobic, superoleophilic, superareophilic surfaces under water [1]. Further, we fabricated artificial materials with smart switchable super-wettability [2], i.e., nature-inspired binary cooperative complementary nanomaterials (BCCNMs) that consisting of two components with entirely opposite physiochemical properties at the nanoscale, are presented as a novel concept for the building of promising materials [3-4].
The smart super-wettability system has great applications in various fields, such as self-cleaning glasses, water/oil separation, anti-biofouling interfaces, and water collection system [5].
The concept of BCCNMs was further extended into 1D system. Energy conversion systems that based on artificial ion channels have been fabricated [6]. Also, we discovered the spider silk&’s and cactus's amazing water collection and transportation capability [7], and based on these nature systems, artificial water collection fibers and oil/water separation system have been designed successfully [8].
Learning from nature, the constructed smart multiscale interfacial materials system not only has new applications, but also presents new knowledge: Super wettability based chemistry including basic chemical reactions, crystallization, nanofabrication arrays such as small molecule, polymer, nanoparticles, and so on [9].
Reference:
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3. Pure Appl. Chem. 2000, 72 (1-2), 73-81.
4.Small 2015, 11, 1071-1096.
5. Adv. Mater. 2011,23 (6), 719-734.
6. (a)Chem. Soc. Rev. 2011,40 (5), 2385-2401; (b) Acc. Chem. Res. 2013,46 (12), 2834-2846; (c) Adv. Mater. 2010,22 (9), 1021-1024. (d) ACS Nano 2009,3 (11), 3339-3342; (e) Angew. Chem. Int. Ed. 2012,51 (22), 5296-5307;(a) Nature 2010,463 (7281), 640-643; (b) Nat Commun 2012,3, 1247.
7. (a) Nat Commun 2013,4, 2276; (b) Adv. Mater. 2010,22 (48), 5521-5525.
8. (a) Nature 2010,463 (7281), 640-643; (b) Nat Commun 2012,3, 1247.
9. (a) Chem. Soc. Rev. 2012,41 (23), 7832-7856; (b) Adv. Funct. Mater. 2011,21 (17), 3297-3307; (c) Adv. Mater. 2012,24 (4), 559-564; (d) Nano Research 2011,4 (3), 266-273; (e) Soft Matter 2011,7 (11), 5144-5149; (f) Soft Matter 2012,8 (3), 631-635; (g) Adv. Mater. 2012,24 (20), 2780-2785; (h) Adv. Mater. 2013,25 (29), 3968-3972; (i) J. Mater. Chem. A 2013,1 (30), 8581-8586; (j) Adv. Mater. 2013,25 (45), 6526-6533; (k) Adv. Funct. Mater. 2012,22 (21), 4569-4576; (l) Acs Nano 2012,6 (10), 9005-9012.

Nature provides a great source of inspiration for new materials which both meet the rising need for biocompatibility as well as minimize negative environmental impacts. In particular, tannic acid, a molecule typically extracted from gallnuts found on trees, spontaneously forms coordination bonds with Fe(III) in aqueous solution and thus generates a color change from a clear or yellow brown to a blue or red depending on pH and concentration of the solutes. Additionally researchers have recently shown that tannic acid and Fe(III) can self-assemble to form thin film coatings on various substrates at room temperature. The combined features of tunable optical properties and coating formation make this molecular system interesting in the context of thin film sensors of for example metal ions and pH. Our research specifically looks at the assembly of tannic acid-Fe(III) coatings on alginate gel beads to elucidate the relationship between optical and mechanical properties of the alginate and thin film system through compression testing. We also examine the effects of calcium, zinc, copper, and iron cross-linked alginate gels on the stiffness of the coated beads. Further tests study the durability and resistance to failure of all the samples. Ultimately, tannic acid and iron based thin film coatings on alginate gels show great promise for further engineering as inexpensive materials for sensing technology in wet environments.

Heterogeneous composites with intricate microstructures are widely spread in the natural world where they are needed to fulfil the specific functional demands imposed by the environment. Understanding the underlying principles of the relationship between microstructure and properties has led to new conceptual designs for composites exhibiting superior properties with simpler and greener processing steps. However, applying the multiplicity of nature&’s strategies to man-made materials is yet a challenge due to the lack of suitable and easily available processing tools. We report on a processing platform that offers unparalleled compositional, texture and shape control, enabling the fabrication of heterogeneous bio-inspired composites with unprecedentedly high mineral volume fractions (35 - 100 vol%) and remarkable functionalities. The technology combines an aqueous-based ceramic process with magnetically-directed particle assembly to create programmed microstructural designs using anisotropic stiff platelets in a ceramic, metal or polymer functional matrix. Proof-of-concept composite designs include periodic patterns of micro-reinforcement orientation or tooth-like bilayers exhibiting intricate shape and site-specific composition and orientation. This processing platform opens the door to an ample scope of fundamental research and of new functional applications.

Shape changing mechanisms are a subject of great interest in materials research. Potential applications for this class of smart materials include tissue engineering, soft robotics and energy harvesting, but will require research efforts improving the material strength and the actuation effectiveness. The understanding of the actuation force and energy of the shape change mechanism is also currently lacking.
We have developed a bilayer polymer structure that is inspired by the mechanism of shape change found in plant organs, such as seed pods and pine cones. These natural shape changing structures rely on microfibrils within their structure allow the tissue to swell/shrink anisotropically, often responding to the humidity of their environment. Our research creates similar anisotropies in a ceramic platelet reinforced polymer matrix. The platelets are functionalized with magnetic particles and their orientation within the polymer can be controlled using applied magnetic fields resulting in the creation of a homogenous composite with anisotropic mechanical properties. By measuring the swell ratio and actuation time, our homogenous materials performs competitively with inhomogeneous shape change materials.
Our research efforts are focused on evaluating the mechanical properties of our composite which can actuate with respect to changes in certain stimuli including pH, temperature, or electric fields. The stiffness of the shape change composites, formed with different concentration of reinforcement, was measured by tensile tests. To obtain the actuation energy, the geometry change was recorded and analyzed followed with a numerical analysis to model the bilayer bending structure. Numerical analysis was also used to analyze the energy generation within the composite over time. Mechanical and piezoelectric methods were also used to obtain experimental data on the shape change behavior in support of numerical model results. The relationship between the actuation energy and the stiffness of the composite was determined by combining the results of these mechanical tests and the actuating behavior.

Growing evidence supports that mussel byssal threads rely on an intricate balance of permanent covalent and reversible metal coordination bonds for their unique mechanical behavior such as high toughness and self#8208;healing. Inspired by the balanced crosslink chemistry present in these threads, polyethylene glycol (PEG) hydrogels were synthesized with two crosslinked networks; a primary permanent network is composed of covalently crosslinked 4#8208;arm PEG and a secondary network composed of 4#8208;arm PEG functionalized with histidine on each arm. The histidine decorated PEG can thereby form mechanically reversible network via metal ion coordinated crosslinks. Using rheometry we study the contribution of the metal#8208;coordinate network to the bulk gels and find that we can control both the amplitude and the frequency of peak mechanical dissipation with the histidine: metal ion ratio and the choice of metal ion, respectively. Furthermore, the mechanical contribution of metal coordinate bonds is shown to correlate with visible gel color changes controllable by pH. These simple bio#8208;inspired gels promise to serve as a new model system for further study of opto#8208;mechanical coupling of metal#8208;coordinate soft materials.

Silicatein, an enzyme found in sea sponges, is responsible for the growth of silicon dioxide (SiO2) spicules. While silicatein has been shown to form amorphous oxide materials such as TiO2, production is limited to laboratory scale due to challenges in large-scale silicatein production in an active form. Our work addresses the challenges of scale, diversifying the range of oxides and crystallinity at ambient conditions. Specifically, we designed a codon-optimized, engineered form of silicatein (r-silicatein) in E. coli, which expresses at significantly higher levels than previously reported (> 10 mg/L culture) and forms oxides from single precursor chelated metal complexes Titanium(IV) bis(ammonium lactato)dihydroxide (TiBALDH; TiO₂) and cerium ammonium nitrate (CAN; CeO₂). High resolution TEM shows < 5nm crystallites in TiO₂ samples and broad XRD peaks in synthesized CeO₂ samples, indicating 2-3 nm crystallites form for both metal oxides. Thus, we have demonstrated the ability of r-silicatein to guide crystal formation along with facilitating reaction, both at room temperature. Our work also suggests a potentially new approach to high-yield, green synthesis of crystalline metal oxide nanomaterials at room temperature.

Creating composites with high-strength and high-toughness is the ultimate goal towards superior engineering applications. Graphene is one of the most promising candidates for developing these new materials due to the remarkable strength that arises from its two-dimensional sp² carbon atoms&’ honeycomb structure. Despite this potential, graphene still has a long way to go before it reaches commercialization since it is extremely expensive and difficult to be produced in mass quantity. An alternative is found with graphene oxide (GO), for which a homogeneous colloidal suspension can be readily prepared in aqueous media for versatile mass production and further treatment. However, as assembling GO sheets into a so-called GO paper, which comprises thousands of layered GO sheets, the strength of the resulting material is much inferior than the GO individual sheets. The reason for this relative weakness relies on the adhesive force provided by the weak van der Waals and pi-pi interactions between layers, as well as the hydrogen bonding between GO sheets and water molecules, which are not strong enough to hold GO sheets together during stretching. As a result, the failure mechanism of GO paper is actually the sliding of GO sheets within themselves but not the breaking of strong carbon-carbon bonds of GO sheets. Dopamine is a bio-inspired building block that mimics the repetitive catechol-amine structure of 3,4-dihydroxy-L-phenylalanine (DOPA) found in mussel foot protein, and it shows excellent adhesion properties. It was found to self-polymerize in alkaline aqueous solutions, via the formation of 5,6-dihydroxyindolequinone (DHI) to form polydopamine (PDA), which adheres onto almost any organic and inorganic surface. Utilizing such outstanding adhesive ability, PDA-based materials have been used as efficient mechanical reinforcing agents. In addition to enhancing the strength of the composite material, dopamine can effectively reduce GO to reduced-GO (rGO) and provide a versatile functional route for further derivation. Compared to simple GO paper, the nanocomposite arising from the combination GO paper and PDA exhibit stronger adhesive force. Consequently, PDA increases the mechanical properties of GO paper, while reducing GO to rGO by oxidative polymerization of dopamine, which in turns leads to recover electrical conductivity. Here we report a computational study based on Density Functional Theory (DFT) calculations and Molecular Dynamics (MD) simulations, which aims to elucidate the crucial role of intercalated PDA on the improved mechanical and electrical properties of rGO-PDA composites.

Alendronic acid (and its sodium salt NaAle) is a second generation bisphosphonate (BP) with therapeutic application for bone resorption blockage in osteoporosis and bone neoplastic diseases. The double phosphonate moiety makes NaAle suitable for Ca²⁺ chemisorption, hydroxyapatite formation via crystallization, osteoblasts enhancement and osteoclasts inhibition.¹ Alendronic acid also has pharmacological action when it is covalently bound to implant screws.² The amino-aliphatic chain of NaAle represents first generation consensus for diatoms microalgae and allows NaAle incorporation into diatoms biosilica shells via Silica Deposition Vescicle uptake. Nanotextured biosilica from Thalassiosira weissflogii has been already studied for bone cell adhesion.³ Here we present a method for in vivo functionalization with exogeneous NaAle of naturally nanostructured biosilica of Thalassiosira weissflogii diatoms cultured in our laboratories. We have produced P-doped (phosphorous probe) cleaned frustules with biphosphonate moieties protruding from the silica shells: these new materials have promising applications in the field of implant medical technology.
[1] G. Russell, Bone, 2011, 49:2-19
[2] P. Tengvall, B. Skoglund, A. Askendal, P. Aspenberg, Biomaterials, 2004, 25:2133-8
[3] S. R. Cicco, D. Vona, E. De Giglio, S. Cometa, M. Mattioli-Belmonte, F. Palumbo, R. Ragni, G.M. Farinola, Chem Plus Chem, 2015, doi: 10.1002/cplu.201402398

The high incidence of traumatic brain injuries affecting both civilians and military personnel has prompted the need for tissue simulant materials. Synthetic polymer gels that accurately mimic the mechanical behavior of brain are valuable tools for assessing protective equipment and understanding injury mechanisms. Here, we investigate the impact response of brain tissues from mice, rats, and pigs using a technique known as impact indentation. With this technique, we can quantify the penetration resistance, energy dissipation capacity, and energy dissipation rate at loading conditions comparable to ballistic strain energy densities. We identify measurable variations in these three parameters among the different species, suggesting that we need a highly tunable materials system to fully capture the impact response of various brain models. To improve tunability, we have designed bilayered composites consisting of a viscoelastic polydimethylsiloxane (PDMS) organogel beneath a more compliant PDMS solvent-free gel. We can leverage the properties of each individual layer to enable the decoupling of the material&’s penetration resistance and energy dissipation characteristics. Additionally, we find that the impact response of this hierarchical design can be optimized to match that of pig brain for all three parameters by sequentially tuning the thickness and stiffness of the top layer. Together, these results demonstrate that the mechanical response of composite gels under impact loading can be precisely modulated to mimic different brain injury models.

In this work we study biocomposites made from a self-assembled filamentous mass of hyphae -the filament cellular building block of mycelium fungi- grown around and securely anchoring agricultural waste cellulosic particles. These materials are grown directly into the desired shape from entirely biodegradable components, after which the fungi are deactivated by thermal treatment. The composites can be used in a variety of applications, ranging from packaging to infrastructure, in which they replace petroleum-based materials. The objective of the work is to relate the structure of the composite to its mechanical behavior, which will allow structural optimization. In this report we present experimental and modeling results addressing this objective. Specifically, we investigate the effect of hyphae density and preferential orientation, and of the density and size of cellulosic reinforcement particles on the response of the material to compression. A method is developed to construct models statistically similar to the actual material miscrostructure, and these are further used to simulate the mechanical behavior of representative structures. Preliminary results indicate that overall density controls the modulus and yield strength, but the degree of hyphal branching is also important.

The vitreous humor of the eye is a biological hydrogel principally composed of water with collagen interspersed with hyaluronic acid. Certain pathological conditions necessitate its removal and replacement. Current vitreous substitutes, like silicone oils and perfluorocarbons, are neither biomimetic nor without complications. We have developed an in-situ forming biomimetic hydrogel with analogues of collagen and hyaluronic acid, using thiolated gellan and synthetic copoly(methacrylamide/methacrylate), also endowed with thiol side groups. We optimized the formulations of hydrogel based on their gelling temperatures and mechanical properties using response surface methodology (RSM) by varying the concentration of thiolated gellan and co-polymer. The in-vitro biocompatibility and effect on tight junction formation of the optimized formulations were evaluated for primary porcine retinal pigment epithelial (ppRPE) cells, human retinal pigment epithelial (ARPE-19) cells and fibroblast (3T3/NIH) cells using an electric cell-substrate impedance sensing (ECIS) system. The storage moduli of composite hydrogels ranged from 3 to 465 Pa and transition temperatures ranged from 35.5 to 43 ⁰C. The refractive index was 1.335 - 1.338. The composite hydrogel has the ability to swell and does not degrade for three weeks in vitro. The optimized formulations from RSM were biocompatible on the tested cell lines and did not impair the tight junction formation. Combinations of the thiolated gellan and copolymer gave biocompatible hydrogels and allowed for the tuning of mechanical properties and transition temperature of composite hydrogel.

Mother nature presents many sophisticated fibrous materials of advanced mechanical property as well as ligth weight, including spider web, cocoon, cytoskeleton and so forth. Spiders spin intricate webs that serve as a prey-trapping architectures that simultaneously exhibit high strength, elasticity and graceful failure. To determine how web mechanics are controlled by their topological design and material distribution, here we create spider-web mimics composed of elastomeric filaments. Specifically, computational modelling and microscale 3D printing are combined to investigate the mechanical response of elastomeric webs under multiple loading conditions. We find the existence of an asymptotic prey size that leads to a saturated web strength. We identify pathways to design elastomeric material structures with maximum strength, low density and adaptability. We show that the loading type dictates the optimal material distribution, that is, a homogeneous distribution is better for localized loading, while stronger radial threads with weaker spiral threads is better for distributed loading. Our observations reveal that the material distribution within spider webs is dictated by the loading condition, shedding light on their observed architectural variations. Our study provides efficient tools to quickly realize complex elastomeric web structures with optimal mechanical functions and low density to meet critical requests of many engineering applications.

Fragmentation of thin layers of materials is mediated by a network of cracks on its surface. It is commonly seen in dehydrated paintings or asphalt pavements and even in graphene or other two-dimensional materials, but is also observed in the characteristic polygonal pattern on a crocodile&’s head. Crocodile&’s unique pattern is seen in handbags, shoes, and jackets today because of its outstanding mechanics. Here, we first build a simple mechanical model of a thin film and investigate the generation and development of fragmentation patterns as the material is exposed to various modes of deformation. We find that the characteristic size of fragmentation, defined by the mean diameter of polygons, is strictly governed by mechanical properties of the film material. Our result demonstrates that skin fragmentation on the head of crocodiles is dominated by that it features a small ratio between the fracture energy and Young&’s modulus, and the patterns agree well with experimental observations. Understanding this mechanics-driven process could be applied to bio-inspired composite designs. We show that by using an advanced multiple material 3D printer, we can combine several materials with distinctly different stiffness to make material samples with the same fragmentation geometry as the crocodile skin. Our mechanical tests on these samples demonstrate that the alligator fragmentation patterns allow the material to perform better in terms of combining fracture toughness and flexibility. Our study provides a feasible way to design and manufacture crocodile skin-inspired composite materials with the similar mechanical performance as their natural counterparts.

The brown recluse (loxosceles) spider is the only spider known to spin high-aspect ratio silk ribbons with a thickness of only 40-60 nm and a width of 6-8 mu;m. With a modulus of asymp;20 GPa and a strength of asymp;1.6 GPa it is one of the stiffest, strongest, and toughest silks ever tested. New electron-microscopic evidence suggests that the reason for these outstanding mechanical properties is a nanofibrillar organization of the material on the molecular scale. Due to their thinness, corresponding to only a few layers of protein molecules, the silk ribbons are so flexible that they can easily conform to other surfaces and thus maximize contact area, leading to strong adhesion. The spider uses this combination of properties to organize these silk ribbons into structures of extraordinary toughness. We suggest that this material can lead to a new generation of bio-inspired materials with ultra-high energy absorption.

The increasing number of potentially harmful pollutants in the environment calls for fast and effective analytical techniques to be used in extensive monitoring programs. The requirements for application of most traditional analytical methods to environmental pollutants analysis often constitute an important impediment for their application. The need for disposable systems for environmental applications has encouraged the development of new technologies. In this context, biosensors appear as a suitable alternative and a complementary analytical tool^1,2. Biosensors can be used as environmental quality monitoring tools in the assessment of biological/ecological quality.
For environmental applications, the main advantages offered by biosensors over conventional analytical techniques are the possibility of portability, miniaturization, work on-site, and the ability to measure pollutants in complex matrices with minimal sample preparation. Although many of the developed systems cannot compete yet with conventional analytical methods in terms of accuracy and reproducibility, they can be used by regulatory authorities and by industry to provide enough information for routine testing and screening of samples.
Our project aims to improve the performance of algal bio-indicator for heavy metals and pesticides detection. The work started firstly by the optimization of the silica matrix prepared by the sol-gel process³, in order to obtain good optical quality (UV-visible), mechanical stability (compression test) and an optimal gel time allowing the matrix homogeneity.
Then we moved to the encapsulation of different algal cells (anabaena flos-aquae, E.Gracilis, C.Vulgaris and C. reinhardtii), verifying if the best conditions that we found for the optical/mechanical proprieties are also available for the different cells viability (fluorescence microscopy, TEM, SEM).
And finally we studied the interaction between different pollutants (Cd²⁺, Pb²⁺, Antracene) and the encapsulated cells.
[1] K.R. Rogers and C.L. Gerlach, Environmental biosensors: A status report, Environ. Sci. Technol. 30 (1996), pp. 486-491.
[2] K.R. Rogers, Recent advances in biosensor techniques for environmental monitoring, Anal. Chim. Acta. 568 (2006), pp. 222-231.
[3] Coradin, T. & Livage, J., 2007. Aqueous Silicates in Biological Sol - Gel Applications : New Perspectives for Old Precursors. Accounts of Chemical Research, 40(9), 819-826.

Recent years we have witnessed the rapidly increased research interests in bilayer actuators that could be driven by various external stimuli such as light, pH value, magnetic field, humidity and electric, among which light-irradiation has been adopted as a preferred method for actuation, since it shows distinct advantages such as remote-control, non-contact manipulation, high efficiency, and even long-distance operation. From the material point of view, as a light-weight and high-strength carbon materials, graphene and related materials demonstrate outstanding physical/chemical properties, and thus reveal great potential for the fabrication of actuators. Generally, the fundamental mechanism for light-driven actuators is photo-thermal effect which can turn photo energy into heat and cause mechanical deformation. However, for graphene-based materials, light absorption efficiency is still low, which hindered their applications in light-driven systems. We reported here the preparation of Au nanorods (AuNRs) / Graphene oxide (GO) composite which shows high photo-thermal conversion efficiency. Using the AuNRs/GO nanocomposite as active layer, novel light-driven smart actuators have been successfully developed. Fast and sensitive response has been observed due to the difference of thermal diffusion coefficient of the two layers. By mimicking natural creatures such as insect and flycatcher, bio-inspired light-driven robotics have been fabricated. Our graphene-based light-driven robotics may find broad applications in future intelligent systems.

The development of stimulus-responsive actuator is of great importance, especially for the remote contactless actuation. Smart actuators are a common occurrence in nature. In this work, we report a versatile and generalizable method for fabricating bioinspired graphene actuators with low cost, highly durable, well-controlled motion, and broad range of bending angles once in quick response to moisture by UV light irradiation. Surface properties of the GO paper could be drastically changed after UV irradiation for tens of minutes due to the photoreduction effects, in which most of the oxygen-containing groups (OCGs) have been removed. Generally, GO sheets bearing plenty of OCGs adsorb water molecules due to the formation of hydrogen bonds, whereas, in the case of graphene, adsorption of water molecules occurs due to the much weaker Van der Waals forces. In this regard, water molecules would be adsorbed by GO layers in preference to RGO layers. The selective adsorption/desorption of water in the GO layers would cause a significant expansion/contraction effect, leading to a reversible and novel bio-inspired graphene actuator operating under moisture and dry conditions over large areas and direction of actuation. The moisture-responsive property of our GO/RGO bilayer actuator has several attractions including simple manufacture ability, large degree of bending, and no delamination along with the tailor ability of the fabrication process provide possibilities for a series of interesting applications for graphene-based bioinspired actuators. Depending on the controlled pattern, the smart actuator can be programed to fold into different 3-dimentional shapes. The bilayer structures are successfully mimicked the cilia of respiratory tract and tendril climber plant have been developed for controllable objects transport.
References:
[1] Dong-Dong Han, et al., Moisture-responsive graphene paper prepared by self-controlled photoreduction, Adv. Mater. 27, 332 (2015).
[2] Dong-Dong Han, et al., Bioinspired graphene actuators prepared by unilateral UV irradiation of graphene oxide papers, Adv. Funct. Mater. (2015).

Pressure sensing devices have potentials for broad applications, such as electronic skin, detecting physiological signals, tactile displays, soft robotics. To date, pressure sensors based on piezoelectricity, pressure-sensitive rubber, self-powered devices, and organic thin-film provide high sensitivity or flexibility. However, developing device with low-cost, high sensitivity is still desired. Recently, mechanical crack-based sensor inspired by the spider sensory system with high sensitivity to strain and vibration was reported. Despite its superior sensitivity, repeatability, and reproducibility, mechanical crack-based sensor has not yet been used in designing pressure sensors. To satisfy the requirements of various applications, controlling the formation of crack is also required.
Herein, we demonstrate low-cost, ultrasensitive sensor by controlled formation of mechanical crack. The sensor will have patterned hole on the surface of the device that concentrates the stress to particular region. Each hole will precisely generate uniform crack throughout the surface with specific pattern. The controlled crack formed due to patterned hole demonstrates a predictable crack formations that allows to fabricate sensors with reproducibility
The sensors are highly sensitive to strain and pressure. The device can detect physiological signal of wrist pulse and be applied on surface with electronic multi-pixel array. The sensors inhabit flexibility and stretchability, conformal contact to human skin is possible. Furthermore, the theoretical model for nanoscale and microscale combined crack system is proposed in good agreement with experiments.

Imitating the cilia receptor concept from nature is very attractive due to the extremely high sensitivity of such microscale hair-like structures [1,2]. We report the development of artificial cilia sensors, which exhibit a high performance in terms of sensitivity, power consumption and versatility. Cilia are made from a novel magnetic nanocomposite material and their magnetic stray field is measured with a magnetic thin-film sensor underneath the cilia. A force that bends the cilia changes the stray field and is therefore detected with the magnetic sensor.
The nanocomposite is made of 6 µm long and 35 nm in diameter iron nanowires (NWs) incorporated into polydimethylsiloxane (PDMS). Iron NWs have a high remanent magnetization, due the shape anisotropy; thus, they are acting as permanent nano magnets. This allows remote device operation and avoids the need for a magnetic field to magnetize the NWs, benefiting miniaturization, integration and the possible range of applications. The magnetic properties of the nanocomposite can be easily tuned by the NW concentration or by aligning the NWs during the fabrication process to define the magnetic anisotropy. We developed a mold-based fabrication process to create artificial cilia from the nanocomposite, which maintain the high elasticity, biocompatibility and corrosion resistance of PDMS. The cilia have different lengths from 20 mu;m to 1 mm with different diameters from 5 mu;m to 200 mu;m.
By using individual cilia sensors as well as arrays of cilia sensors, we realize tactile sensors on flexible and rigid substrates that can detect flow, vertical and shear forces statically and dynamically. Tactile sensors are core elements of, e.g., smart skins to mimic the complex sense of touch in humans. These skins are important for applications like robotics, smart surgical tools or health monitoring system.
The sensors can detect forces with a high resolution of 0.8 mN (0.22 kPa), an operating range up to 750 mN (190 kPa) and an extremely low power consumption of 80 nW. The advantage to operate the sensors in liquids and air has been utilized to measure flows in different fluids in a microfluidic channel. Flows are detected with a resolution of 0.95 mm/sec for air, and 16 mu;m/s for water. Various dynamic studies were conducted with the tactile sensor demonstrating the detection of moving objects or the texture of objects.
Overall, the results confirm the possibility to easily control the sensors&’ performance with the cilia arrangement and dimensions. The microfabrication process and magnetic operation enable a high degree of integration, which together with the extremely low power consumption make the artificial cilia sensor reported here an attractive solution for many applications.
[1] C. Liu, “Micromachined biomimetic artificial haircell sensors,” Bioinspir. and Biomim., vol. 2, pp. S162, 2007.
[2] A. Alfadhel, et al., “Magnetic nanocomposite for biomimetic flow sensing,” Lab Chip, vol. 14, pp. 4362, 2014.

Electronic skin (E-skin) imitates the sophisticated human skin in sensing various surrounding, such as perceiving multifariously dimensional object, temperature changing, multiscally physical pressure variation. Creating emulational skin for obtaining the corresponded electrical signal leads in intelligent robot, prosthetics, real-time ubiquitous health care. Recently, visible efforts have promoted the development of electronic skin frontiers demonstrated with organic/inorganic semiconductor by Bao, Someya, Javey groups, inorganic serpentine interconnects by Rogers and Kim groups, reversible interlocking of nanofibres by Suh group etc (for example, conductive polymer, graphene, and carbon nanotube or silver assemblies). However, insufficient sensitivity and instability in detecting high pressure regime of these devices still presents challenge in 'real skin' detecting range.
In this work, we present the whole new type of multimodal pressure sensor based on the hierarchically assembled ionic material operating by 1mV ultralow power supplement shows a remarkable sensitivity up to 8.96 nF kPa^-1 at extremely small dimension. Significantly, the stably sensitivity range of our ionic mechanotransduction sensor unprecedentedly covers broad detecting pressure regime applied in intelligently voice identification, human health monitoring and heavy measurement towards the realization of sophisticated human skin.
Our model system based on ionic mechanotransduction mechanism provides a worthy route for the future electronic skin development into maturity.

Electronic skin (e-skin) is of great importance in the various fields including robotics, healthcare, wearable electronics, and medical applications. Achieving the highly-sensitive and ultra-fast e-skin, we introduce a novel design of bio-inspired structure composed of hierarchical polydimethylsiloxane (PDMS) micropillar arrays decorated with ZnO nanowire (NW) arrays in an interlocked geometry. The interlocked and hierarchical structured e-skin based on ZnO NW arrays can perceive both static and dynamic tactile stimuli through piezoresistive and piezoelectric transduction modes, respectively. In addition, the interlocked hierarchical structures enable a stress-sensitive variation in the contact area between the interlocked ZnO NWs and also the efficient bending of ZnO NWs, which allow the sensitive detection of both static and dynamic tactile stimuli. Our e-skin in a piezoresistive mode shows a high pressure sensitivity (-6.8 kPa^-1) and an ultra-fast response time (<5 ms), which enables the detection of extremely small stimuli such as minute static pressure (0.6 Pa), vibration level (0.1 m/s²), and sound pressure (~57 dB). On the other hand, our flexible e-skin in a piezoelectric mode can perceive fast dynamic stimuli such as high frequency vibrations (~250 Hz). The suggested design of our bio-inspired e-skin, which allows the simultaneous perceptions of static and dynamic tactile stimuli, may find applications requiring both static and dynamic tactile perceptions such as robotic hands for dexterous manipulations and various healthcare monitoring devices.

One of the most basic principles of materials science is that materials respond, adapt, and undergo transformations in the presence of an applied stimulus. Though atoms and their transformation processes are fairly well understood, it yet remains a big challenge to dynamically control and generate reversible transitions of nanoparticle assemblies. DNA-mediated nanoparticle assembly has generated superlattices with synthetically adjustable lattice parameters and crystal symmetries, just as cells differentiate into tissues or as atoms assemble into solid state structures. However, the majority of these superlattice structures remain static once constructed, and factors such as interparticle distance or crystal phase cannot be controllably altered in a facile and rapid manner, furthering the analogy to atoms. Incorporation of these materials into functional devices would be greatly benefitted by the ability to change various aspects of the crystal assembly after the lattice has been synthesized. In this work, we present a reversible, rapid, and stoichiometric on-the-fly manipulation of nanoparticle superlattices that, like biological entities or atoms, respond and undergo transformations in the presence of an applied stimulus. Unlike atomic systems in which change in crystal structure requires a complete change in the composition of the building blocks, DNA can introduce dynamicity in lattices without having to change the entirety of every construct.

Enzyme-mediated signal amplification has been extensively used in labs for sensitive detection of analytes, but its application for point-of-care (POC) detection has been limited due to the fragile nature of enzymes. Herein, we developed a simple and sensitive bioassay device based on enzyme-mimetic nanoparticles (NPs) that retain enzyme-like activity under harsh environments. Hierarchically-structured Platinum NPs (H-Pt NPs) with excellent peroxidase-like activities were synthesized and characterized. H-Pt NPs were conjugated to an antibody for detecting analytes, and successfully integrated into lateral-flow immunoassay (LFIA) strips, which are widely-used POC bioassay devices. Quantitative analysis based on digital images of strips acquired by smart cellular phones revealed that H-Pt NP-based LFIA strips were about 20 times more sensitive than conventional LFIA strips.

In the immune response cells are able to detect extremely small differences in chemoattractants or chemokines concentrations, they can detect a 1% difference in concentration across the cell body, and move along those gradients to heal a wound or attack invading cells. This process is most commonly referred to as chemotaxis however leukocytes, endothelial, axons, and numerous other cell types perform a related type of directed motion called haptotaxis. Haptotaxis is distinguishable from chemotaxis in that the gradient in chemoattractant is bound to a surface, typically the ECM, as opposed to a developing in a soluble fluid. The cell will then migrate toward regions with the largest number of binding sites or alternatively towards more highly adhesive regions. This is perhaps most notably observed in the rolling of leukocytes and adhesion to blood vessel walls via interaction with selectins. However, in biological systems there are a myriad of interactions occurring instantaneously and these interactions can vary drastically in the strength of the interaction, the speed at which interactions occur, and the duration of the interaction. When multiple interactions occur any of these factors can determine which particular interaction dominates or more accurately which interaction is more adhesive. Here we propose a novel and versatile bioinspired artificial system that is able to detect differences in effective friction induced by a wide range of transient interactions. Our system utilizes ferromagnetic particles that can be easily functionalized with a receptor of interest and a substrate which can similarly be coated with the corresponding ligand. A rotating magnetic field is applied which couples to the magnetic moment of the ferromagnetic particles causing them to rotate and this rotational motion is then converted into translational motion via the effective friction or adhesion induced by binding events between the ferromagnetic particles, henceforth referred to as rollers, and the substrate. By measuring the translation of the rollers, relative to a baseline where only hydrodynamic friction occurs, we can measure the effective friction induced by a myriad of transient interactions including ionic, metal-coordination, hydrophobic, antibody-antigen, biotin-streptavidin, and amino acid interactions. By changing the rotational frequency of the magnetic field the dynamics of these interactions and the subsequent effect on the effective friction between the rollers and the substrate can be measured as well. These rollers can also detect extremely small gradients in the density of binding sites and when randomly actuated exhibit a haptotaxis like response by migrating towards more adhesive regions. This bioinspired haptotatic sensing roller system will allow us to study the underlying physical phenomenon of haptotaxis and in doing so allow us to better understand the more complex biological system and processes of interest.

Cephalopods can display dazzling patterns of colors by selectively contracting muscles to reversibly activate chromatophores - pigment-containing cells under their skins. Inspired by this novel coloring strategy found in nature, we design a mechano-chemically responsive elastomer system that can exhibit a wide variety of color patterns under the control of mechanical forces and electric fields. We covalently couple a stretchable elastomer with mechanochromic molecules, which change color and emit strong fluorescent signals if sufficiently deformed. We then use electric fields to induce various patterns of large deformation on the elastomer surface, which displays versatile color patterns including lines, circles and letters on demand. Theoretical models are constructed to understand the mechano-chemical behaviors and to guide the design of elastomers and devices. The material and method open promising avenues for creating flexible displays with topological and chemical changes in response to a single remote signal.

Magnetic nanoparticles (MNPs) are essential materials in the quest to miniaturize a variety of devices and in several biomedical applications. Controlling the morphology of these MNPs and the higher order structures that they form is crucial for controlling and manipulating their functional properties. There are several inorganic processes to synthesize uniform MNPs, but they typically require extreme reaction conditions such as high temperatures or harsh reagents, rendering them unsuited for making functionalized MNPs with tunable properties controlled by biomolecules. Biomimetic procedures, inspired by the production of uniform magnetite crystals in several magnetotactic bacteria, provide an alternative method, which can be performed at ambient conditions. Mms6, an amphiphilic protein found in the magnetosome membranes in Magnetospirillum magneticum strain AMB-1, has been shown to control the size, shape and monodispersity of magnetite nanoparticles, both in-vivo and in-vitro. In this work, we show patterning of Mms6 and magnetite nanoparticles on surfaces by directed self-assembly, which has applications in the field of bit-patterned media and biosensors. A template stripped gold surface was patterned with 1-Octadecane thiol (ODT) by microcontact printing and backfilled with a protein resistant poly (ethylene glycol) methyl ether thiol (PEG) layer. It has been found that hydrophobic surfaces such as ODT monolayer on gold have a higher affinity for Mms6 than bare gold or PEG coated surfaces because of the hydrophobic N-terminal region of the protein. Mms6, expressed in E. coli, was incubated on this pattern. Hydrophobic interactions between the self-assembled monolayer of ODT and the N-terminus of Mms6 are expected to cause the protein to adsorb on ODT and align so that the C-terminus is exposed. This is significant for the binding of iron ions and forming nanocrystals as the C-terminus of Mms6 has been shown to play a critical role in the formation of uniform magnetite nanoparticles. AFM and fluorescence microscopy studies show the patterning of Mms6 on the ODT-PEG template. A polyclonal, FITC-conjugated antibody that binds to a specific region in Mms6 was used as the fluorescent tag. AFM scans showed a network structure of the protein on the ODT monolayer, with an average structure height of around 10 nm. Magnetite was grown on these surfaces by a co-precipitation method and was immobilized by the protein. AFM and SEM results show the patterning of magnetite on the Mms6 template, which in turn was templated by the ODT-PEG pattern. Elemental mapping on the patterns was obtained by XPS to corroborate the templating action of ODT-PEG patterns and Mms6. Magnetic force measurements were conducted to assess the localization of magnetic nanoparticles on the pattern. Thus, we were able to create patterned magnetite structures on gold surfaces templated by Mms6.

The tunable structural colors exhibited by organisms such as cephalopods and chameleons provide inspiration as a motif for sensors, display elements, and adaptive camouflage. In particular, one-dimensional (1D) photonic crystals containing stimuli-responsive elements have received considerable attention as bio-mimetic systems due to their relatively simple structure and fabrication. While polymer-based multilayers have met with considerable success in this regard, the inherently limited range of refractive indices available from typical polymers limits the device performance that can be achieved. In this regard, hybrid multilayers containing both responsive polymers and high-index inorganic materials hold great potential. We present a straightforward approach to fabricate composite photonic multilayers with high reflectance efficiency based on photo-crosslinkable polymer nanocomposite films prepared from suspensions of high index ZrO₂ nanoparticles and benzophenone-containing copolymers. Through incorporation of 40 - 50% by volume of nanoparticles, refractive indices are increased by up to 10%, allowing 2.5-fold improvements in reflectance efficiency at constant layer number, without deterioration of optical characteristics. Using temperature-responsive hydrogels as the low index layers, we characterize the thermochromic behavior of these nanocomposite photonic multilayers.

Large-area arrays of flexible electric double-layer micro-capacitors (m-EDLC) have been fabricated into mechanically robust graphene oxide-silk fibroin (GO-SF) nanocomposite biopapers using a parallel electrochemical reduction technique that produces high-resolution, high-conductivity patterns which can be used as microelectrodes. In contrast to previously reported GO-based devices that have carbonized electrodes or laser-scribed electrodes, this technique produces functional integrated microelectrodes that retain the superior mechanical properties of freestanding GO-SF bionanocomposites (elastic modulus ~ 26 GPa, ultimate stress ~ 320MPa). High resolution of reduction enables fine interdigitation, increasing the ion-accessible interface for maximizing charge storage. In the precursor GO-SF nanocomposites, silk acts as a binder coordinating the lamination of graphene oxide flakes—adjusting the silk concentration in m-EDLCs enables a facile route for controlling spacing between the lamellar GO flakes, tuning ion mobility and device performance. Preliminary work show sandwich-type GO-SF EDLCs exhibiting a specific capacitance of around 100 F/g when cycled at 5 mV/s that are both flexible and highly resilient under mechanical stresses. These proof of concept m-EDLCs fabricated in GO-SF bionanocomposites demonstrate a novel technique for producing energy storage components in strong, yet flexible, bio-inspired composite materials, with diverse promising applications ranging from self-powered devices to human-interfaced sensors.

Although sutures, staples and clips are commonly used for wound closure and surgical repair, these mechanical devices are a source of chronic pain and nerve damage. Tissue adhesive can potentially overcome these limitations. However, the existing adhesives present many drawbacks such as poor adhesive strength (e.g., fibrin glue), cytotoxicity (e.g., cyanoacrylate adhesive) and lacking bioactivity (poly(ethylene glycol) (PEG)-based adhesive). PEG is a biocompatible and bioinert polymer commonly used in designing various biomaterials. However, its lack of bioactivity limits its ability to promote cellular attachment and infiltration needed for rapid tissue repair and regeneration. To simultaneously improve the adhesive property and bioactivity of PEG-based adhesive, gelatin microgels were incorporated into dopamine-modified poly(ethylene glycol) (PEGDM) adhesive. Dopamine mimics the catechol group-containing amino acid found in the mussel adhesive protein, which is responsible for rapid curing and interfacial binding of the protein in a saline and wet environment. Gelatin microgel, with an average diameter of 53.6±14.2mu;m, was prepared with water in oil emulsification method and chemically crosslinked with EDC and NHS. Gelatin microgels were incorporated into PEGDM adhesive precursor solution at 1.5wt%, 3.75wt% and 7.5wt%. The cure time of the adhesive reduced from 54 seconds to 37 seconds with increasing gelatin content. Additionally, the incorporation of the gelatin microgelalso increased the crosslinking density of the adhesive network as indicated by the reduced equilibrium water content and increased elastic modulus based on compression testing. The compliance of adhesive was not compromised with the increased crosslinking density, as the failure strain showed no significant decrease from the compression testing result. Results from oscillator rheometry indicated that both the storage and loss moduli of the adhesive increased with increasing microgel content. From lap shear adhesion testing, the addition of gelatin microgel improved the adhesive property of PEGDM by more than 1.5 fold using wetted pericardium tissue as a model substrate. In the in vitro degradation test, samples of different formulation groups degraded gradually under a similar rate after soaked in the phosphate buffer solution and incubated at 37#8451;. After 8 weeks samples were completely degraded. The cell viability was tested with L929 mouse fibroblast and the results showed no cytotoxicity in each test formulation. The in vitro cell attachment experiment revealed an enhanced cell attachment and spreading of primary rat dermal fibroblast on gelatin microgel containing PEGDM adhesive compared to the adhesive without gelatin microgel. In conclusion, gelatin microgel incorporation presents a simple method to simultaneously enhance the adhesive property and bioactivity of PEG-based adhesive.

Despite the material selection limitations faced by biological systems, many natural composites achieve superior toughness and strength to weight ratios through the precise ordering of their microscopic building blocks. Structural bio-composites such as bone, nacre, and stomatopod shells exhibit mechanical properties far exceeding that of their individual elements due to their hierarchical reinforcement. Understanding the strengthening mechanisms of various structural bio-composites can lead to implementing these designs in high performance man-made composite materials. However, there is currently a gap between understanding these structures and being able to successfully assemble them. This research covers a new approach for obtaining polymer-based composites exhibiting bio-inspired, deliberate orientation of reinforcing particles using additive manufacturing.
In this work, we detail a distinctly different approach termed 3D Magnetic Printing that employs directed colloidal assembly in concert with the 3D printing process to provide complete and programmable control over the orientation of reinforcing particles within a composite. Our method uses super-paramagnetic iron oxide nanoparticles which coat less than 5% of the surface of each filler element. The labeled fibers can then be manipulated using low magnetic fields (<100 Gauss) during the printing process to create composites with tunable, hierarchical reinforcement. We have manufactured composites with elegant reinforcement architectures that feature hard and soft phases on the order of microns. The printed materials are designed with feedback from finite element analysis in order to optimize reinforcing architectures and lead to enhanced stiffness (3-fold increase over neat polymer), increased strength, and higher fracture energy properties.
This method is robust, low cost, scalable, sustainable, and will enable an entirely new class of strong, lightweight composite prototypes with programmable properties. To demonstrate the capability of this technique, we recreate choice reinforcement architectures exhibited by biological discontinuous fiber composite systems including the osteon structures within human cortical bone, the layered nacreous shell of mollusks, and the cholesteric reinforced dactyl club of the peacock mantis shrimp. The overarching architectural design in each natural composite is conveyed in terms of a microstructure translated to platelet reinforcement. These microstructures are imported into our 3D magnetic printing framework to create bulk composite blocks with fine-tuned, bioinspired microstructural design. We offer a path forward on using 3D Magnetic printing to produce composite materials with tailored, optimized mechanical properties regardless of having complex geometries. The capability of creating materials with deterministic material properties lends itself to multifunctional materials with applications in aerospace, biomedical, and embedded electronics.

Recent advances in biomimetic fabrication continue to stimulate the development of artificial materials and functional surfaces that possess fascinating properties similar to natural creatures. Biomimetic fabrication has long been considered a short cut to the rational design and production of artificial materials or devices that possess fascinating properties, just like natural creatures. Considering the fact that graphene exhibits a lot of exceptional properties in a wide range of scientific fields, biomimetic fabrication of graphene multiscale structures, denoted as biomimetic graphene, is of great interest in both fundamental research and industrial applications. Especially, the combination of graphene with biomimetic structures would realize structural and functional integrity, and thus bring a new opportunity of developing novel graphene-based devices with remarkable performance. Additionally, femtosecond laser direct writing (FsLDW) has been established as a nano-enabler to solve problems that are otherwise not possible in diversified scientific and industrial fields, because of its unique three-dimensional processing capability, arbitrary-shape designability, and high fabricating accuracy up to tens of nanometers, far beyond the optical diffraction limit. In this presentation, we highlight our recent advances in biomimetic graphene films and their structuredefined properties. Functionalized graphene films with multiscale structures inspired from a wide range of biomaterials including rose petals, butterfly wings, the cilia of respiratory tract and tendril climber have been presented. Moreover, both current challenges and future perspectives of biomimetic graphene fabricated by Femtosecond laser are discussed. Although research of the so-called ‘‘biomimetic graphene&’&’ is still at an early stage, it might become a ‘‘hot topic&’&’ in the near future. We anticipate that the bioinspired graphene films would find broad application in various scientific fields, maybe beyond we can expect.
References:
[1] Yong-Lai Zhang, et al., Designable 3D nanofabrication by femtosecond laser direct writing, Nano Today 5, 435 (2010).
[2] Yong-Lai Zhang, et al., Direct imprinting of microcircuits on graphene oxides film by femtosecond laser reduction, Nano Today 5, 15 (2010).
[3] Yong-Lai Zhang, et al., Bioinspired fabrication of superhydrophobic graphene films by two-beam laser interference, Adv. Funct. Mater. 24, 4595 (2014).
[4] Yong-Lai Zhang, et al., Moisture-responsive graphene paper prepared by self-controlled photoreduction, Adv. Mater. 27, 332 (2015).
[5] Yong-Lai Zhang, et al., Bioinspired graphene actuators prepared by unilateral UV irradiation of graphene oxide papers, Adv. Funct. Mater. (2015).
[6] Yong-Lai Zhang, et al., Biomimetic graphene films and their properties, Nanoscale 4, 4858 (2012).

The capability of manufacturing patterns in sub-wavelength is crucial in nanotechnology. However, most strategies involved in the fabrication of sub-10 nm features are tedious and require complicated instruments. In the current study, a simple and facile spacer lithography approach utilizing mussel inspired dopamine chemistry has been demonstrated for the fabrication of sub-10 nm patterns. Poly (methyl methacrylate) (PMMA) was nanoimprinted to form resist patterns and a thin layer of polydopamine (PDA) directly self-polymerized on the sidewall of PMMA patterns. After removing of PDA residue layer and PMMA resist, free-stand PDA sidewall patterns were achieved with higher pattern density and smaller size than the initial resist patterns. The feature size of PDA patterns can be tuned to less than 20 nm by controlling PDA coating condition and further reduced to around 10 nm by carbonation. This report represents a scalable and cost-efficient technique for preparing ultrafine nanopatterns.

Graphene oxide-Silk composites have gained a significant interest in the recent times because of their ability to form layered structures that exhibit a striking resemblance to the hierarchical materials in nature such as nacre. However, the mechanism of the interaction of silk and graphene oxide still remains unclear. Silk proteins are comprised of hydrophobic and hydrophilic domains that possibly interact preferentially to the respective domains on the amphiphilic surface of graphene oxide. We note that the interaction between the silk molecules and graphene oxide (GO) can be modulated by tuning the pH of the silk solution and the degree of reduction of GO. While under acidic pH conditions (pH

Developing effective and environmentally friendly methods for environmental applications such as cleaning oil spills and frictional drag reduction has attracted significant research efforts worldwide. In nature, many exceptional properties of organisms originate from micro- and nanostructures on their surfaces. Inspired by examples of water-repelling semiaquatic insects and floating plants, we developed a nanofur material covered by a layer of densely packed randomly distributed nano- and microhairs. Nanofur is fabricated by structuring conventional and biodegradable polymers using a highly scalable hot pulling method. In this technique, a heated sandblasted plate is used to soften polymers and locally elongate them, resulting in wettability change from hydrophilic to superhydrophobic with contact angles up to 174^o. The properties of the as-prepared superhydrophobic nanofur can be tailored to satisfy specific requirements in cleaning oil spills and frictional drag reduction applications.
The as-prepared superhydrophobic/superoleophilic nanofur absorbs crude oil out of water and separates oil/water mixtures. Its oil absorption capacity can be varied by the nanofur fabrication parameters. Moreover, inspired by underwater superoleophobicity of fish scales, the nanofur surface properties can be changed to underwater superoleophobic by plasma treatment, making the nanofur capable of removing water from oil/water mixtures. Also, we fabricated microporous nanofur filters which allow continuous selective removal of water or oil from oil/water mixtures, and emulsion separation. Furthermore, bioinspired nanofur possesses an air-retaining property necessary for reducing frictional drag, as the underwater air film minimizes the water-solid contact area. The measured pressure drop across microfluidic channels lined with nanofur is approximately 50% lower than in unstructured channels, indicating a significant drag reduction by the nanofur. In addition, the air film retained by the nanofur underwater is highly stable under applied hydraulic pressure.

Regulating permeation through materials is crucial for selective membranes, controlled drug delivery, and packaging. An ideal membrane material passes the desired molecules with little resistance while preventing the passage of all else, but synthetic materials today cannot meet this challenge. There are no commercially available membranes that can separate small molecules of similar size in the liquid phase based on their chemical properties. In contrast, biological pores like porins and ion channels regulate the transport of a huge array of molecules and ions into and out of cells with great efficiency and selectivity. These highly selective pores are lined with functional groups that selectively interact with their target. Pores are only slightly larger than their target molecule, confining permeation and forcing contact with the chemically functional walls. Mimicking these systems, we have developed two methods to create networks of functional nanochannels as small as ~1 nm in diameter through polymer self-assembly, and studied their effectiveness in regulating permeation.
The first method utilizes the self-assembly of a graft copolymer with poly(ethylene glycol phenyl ether acrylate) (PEGPEA) side-chains into bicontinuous ~1-3 nm PEGPEA domains through which transport occurs. We compared the diffusion rates of several small molecules through this copolymer with those through a cross-linked, homogeneous film of PEGPEA., and correlated these rates with the size of each solute, and its chemical affinity to PEGPEA. Diffusion rate through the homogeneous polymer film was controlled by solute size, whereas diffusion rate through the copolymer was strongly controlled by the difference between the solubility parameters of the solute and PEGPEA. Permeation selectivity between two selected molecules was significantly higher for the nanostructured copolymer, likely enhanced by the nanoconfinement effects.
In the second study, we prepared random copolymers that combine hydrophobic fluorinated repeat units of trifluoroethyl methacrylate (TFEMA) with ionizable repeat units of methacrylic acid (MAA). We found that these copolymers form micelles in methanol. Micelle size can be tuned between 8-35 nm by the addition of various salts. When these micelles are coated onto the surface of a porous support membrane, a selective layer of micelles packed together is formed. The gaps between the micelles act as carboxylic acid functionalized nanochannels. The membranes show charge-based selectivity between organic dyes. A negatively charged dye is retained by >85% whereas a positively charged dye with a similar molecular size is retained by <30.
These two studies demonstrate new ways of using polymer self-assembly and functionality to design membranes that mimic biological pores while maintaining scalable manufacturing methods. These approaches may lead to novel membranes that can separate molecules based on their chemical structure.

Small molecular hydrogel formed by supramolecular interaction is a raising category as a new and potent soft material. One group of small molecular hydrogelator based on peptide motif is gaining particular interests in biology applications for their high compatibility and degradability in bio-system. As peptides are naturally the building block of life system, they can be easily designed to avoid immune response and also be clean from circulation without extra burden to body via the help of peptidase. These properties of peptide based small molecular hydrogels are right the problems that traditional polymer hydrogel faced in real-case application. Encouraged by these natural advantages, many groups have developed hydrogel systems based on peptide for bio-application ranging from tissue engineering, 3D-culture, controlled release of cargo drug to cancer therapeutics. Although many efforts have been given to peptide based small molecular hydrogels, the majority of works focus on the chemical and physical properties of the hydrogels (chemical composition, mechanical properties, ect.), the biological properties, the cellular response to the hydrogelators, are still lack of systematic study.
In the recent years, our group have developed many small molecular hydrogelators consisting of a naphthalene group and short peptide sequence. All hydrogelator has a head group of naphthalene and a phenylalanine, which serve to provide sufficient aromatic-aromatic interaction for supramolecular assembly. In the work, we investigate the cell response to hydrogelators in several of our model peptide based small molecular hydrogel systems featuring conjugation with functional groups, peptidase substrate and fluorophore. The results will serve, as instruction for better design of hydrogel to either avoid or induce desired cellular response.

Organ-on-chip technologies rely on the ability to precisely and reliably engineer organized tissues in order to achieve quantitative impact in small tissue sizes. Current techniques to build organized cardiac tissue rely on the micropatterning of hydrogels. However these techniques are costly, imprecise, low-throughput, and labor intensive approaches that require the design, fabrication and manual alignment of masks and stamps. To address these limitations, we have developed a high-throughput maskless optical method for micropatterning gelatin hydrogels for heart-on-chip applications. Here, we have exploited the established clinical approach for optically stiffening and shaping collagen matrixes using a UV-A sensitive crosslinking agent, riboflavin 5-phosphate. We have adapted a UV laser engraver with a wavelength of 355nm and 15um beam size to selectively etch and cross-link the surface of a riboflavin-treated gelatin substrate and - through the resulting differences in gelatin height and swelling - create a microscale line topology. This procedure can be easily scaled to batch-processing without losing precision, and the pattern can easily be modified by adjusting laser path and etching parameters. We used liquid contact atomic force microscopy (AFM) to quantify line parameters and substrate stiffness as a function of laser parameters. For our particular line pattern, AFM revealed a sinusoidal surface topology with wave amplitudes on the order of micrometers, and wavelengths on the order of 10^th of micrometers, which is consistent with the spatial resolution of the laser beam and suitable for mammalian tissue engineering. Further, UV-cross-linked trenches exhibit a Young&’s Modulus of 550kPa compared to 50kPa on the untreated surface, suggesting that differential swelling contributes to the surface topology. We next identified line patterns suitable for cardiac tissue alignment using the standard micropatterning technique (micromolding) as our benchmark. Neonatal rat ventricular myocytes (NRVMs) seeded on optimally UV-laser patterned gelatin and micromolded gelatin exhibit a similar degree of anisotropy as cells on micromolded gelatin, as quantified using the orientational order parameters (OOP) [0.5-0.7]. Furthermore, to demonstrate contractile function, we have successfully engineered NRVM muscular thin films on UV-patterned gelatin. Maskless UV-laser optical micropatterning allows for fine control of structural properties of hydrogels such as elastic modulus and feature size. Furthermore, this tissue engineering approach also enables the high-throughput fabrication of precisely patterned substrates for organs on chip technologies.

Two-dimensional materials are of increasing interest due to their unusual properties for use in filtration, sensing, nanoelectronics and biomedical devices. Using a class of biomimetic polymers called peptoids, we have succeeded in making defect-free 2D crystalline materials that exhibit the ability to self-repair on a range of solid substrates under suitable pH conditions, regardless of whether the substrates is negatively or positively charged. Moreover, we have shown that we can utilize this property to create nanoscale patterns of one peptoid within 2D sheets assembled from a different peptoid. To do so, we use an AFM-based method called nano-shaving to produce peptoid-free patterns within a pre-assembled sheet. Upon introduction of a second peptoid solution, the peptoids begin assembling at the active edges generated by nanoshaving. During the repair process, we find that the speed of the advancing edge depends on the direction of edge relative to the outer edge of the sheet and correlates with the aspect ratio of the as-grown sheets. This in turn reflects the two-fold symmetry of the underlying peptoid lattice. The mechanism of self-repair will be discussed. Finally, because these sheets are stabilized by hydrophobic interactions, if the solution contains peptoids having an identical sequence in the hydrophobic block, they will fill in the defects to form the nanopatterns even if the hydrophilic regions are distinct. Consequently, we can assembly sheets exhibiting multiple functional groups on their surfaces for a range of potential applications.

Cephalopods such as squid, cuttlefish, and octopus have the ability to dynamically alter their appearance for camouflaging and signaling. This capability is supported by the selective areal expansion of pigmented organs, known as chromatophores, in the dermal tissue. Chromatophores house networks of pigmented granules within a cytoelastic sacculus that is anchored radially by muscle fibers. As they are actuated, the chromatophores expand by 500% distributing the pigmented granules throughout the organ while maintaining their richness in color. The optical properties of these structures are thought to arise from the interaction between the various proteins and small molecules present in the granules; however, the molecular contribution to bulk coloration remains unknown. We measured the absorbance and fluorescence of chromatophore pigment granules isolated from squid Loligo pealei. The granules showed a peak absorbance at 555 nm and at least 5 distinct fluorescence emission peaks, ranging from 422 nm to 700 nm. An acidified methanol solution was used to isolate visible color of the granules, suggesting most visible color can be extracted, leaving behind weakly absorbing protein granules. After extraction, the soluble pigment exhibited an absorbance peak at 500 nm, a shift of 55 nm from the original granules, and only three fluorescence emission peaks, at 538 nm, 587 nm, and 630 nm. Mass spectrometry and scanning electron microscopy of the pigments extracted from the chromatophore granules suggest that both granule structure and composition influence the spectral properties of the pigments—an important design feature that may lead to the development of artificial chromatophores for flexible optical displays.

A new concept of organic-inorganic interface compatibilization using specifically selected peptide-polymer conjugates is successfully applied for the improvement of mechanical properties of hybrid materials. The concept is based on the sequence specific interaction of peptide with the inorganic surface. ^1,2 The idea of using peptide-polymer conjugate³ as compatibilizers is inspired by natural hybrid materials such as nacre or bone, where proteins or conjugated systems (proteoglycans) recognize the inorganic surface and optimize the connection between the inorganic filler and organic matrix, thereby giving rise to the outstanding mechanical performance of biomaterials. ⁴
The compatibilizer combines a selected peptide sequence, which specifically adheres to MgF₂ surface, and a polymer-block to compatibilize the inorganics with the polymer matrix. A peptide sequence was biocombinatorially selected from a phage display library containing ~10⁹ different sequences.⁵ Peptide-PEO conjugate as a tailor-made compatibilizers is incorporated in the polymer composite material, composed of MgF₂ submicron particles and PEO, which is considered as a model system for complex biomaterials.
The material structure is studied with electron microscopy techniques (SEM, TEM) and AFM. The interactions in the material and the changes in the material are followed with IR spectroscopy, while material properties are explored with tensile tests. We find that both stiffness and toughness of the material increase simultaneously by the addition of the conjugates to the system. Moreover, the fracture mechanism upon deformation is changed from shear bands to crazes.
Rearrangement of amino acid sequence in the peptide does not lead to improved mechanical properties, indicating specificity of compatibilizer and peptide-particle interaction. Several amino acids residues were identified that play a crucial role in the interaction of nanoparticles with peptides. Interaction of peptide sequence with the inorganic surface is studied by NMR spectroscopy in the solution. The new concept of bioinspired interface compatibilization and resulting polymer-based materials enable to draw links to biological systems like for instance bone and nacre and offer the new ways for the design of biomimetic materials.
¹ T. Schwemmer et al, J. Am. Chem. Soc, 2012, 134 , 2385-2391.
² M. Sarikaya et al, Nature Mater., 2003, 2, 577
³ H.G.Börner, Prog. Polym. Sci., 2009, 34, 811-851.
⁴ P.Fratzl et al, Phys. Chem. Chem. Phys.,2004, 6, 5575
⁵ F.Hanszlig;ke et al, Small. 2015, DOI: 10.1002/smll.201500162

Natural materials have extraordinary mechanical properties, which are based on sophisticated arrangements and combinations of multiple building blocks. One key aspect of current materials research therefore is to develop bio-inspired materials reaching to the properties of natural materials - or even exceeding those in certain functionalities. Most constituents used in biology are in terms of their intrinsic properties inferior to synthetic materials because energy as well as material quality and availability are scarce. The excellent performance of many biomaterials originates from a combination of hard and soft building blocks in a multilevel hierarchical structure. A hard inorganic component serves as the reinforcing part while the soft (bio)polymer allows dissipating energy. The morphology of the mineral blocks and chemical bonding between them provides a physicochemical basis for stiffness and flexibility at multiple scales, leading to an increased robustness against catastrophic materials failure. Although strong and stiff synthetic composites have long been developed, the microstructure of today&’s most advanced composites has yet to achieve the order and sophisticated hierarchy of hybrid materials built up by living organisms in nature.
We have exploited the structure-function relation of nanoscale assembly to synthesize hard and tough nanocomposites from metal oxide nanoparticles (Fe₂O₃ and BaTiO₃) and “sticky” polymers. With Young&’s moduli close to 20 GPa and a hardness of approximately 1 GPa the resulting materials exhibit high resistance against elastic as well as plastic deformation. The cross-linked composites are highly uniform, flexible, and transparent. These results can be explained from the nanoscale dimensions of the inorganic phase and the close packed arrangement of the cubic nanoparticles. The metal oxide nanoparticles and polymer are strongly cemented together by chelation of the polymer or its molecular precursors cross-linked in a subsequent step by radical polymerization.
In conventional particle-reinforced composites the particle size is in the micron range, and the particles carry a major portion of the load. They strengthen the material by impeding slip and dislocation, but do not react with the matrix. In the polymer-crosslinked colloidal crystals many strong metal-polymer (e.g. M-catechol or M-hydroxamic acid) bonds must be broken prior to mechanical failure. The individual nanoparticles are too small to break. In essence, (i) the perfectness of the colloidal crystal and (ii) the strong crosslinking between the particles and the multidentate polymer ligand make the matrix resistant to deformation and the resulting composite hard and strong. The resulting structure has the characteristics of adhesion and high tensile strength, the hallmark of the original biocomposites in nature. The E-moduli of the new metal oxide/polymer nanocomposites are among the highest reported for inorganic nanoparticle/polymer composites.

Human mechanoreceptors, located at the fingertip, generate electrical pulses (action potentials) at dynamic pressurizing events, such as object contact or slip. To mimic the action potential and the selective response made by the mechanoreceptors only at dynamic pressurization events, a graphene-based pressure variation sensor, called a graphene mechanoreceptor, was devised utilizing a graphene field-effect transistor structure. A flexible membrane type gate electrode was placed hovering over the graphene channel, and when the pressure was applied on the gate, it approached the graphene modulating its transport by field effect and shifted the graphene Fermi level. If the Dirac point was within the shift range of the Fermi level, the device will generate a resistance spike, similar to a human mechanoreceptor.
The graphene layer was grown by CVD and transferred to a silicon nitride substrate. Excessive hole doping was reduced by wet chemical treatment using NH₄F solution for two hours, so that the Dirac point was located inside the shift range of Fermi surface. After metal electrode deposition and graphene channel (100 mu;m x 100 mu;m) etching, a SU-8 spacer pit was fabricated around the graphene channel. The diameter of the spacer pit was 500 mu;m and was 2 mu;m in thickness. Finally, a flexible PET with an evaporated gold layer covered the spacer pit. When the gate potential was set to 10 V, a resistance spike was generated as the applied pressure passed 0.3 kPa. The resistance spike was a 30% increase in resistance with the width depending on the speed of the moving gate. Dirac point crossing was verified by twin spikes both in the gate approaching phase and in the gate retracting phase when the pressure was diminished. When the gate potential was raised to 30 V, the resistance change was up to 60%, while the spike was generated at 0.17 kPa of applied pressure demonstrating that the spiking pressure was controllable for the graphene mechanoreceptor.
A graphene mechanoreceptor having multiple graphene channels in series was also fabricated where each graphene channel would generate a resistance spike at increasing pressures as they were place in sequence from the center of the spacer pit outward. From a pressurizing test, we observed a series of resistance pulses, similar to a fast adapting mechanoreceptor.

Droplet impacting on solid or liquid interfaces is a ubiquitous phenomenon in nature. Although complete rebound of droplets is widely observed on superhydrophobic solid surfaces, the bouncing of droplets on liquid is usually vulnerable due to the easy collapse of air pocket entrapped between the impinging droplet and slippery and soft liquid interfaces. Here, we report a robust superhydrophobic-like bouncing regime on thin liquid films, characterized by the contact time, the spreading dynamics, and the restitution coefficient independent of the underlying liquid substrate. Through experimental exploration and theoretical analysis, we demonstrate that the manifestation of such substrate-independent (superhydrophobic-like) bouncing necessitates an intricate interplay between the Weber number, and the thickness and viscosity of the liquid substrate. Such insights allow us to tune the substrate-independent and substrate-dependent bouncing on liquid interfaces in a well-controlled fashion. Our results shed new light on the study of classical wetting phenomenon and reveal the important and previously unexplored effect of liquid substrate on the interfacial dynamics. Moreover, the droplet shedding on the tilted surface in the substrate-independent bouncing regime can be enhanced significantly and we anticipate that the combination of robust superhydrophobic-like bouncing with inherent advantages of emerging slippery liquid interfaces will find a wide range of applications.

Enhancing the mobility of liquid droplets on rough surfaces is of great interest in industry, with applications ranging from condensation heat transfer to water harvesting to the prevention of icing and frosting [1-3]. Lotus-leaf inspired superhydrophobic surfaces consist of hierarchical micro/nanoscale textures which cannot effectively remove tiny condensate droplets due to pinning at elevated pressure. On the other hand, pitcher-plant inspired slippery surfaces consist of a slippery liquid interface which allows them to repel small droplets but with limited surface area due to the absence of roughness. By combining the architectural advantages of both lotus leaves and pitcher plants, we have created a new form of liquid repellent surface — slippery rough surfaces (SRS). SRS consist of hierarchical micro/nanoscale surface textures where the nanotextures alone are infused with lubricant. We have demonstrated that these SRS, owing to their high surface area and slippery interface, outperform the state-of-the-art liquid-repellent surfaces in fog harvesting and dropwise condensation applications. Moreover, many attempts to maintain droplet mobility have focused on Wenzel-to-Cassie transition; our new technology provides a simple solution to maintain droplet mobility regardless of the wetting states, creating a new direction for liquid-repellent surface design.
References
[1] T. Liu, C.-J. Kim, Turning a surface superrepellent even to completely wetting liquids, Science, 346(6213) (2014) 1096-1100.
[2] T.-S. Wong, S.H. Kang, S.K.Y. Tang, E.J. Smythe, B.D. Hatton, A. Grinthal, J. Aizenberg, Bioinspired self-repairing slippery surfaces with pressure-stable omniphobicity, Nature, 477(7365) (2011) 443-447.
[3] A. Tuteja, W. Choi, M. Ma, J.M. Mabry, S.A. Mazzella, G.C. Rutledge, G.H. McKinley, R.E. Cohen, Designing Superoleophobic Surfaces, Science, 318(5856) (2007) 1618-1622.

Many biological processes such as enzyme activities and cell differentiation rely on well-controlled microenvironments. Recently research on hydrophobic particles enveloped liquid droplets namely liquid marbles, demonstrated their applications as versatile miniature reactors and their capability of ease-to-manipulate. In this work, a series of liquid-marble based bio-reactors have been developed for the target of mimicking natural microenviroments of biological processes. Nanoparticles with well controlled physical and chemical properties were fabricated to envelop small amount of biofluids such as cell medium to form liquid marbles. Unique cellular behaviors were observed inside the liquid marbles, which were ascribed to the interfacial properties offered by the nanoparticle mediated micro-bio-reactors.

Synthetic lipid bilayers are highly useful biomimetic tools for studying biomolecular transport and characterizing transmembrane proteins. The droplet interface bilayer (DIB) technique is one of the simplest assembly approaches, which involves connecting two lipid-coated aqueous droplets placed under suitable organic solvent to form a lipid bilayer at the region of contact. This convenient technique has also been proven to be powerful by its applications to study ion-transport properties of transmembrane proteins, develop bioinspired batteries, sensors, energy converters, and ion rectifiers, and to construct tissue-like soft materials. These DIBs have almost always been implemented as a liquid-in-liquid system, i.e. liquid aqueous droplets in liquid organic solvent. The liquids are typically contained in an open, shallow substrate or within closed microfluidic channels. Although open substrates are convenient for DIB assembly and cleaning, they exhibit limited portability and are susceptible to contamination from the local environment, which could affect the stability and transport properties of the bilayer. As a result, liquid-in-liquid DIBs are unsuitable for portable or long-term applications.
In this work, we substitute the droplet phase and bulk oil phase with water-swollen hydrogel and oil-swollen organogel materials, respectively, to sandwich the lipid bilayer in a gelled environment. Specifically, aqueous droplets are replaced by PEG hydrogel volumes coated with lipid molecules, while the bulk liquid organic phase is replaced with a mixture of styrene-ethylene/butylene-styrene (SEBS) in hexadecane, which forms a clear and flexible organogel. With a temperature induced, reversible phase change feasible with SEBS organogel and an irreversible gelation of PEG hydrogel droplets with UV-light, this system retains electrical & optical access to the membrane, reconfigurability (e.g. for changing droplet/bilayer arrangement) and reusability (e.g. exchanging droplets for multiple uses in the same substrate) offered by liquid-in-liquid systems in open substrates. Likewise, bilayer properties such as electrical resistance, maximum rupture potential and thickness of bilayers formed in gel-in-gel system are found to be comparable to those of bilayers formed in traditional liquid-in-liquid system as the gelation of external and internal phases do not interfere with bilayer assembly. In addition, we compare the electrowetting characteristics and physical durability of DIBs formed in both the systems to quantify droplet immobility and cushioning. With decreased exposure to contaminants, improved portability, and the ability to apply mechanical forces through the organogel for characterizing the mechanical transduction response of the bilayer, this new form of functional soft material paves the way for a wider range of capabilities with DIBs.

In many plant species, hierarchical structures in the plant vasculature allow efficient water transport from the soil to the air via passive wicking. Such structure designs in nature have inspired new opportunities for the development of high performance lab-on-a-chip, desalination, thermal management, and energy conversion devices. In this work, we discuss single length scale and hierarchical structure designs that can promote high capillary wicking to increase the performance in boiling and thin film evaporation based heat transfer devices. We first demonstrated that in pool boiling, copper oxide nanostructure on top of copper micropillar designs extend the contact line length to enhance the critical heat flux (CHF). Next, we incorporated these micro/nanostructures in microchannels to promote high wicking capability. These surfaces not only increased CHF, but also increased flow stability during liquid to vapor phase change, which has been a well-known challenge in microchannels. Finally, we show how hierarchical fluidic networks can enable high heat flux and efficient heat dissipation through nanoporous membranes. These studies provide insights into the physical processes underlying structure-fluid interactions. Furthermore, this work shows significant potential for the development and integration of such structures to advance next generation energy systems.

Harvesting water directly from the atmosphere is a sustainable method of collecting water. The idea of condensing and collecting atmospheric water originates from the observation of the Stenocara beetle, which captures fog as a source of drinking water in the Namib desert.[1] The patterned elytra of this desert beetle facilitates water droplet nucleation and growth on hydrophilic micron-scale bumps and droplet roll-off in hydrophobic troughs. Biomimetic surfaces designed to replicate this structure have been produced by various methods, however these are limited to the lab scale due to expense and complexity.[2-4]
We have previously described a simple synthetic procedure that relies on the dewetting of thin films of a hydrophilic polymer (P4VP) on hydrophobic (polystyrene) film, to yield a surface with micro-scale hydrophilic bumps on top of a hydrophobic matrix.[5,6] This surface was found to be effective in collecting substantial amounts of water (2-3 L / m² / hour).
Having designed a new controlled condensation environment, we are now able to quantify with high throughput the water collecting performance of our micro-patterned surfaces, and correlate this data with early time droplet nucleation and growth data obtained by optical microscopy, to provide a holistic picture of the nucleation, growth, coalescence and roll-off of droplets on each surface. We have investigated the effect of topography, size and density of surface features and wettability contrast on water collection performance efficiency. The results presented here demonstrate a facile and scalable methodology to create surface coatings that capture significant volumes of water using low-cost materials and requiring only the cooling of the surface below the dew point.
[1]. Parker, A.R.; Lawrence, C.R. ; Nature 2001, 414(6859), 33-34. [2]. Garrod, R.; et al.; Langmuir 2007, 23(2), 689-693. [3]. Furuta, T.; Sakai, M.; Isobe, T.; Matsushita, S.; Nakajima, A.; Langmuir 2011, 27(11), 7307-7313. [4]. Lee, A.; Moon, M.W.; Lim, H.; Kim, W.D.; Kim, H.Y.; Langmuir 2012, 28(27), 10183-10191. [5]. Thickett, S.C.; Neto, C.; Harris, A.T.; Advanced Materials 2011, 23(32), 3718-3722. [6]. Thickett, S. C., Harris, A. & Neto, C.; Langmuir26, 15989-15999 (2010).

Promoting rapid drop detachment by varying the surface morphology is of significant interest for a broad range of applications, including anti-icing, self-cleaning and heat management. Drops impacting on superhydrophobic surfaces spread, retract and then leave the surface with little loss of energy. The time the drop is in close contact with the substrate is constant, independent of the impact velocities and the drop retains a circular symmetry during the whole process. Here, we report on symmetry-breaking bouncing dynamics motivated by observing a drop impacting on natural Echevaria leaves with curvature which is comparable to that of the drop. We find asymmetric bouncing that results from the cylindrical leaves which have a convex/concave architecture enabling distinct spreading along the axial and curved directions. The bouncing allows for a contact time reduction by ~40%. Further systematic experimental investigations on mimetic surfaces and lattice Boltzmann simulations reveals that this novel phenomenon results from an asymmetric momentum and mass distribution that drives preferential fluid flows around the drop rim. This research reveals undiscovered impact dynamics on cylindrical surfaces and will provide important insights into surface design for many practical applications.

The plant of the world has an antigravity ability to transport the liquid from the roots to the crown, which attracts everyone's attention. Antigravity transportation of fluid is a vital demand in the field of microfluidic systems and advanced equipment. Many researchers have achieved pumpless water transport on a horizontal or inclined substrate in an open air environment. However, the spontaneous oil motion, especially antigravity oil delivery underwater on open substrates, still remains considerable challenges. Underwater liquid transport with an open environment has potential application prospects in the field of biomedicine and package of volatile substances. Here, a method of underwater antigravity pumpless fluid transport on extreme wettability patterns has been proposed. Extreme wettability patterns, which have a wedge-shaped superoleophilic track and a superoleophobic background to generate capillary force to drive the oil, were obtained using plasma treatment. Variation in the transportation distance, velocity and force of dichloromethane underwater with the time at different wedge-shaped angles is investigated. The maximum velocity (472 mm/s) and acceleration (11 m/s²) is realized at a wedge-shaped angle of 3°. The result indicates that the maximum transport height underwater of dichloromethane is 11 mm on the patterned surface with a length of 80mm and a tilted angle of 8°. Underwater split and directional transport of oil is also achieved using this method. The present facile underwater transport method should serve as an inspiration for the exciting applications in microfluidic systems, liquid management in fuel cells, and intelligent systems.

Biological applications which utilise enzymes, or other proteins, require the tertiary structure of the protein to be retained. However, many proteins readily undergo aggregation or denaturation when outside their native environment, and/or over longer timescales. The stability of proteins in solvents other than water is usually considered unappealing due to an assumption that the protein will be insoluble or denatured. However, a few solvents, such as glycerol and dilute alcohols have been shown to have protein stabilising properties, such as in cryopreservation.
Previously we have developed extensive structure-property relationships between the chemical structures and mesostructures of non-aqueous solvents and the solvophobic effect experienced by amphiphiles for molecular solvents [1] and protic ionic liquids [2]. Here we have extended this to develop a greater understanding of what solvent features are important for protein stability. We have utilised a series of small polar non-aqueous molecular solvents and protic ionic liquids consisting of the four acid-base combinations of ethyl- and ethanolammonium cations paired with formate or nitrate. Solutions were prepared of these solvents combined with water, and with added formate or nitrate for the ionic liquids to explore a broad range of pH effects. For this initial work egg white lysozyme (HEWL) was used. These solvent systems enabled us to explore the effect of pH, solvent concentration, solvent cohesive energy density and polarity towards protein stability. The activity of the lysozyme was assessed based on its lytic activity towards Micrococcus lysodiekticusce using UV-Vis spectroscopy. The secondary and tertiary structures of the lysozyme were determined using Small angle X-Ray scattering (SAXS) and IR spectroscopy. Protein crystallisation studies have been successfully conducted for many of these protic ionic liquid solvent systems, with significant differences in the crystal structures formed.
This work extends our understanding of protein stability in a wide variety of solvent environments, and has enabled structure-property relationships to be developed for a protein in concentrated molecular solvent and protic ionic liquid solvent systems. This work has the potential to lead to the development of tailored solvent systems to optimise protein stability.
[1] E. C. Wijaya, T. L. Greaves and C. J. Drummond, Faraday Discuss. 2013, 167, 191-215.
[2] T. L. Greaves and C. J. Drummond, Chem. Soc. Rev. 2013, 42, 1096-1120

The precise and consistent control over the size and shape of magnetic nanoparticles (MNPs) is critical for their reliable use in biomedical and nanotechnological applications. Furthermore, the ability to tailor these requirements under ambient environmentally friendly synthetic production is a key goal.
Magnetotactic bacteria take up soluble iron from the environment and synthesis MNPs of magnetite within dedicated internal organelles (known as magnetosomes). These magnetosomes are highly monodispersed, with strict morphology conservation within each strain but a varity of shapes shown across different strains, showing a high degree of biological precision and control over the process. Proteomic and genetic studies have identified a “magnetosome island” harbouring the genes that produce proteins specifically for the biomineralisation of these magnetosomes. Here we report our research into understanding how these proteins control the nucleation and crystallisation of magnetite MNP. This understanding helps to inform our protein mediated chemical precipitation of precise MNP. Furthermore we have produced a range of mimics that are easier to express and purified. Thus, we are building up a “toolbox” of protein additives for tailored magnetite MNP synthesis. This has been extended to patterning these proteins on a surface to form precise MNPs on patterned arrays.

Creating liquid repellent surfaces on stretchy substrates that work in liquid environment is an important and challenging work since the stretch of these substrates would “dilute” and even damage the surface structures which are essential for super liquid repellence. In this paper, we reported a new method to fabricate superamphiphobic surfaces on rubber. Firstly, superamphiphobic coatings were fabricated by a simple chemical deposition and low surface energy materials modification. Then the prepared coatings were bonded to a piece of rubber (2.0×3.0 cm²) by commercial spray-adhesive. Water, glycerol or peanut oil droplets were supported as near spherical shapes and could easily roll-off from the tilted surface, exhibiting excellent water and oil non-wetting properties. The crystal structures and chemical compositions of the coatings were characterized by X-ray diffraction (XRD), Fourier transform infrared spectrometry (FTIR) and energy-dispersive X-ray spectroscopy (EDS). The surface morphologies observed by scanning electron microscope (SEM) demonstrated that the superamphiphobic coatings successfully constructed reentrant structures, which are essential for superamphiphobicity, on the rubber surface. The coated rubber remained superamphiphobic after being stretched to twice its original length with mechanical stress, and little superamphiphobicity lose was observed after repeatedly stretching and releasing for more than 50 cycles. The results demonstrate that the superamphiphobic coatings can be coated on stretchable substrates where often undergoing intense strain but super-liquid repellency is required.

New materials inspired by nature could find applications as coatings in the civil and aeronautical/aerospace industries. Mollusks have developed hard shells to protect themselves from predators. One of the main components, nacre, is a composite consisting of calcium carbonate platelets, which are connected by an organic matrix. Nacre has caught the attention of researchers due to its outstanding material properties such as very high compressive and tensile strength. Even though 95% of nacre&’s weight is calcium carbonate, its work of fracture is 3000 times higher than that of pure calcium carbonate crystal.
We use the metabolic diversity of prokaryotes to generate new, nacre-inspired materials, consisting of calcium carbonate and an organic polymer. Calcium carbonate is precipitated on a glass substrate by the action of Sporosarcina pasteurii, which hydrolyzes urea, increasing the pH of its growth medium and thus making calcium carbonate fall out of solution.
Poly-gamma-glutamate (PGA) serves as a simple replacement for the complex organic layer found in natural nacre. Poly-alpha-glutamate was shown to be a good substrate for calcium carbonate precipitation, as its negative side chains allow binding of calcium ions, which in turn act as nucleation centers. PGA, produced by Bacillus licheniformis, is isolated and deposited on the calcium carbonate layers. Alternating calcium carbonate precipitations and PGA applications yields our final product.
Scanning electron microscopy reveals layered calcium carbonate structures in large parts of the sample, which resemble the ones found in nacre, although they are much thicker (5-8 µm compared to 0.5 µm in nacre). In the negative control (multiple calcium carbonate precipitations without PGA application), layered structures are much less prevalent and limited to spherical crystals. We conclude that PGA is incorporated in the material, controlling the crystallization of the next calcium carbonate layer. X-ray diffraction studies and Fourier transform infrared spectroscopy show that calcium carbonate is mainly present as calcite, as opposed to aragonite in nacre. Mechanical properties are also tested via microindentation.
This new biological approach to generate high-performance composite materials is sustainable and environmentally friendly, and can find applications in e. g. construction or medicine.

Two-photon lithography (2PL) is a versatile technique that allows for the direct write, high-resolution fabrication of complex, 3D structures via the spatially controlled polymerization of a variety of monomer chemistries, including proteins. In this method, a focused pulsed laser is translated in a solution containing a photo-activator dye and protein “resist”. Within the focus of the laser, the excited dye induces the production or tyrosine radicals that form covalent bonds with nearby Tyr, Lys, or Cys residues. The formation of these covalent bonds produces a small volume of cross-linked protein hydrogel. The precise production of solid, 3D structures with sub-micron feature sizes is accomplished by translating the laser focus through the protein/dye solution in a controlled pathway. In this work, we have explored the application of 2PL for the fabrication protein microstructures from regenerated silk fibroin (RSF) solutions. RSF contains a high proportion of Tyr residues, exhibits excellent biocompatibility, high toughness, tailorable biodegradability and optical clarity, making it an ideal material for 3D printing. The effect of 2PL processing and writing parameters on the structure and fidelity of 3D printed silk fibroin will be discussed in this presentation. The 2PL method explored in this study provides for a facile approach for the further development and production of silk-based (and other biomaterials) structures for biocompatible optics, tissue engineering scaffolds, bioelectronic devices, bio-inspired structures, and localized biomimetic mineralization reactions.

Inspired by the typical “brick-and-mortar” laminated nanostructures of natural nacre, we have fabricated ultrathin and robust nanocomposite membranes by incorporating graphene oxide (GO) sheets into a silk fibroin (SF) matrix by the novel dynamic spin-assisted layer-by-layer assembly (dSA-LbL). The dSA-LbL technique effectively reduced the volume fractions of the “mortar” polymeric phase in the nanocomposites, successfully reproduced similar nanomorphologies of the natural nacre, where tiny amount of organic binders are confined between the inorganic reinforcing flakes. The enhanced surface interactions and significantly accelerated solution removal during the dynamic spinning process resulted in the fabrication of laminated nanocomposites with outstanding mechanical properties. We employed bulging technique to extract the comprehensive mechanical properties of the GO-SF nanocomposite membranes. The tensile modulus values reached 170 GPa, the ultimate strength close to 300 MPa, and the toughness was above 3.4 MJ m^-3, being all exceptional characteristics. The ultra-high tensile elastic modulus exceeds the highest rule-of-mixture predicted value for composite materials by over two folds. The failure modes observed for these membranes suggested the self-reinforcing mechanism of adjacent graphene oxide sheets with strong 2 nm thick silk interphase of individual backbones. Theoretical model fitting reveals that the interfacial interaction is almost two folds stronger than the nanocomposite membranes fabricated using the conventional LbL assembly techniques, pushing the reinforcing effect of graphene oxide in the polymeric matrix close to the extreme. The failure analysis by high-resolution TEM further undercovers three hierarchical failure modes that promote the toughness by dissipating the rupture energy: compliant crack initiation, yield failure, and rupture propagation. This reinforcement leads to the effective load transfer between the graphene oxide components and introduces novel reinforced laminated nanocomposite materials with excellent mechanical strength that surpasses those known today for conventional flexible laminated carbon nanocomposites.

Nature provides prime examples of lightweight, strong, stiff and yet tough materials. Their unique properties are realized via the hierarchical self-organizing growth of hard (inorganic, protein crystals, crystalline polysaccharides) and soft (organic, biopolymeric) building blocks into well-ordered structures with tailored energy dissipation mechanisms. Nacre, wood or silk are paradigms in materials design and considered near perfect marriages of hard and soft components. Herein, we will demonstrate large-scale self-assembly approaches to mimic the natural structure found in the nacreous layer in mother of pearl and focus on how to tune the mechanical and functional properties.
We use polymer-coated inorganic nanoclay platelets with intrinsic hard/soft character, which form nacre-mimetic composite films with highly defined and tuneable mesostructure upon water-removal due to excluded volume effects. This has so far enabled high modulus (45 GPa) and high strength (350 MPa) combined with low density. We will show how nanoplatelet dimensions (aspect ratio from 25 - 3500), thickness of the organic layers, supramolecular bonds in the soft phase and humidity influence local dynamics and macroscopic material and fracture properties. The combination with highest aspect ratio synthetic nanoclays allows extremely low gas permeability and transparency close to glass, as e.g. needed for sealing organic electronics. These functionalities are complemented by excellent fire/heat shielding capabilities of coatings and free-standing films. In combination with supramolecularly-bonded, self-healing polymers, we demonstrate molecular engineering of synergetic mechanical properties uniquely combining high stiffness and toughness. The achieved understanding allows rational design of high-performance, multifunctional biomimetic composites with excellent control over nanostructure using energy-efficient and environmentally friendly methods, even suitable for continuous roll-to-roll processes.
Selected References:
(1) Das, P. Malho, J.-M. Koshrow, R. Schacher, F. Wang, B. Walther, A. Nature Comm. 6, 5967. (2015) (2) Zhu, B. Jasinski, N. Noack, M. Park, D. Goldmann, A. S. Barner-Kowollik, C. Walther, A. Angew. Chem. Int. Ed. doi: 10.1002/anie.201502323. (2015) (3) Das, P.; Walther, A. Nanoscale, 5, 9348 (2013). (3) Das, P.; Schipmann S.; Malho, J.-M.; Zhu, B.; Klemradt, U.; Walther, A. ACS Appl. Mater. Inter. 5, 3738 (2013). (6) Walther, A.; Bjurhager, I.; Malho, J.-M.; Pere, J.; Ruokolainen, J.; Berglund, L.A.; Ikkala, O.: Nano Letters, 10, 2742 (2010).

Silk fibers from the Bombyx Mori silkworm are well known for their impressive strength and toughness. They have mechanical properties that are on par with the best synthetic fibers available, but are produced naturally by silkworms using very low energy inputs. These fibers have been used extensively as a fabric and more recently have found utility in biomedical engineering. Despite the widespread use of silk fibers and the silkworms' highly efficient spinning mechanisms, a comprehensive understanding of the how the sequence of the structural protein, fibroin, impacts the spinning process still eludes researchers. In this research we present recent findings that suggest that the tyrosine residues in the amorphous protein regions act as templates, orienting the molecules to allow for rapid crystallization with the application of osmotic stress and shear strain. Experimental data indicate that π-π interactions of the phenol rings on the native tyrosine residues play an important role in the self assembly and aging of silk solutions. Furthermore, covalent crosslinking of these amino acids results in spontaneous β-sheet formation upon removal of water, while non-crosslinked samples require post treatment to induce similar levels of crystallinity. To support the empirical data, molecular modeling of silk-mimetic peptide fragments has similarly shown a propensity for the tyrosine residues to collocate and that this association may lead to β-sheet formation.

Certain biological materials, such as deep-sea glass sponges, have a microstructure consisting of layers made of brittle bulk material (bio-glass) with high elastic modulus connected by thin, compliant interlayers (protein). Numerical modeling and application of the concept of configurational forces has revealed that the multi-layered structure with strong spatial variation of the Young&’s modulus is the dominant reason for the high fracture resistance of the glass sponge [1].
In the current presentation, models are presented to predict the fracture stress and fracture toughness of multilayered composites made of elastic, inherently brittle bulk materials [2]. It is demonstrated that the composite architecture has to fulfill certain design rules, in order that the structure becomes strong and fracture resistant. Optimum interlayer configurations are deduced by applications of finite element analyses and analytical estimates. Finally, it is shown that the idea can be extended to non-elastic materials. The reason is that the beneficial effects of material property variations also occur, if the Young&’s modulus is constant, but the yield stress exhibits a spatial variation [3].
References
[1] O. Kolednik, J. Predan, F.D. Fischer, P. Fratzl, Bioinspired design criteria for damage-resistant materials with periodically varying microstructure. Adv. Funct. Mater. 21, 2011, 3634-3641.
[2] O. Kolednik, J. Predan, F.D. Fischer, P. Fratzl, Improvements of strength and fracture resistance by spatial material property variations, Acta Mater. 68, 2014, 279-294.
[3] M. Sistaninia, O. Kolednik, Effect of a single soft interlayer on the crack driving force. Eng. Fract. Mech. 130, 2014, 21-41.

It is commonly accepted that the combination of nanosize and high aspect ratio of mineral constituents in biological materials is the main reason for their exceptional mechanical properties as compared to their rather week mineral and organic constituents. Nanosize is the reason why mineral crystals like hydroxyapatite or aragonite are flaw tolerant and 10-100 times stronger than their macroscopic counterparts. High aspect ratios of these minerals allow the much softer and weaker protein matrix, surrounding them, to transfer the load via shear stresses very effectively. Here we show that the self-assembly of monodisperse Fe₃O₄-nanoparticles linked together by crosslinked oleic acid molecules leads to a nanocomposite with exceptional mechanical strength and nanohardness of up to 600 MPa and 5 GPa, respectively. Because the Fe₃O₄-nanoparticels are not elongated, the shear load transfer mechanism is not responsible for the high strength. It is the mechanical behaviour of the oleic acid molecules instead, which determines the mechanical properties.

Current dental resin-based restorative systems suffer from a short service life; one challenge to improve filling longevity is the detection and restoration of micro-cracks and fractures in the material after implanting it in the patients&’ tooth. To overcome this, we introduce here a new type of self-healing dental composite (SHDC) made with traditional dental composite and two additional components: healing powders and healing liquid encapsulated by silica microcapsules. Micro-cracks, which are difficult to be detected and almost impossible to be repaired manually, break microcapsules along the path of propagation and release the healing liquid, which will then react with healing powder to fill the micro-cracks with a cement-like new material. The autonomous healing process was confirmed by measuring the resistance to crack growth with compact tension tests. The new composites have elastic modulus in the range of 6 - 12 GPa depending on the mass fraction of microcapsules added. This value falls in the range of existing commercial resin composites (5 - 18 GPa), and satisfies the required stiffness to survive in the harsh oral environment. The SHDCs restore micro-cracks without external intervention, potentially increasing service life. In addition, the SHDCs were made with clinically-tested, biocompatible materials, which makes them readily applicable as medical devices. This research is supported by NIH U01DE023752.

Biological organisms have rather limited resources they can use to build the materials they are made of. Given these limitations, the range of properties of natural materials is amazing and in many instances not easily surpassed by man-made substitutes. One important aspect of many natural materials is their intricate structure, extending often from a few nanometers to macroscopic dimensions. Here, I will introduce several concepts how synthesis strategies of natural organisms can be adopted for the creation of materials and how various materials properties can be tuned by these synthesis strategies. Examples include artificial nacre, cellulose self assembly, and photonic materials.

Nature uses metal binding amino acids to engineer both mechanical properties and structural functionality. Some examples of this metal binding behavior can be found in both mussel foot protein and DNA binding protein. The mussel byssal thread contains reversible intermolecular protein-metal bonds, allowing it to withstand harsh intertidal environments. Zinc fingers form intramolecular protein-metal bonds to stabilize the tertiary structure of DNA binding proteins, allowing specific structural functionality. Inspired by both these intermolecular and intramolecular metal- binding materials, we present mechanical, thermal and optical characterization of a model polymer system designed to mimic the intramolecular and intermolecular bonding characteristics. Through these studies, we are able to answer fundamental polymer physics questions critical to building a better understanding of the bonding characteristics of the intermolecular vs. intramolecular metal-ligand bond. These understandings provide insight into bio-inspired engineering techniques that are used to design soft materials.

Bioinspired adhesives have attracted a lot of attention for robotics and medical applications. Of particular interest is the smart adhesive with the capability of active control of adhesion strength. Here, mimicking the wet adhesion of the octopus suckers, we demonstrate that the combination of a thermo-responsive polymer (poly(N-isopropylacrylamide) (pNIPAM)) and an elastomeric (polydimethylsiloxane (PDMS)) microstructure enables a switchable adhesion induced by differential pressure in response to thermal stimulus. In this smart adhesive pad, the differential pressure between the pNIPAM coated microstructure arrays and the opposing surface can be actively controlled by swelling or shrinking behavior of pNIPAM in response to the temperature change, resulting in reversible smart adhesion. Through control of temperature, the adhesion strength of smart adhesive pad can be switched between ~59 kPa at high temperature and ~0.3 kPa at low temperature. Furthermore, we show that the switchable adhesive pad can be employed in transfer printing process to heterogeneously integrate silicon and compound semiconductor nanomembranes onto arbitrary substrates. For applications in transfer printing electronics, InGaAs back-gate transistor was fabricated and it showed high-performance in electrical characteristics, such as mobility (~3000 cm²/Vs) and on/off ratio (~5x10³). The bioinspired smart adhesive pad suggested in this study is applicable to heterogeneous integration of arbitrary micro- and nanoscale objects, which have great potentials in high-performance transistors and optoelectronic devices.

In nature, many cell types are embedded into three-dimensional micro- and nanostructures, such as fibrous scaffolds. It is well-known that cells adapt in a very different way to such three-dimensional structures compared to two-dimensional surfaces. In order to control the behavior of cells in 3D, we fabricated graphite-based fibrous materials with a template-assisted CVD process, leading to so-called aerographite. We demonstrate the bioactive function of aerographite in in vitro cell adhesion experiments and present biocompatibility studies. A further important aspect is that in such environments cell adhesion is directly associated with the mechanical adaptation of cells. These mechanisms, by which cells sense and react to external stress, can also be mimicked by 3D microstructures. We show a demonstration material for mimicking cellular stress adaptation and response that is based on a composite of micron-sized PDMS surface structures in combination with microparticles. Such cell-inspired intelligent materials with directional and temporal control of mechanoresponsive behavior have great potential for use as future biomaterials.

The crystalline structure of vaterite, a metastable polymorph of calcium carbonate (CaCO₃), has remained without definitive characterization despite its myriad commercial and biomedical applications. Natural sources of vaterite are few but include biological sources such as sea squirt spicules, cultured freshwater pearls, and fish ear bones, better known as otoliths. Most fish otoliths are comprised of the most dense and energetically stable CaCO₃ polymorph, aragonite. Sturgeon otoliths, on the other hand, have been characterized as being of vaterite composition. We therefore sought to characterize the structure and microstructure of sturgeon otoliths using optical microscopy, powder diffraction (X-ray and neutron), and thermal analysis. We found that while sturgeon otoliths are primarily composed of vaterite, they also contain variable amounts of the denser CaCO₃ polymorph, calcite. Our neutron data provide somewhat enhanced discrimination of the carbonate group compared to x-ray data, owing to the different relative neutron scattering lengths, and thus offer the opportunity to test the more than one dozen crystal structural models that have been proposed for vaterite. In addition, neutron diffraction allows entire intact otoliths to be non-destructively examined for phase abundance, crystallinity, crystal structure, and preferred orientation. Research conducted at ORNL's Spallation Neutron Source and High Flux Isotope Reactor was sponsored by the Scientific User Facilities Division, Office of Basic Energy Sciences, U.S. Department of Energy.

Water contamination caused by dye, leather, textile, plastics and cosmetics industries has been received more and more attention, since most heavy metal and organic materials are harmful to human being and environments. Currently, much attention has been paid to the detection or removal of harmful materials from industrial wastewater. To date, lots of approaches have been reported to detection or remove them from wastewater, e.g., biological treatment, chemical technologies (e.g., ion-exchange, oxidation, and catalytic degradation), and physical methods (e.g., adsorption and membrane filtration). Among these techniques, the sensing method and a catalytic degradation were examined in this study.
The recent advancements in the field of nanoscience and nanotechnology have opened up new arenas for the applications of nanomaterials including the development of ultrasensitive detection and imaging methods in the analytical science. Particularly, colorimetric sensor based on silver nanoparticles (Ag NPs) is gaining increasing attention because of their strong localized surface plasmon resonance absorption and interparticles distance dependent optical properties. Colorimetric sensing methods have many advantageous such as simplicity and rapidity, high sensitivity, cost-effectiveness and ease of measurement.
Electrospinning is a facile and low-cost method to fabricating continuous polymer, inorganic, and organic/inorganic hybrid fibers with a high surface area to volume ratio and a high porosity. Many synthetic and natural polymers have been electrospun to form nanofibers with a small diameter ranging from tens of nanometers to a few microns for various applications in solar cells, filtration, environmental remediation, biosensors, protective clothing, and tissue engineering scaffolds. The electrospun fibrous mats have a great advantage in terms of the recovery and easy handling of the materials. Generating NP-containing nanofibrous webs is expected to be important for the development of NP-based nanocatalyst systems. Compared with other high-surface area, high-porosity materials for catalytic applications, electrospun polymer nanofibrous materials are easy to make, and the fiber diameter can be controlled by varying the electrospinning parameters. More importantly, 3-dimensional complex organic/inorganic hybrid functional materials can be fabricated through selection and modification of the fiber components.
In this study, Ag NPs stabilized with the 3,4-dihydroxy phenylalanine (DOPA), which is known as mussel-inspired protein component, were prepared using simple and green chemistry. The synthesized Ag NPs was investigated as a colorimetric sensor for detecting copper (II) and lead (II) ions. Also, polymer nanofibrous web containing Ag NPs with DOPA was examined as a catalyst for the reduction of a model dye.

Nature is an unlimited source of knowledge and advice for scientists and engineers. In particular, the optimized natural hierarchical materials are a good source of inspiration for the design of new smart materials. Among these, an intriguing material is bone, with a lightweight structure, providing support for animal bodies. The optimal combination of mechanical properties, in particular the significant toughness, makes it very attractive for research studies. The fracture behavior of bone is an interesting field of research from both medical and engineering viewpoints. In particular, engineers are interested in studying bone to get inspiration for the design of new materials. The design of new materials inspired by nature is an innovative and interdisciplinary research area, particularly attractive and known as biomimetics. By using a biomimetic approach, we design and realize a new composite material with an internal structure inspired to the microstructure of cortical bone. The new material, which is a 3D-printed synthetic polymer composite, is characterized by a repeating structural unit with a circular-cylindrical shape, designed to mimic the osteons. We characterize the material under static loading conditions (i.e. tensile) and we investigate the fracture behavior by performing tests in presence of a crack. We carried out tests in two directions, accounting for the anisotropy the bone-like composites. To investigate the effect of the osteon geometry, we designed two materials: i) characterized by perfectly circular osteons and, ii) characterized by elliptical osteons. In both cases, we paid attention to keep the osteon volume ratio constant and equal to that measured in mid-age human bone. The results of the tests prove how the osteon geometry and their arrangement affect the crack path and the overall behavior of the composite. By observing the failure mode, we also noticed several similarities with the toughening mechanisms occurring in cortical bone, such as crack deflection and branching, constrained microcracking and fibril bridging. This confirms the validity of the bone-inspired design to mimic the fracture behavior of cortical bone at microstructural level.

Melanin pigments are a class of naturally occurring amorphous extended aromatic biopolymers that exhibit diverse chemistry and unique physical properties such as high photon-phonon conversion efficiency, broadband UV absorption, and redox activity. Melanins also have prospective technical applications as adhesive films, functional coatings, and biologically-derived materials for energy storage. In the latter use case, the charge storage capacity is only approximately 20% of the theoretical charge storage capacity. We assert that charge storage capacities are limited in part by cation transport through dense (ρ ~ 1.3 g/cm³) melanin films. Here we describe a method to measure cation mobility through synthetic dopamine-melanin (DM) thin films. We synthesized amorphous melanin films with characteristic granule areal densities of 910±50 to 3800±260 granules/um². Raman microscopy is used to fingerprint metal-bound semiquinones in melanin, and this technique was used to spatially locate Ca⁺² and Mg⁺² diffusion and electromigration fronts in DM thin films. FTIR spectroscopy serves as a complementary technique for identifying ether-like metal chelation in the films. Voltage and time-dependent concentration profiles provide initial estimates of ionic mobilities in melanin films. Cation-specific mobilities are described as a function of granule size to reveal the characteristic diffusion mechanism. Overall, these studies advance spectroscopic techniques for characterizing cation transport in melanin films to understand structure-property relationships for prospective applications ranging from water purification to electrochemical storage devices.

Over the last decades, there were tremendous attempts to create an advanced artificial system for mimicry of living organisms. To specially comprehend the function and selective evolution of a cell, its compartmentalization has attracted much interest in recent years owing to the characteristic appearance and intrinsic regulatory system. Yet, few studies have been investigated to realize both external and internal aspects of real cellular subdivision. Here we first present a copy of cell&’s nucleus which is able to function as a transcript decoder for an enhanced mRNA level. It is simply created by enzymatically knitting a genome with histone-like DNA block crosslinkers. After further processing of lipid encapsulation and successive addition of transcription factors, it promoted the controllable expression of mRNA. In comparison with other control groups (e.g., nucleus-free system), it exhibited the increment of green fluorescent protein (GFP) mRNA tested. As being internalized by target cell (e.g., MCF-7), it resulted in higher and longer expression of GFPs. Inspired by these achievements, such synthetic nucleus model was embedded into any damaged cell line possessing malfunctioned genes. It successfully replaced the older and restored the system. It is highly speculated that this synthetic cell nucleus may be a new paradigm for traditional gene therapy which is presently bottle-necked by lower genome integration via several cellular barriers.

Excellent mechanical strength, programmable biodegradation, optical transparency, and extremely low surface roughness of re-engineered silk micro- and nanostructures makes them highly attractive for a broad range of applications in biophotonics, bioresorbable electronics, and targeted drug delivery. The mechanical behavior of re-engineered silk structures at micro- and nanometer length scales is not well understood due to the challenges associated with the testing of silk structures at these length scales. One can expect dramatically different mechanical behavior as the length scale of the silk structures approaches the characteristic length scales of polymer chains (e.g., β-sheet domains). A comprehensive understanding of the thermomechanical properties of silk at length scales relevant to the aforementioned applications provides invaluable guidelines for the efficient design and fabrication of silk micro- and nanostructures. In this study, we demonstrate facile methods to fabricate low-dimensional patterned silk films and silk micro/nanopillars. The successful transfer of the patterned silk films to stretchable substrates without using any chemical solvent enabled us to investigate the relationship between the mechanical deformation at the micro- and nanoscale and the associated changes in the secondary structure of the proteins. Low-dimensional re-engineered silk structures exhibited extremely high ductility that was found to be secondary structure-dependent. Our results provide novel insight into the structure-function relationship of protein-based materials, and holds promise for applications in tissue engineering, controlled drug delivery, electronic and optical devices.

Particle synthesis involves selection and design of core materials which imparts physical properties and encapsulation with appropriate shell of ligands, often times a polymeric variety, that imparts surface and chemical properties for colloidal stability and supplemental functionalities. Despite being very successful and bench-marked, the current core-ligand system is not without its flaws. The polymeric ligand binding to the core substrate is diffusive and dynamic in nature, and hence unbinding could result in a dispersion environment not in excess of such ligands. In addition, surface oxidation can lead to ligand desorption, all of which can lead to destabilization and ultimate irreversible aggregation. Especially in the case of colloidal dispersion in ‘phobic&’ solvents, post synthetic processing is required to render polarity matching with the environment, which adds cost and environmental load as such processes are done in organic solvents. We have found that by imparting mechanically rigid interfacial high aspect ratio nano-topography on a core micro-particle, which we call ‘hedgehog&’ particles (HP) reflective of its morphology, we are able to form stable dispersion in ‘phobic&’ solvents without the aforementioned polarity matching chemical canopy, thereby defying the ‘similarity rule&’. This presentation will elucidate the mechanisms of such anomalous dispersion by probing physical and chemical traits of such interfacial geometry and its resulting physical manifests. A detailed calculations using the E_DLVO theory tailored to the HP geometry will be demonstrated to quantify the dynamics between the HPs and support the experimental observations.

Polymeric composite has long been adopted as adhesive. However, it introduces unavoidable mechanical mismatch between bonded parts and therefore significantly downgrade strength of the whole structure. In addition, debonding occurring at the interfaces between the adhesive and bonded parts can further deteriorate the structural strength. How to enhance the strength of bonded multilayer structures remains a challenging topic to researchers.
Meanwhile, nature develops excellent adhesives. Natural tooth is a remarkable example. It consists of enamel, dentin and an “adhesive” layer, dentin-enamel-junction (DEJ). Enamel, although brittle, forms a hard and wear resistant surface for mastication. Dentin plays a strong, supporting and crack-resisting role to the whole crown. The delicate structure of DEJ not only allows it to bond dentin and enamel, but also enables it to resist cracks that originate in enamel from penetrating into the dentin. Benefited from this remarkable design of the Mother Nature, natural tooth has superior overall mechanical strength and life span.
The talk presents a recent design of polymeric composite adhesive inspired by the DEJ of natural tooth. A bio-inspired adhesive (BA) made of polymeric composite was fabricated and applied to form the ceramic/BA/substrate multilayer structure. Ceramic nano particles were utilized to tune the structural property of the BA. The performance of the multilayer structure under both monotonic and cyclic mechanical loading was studied. The multilayers bonded by BA showed significantly enhanced strength and other functional performance. The failure mechanism of the bio-inspired design was also examined both experimentally and computationally.

In nature, some organisms can form hard tissues composed of mostly organic materials; for example, the jaw of the marine worm Nereis consists of mostly protein with a small amount of coordinated metal ions. The material processing from an initially soft hydrated state towards a hard dehydrated functional material follows pathways that are different from biomineralization. Studying the change in properties during such biological material transitions may unveil the underlying biological processing mechanisms yet only a few examples of such studies have been reported. Herein, we focus instead on characterizing the dehydration-rehydration dynamics of a simple bio-inspired synthetic model material system. In particular, we studied the changes in mechanical and optical properties between the soft (hydrated) state and hard (dehydrated) state of mussel-inspired catechol-PEG or histidine-PEG gels crosslinked via coordination bonds with various metals. We found that the catechol- and histidine-PEG gels serve as a good model system showing reversible transitions between soft and hard states. The dehydrated gel was stiff, solid-like and showed firm adhesion to the substrate with brittle fractures due to the surface tension during the dehydration. When rehydrated, it returned to a visco-elastic hydrogel state re-healing the fractures. The visco-elastic and optical properties were quantified during these transitions as a function of time, amount of water content and choice of coordinating metal. We expect this study can help provide additional insights on the biological processing from soft to hard materials as well as inspire new ideas on sustainable material processing.

Drawing upon the extraordinary mechanical properties of graphene, we have developed a biomimetic graphene-polymer composite with a similar microstructure to nacre, which in part derives its strength from a highly ordered laminated structure. We present a unique and innovative method of preparing the laminated structure by printing multiple layers of a graphene suspension on a 3D printer with an inkjet nozzle. The small droplets from the inkjet nozzle align the graphene due to their capillary force, resulting in the strength enhancing brick and mortar microstructure seen in nacre. We anticipate this technology will lead to stronger composite materials that can be used in high impact applications, as well as promote further research of composites with aligned nanoparticles.

Quantifying mechanical properties of intact organs and tissues provides important access to target properties of bioinspired materials that are both stable in aqueous electrolyte and of very low stiffness. Several material characterization methods developed for polymer gels, which can share those hydration stability and mechanical properties, have been implemented on tissues. However, most such techniques such as rheology and indentation require tissues to be removed from the body (ex vivo) and dissected (sliced) to obtain flat samples that often distort the tissue structure. Additionally, surface effects from the probe-tissue interface (i.e., adhesion) can complicate analysis of such measurements. Cavitation rheology is a relatively novel technique developed by Crosby et al. [1] which has been used to measure the Young&’s modulus E of polymer gels and bovine eye tissue. In this technique, a needle is inserted into the material and air pressure is increased in the needle, creating a cavity. At a certain applied strain, an elastic instability occurs; the air pressure at which the instability occurs may be used to calculate the Young&’s modulus. Cavitation rheology can be used to find the local material properties of intact tissues on the length scale of tens of micrometers to millimeters, and adhesion does not affect analysis. Here, we extend and adapt cavitation rheology to determine the mechanical characteristics of porcine brain tissue. We show that the Young&’s modulus thus obtained is in relative agreement with various techniques reported in the literature (E ~ 1-2kPa). These results suggest that cavitation rheology can be used to measure the local characteristics of fully intact tissues, which can aid in the design of tissue mimetic polymers as compliant as brain tissue.

We have developed a new class of intelligent, temperature-sensitive glazing (smart window) that greatly reduces the energy requirements for cooling and heating commercial, residential and industrial buildings. Our window surfaces mimic the nanostructurs found on the eyeballs of moths and are conformally coated with a chromogenic phase-changing metal oxide (vanadium dioxide, VO₂). The affect of the nanostructure is to induce key functionalities. Firstly, solar-thermal radiation entering a building is passivley modulated which contributes to a self-regulated building temperature. Secondly, the combined effects of this bio-inspired nanostructure and the surface chemistry of our metal oxide overcoat creates a super-hydrophobic window surface with the ability to self-clean under the action of rain.
We will present our complete method of fabricating these bio-inspired nanostructured surfaces at low-cost and over large areas. Our nanostructuring process involves only three steps and exploits the high-resolution offered by self-assembled colloidal polystyrene-nanosphere lithography (better than 100nm resolution over tens of square-centimeters). The deposition of our metal oxide overcoat, via Atomic Layer Deposition, manifests the fourth and final step in our fabrication process. It provides monolayer thickness resolution and is achieved at lower temperatures, with smaller volumes of precursor than conventional Atmospheric Pressure Chemical Vapour Deposition processes to deposit the same metal oxides.
Finally, we will present our most recent work towards simultaneous dual-layer depositions of metal oxides (both oxides in a single Atomic Layer Deposition process). By capping our nanostructures with an additional metal oxide (titanium dioxide, TiO₂) we show that the chemical and physical robustness of our nanostructures is improved. In addition, the combination of our bio-inspired structure&’s high surface-roughness enhances the metal oxides photocatalytic activity. This lend these windows an additional mode of self-cleaning through the production of oxygen radicals when illuminated by solar-UV light.

Fatty acids are materials with high enthalpy of melting and being good candidates to use in thermal protection and energy storage technologies. They are organic compounds largely found in vegetal and animal organisms responsible for fundamental functions in that. One of the most abundant fatty acids is the stearic acid (18,0), a normal saturated acid. This acid is composed by a main chain containing 18 carbon atoms linked to a carboxylic group. Like all fatty acids, stearic acid when in solid form, show polymorphism a phenomena associated with the different way of molecular arrangement originating different crystalline structures. The diversity of observed polymorphic forms in fatty acid to date makes this study a interesting research area. Several features of fatty acids influences its polymorphic behavior as crystallization conditions as temperature, solvent polarity and solvent evaporation rate and the own molecule characteristics as parity of the chain. For fatty acids with even chain is observed the forms denominated by A₁, A₂, A₃, A_super (triclinic forms), Bshy;_m, E_m, C (monoclinic forms), B_o, E_o (orthorhombic forms). In this work, several crystals were obtained in five different solvents with different polarities. Measurements of X-Ray Diffraction evidences the presence of more than one polymorphic form in each obtained sample, one of these being predominant. Isolated crystals were used to measurements of polarized Raman spectroscopy in the predominant forms. Raman results show that the different forms show particular Raman spectra being possible identify different forms using this technique. The polarized configuration allows obtaining information about group representations and crystal symmetry.

Silk is one of the strongest biomaterials with outstanding mechanical strength, toughness and robustness. Optimized by nature, it is able to combine both extensibility and toughness in order to achieve its various biological functions. For example, cocoons made of Bombyx mori silkworm silks work perfectly for protecting silkworm and moth inside. Such silk is made of pure protein and its stiffness comes from the crystalline region of the semi-crystalline fibroin and the extensibility from the hidden length within the amorphous region. Mechanical properties can be enhanced with forced reeling of silk, in particular fast spun silks are stiffer and less extensible than slow reeled silk. As a complex multi-layered composite structure, cocoons are designed to withstand wind load. However, this study investigates how a single-layer silk structure deflects and fails under wind load.
Here, computational modeling and experiments in the wind tunnel are combined to investigate the behavior of a single silkworm cocoon layer web under wind load. The webs are created by silkworms and tested under an increasing wind load until failure. For the computational simulations, the structure of the web is modeled on the random arrangement and reeling speeds of the fibers in the actual web.
For both the experiments and the simulations the deflection of the web increases with wind load. The webs can deflect up to 11.4 mm at 38.9 m/s wind speed before failure. These tests also reveal that webs are not necessary stiffer and less extensible as the fibers they are composed of are stiffer and less extensible, and the opposite, because of the high randomness and redundancy of the structure. Understanding this relation between the complex structure of the web and the fibers could lead to structural and material optimization for composite material design.

Collagen is the major structural proteins in mammals, providing mechanical stability, elasticity and cell-conducive environments to connective tissues such as tendon, skin, bone and cartilage. The molecular and higher level of ordered structures of collagen has gone through the nature&’s evolutionary process, supporting diverse biological functions. In an effort to elucidate the assembly mechanism and to develop advanced functional biomaterials, various synthetic collagen-like peptides have been demonstrated as potential collagen-mimetic systems, which strongly contributed to understanding triple helix formation. However, controlling the assembly of building blocks into the higher level of the ordered structures that incorporate the desired biochemical functionalities is still challenging and needs to be addressed. Here we show a novel approach to developing collagen mimetic materials based on rational design of functional biomacromolecules using evolutionary screening of M13 bacteriophage (phage). Single crystal hydroxyapatite-binding phage was identified using major coat protein-engineered library and was found to display collagen-like peptide sequence on the nanofibrillar structure. We found that the identified collagen-like phage can be assembled into long range ordered supramolecular film composed of periodically banded (~240 nm) microfibrillar structures by using controlled pulling method. The assembled structural films were demonstrated as potential collagen-mimetic materials showing the capability to direct bone cell and hydroxyapatite crystal growth. Reproduction of the characteristic banded fibrous structures using large building blocks may pave the way to better understanding the structure-function relationship. Our results demonstrate how the evolutionary engineering approach can be exploited to undermine new macromolecular structural building block with desired biological functions for the rational design of biomimetic system. We anticipate that our approach to be one of the starting point for developing novel biomaterials exhibiting biomolecule-mimetic or enhanced biological activities.

Inspired by the weeping lubrication mechanism of cartilage, in our project we study the tribological properties and mechanisms of porous polymer based surfaces under induced loads in aqueous conditions. Using a universal materials tester, we show how it is possible to change the lubrication regime from boundary lubrication to hydrodynamic lubrication even at relatively low shearing velocities. We hypothesize that the compressed liquid under pressure produces a repulsive hydrodynamic force as it is extruded from the pores. This reduces the effective area of contact between two shearing surfaces resulting in low coefficient of friction. The porous polymer samples are prepared from poly methyl siloxane (PDMS) using conventional photolithography and molding techniques. Specifically the effect of pore density and the pore depth is studied to optimize the design that offers the least coefficient of friction. The potential applications of such low friction, biocompatible, flexible surfaces could be as a coating in joint replacement implants.

One of the great challenges of science is the manipulation of materials at the nanometer scale to achieve tailored properties. An effective path forward is conducting biomaterials research to adapt biological structures and drive novel design techniques. One promising example is found in ubiquitous diatoms, which are microscopic algae with intricate porous shell morphologies and features ranging from the micrometer to the nanometer scale. Diatom shells are viable examples for nanotemplates, drug delivery carriers, optical devices, and microfluidic systems. In some diatom species it is typical to find shells naturally deformed in patterns suggestive of structural instability phenomena. This occurrence opens the door to design and manufacturing techniques based on the potential micromanipulation of bio-inspired structures. An experimental study of instability in diatom shells would be too costly and cumbersome to be practical, hence the need for complementary methods that can drive novel design and fabrication techniques. In this work, the mechanical instability of diatom shells was investigated using the Finite Element Method (FEM) in combination with morphology and material properties obtained using high-resolution Scanning Electron Microscopy (SEM) and independent mechanical tests. The SEM images have allowed the classification of a series of deformation patterns observed frequently on the shells of centric diatom species, with specific attention given to Coscinodiscus sp. In order to elucidate the nature of these deformations, a three-dimensional diatom shell CAD model of a centric diatom species was created. The geometry was simplified to a single porous silica layer (instead of the hierarchical array found in nature) in order to reduce the computational cost. This simplified domain was discretized using shear-deformable shell finite elements. Using this shell model, linear buckling and modal analyses of the diatom shell structure were performed in an attempt to correlate the deformation modes obtained with the geometries observed experimentally. These studies have led to conclude that these biostructures experience mechanical instability naturally. More specifically, it has been determined that these shell deformations are dynamic in nature and consistent with current theories on diatom morphogenesis. Additionally, FEM models were used to study the relation between diatom morphology and the onset of instability. In this diatom species, a clear quadratic correlation was found between the size of the pores and the critical buckling load (i.e. the onset of instability phenomena) as well as between the shell thickness and the critical buckling load. This research contributes to improving understanding of the mechanical response of biomaterials and represents a step toward innovative design and manufacturing process of bio-inspired microstructures.

Electrospinning is favorable technique to prepare artificial to extracellular matrix (ECM) structure using synthetic or natural polymer. However, it is mostly limited to two dimensional (2D) structures that is not actually function as 3D cell culture system. There is a few trial of three dimensional (3D) structure of nanofiber mesh that the cells penetrate into the mesh and shows multi directional proliferation. Instead of solid ground for depositing nanofiber, liquid ground and ball shape ground were introduced and showed low density of sponge nanofiber mesh. Some polymer shows unique 3D mesh structure during electrospinning.
When sodium alginate, composed of (1-4)-linked β-D-mannuronate and α-L-guluronate, is electrospun to solid ground, repulsion between fiber is occurred by anionic charge, and formed low density nanofiber mesh. It is not electrospinnable alone, lacking of entanglement, high molecular weight of poly (ethylene oxide) is generally blended with alginate. Crosslinking is necessary after electrospinning to maintain fibrous structure in aqueous environment. We found out the morphology of nanofiber is not clearly kept during crosslinking step, the diameter of fiber is thicker, whole mesh becomes flat in several literatures of alginate nanofiber. To overcome of it, we speculated the boundary is able to retard dissolution of alginate molecules during crosslinking process.
In this study, we fabricated electrospun alginate nanofiber covered with poly (ε-caprolactone) (PCL) shell using co-axial nozzle. Alginate and PCL were respectively injected through inner and outer nozzle with various flow rate to regulate fiber diameter. After that, the nanofiber was cross-linked in 2 wt% CaClshy;₂ solution. Freeze dried nanofiber was immersed in chloroform to remove PCL shell, and obtained only alginate nanofiber suspension. Alginate nanofiber was physicochemically characterized. The morphology of alginate nanofiber was visualized by scanning electron microscope. Alginate crosslinking density was differently regulated during crosslinking process using 0.5% to 2wt% CaClshy;₂ solution.
Alginate/PCL core/shell nanofiber was electrospun on aluminuim hoil in 3D structure because of charge repulsion from alginate. After PCL shell was removed by chloroform, the nanofiber mesh structure showed fiber suspension in chloroform, methanol and water. The morphology of alginate mesh is totally different comparing with PCL shell covered state that the nanofiber was inter-connected between single fiber. The morphology of alginate nanofiber mesh showed nano-scale fibrous structure, and partly inter-connected between fiber was confirmed by SEM. Pore distribution of the mesh was about tens of micrometers. We expected this structural property is advantage for 3D cell culture system. In further study, in vitro test is proceed, and evaluate cell proliferation efficiency, the property of the mass composition of cells and alginate nanofiber.

We have developed the colorimetric sensing materials with amyloid fibrils of α-synuclein and 10,12-pentacosadiynoic acid (PCDA) by using specific fatty acid interaction of α-synuclein and structural regularity of amyloid fibrils. PCDA interaction of α-synuclein resulted in proteins self-oligomerization and accelerated α-synuclein fibrillation with localizing PCDA molecules on amyloid fibrils. The PCDA-containing amyloid fibrils prepared by either co-incubating with α-synuclein (AF/PCDA) or mixing with the pre-made amyloid fibrils (AF+PCDA) turned to blue upon UV irradiation and became red with external stimuli of heat, pH and organic solvents. Interestingly, AF/PCDA and AF+PCDA on paper can also exhibit blue color with UV treatment and blue-to-red color transition with heat and organic solvents. The two types of paper sensors from AF/PCDA and AF+PCDA showed substantially different sensitivities toward temperature and solvents because of the molecular freedom of PCDA on amyloid fibrils which is dependent on the tightness of PCDA binding to amyloid fibrils. For example, AF/PCDA-containing paper sensors responded to the higher temperatures from 55#730;C to 90#730;C showing the blue-to-red color transition, but AF+PCDA on paper detected the lower temperatures from 25#730;C to 60#730;C. For this same reason, the AF/PCDA sensor showed color changes only after direct contact with the solvents in solution while the AF+PCDA sensor exhibited color transition against organic solvents with a brief exposure to their vapors. Additionally, AF+PCDA was capable of monitoring thermal history of materials by showing blue-to-red color changes in response to the increased temperatures and indicating an exact location of spot exposed to heat. Taken together, amyloid fibrils can provide adequate templates for PCDA to be developed into paper-type sensors and then the PCDA-containing amyloid fibrils can be considered as novel polydiacetylene-based thermochromics and solvatochrmic sensors.

Nature is a wonderful inspiration to design and fabricate tough, stiff while strong composites. Bone and nacre are prime examples of natural ceramic-based composites with high strength and toughness. Previous studies on mechanical performance of these structural materials show that their outstanding properties are direct results of the nano-scale features and the optimized arrangement of the elements. Moreover, to provide the outstanding mechanical functions, nature has evolved a complex and effective functionally graded interfaces. Particularly in nacre, organic-inorganic interface in which the proteins behave stiffer and stronger in proximity of calcium carbonate minerals provide an impressive role in structural integrity and mechanical deformation of the natural composite. However, further research on the toughening mechanisms and the role of the interface properties as a guide on design and synthesize new materials is essential. In this study, a micromechanical analysis of the mechanical response of “Brick-Mortar” and “Brick-Bridge-Mortar” composites is presented considering interface properties. The closed-form solutions for the displacements in the elastic components as a function of constituent properties can be used to calculate the effective mechanical properties of composite such as elastic modulus, strength and work-to-failure. Detailed relationships are presented to identify future directions for material development.

Introduction. Biofilms are often found on biomedical devices and are very difficult to eliminate. In this study, our aim was to establish biofilms using Staphyloccocus aureus (S. aureus) and to determine the effectiveness of antimicrobial peptides and conventional antibiotics in disrupting the biofilms.
Method. Five S. aureus strains were examined including bioluminescent strains (Xen36, Xen29, Xen8.1), ATCC25923, and clinical 1004. Four sets of experiments were carried out: (i) Optimizing bacterial concentration in establishing biofilms using S. aureus Xen36. (ii) Establishing biofilms using the five bacterial strains. (iii) Examining the effect of antimicrobial peptides in disrupting biofilms. (iv) Comparing the effect of antimicrobial peptides with conventional antibiotics in disrupting S. aureus biofilms.
Results and Discussions. We found that a concentration of 10² CFU/mL of S. aureus Xen36 could provide detectable bioluminescent intensity, and the growth profiles of 10², 10⁴, and 10⁶ CFU/mL had similar patterns at the time points studied. The biofilm-forming capacity of the various S. aureus strains were observed by cultivating the biofilms on polystyrene and stainless steel surfaces. We found that all S. aureus strains examined formed biofilms but their biofilms had very different morphologies; biofilms formed quicker on polystyrene surfaces compared to stainless steel ones. We found that antimicrobial peptides like LL-37 were highly potent in disrupting S. aureus biofilms compared to conventional antibiotics such as clindamycin, vancomycin, and cefazolin. The disruption of S. aureus biofilms was believed to take place through the lysis of the Staphyloccocci which leads to destabilization of the biofilm matrix. S. auerues has been commonly found to grow biofilms on biomedical devices and has been a significnat clinical concern. Unfortunately, very few therapeutic approaches have been reported as effective in disrupting or eliminating such biofilms. In this study, antimicrobial peptides disrupted the bioluminescent biofilms and were much more effective compared to commonly used conventional antibiotics (e.g. clindamycin, vancomycin, and cefazolin), and therefore could potentially contribute to biofilm removal clinically.

Impressive examples can be found throughout nature of the biological assembly of intricate hierarchically-patterned, rigid structures. While the morphological complexity and diversity of such self-assembled 3-D biogenic structures is breathtaking, the range of chemistries (particularly inorganic chemistries) possessed by such structures pales in comparison to the rich variety of synthetically-derived materials. Although valiant attempts have been made to induce organisms to assemble 3-D structures comprised of new, non-naturally-occurring inorganic materials, such efforts have met with limited success. An alternative strategy is to utilize synthetic chemical approaches to alter the chemistry, but not the morphology, of biogenic structures. For the case of bio-inorganic templates, gas/solid reactions may be used to generate positive replicas that, with appropriate reaction conditions, retain nanoscale features as well as the 3-D shapes of the starting templates. For bio-organic templates with appropriate native surface chemistries (or with appropriately-modified surface chemistries), layer-by-layer (LbL) wet chemical coating strategies may be used to generate highly-conformal coatings that, upon removal of the underlying template, yield structures that retain the overall shapes and fine surface features of the starting template. In this presentation, the conversion of biogenic and synthetic silica-based structures (diatom silica microshells, self-assembled silica templates, microlithographically-patterned silica-bearing structures) into replicas comprised of new functional porous inorganic materials via the use of gas/solid reactions will be discussed. The conversion of bio-organic templates (e.g., pollen, butterfly scales) into functional oxides via an automated LbL surface sol-gel process will also be described. Such chemically-tailored, 3-D biogenic and synthetic structures can be attractive for a variety of catalytic, optical, sensor, energy, and other applications. By analogy to the medieval concept of alchemy (conversion of common materials into more precious ones), such shape-preserving chemical transformation of readily-formed materials into new functional materials may be considered to be a modern type of materials alchemy.

Fascinating properties of many surfaces found in nature originate from nano- and microstructures covering them. With the help of these smart surfaces many animals and plants adapt in an optimal way to their environment. The well-known hierarchical nano-scale hairs at the toes of geckos show high adhesion and self-cleaning abilities at the same time. The blue Morpho butterfly developed “Christmas”-tree like nanostructures to obtain a high reflection of blue light for extremely wide view angles. The air retaining water beetle is an inspiration to develop drag reducing surfaces while high aspect ratio fur-like microhairs found on the water plant Salvinia can be used to clean oil/water mixtures.
These and other features of surfaces observed in nature can be mimicked to design smart surfaces which are useful for various technological applications ranging from non-bleaching colors to self-cleaning, adhesive surfaces and oil/water separation. Advanced technologies have to be applied to fabricate these bio-inspired nano- and microstructures. Since e-beam lithography and 3D direct laser writing are only suited for research purposes we develop hot embossing and pulling methods for large scale fabrication. We will present our recent developments for fabrication of bio-inspired smart surfaces mimicking the features of butterflies, geckos, beetles, and water plants.

Sequence-defined polymers, epitomized in nature by polypeptides and poly(nucleic acids), are polymers composed of a multiplicity of monomers, each monomer distinguished from another by having a different side chain, and sequencing of the various monomers into a polymer in a predetermined order. These are distinguished from random copolymers. In nature, sequence-defined polymers create biomaterials, encode information, perform biocatalysis, participate in molecular recognition, and shuttle species across membranes. To date the vast majority of synthetic sequence-defined polymers are either laboratory examples of the natural sequence-defined biopolymers, or close analogs based on similar structural units and bond-forming reactions. For example, peptides, pseudopeptides, and peptoids all rely on amino acid structures and peptide bonds.
We have developed a new class of synthetic biomimetic polymers. Molecular precursors and monomers derived by nucleophilic aromatic substitution reactions on cyanuric chloride provide facile approaches for the incorporation of side-chains as "R-groups" into the monomer structures, such that diverse monomers can be produced. These monomer structures are then assembled into polymer chains in predetermined order to create a new architecture for sequence-defined polymers that has no peptide bonds. Demonstrated side chains include neutral alkyl or aromatic groups, as well as amino or carboxyate groups. Hence sequences can contain side chains with diversity similar to those of peptides including ionizable side chains. Trimer, hexamer, and dodecamers have been synthesized using a new submonomer solid phase synthesis approach. Using this method, we have synthesized homopolymers of defined length, block copolymers, sequence controlled polymers, and fully sequence defined polymers.
In addition to the synthetic work, molecular dynamics simulations of these new types of structures have demonstrated conformational order due to hydrogen bonding and other interactions that are suggestive of protein secondary structure. One common motif seen in several simulations is a nanorod structure with evenly spaced side chains, held together by a combination of hydogen bonding and pi-pi interactions. New simulation methods with enhanced sampling are being applied to better sample the conformational possibilities, observe rare conformational changes, and find the thermodynamically stable states.
It is anticipated that side-chain functionality, self-organizing conformations, and intermolecular self-assembly of these sequence-defined polymer materials will lead to biomimetic functionality and application.

About 40% of domestic energy in USA is consumed in heating, ventilation, and air conditioning (HVAC) in the building. To save energy in HVAC, we have investigated novel textile structures which can adaptively protect body temperature from cold or hot environment. We discovered that our natural primary protection layer, the humane skin, is a good example to mimic for designing smart clothes because it has physiological mechanisms to regulate body temperature by controlling sweat evaporation and air layer trapped around skin hair.
Inspired by skin&’s thermoregulation, we have developed self-adaptive textiles using humidity sensitive shape memory polymer (HSSMP) which consists of two dissimilar components of hydrophobic material and hydrophilic material. Such a designed materials can change its shape under specific temperature and relative humidity (RH) while hydrophilic polymer absorbs water and swells. We have designed HSSMP to be able to increase air permeability in textiles for better sweat evaporation and decrease the amount of air trapped in textiles for better conduction under high temperature and high humidity.
In this study, hydrophilic and hydrophobic materials for HSSMP were chosen based on vans OSS-Chaudhury-Good theory, and the interaction between HSSMP and water was evaluated by measuring contact angle of water droplet on HSSMP. We synthesized HSSMP that has a two-layer film composed of hydrophilic and hydrophobic material. Two types of self adaptive clothing structures have been designed and tested: flap patterned HSSMP (one-layer structure) and HSSMP with dual inserted textiles layers (two-layer structure). We found that both one-layer structure and two-layer structure exhibit self-adaptive properties in a different way, to make a person feel cooler under warm temperature and high humidity by opening flaps, and decreasing the thickness between the two layers. The reverse reaction on cold environment can also occurs in a controlled manner. The energy transfer model of our clothed body considering heat loss by conduction, radiation, convection, and evaporation was also studied to simulate and evaluate the ability of the adaptive clothing. The hydrophilic network structure in a hydrophobic material will be investigated by measuring water absorbing property using time dependent contact angle and QCM (quartz crystal microbalance), and the results will be also discussed based on Flory-Huggins solution theory.

Vesicles, supramolecular assembly like cellular membranes, possess an inner water pool, which is segregated from their external aqueous environment by a thin curving and flexible membranes. Owing to their unique architectures, vesicles have emerged wide applications in biomedicine and biocatalysis fields. In traditional methods, vesicles are self-assembled from amphiphilic lipids, surfactants, polymers, and peptides. Among them, pepsomes from amphiphilic peptides have exhibited a rising applications in biomedical filed, because of their good biocompatibility. However, peptides chemical and thermal instability has limited pepsomes wide applications. Peptoids, or poly-N-substituted glycines, have a similar structure with peptides, while they have no side-chain backbone hydrogen bonding and are highly stable. Benefited from the programmable synthetic process, peptoids are highly designable or polymer with an almost 1.0 PDI.
In this presentation, we report the self-assembly of highly-stable pepsomes from environment-responsive amphiphilic peptoids. In specific, we have synthesized amphiphilic peptoids with terminals modified by anhydride and amine groups, respectively. Through the covalent interactions between anhydride and amine groups under base condition, they self-assemble and form multi-layer pepsomes with an average diameter around 500 nm. Pepsomes morphology was verified by TEM, AFM and DLS. Due to the pH-responsibility of Schiff base molecular structure, these pepsomes exhibited reversible disassembly and reassembly process in response to pH changes. Under low pH conditions, pepsomes disassemble into clear aqueous solution with some white precipitate; on the other hand, under high pH conditions, they could reform pepsomes again with strong stirring. Because peptoids are biocompatible and highly stable, we expect that these pepsomes self-assembled from peptoids will have great potential applications in the biomedicine field by being used as the drug/protein/gene carrier.

Responsive surfaces have become one of the most active area in the field of materials. To induce a specific response, numerous triggers were reported. Yet, only few studies report about the design of systems that respond to a mechanical stimulus such as a stretching. Such systems are largely found in nature and constitute the heart of mechanotransduction events.
The layer-by-layer deposition process of polyelectrolytes is used to design polyelectrolyte multilayer films. By embedding and anchoring enzymes in these films, we designed biocatalytic surfaces and we demonstrated that a macroscopic mechanical stretching allows to induce local deformation on enzymes and finally switch off the biocatalytic activity of the enzymes. This mechanism is reversible, i.e. enzymatic activity can be recovered in non-stretched conditions. Control of drug release by mechanical stimuli is also obtained by using other kind of polyelectrolyte films.
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Mertz D., Vogt C., Hemmerlé J., Debry C., Voegel, J.-C., Schaaf P., Lavalle Ph. "Tailored design of mechanically sensitive biocatalytic assemblies based on polyelectrolyte multilayers", J. Mater. Chem., 2011, 21, 8324-8331.
Mertz D., Vogt C., Hemmerlé J., Mutterer J., Ball V., Voegel J.-C., Schaaf P., Lavalle Ph. "Mechanotransductive surfaces for reversible biocatalysis activation", Nature Mater., 2009, 8, 731-736.

Compared with cooled infrared (IR) detection systems, which require cryogenic cooling, the uncooled IR detection systems are highly desirable due to their advantages of room temperature operation, and the associated low cost and portability. The development of high performance uncooled IR detection systems will greatly expand the application of IR technology in different areas such as transportation, surveillance, medical care, etc. In nature, some biological species such as fire beetles, snakes, bats, have developed amazing capability in the detection of IR through billions of years evolution. Such biological IR detection systems have attracted lots of attention recently in the design of new artificial IR detection devices. In this study, inspired by the outstanding IR detection ability and the detection principle of fire beetle Melanophila Acuminata, we will report our effort in combining Surface Plasmon Resonance (SPR) and thermally responsive hydrogel nanoparticles(NPs) as a new type of IR detecting system. Poly(N-isopropylacrylamide-co-acrylic acid) (poly(NIPAM-co-AAc)) copolymer hydrogel NPs with different sizes were synthesized. Due to the sensitive volume change and the corresponding refractive index change of NPs that was induced by the IR radiation, the optical transmission of the NP solution showed a ~ 30 mK temperature sensitivity, which is comparable to the natural system. When these hydrogel NPs were attached onto the gold thin film, the IR-induced refractive index change of NPs resulted in the SPR signal changes of the gold film, and a sensitive IR response was also achieved. The correlations between the hydrogel NP size, optical property, and IR sensing performance will be discussed in detail. This study not only provides a new material system for the development of highly sensitive and low cost uncooled IR detection, but also helps expand the application space of SPR in the area of IR imaging.

By capturing human physiological or behavioral characteristics, wearable electronic sensors in biomonitoring and biometric systems carry significant importance in daily life such as in personalized health monitoring and assessment, disease diagnosis, entrance and mobile control, secured financial transactions and others. Measurements of human physiological or behavioral characteristics are the main designing functions of wearable and interactive electronics. And a lightweight and self-powered technology is highly desired for simultaneously acquiring multifunctional characteristics.
Here, we report the first bionic membrane sensor (BMS) based on triboelectrification for self-powered physiological and behavioral measurements such as local internal body pressures. Enabled by the unique and fundamentally new sensing mechanism and an eardrum-inspired structure, the self-powered BMS holds a collection of superior performances, including fast response time (< 6 ms), low pressure detection limit down to 2.5 Pa, high sensitivity (>51 mVPa^-1), high stability (>40,000 loading and unloading cycles), as well as an exceptional wide working bandwidth (from 0.1 Hz to 3.2 kHz). Such advantages enable the BMS to monitor pressure-induced human physiological and behavioral signals, and it is demonstrated that the BMS can serve non-invasive human health assessment, self-powered anti- interference throat voice recording and recognition, as well as high-accuracy multi-modal biometric authentication, thus potentially expanding the scope of applications in self-powered wearable medical/health monitoring, interactive input/control devices as well as accurate, reliable and less intrusive biometric authentication systems.
References: (* indicate co-first author).
1.J. Chen*, J. Yang*, Y. Su, Q. Jing, Z. Li, F. Yi, X. Wen, Z. Wang and Z. L. Wang. Adv. Mater. 27 (2015), 1316-1326.
2.J. Chen*, G. Zhu*, J. Yang, Q. Jing, P. Bai, W. Yang, X. Qi, Y. Su and Z. L. Wang. ACS Nano 9 (2015), 105-116.
3.J. Chen*, G. Zhu*, T. Zhang, Q. Jing and Z. L. Wang. Nat. Commun.5 (2014), 3426.
4.J. Chen*, G. Zhu*, W. Yang, Q. Jing, P. Bai, Y. Yang, T. C. Hou and Z. L. Wang. Adv. Mater.25 (2013), 6094-6099.
5. J. Chen*, J. Yang*, Z. Li, X. Fan, Y. Zi, Q. Jing, H. Guo, Z. Wen, K. C. Pradel, S. Niu and Z. L. Wang. ACS Nano 9 (2015), 3324-3331.

Advance smart sensor network systems that are cost effective, user friendly, reliable, miniaturized, and inexpensive to manufacture are in tremendously high demand for energy, defense, and health applications. This advanced sensing system can be used to detect and monitor small molecule chemical vapors with high sensitivity and selectivity. As a novel bio-inspired approach, we have demonstrated that genetically modified peptide receptors expressed in the M13 bacteriophage, and its corresponding hierarchical phage color film can be used as a colorimetric responsive bioanalytical platform; the platform not only enables facile and rapid detection of various volatile organic chemicals (VOCs) such as hexane, diethyl ether, isopropyl alcohol, ethanol, and methanol, and trinitrotoulene (TNT) but also provides modes for gas identification.^{1, 2} To further expand our system to detect NH₃ or CH₄, we demonstrate our recent efforts on designing phage engineered with 3,4-dihydroxy-phenylalanine (DOPA) and transition metals that can detect NH₃ and CH₄ with high sensitivity and selectivity. We first optimize the synthesis conditions of DOPA phage and the DOPA-transition metal complex. By comparing various transition metals (e.g. Pt, Pd and others), we then investigate conditions to synthesize phage with high colorimetric response to analyte gas. In addition, to enhance the accuracy and specificity of gas sensing ability in phage system, mimicking the olfactory system of mammals, we construct arrays of phage-based thin films as a cross-responsive platforms for “artificial nose” type pattern recognition: (1) two different types of genetically engineered phage displaying target-binding peptide motifs, and (2) two different types of the transition metal-DOPA phage matrices. We fabricate phage color sensors with these 4 different engineered phage films and 4 different pulling speeds. With this 4 × 4 array, a difference intensity is generated for each analysis; the resulting color difference profiles (i.e., 48-dimensional vectors made up of the changes in red, green, and blue values of the 16 phage films) represent a unique “molecular fingerprint” for each gas analyte over similar chemical vapors. To evaluate the variation between responses from this multiplexed analysis, principal component analysis (PCA) is used to probe the dimensionality of sensor array data; PCA creates linear combinations of the array&’s responses, maximizing the total variance among the data into as few dimensions as possible.
Reference
1. Chung WJ, Oh JW, Kwak KW, Lee BY, Meyer J, Wang E, Hexemer A, & Lee SW. Biomimetic self-templating supramolecular structures. Nature. 478, 364-368, (2011).
2. Oh, J.-W., Chung, W.-J., Heo, K., Jin, H.-E., Lee, B. Y., Wang, E., Zueger, C., Wong, W., Meyer, J., Kim, C., Lee, S.-Y., Kim, W.-G., Zemla, M., Auer, M., Hexemer, A., and Lee, S.-W. Biomimetic virus-based colourimetric sensors. Nat Commun5, 3043 (2014).

In nature, many biological materials use water to generate force or tune their mechanical properties for specific functions. For example, in response to environmental humidity changes, the awns of the wheat can open and close, and act as “plant muscles” to penetrate the seeds into the soil. Spider&’s silk can super-contract in high humidity, which is essential to maintain tension in the web after prey capture (Liu Y et al., Nature Mater., 2005). Inspired by nature, here we report that the mechanical properties of metals can also be tuned by water when they gain a nanoporous structure. The tuning was achieved through the action of water capillarity in the nanopores. We show that the strength of nanoporous Au-Pt can be tuned reversibly by as large as 23 MPa. Moreover, by controlling the water content, the nanoporous Au-Pt contract and expand reversibly by up to 1.3% (linear strain). The water-responsive mechanical behavior of nanoporous metals may find applications in many areas, such as micro-robots that may operate by harvesting energy from the environment.

A bilayer film composed of a thin polymer film atop thick elastomer substrate was prepared. Reversible switching between wrinkled and flat surface can be achieved by a facile stretch and release method. This system shows a very high opaqueness as released from a small strain (ca. 5%), which leads to a potential application for smart windows. By altering the chemical composition of the polymer thin film, simply applying moisture can also instantaneously induce a wrinkled surface, which can be reversed as the moisture is removed. The alignment of wrinkle pattern can be achieved through coordinating with mechanical strain. Selective inducing chemical modification on the polymer thin film surface can create patterned wrinkles, which is expected to lead to specific applications.

Silicon nanocrystals, considered as the greener alternatives to other semiconducting nanocrystals such as CdSe and PbS, naturally offer the benefits of being inexpensive, purportedly less toxic and compatible with existing silicon electronics. A significant rise can be seen in the number of publications on silicon nanocrystals recent years, which witnesses a rising interest in this material. However, the instability against oxidation has been a major drawback for nanostructured silicon in various applications. There are situations where silicon nanostructured materials could benefit from water resistance, and this can, in principle, be achieved by protecting the surface with super-hydrophobic molecules or polymers, the best documented examples being based on perfluorohydrocarbons.
Herein we report our innovative surface engineering of silicon nanocrystal films by capping them with perfluorocarbon chains. The as-prepared films have multiscale roughness and a Cassie-Baxter surface state endows them with a water contact angle of nearly 170 degrees. Comparison with the properties of the perhydrodecyl-capped relative shows its huge advantage in terms of resistance to both water and air oxidation. The superior hydrophobicity of the perfluorodecyl group compared to the perhydrodecyl capping group yields higher contact angle films, the enhanced electron withdrawing character induces blue shifts in the wavelength of photoluminescence and the lower frequency carbon-fluorine stretching modes disfavor non-radiative relaxation pathways and boost the absolute photoluminescence quantum yield. Collectively these observations speak well for advanced materials and biomedical uses of such bi-functional (brightly-photoluminescent and superhydrophobic) films.

Hierarchical topography is an essential feature of bio-systems for achieving their functionality. Examples include superhydrophobicity of lotus leaf, drag-reduction of shark skin, anisotropic adhesion of gecko feet, and anti-reflection of moth&’s eye etc. Understanding the role of topography has enabled realization of these intriguing properties in man-made materials. However, majority of such feats have been limited to polymers and semiconductors because of their superior patterning capabilities. Here, we utilize thermoplastic embossing of metallic glasses to build hierarchical patterns and control the surface properties of metallic materials. Sub-100 nm to millimeter sized features are sculpted sequentially to allow an exquisite control of surface properties. Wetting, reflectance, and adhesion of metallic surfaces are controlled through topography. The role of surface chemistry and topography are isolated through studying metallic glasses of different compositions.

Detecting target analytes with high specificity and sensitivity in any fluid is of fundamental importance to analytical science and technology. Surface-enhanced Raman scattering (SERS) has proven to be capable of detecting single molecules^[1] with high specificity but achieving single molecule sensitivity in any highly diluted solutions remains a challenge. Here we demonstrate a universal platform that allows for the enrichment and delivery of analytes into the SERS-sensitive sites in both aqueous and non-aqueous fluids, and its subsequent SERS detection down to the attomolar level (10^-18 mol l^-1). These levels of detection represent at least five orders of magnitude improvement in non-aqueous solutions and an order of magnitude improvement in aqueous solutions compared to those of state-of-the-art SERS detection methods. The platform is based on a pinning-free, bio-inspired omniphobic slippery substrate,^[2] which enables the complete concentration of analytes and SERS substrates (e.g., Au nanoparticles) within an evaporating liquid droplet. Our method allows for ultra-sensitive airborne and molecular detections in a broad range of common fluids for applications related to analytical chemistry, molecular diagnostics, environmental monitoring, and national security.
References
[1] Nie, S. M. & Emory, S. P. Probing single molecules and single nanoparticles by surface enhanced Raman scattering. Science 275, 1102-1106 (1997).
[2] Tak-Sing Wong, Sung Hoon Kang, Sindy K. Y. Tang, Elizabeth J. Smythe, Benjamin D. Hatton, Alison Grinthal & Joanna Aizenberg, Bioinspired self-repairing slippery surfaces with pressure-stable omniphobicity. Nature477, 443-447 (2011).

Preventing bacterial attachment to material surfaces in the absence of antibiotic agents are currently in great demand due to the growing prevalence of antimicrobial resistance strains. Herein, we present rice leaf inspired bacterial anti-adhesive materials. “Rice leaf-like surfaces” (RLLS) are fabricated by facile and templateless self-masking reactive-ion etching (SM-RIE) approach. Bacterial attachment on RLLS were determined by under both static and dynamic conditions using Gram-negative Escherichia coli O157:H7 and Gram-positive Staphylococcus aureus. RLLS surfaces show exceptional bacterial anti-adhesion properties with higher than 99.9% adhesion inhibition efficiency. Furthermore, the optical properties of RLLS was investigated using UV-Vis-NIR spectrophotometry. Different from most other bacterial anti-adhesive surfaces, RLLS demonstrates optical grade transparency (i.e., ge; 92% transmission). We anticipate that the combination of bacterial anti-adhesion efficiency, optical grade transparency, and convenient single-step method of preparation makes RLLS very attractive candidate as surfaces for biosensors; endoscopes; and microfluidic, bio-optical, lab-on-a-chip, and touchscreen devices.

Plants and animals utilize intricate micro/nanostructures to perform complex biological functions, such as self-cleaning, dry/wet adhesion, and camouflaging; and these unique properties have inspired many scientists to attempt to reverse engineer these structures. However, the requirement for curved and re-entrant structures render difficulty to top-down manufacturing methods, and limits the flexibility in materials choice and/or in control of key properties such as mechanical compliance and structural porosity. In contrast, existing bottom-up methods such as 3D printing are limited in large scale production due to the low throughput. We have invented and demonstrated a bottom-up method for scalable fabrication of curved and twisted microstructures by strain-engineered growth of carbon nanotubes (CNTs). The complex 3D CNT microarchitectures can also be further tuned to have large range of stiffness (modulus from ~14 MPa to ~20 GPa) and porosity (up to 99%) by additional deposition methods.
We demonstrate that the geometry of these 3D microstructures can be predicted using a step-wise finite element model that incorporates measured anisotropic mechanical properties of the aligned CNTs, and the relative growth rates which are mapped to a parametric study of the CNT growth parameters. We show that the geometry of individual CNT microstructure assigned by catalyst patterning can be predicted with the developed model to a high fidelity, and the effect of temporal evolution of process parameters such as CNT growth rates can also be incorporated to simulate more realistic growth scenarios. Using the developed model, we also study how stress evolves within each structure during the strain-engineered growth and identify the failure modes such as local buckling and interfacial shear splitting. Then we present the guidelines for designing the appropriate 2D catalyst patterns and growth conditions such that they result in 3D CNT microstructures with desired geometry. Last, we show how this approach is used to design and manufacture textured microstructures mimicking the scales of the Morpho butterfly.

The human beings could make proper decision under the unfamiliar situation based on the past experience and memory, since the brain consists of 100 billion neurons and 100 trillion synapses, which can proceed and transmits the information through electrical and chemical signals. For realizing the trainable and fault-tolerant computing system, operating principle of neurons and synapses, the building block of the brain, has been emulated recently. The basic operation of neurons and synapses for learning and memorizing is the plasticity, where the synaptic strength (or weight) can be changed according to the history of the stimulation, and facilitate unique behaviors such as short-term memory (STM), long-term memory (LTM), symmetric spike timing dependent plasticity (STDP), neural facilitation and image auto-association.
Here, we demonstrate a brain-inspired synaptic thin-film device using indium-gallium-zinc-oxide thin-film transistors (IGZO TFTs), emulating various synaptic behaviors. The IGZO TFTs were fabricated by a well-known sol-gel process and thermal annealing. On our experiments, the conductivity of IGZO channel, which stands for the synaptic strength (or weight), is manipulated by an exposure of light pulse as a neural activity or a stimulus. We implemented STM that retention for few seconds in a Hippocampus and LTM in a Cerebrum cortex that give rise to the persistent photoconductivity by controlling the frequency of the exposing light pulse, according to Atkinson and Shiffrin model in cognitive neuroscience. Symmetric STDP, which displays the connection strength based on the relative timing between neural activities of the presynaptic and postsynaptic cells, could be also operated on the IGZO TFTs. In addition, waxes and wanes of IGZO channel conductivity depend on the frequency of the light stimulation and the history of prior activity same with the neural facilitation. For demonstrating the simple synaptic function of learning and memory, we performed image auto-association that the TFT array memorize the specific shape and recall the appropriate memory when provided with a fragment of the images. Finally, to explain the various photo-related activities in the IGZO thin films, photo-induced conductivity and stretched exponential photo-relaxation properties of solution-processed IGZO TFTs were examined.

Using computer simulations, we investigate the mechanical properties of a network of polymer-grafted nanoparticles (PGNs) that are interlinked by a combination of labile “catch” and “slip” bonds. In contrast to conventional slip bonds, the life time of catch bonds can potentially increase with the application of force (i.e., the rate of rupture can decrease). In effect, the bond becomes stronger under an applied force (if the strain rate is sufficiently high). Such catch bonds play a vital role in regulating the rolling of leukocytes on the extracellular matrix and provide a useful design motif for creating high-strength synthetic materials. In this design process, we initially focus on rectangular samples that encompass a shell of catch bonds and an inner core of slip bonds. We subject this PGN network to a tensile deformation to determine the benefits of a strong coating on the strength and toughness of the material. We then compare the behavior of materials with this core-shell architecture to the properties of composites that encompass a random distribution of catch and slip bonds throughout the sample. We also compare the behavior of these different samples as the applied tensile force is released, and we measure the residual strain and hysteresis of the networks. The findings provide guidelines for creating nanocomposite networks that are highly resistant to mechanical deformation and show rapid strain recovery. The results can also provide insight into factors that contribute to the remarkable strength of biological fibers, such as the mussel adhesive fibers.

Gelatin is a degradation product of collagen.^[1] The latter is the most abundant structural protein in vertebrates which makes it available in megaton quantities.^[2] On these grounds, gelatin would be a plausible substitute for synthetic polymers. However, unprocessed and untreated gelatin is highly susceptible to water: it swells and dissolves, making it unsuitable for most applications.
We developed a 2-step procedure, which combines processing technology and polymer material chemistry to render gelatin useful as a fibrous polymer replacement: For this we utilized an unique gelatin/water/non-solvent “dope”, which proved to be beneficial for both the dry and wet spinning of gelatin fibers.^{[3, 4]} The spinning process was up-scaled in order to continuously fabricate thin gelatin filaments (20 - 25 mu;m; 200 m min^-1), which were twisted into 2-ply yarns. These gelatin yarns showed good processability and could e.g. be knitted into a textile structure with haptics similar to a merino sheep wool analogue.^[5]
In order to render the gelatin yarns water-resistant, we systematically investigated different crosslinking methods based on epoxide and aldehyde reactive groups. The combination of ethylene glycol diglycidyl ether and gaseous formaldehyde yielded high crosslinking degrees and a significant reduction in swelling. In an attempt to mimic the hydrophobic nature of sheep wool, the yarns were impregnated with lanolin (wool grease). Gelatin yarns treated in this manner could be repeatedly washed in detergent solution. To further improve the thermal properties of the years, process parameters were adapted to achieve fibers with internal cavities (~ 30 % porosity). The porous nature of these fibers resembles the morphology of specialty natural fibers such as angora rabbit wool and achieve similar thermal properties.
Aside of presenting the details of the gelatin processing, we will discuss performance thresholds for protein-sourced fibrous polymer replacement materials.
[1] W. F. Harrington, P. H. Von Hippel, in Advances in Protein Chemistry, Vol. 16 (Ed.: C. B. Anfinsen, M. L. Anson, K. Bailey, J. T. Edsall), Academic Press, 1962.
[2] M. Djabourov, Contemporary Physics, 1988, 29, 273-297.
[3] P. R. Stoessel, R. N. Grass, A. Sanchez-Ferrer, R. Fuhrer, T. Schweizer, R. Mezzenga and W. J. Stark, Adv. Funct. Mater., 2014, 24, 1831-1839.
[4] P. R. Stoessel, R. A. Raso, T. Kaufmann, R. N. Grass and W. J. Stark, Macromol. Mater. Eng., 2015, 300, 234-241.
[5] P. R. Stoessel, U. Krebs, R. Hufenus, M. Halbeisen, M. Zeltner, R. N. Grass, W. J. Stark, Biomacromolecules, 2015, DOI: 10.1021/acs.biomac.5b00424

DNA is a suitable tracer for labeling all kind of materials in order to identify products and properties. Its high potential is based on the chemical encoding of information (= unique barcode) and measurement of concentration at a single-molecule level with minimal laboratory equipment. Several investigations were dealing with DNA as tracer by incorporating DNA into complex-shaped nanomaterials.^{[1, 2]} However, DNA is sensitive towards harsh environmental conditions and elevated temperatures. For implementing DNA for tracing, we have to ensure a high stability of the DNA in order to read-out the barcode in products even after extreme processing conditions (heat, pressure, light exposure). We developed a protection system for DNA by encapsulating DNA into glass spheres, mimicking natural fossils (e.g. ambers or fossils), which protects the DNA against chemical attack and high temperatures.^{[3, 4]} The most efficient damage of DNA is, however, induced by solar irradiation, which cannot prevented by encapsulation in silica. Bioinspired by microbial spores, which have an outstanding resistance to UV radiation, we further developed a TiO₂ coating giving the encapsulated DNA a UV resistance similar to bacterial spores.^[5] With this high stability of DNA, the encapsulated DNA system can now be used as tracer in various applications. Aside of giving information about the encapsulates and process for designing them I will present the successful implementation of the encapsulates as tracers in ecological studies^[6], monitoring wastewater plants^[7] and for barcoding oils^[8]. In the most elaborate cases, we are even able to detect and count individual 60 nm sizes nanoparticles.
[1] J. H. Choy, S. Y. Kwak, J. S. Park, Y. J. Jeong, J. Portier, J. Am. Chem. Soc. 1999, 121, 1399-1400.
[2] J. H. Choy, J. M. Oh, M. Park, K. M. Sohn, J. W. Kim, Adv. Mater. 2004, 16, 1181-1184.
[3] D. Paunescu, R. Fuhrer, R. N. Grass, Angew. Chem. Int. Ed. 2013, 52, 4269-4272.
[4] D. Paunescu, M. Puddu, J. O. B. Soellner, P. R. Stoessel, R. N. Grass, Nat. Protoc. 2013, 8, 2440-2448.
[5] D. Paunescu, C. A. Mora, M. Puddu, F. Krumeich, R. N. Grass, J. Mat. Chem. B 2014, 2, 8504-8509.
[6] C. A. Mora, D. Paunescu, R. N. Grass, W. J. Stark, Mol. Ecol. Resour. 2015, 15, 231-241.
[7] R. N. Grass, J. Scha#776;lchli, D. Paunescu, J. O. Soellner, R. Kaegi, W. J. Stark, Environ. Sci. Technol. Lett. 2014, 1, 484-489.
[8] M. Puddu, D. Paunescu, W. J. Stark, R. N. Grass, ACS Nano 2014, 8, 2677-2685.

Membrane proteins are important to understanding disease and designing therapeutics, but these proteins are complicated and challenging to study. Studying proteins in cells preserves native lipid interactions, but is limited because of the system complexity. Proteins can be extracted from the cell membrane before assaying their behavior, but this can alter protein structure and function from the native state. Local interactions between lipids and proteins regulate membrane protein activity and thus are a crucial component of their study. Therefore, new techniques bridging whole-cell complexity and membrane interactions with quantitative in vitro methods are needed. Model membranes such as supported lipid bilayers (SLB) retain critical membrane components and features while simplifying the system. SLBs provide a chemically tunable, planar platform that is compatible with many surface characterization tools, like total internal reflection fluorescence microscopy, atomic force microscopy, and quartz crystal microbalance. However, several challenges remain for incorporating membrane proteins into SLBs: reconstitution and maintaining fluidity. The most common method is to use detergent-mediated reconstitution. This method involves tedious optimization of detergents, lipids, and conditions for each protein, and the process can alter the protein structure. An alternative method is to deliver membrane proteins to the SLB via cell blebs. Cell blebs are cell membrane proteoliposomes that bud off when the membrane locally detaches from the actin cystoskeleton. Expressing membrane proteins into cell blebs circumvents difficult purification and reconstitution procedures and preserves native lipid interactions. However transmembrane proteins embedded in SLBs are immobile, presumably due to interactions between the proteins and the underlying support. In a typical SLB there is ~1 nm water gap between the support and lower leaflet, which is too small to accommodate extracellular or cytosolic domains of membrane proteins. Here we overcome protein immobility using a polyethylene glycol cushioned bilayer, but modified to be compatible with cell bleb rupture onto the solid support. We use single molecule tracking of individual proteins to measure diffusion and mobile fractions and have achieved upwards of 60% mobility in multi-pass transmembrane oligomeric proteins in this platform. While the mobile fraction is not yet 100%, recent characterization sheds some light on the structure of the cushion and directions for improving the platform to reach full protein fluidization. We show that this platform is widely-applicable to proteins derived from various cells, membrane spanning proteins, and peripheral proteins. It provides a simple way to build more biological complexity into SLBs while addressing the key challenges of membrane protein reconstitution and mobility, and thus should prove a valuable tool for biologists seeking to understand membrane protein function.

Within cells, nanostructures are often organized using local assembly rules that produce long-range order. Because these rules can take into account the cellular landscape, they can enable complexes, organelles or cytoskeletal structures to dynamically assemble and disassemble around existing cellular components to form architectures. While many methods for self-assembling complex biomolecular nanostructures have been developed, few allow adaptation. Here we demonstrate a fundamental primitive for adaptive self-assembly, the growth of a connector for molecular landmarks whose separation and relative orientations are unknown. DNA tile nanotubes nucleate at landmarks and grow while their free ends diffuse, and then join at their ends to form stable connections. Connections can form between >75% of paired landmarks separated by 1-10 microns following the predictions of a quantitative model, 3-dimensional connections can be assembled and unconnected nanotubes can be selectively melted away. This point-to-point assembly process could be a route to assembling circuits that connect self-assembled devices or biological components. It also illustrates how emergent, adaptive assembly processes can be programmed by coupling different physical processes operating far from equilibrium.

The increasing molecular understanding of many diseases permits the development of new diagnostic methods. However, few easy-to-handle and inexpensive tools exist for common diseases such as food disorders. Recently, bioinspired stimuli-responsive materials containing living organisms have been reported [1, 2]. By enclosing micro-organisms into a sandwich consisting of a solid bottom and a size-selective porous top polymer sheet, the organisms could not escape but were still able to interact with the outer environment. Based on this, we developed a sensor material that combines the diffusion behavior of an analyte with an analyte-specific bacterial fluorescence reporter system [3]. The analysis requires only a photo camera, a blue-light source and a blue-light optical filter sheet. The well-established model bacterium Escherichia coli, genetically modified with a fluorescent reporter system, was incorporated in a matrix of different polymers to create a programmable living material-based analytical sensor (LiMBAS). This material shows an easily quantifiable and specific response when coming into contact with dissolved analyte anywhere on its surface. In a realistic application, we programmed LiMBAS to detect lactose directly from cow's milk and galactose from lactose-free milk without previous dilution. We chose milk for our proof-of-principle experiment since it is a widely used food product and a source of several common food disorders including lactose intolerance, allergies as well as galactosaemia. LiMBAS could accurately quantify lactose or galactose in undiluted food samples and was able to measure food intolerance relevant concentrations in the range of 1-1000 mM requiring a sample volume of 1-10 mu;L. It worked at ambient temperature and humidity conditions and was storable ready-to-use for more than one week. We additionally discuss how the quantification principle of combining diffusion behavior with matrix-embedded microbial whole cell reporter systems could be applied to develop a variety of biomedical diagnosis tools for the analysis of food, blood or environmental constituents that can be used in domestic or outdoor applications. A wide range of genetic tools for E. coli are readily available thus allowing the reprogramming of the material to serve as biosensor for other molecules. LiMBAS as biomaterial offers the possibility to safely use engineered micro-organisms outside of a laboratory environment without the need for culturing or complicated analysis. In combination with smartphones, an automated diagnostic analysis becomes feasible which would also allow untrained people to use LiMBAS.
[1] L.C. Gerber, F.M. Koehler, R.N. Grass, W.J. Stark, Proc. Natl. Acad. Sci. U. S. A., 109 (2012), pp. 90-94
[2] L.C. Gerber, F.M. Koehler, R.N. Grass, W.J. Stark, Angew. Chem. Int. Ed., 51 (2012), pp. 11293-11296
[3] C.A. Mora, A.F. Herzog, R.A. Raso, W.J. Stark, Biomaterials, 61 (2015), pp. 1-9

Nanoscale assembly of tunably metastable “reflectin” proteins creates high refractive index Bragg lamellae or Mie reflectors within and between specialized cells in the epithelia of certain molluscs. In squids, this assembly and the resulting coloration and brightness of reflectivity are tunable by neuronal signaling for underwater optical communication and camouflage. We discovered that signal dependent neutralization of the cationic reflectins overcomes their Coulombic repulsion, with the resulting condensation initiating secondary folding of canonically repeated domains that act as molecular Velcro-like patches to drive further tertiary and quaternary condensation and hierarchical assembly with consequent dehydration of the Bragg lamellae, thus changing the brightness and color of the reflected light. In other cells or species, this assembly is fixed, creating permanently bright, broadband (white or silver) or spectrally selective (colored) reflectivity. Among this latter group, we discovered that giant clams use Mie-scattering to redistribute solar photons to symbiotic algae living within the animal host, increasing the algae&’s photosynthetic efficiency. These discoveries are guiding the development of electrically switchable shutters for IR detectors and new geometries for higher efficiency flexible solar cells.
In contrast to these highly reflective systems, the visual system of the moth -that flies and locates food and mates by dim starlight - cannot afford to lose photons to reflection. Sub-wavelength projections covering the moth&’s eye surface provide a graded refractive index that eliminates visible reflection. Inspired by this principle, we developed a facile, scalable and generic surface modification protocol, based on colloidal lithography and plasma etching, that yields ‘moth-eye&’ anti-reflective structures on Si, Ge, GaAs and CdTe substrates and optics. Large increases in transmission, bandwidth, and omni-directional response were obtained in these nanostructured materials at mid- and far-IR wavelengths (from 5 to >50 micrometers), with performance better than commercially available interference-based coatings. Effective medium theory, transfer matrix calculations, and quantitative measurements of transmission, reflection and scattering were used to investigate how photon trajectories were affected by moth-eye geometry. Applications are readily available for IR and optical detectors, thermo-photovoltaics, glint reduction and camouflage.

Gas sensors are needed in modern applications for reliable and unobtrusive measurements. Existing gas sensors often degrade their measurement accuracy in the presence of interferences and cannot quantitate several components in complex gas mixtures. Thus, new sensing approaches are required with improved sensor selectivity. In this talk, we will present an assessment of the capabilities of natural and bio-inspired nanostructures for selective gas sensing. We will provide details of our approach for selective vapor sensing by taking advantage of the hierarchical photonic nanostructure formed in the scales of Morpho butterfly wings. Upon interactions with different vapors and mixtures of vapors, such photonic structure produces remarkably diverse differential reflectance spectra. While we have found that the response selectivity of iridescent scales of the Morpho butterfly wings dramatically outperforms existing sensors, our interest was to fabricate such structures. Upon fabrication of bio-inspired nanostructures, we have found that individual nanofabricated sensors not only selectively detect separate gases in pristine conditions but also quantify these gases in mixtures, and even when blended with a variable moisture background. We will show that while quantitation of analytes in the presence of variable backgrounds is challenging for most sensor arrays, we achieved this aspirational goal using individual bio-inspired multivariable sensors. These colorimetric sensors can be tuned for numerous gas sensing scenarios in confined areas or as individual nodes for distributed monitoring.

A wide class of classical and quantum optical devices are based on the coupling of individual atoms, molecules, quantum dots, or other emitters to the electromagnetic field of nanofabricated optical cavities. The coupling efficiency, which can be precisely simulated using numerical codes, is strongly governed by the position of the emitter within the optical modes of the device. For example, the enhancement of an emitter's fluorescence is proportional to the mode-dependent local density of optical states (LDOS) via the Purcell effect. A number of existing experimental techniques variously combine AFM, SEM, and sophisticated lithography to position single emitters within single devices but currently there is no scalable technique to deterministically position emitters within nanooptical environments. This limits our ability to make and study devices based on cavity-emitter interactions---entire papers are often based around the performance of a single, heroically-fabricated device.
Here we experimentally demonstrate the deterministic coupling of fluorescent molecules to photonic crystal nanocavities (PCC) at a large scale. Individual DNA origami molecules carrying discrete numbers of fluorescent molecules are positioned, with the resolution of e-beam lithography, in thousands of microfabricated devices. We first validated our approach by taking spectra of 21 different cavities in which each cavity featured an origami placed at a different position along the midline of the cavity. Periodic variation in the peak intensity of the emission demonstrated our ability to control emitter-cavity coupling by "walking" the origami in 50 nanometer steps through the modal pattern of the cavity. Next we used the same technique to create a complete two-dimensional map of one mode of our PCCs with 25 nanometer resolution. For each of 600 precise x-y locations within the mode, a separate device was constructed having a DNA origami at location x-y. The devices are arranged to recapitulate the x-y position of the devices at a large scale, so that simple epifluorescence microscopy creates an "image" of the LDOS. Lastly, we demonstrate the programmability and scalability of our approach by building a 3-bit 65,536 nanocavity array in which the intensity of each pixel is independently programmed by controlling the location and number of molecules within a specific nanocavity.

Natural biological structures, in particular, moth&’s eye and lotus leaf were the inspirations for the formation of low-refractive index antireflective glass film that embody omni-directional optical properties over a wide range of wavelengths, while also possessing water-repelling, or superhydrophobic, capability that holds significant potential for solar panels, lenses, detectors, architectural windows, optical components used in weapons systems and in many other products. The coatings comprise an interconnected network of nanoscale pores surrounded by a nanostructured silica framework. These structures result from a novel fabrication method that utilizes metastable spinodal phase separation in low-alkali borosilicate glass materials. The approach not only enables design of surface microstructures with graded-index antireflection characteristics, where the surface reflection is suppressed through optical impedance matching between interfaces, but also facilitates self-cleaning ability through modification of the surface chemistry. Based on near complete elimination of Fresnel reflections through a single-side coated glass and corresponding increase in broadband transmission, the fabricated nanostructured surfaces are found to promote a general and an invaluable ~ 3-7% relative increase in current output of multiple direct/indirect bandgap photovoltaic cells, while preventing dust/pollution accumulation. Moreover, these antireflective, self-cleaning surfacesdemonstrate superior resistance against mechanical wear and abrasion andcan be engineered to block ultraviolet radiation, provide antifogging as well as omniphobic functionalities. With demonstrated scalable and manufacturable formulations, providing an all-in-one combination of multiple salient and unique performance enhancers, our approach represents a conceptually fundamental basis to be developed for leading edge coated optical quality products.

We describe the synthesis, characterization, and self-assembly of bio-inspired six-tailed amphiphiles that trigger optical transformations in water-dispersed microdroplets of thermotropic liquid crystals (LCs). These synthetic amphiphiles mimic structural features of the six-tailed glycolipid component of Lipid A (a component of bacterial endotoxin) and trigger bipolar-to-radial transitions in droplets of LCs at exceedingly low (pg/mL) concentrations. This is the first synthetic amphiphile demonstrated to trigger transitions in LC droplets at these ultralow concentrations. We hypothesize that both Lipid A and these mimics trigger transitions through a process that involves the self-assembly of the amphiphiles at topological defects (boojums) in LC droplets. Our synthetic amphiphiles and Lipid A exhibit similar interfacial behaviors and sizes, and we demonstrate using SAXS that these mimics self-assemble into inverted nanostructures similar to those exhibited by Lipid A. The structures and properties of these synthetic Lipid A mimics can be tuned readily: below a critical tail length, for example, the amphiphiles do not form self-assembled nanostructures and do not trigger orientational changes in LC droplets. These observations support the conclusion that molecular architectures that promote formation of self-associated nanostructures are needed to trigger optical transitions. They also provide insight into the mechanisms through which LC droplets respond to six-tailed amphiphiles at extremely low (pg/mL) concentrations. This class of synthetic amphiphiles mimics key structural features and aspects of the self-assembly behaviour of Lipid A. The synthetic route used to design these amphiphiles permits control over architecture and molecular functionality in ways that are difficult to achieve through synthetic modifications to Lipid A, but that could be used to tune self-assembly behaviour or the nature of the interactions of self-associated nanostructures with LC droplets. We therefore anticipate that this class of bio-inspired amphiphile will open the door to the development of new and exquisitely sensitive LC-droplet based environmental sensors.

Cell lasers have potential applications in biology and medicine, including in biomolecular sensing and cytometry.[1, 2] So far, cell lasers have been realized either by using an extracellular semiconductor gain medium or by intracellular fluorescent proteins.[3-5] Fluorescent proteins were found to be an attractive option for providing optical gain in these lasers as they offer biocompatibility, high quantum yield and good photostability. However, the transfection required to trigger expression of fluorescent proteins in cells is a time-consuming process, typically taking more than 24 hours. Such long preparation times are inconvenient for applications not requiring genetically encoded gain.
In the wider context of visualizing cells and studying intracellular processes, synthetic fluorescent molecular probes that can penetrate the membrane of live cells are widely used.[6, 7] Compared to fluorescent proteins, a much greater variety of such small organic dyes is available, providing a wide range of different biochemical and spectral properties.[8] In general, these probes are detected via their fluorescence, i.e. spontaneous emission.[9] However, here we show that integrating these probes into an optical resonator turns them into an optical gain medium supporting efficient stimulated emission with distinct spectral characteristics [10]. Advantageously, this approach provides a fast and simple method to obtain lasing from normal cells within less than one hour by using a biocompatible cell-tracker dye that becomes highly fluorescent upon entering the cytoplasm, thus forming a localized gain volume. We demonstrate lasing with this approach from both spherical cells in suspension and from elongated, adherent cells grown and stained directly on one of the reflectors forming the cavity. Fluorescent dyes offer a convenient method for transforming normal cells into biolasers for a variety of applications in cell-culture and lab-on-a-chip settings.
References
[1] X. Fan, S. H. Yun, Nature Methods2014, 11, 141.
[2] M. T. Hill, M. C. Gather, Nature Photon.2014, 8, 908.
[3] P. Gourley, Nature Med.1996, 2, 942.
[4] P. L. Gourley, M.F. Gourley, Trends Biotechnol.2000, 18, 443.
[5] M. C. Gather, S. H. Yun, Nature Photon.2011, 5, 406.
[6] T. Ueno, T. Nagano, Nature Methods2011, 8, 642.
[7] R.Y. Tsien, Annu. Rev. Neurosci.1989, 12, 227.
[8] J. Zhang, R. E. Campbell, A. Y. Ting, R. Y. Tsien, Nat. Rev. Mol. Cell Biol.2002, 3, 906.
[9] J. R. Lakowicz, Principles of fluorescence spectroscopy. 2007: Springer Science & Business Media.
[10] S. Nizamoglu, K.-B. Lee, M. C. Gather, K. S. Kim, M. Jeon, S. Kim, M. Humar, and S.-H. Yun, 2015Advanced Optical Materials. doi: 10.1002/adom.201500144

When the constitutive materials of photonic crystals (PCs) are stimuli-responsive, the resultant PCs exhibit optical properties that can be tuned by the stimuli. This can thus be exploited for promising applications in colour displays, biological and chemical sensors, inks and paints, and many optically active components. However, the preparation of the required photonic structures is the first issue to be solved. In the past two decades, approaches such as microfabrication and self-assembly have been developed to incorporate stimuli-responsive materials into existing periodic structures for the fabrication of PCs, either as the initial building blocks or as the surrounding matrix. Generally, the materials that respond to thermal, pH, chemical, optical, electrical, or magnetic stimuli are either soft or aggregate, which is why the manufacture of 3D hierarchical photonic structures with responsive properties is a great challenge. Recently, inspired by biological PCs in nature which exhibit both flexible and responsive properties, researchers have developed various methods to synthesize metals and metal oxides with hierarchical structures by using a biological PC as the template. This review will focus on our recent developments in this field. In particular, PCs with biological hierarchical structures that can be tuned by external stimuli have recently been successfully fabricated. These findings offer innovative insights into the design of responsive PCs and should be of great importance for future applications of these materials.

As its name suggests, the Glasswing butterfly (Greta oto) has transparent wings with remarkable low reflectance below 5% even for large view angles [1]. This omnidirectional anti-reflection behavior is caused by nanopillars with subwavelength radii covering the transparent region of its wing membrane. In difference to the classical biological anti-reflection structures, these pillars feature a random height and width distribution. Simulating the optical properties of these structures we demonstrate that this randomness is responsible for the omnidirectional anti-reflection properties of the Glasswing butterfly. Especially, the random height distribution drastically reduces the reflection for large view angles of 80° enabling efficient camouflage by transparency during the flight of this butterfly. Based on this design principle almost perfect anti-reflection surfaces can be engineered for a broad band of wavelength and an extremely wide range of view angles. Such anti-reflective surfaces are needed for applications ranging from efficient solar cells, sensors, surface emitting lasers, LED and various opto-electronics application. Finally, we will discuss possible options to fabricate artificial replicas of these highly random nanostructures.
[1] Siddique, Gomard, Hölscher, Nat. Comm. 6, 6909 (2015)

We propose a butterfly-cornea-inspired nanoplasmonic array that provides angle-insensitive reflectance for use in optical-cavity-based implantable intraocular pressure (IOP) sensors with remote optical readout. The proposed structure can be easily fabricated on flexible membranes that form the pressure-sensing optical cavity, provides relatively flat broadband reflectivity up to ±20° from the normal incidence, and generates strong optical resonance. These properties are a must for the implementation of practical IOP sensors.
The surface of the butterfly cornea is covered with an array of nanoscale optical structures whose reflection is insensitive to angle variations up to ±60° from normal incidence. This layer is composed of a hexagonal array of nanoscale semispherical protuberances that introduce a gradual increase of refractive index and minimize reflection and angle dependence. Inspired by the geometry and optical properties of the biological structure, we designed a biomimetic plasmonic membrane (BPM) that provides an angle-insensitive reflection layer.
The core feature of our BPM is a hexagonal array (lattice constant: 300-400 nm) of gold hemispheres (radius: 120-180 nm) placed on the bottom surface of the deformable silicon-nitride membrane (inside the cavity). The top surface is in contact with saline during IOP sensing. In our study, the reflectance of the BPM becomes larger and flatter over a wider range of wavelengths as the ratio r of the radius to the lattice constant increased, while the angle-insensitivity improved as r decreased. The BPM with the largest r of 0.45 exhibited the largest reflectance (~0.92) that was very flat over the wavelength range of 700-1200 nm, with an angle insensitivity up to ±5° from normal incidence. For r = 0.4, the BPM showed the slightly reduced reflectivity (~0.8) that was flat over the wavelength range of 700-1000 nm, yet its angle insensitivity improved to ±15°. Further reduction in r down to 0.35 lowered the reflectivity to ~0.7 yet provided the best angle insensitivity up to ±20°. It is also important to mention that our BPM does not exhibit thin-film interference, and varying the thickness of the silicon-nitride membrane (0.3-1.3 µm) has a negligible effect on its reflectance profile.
We also examined the possibility of using the BPM for IOP sensing in the range of 0-40 mmHg (normal IOP: 10-20 mmHg) in simulation. Being illuminated with broadband light, the cavity formed by a 500-nm-thick PBM (r=0.45) and a silicon substrate (coated with a 50nm-thick gold layer) generated sharp, highly detectable resonances (quality factor: ~320). As the cavity gap decreased from 4.6 to 4 µm at a step of 0.1 µm (which implies step increases in the ambient pressure), the resonance peak shifted linearly from 0.8 to 0.9 µm at a step of 20 nm (linearity: 0.96). The required spectral resolution is 2.5 nm shift per 1 mmHg, which can be easily obtained using a commercially available miniature spectrometer.

The skin structure of cephalopods endows them with remarkable dynamic camouflage capabilities. Consequently, much research effort has focused on understanding and emulating these animals&’ color changing abilities in the visible region of the electromagnetic spectrum. In contrast, despite the importance of infrared signaling and detection for many industrial and military applications, few studies have attempted to translate the principles underlying cephalopod adaptive coloration to infrared camouflage. We have drawn inspiration from nanostructures implicated in cephalopods&’ camouflage abilities and developed strategies for the self-assembly of unique cephalopod structural proteins into dynamically tunable biomimetic camouflage coatings on both transparent and flexible substrates.^1,2 Our substrates can adhere to arbitrary surfaces, and their reflectance can be reversibly modulated from the visible to the near-infrared regions of the electromagnetic spectrum with both chemical and mechanical stimuli.^1,2 Thus, we can endow common objects with any shape or form factor with tunable camouflage capabilities.^1,2 Our work represents a key step toward the development of wearable biomimetic color and shapeshifting technologies for stealth applications.
Phan, L.; Walkup IV, W. G.; Ordinario, D. O.; Karshalev, E.; Jocson, J.-M.; Burke, A. M.; Gorodetsky, A. A. Adv. Mater.2013, 25, 5621-5625.
Phan, L.; Ordinario, D. O.; Karshalev, E.; Walkup IV, W. G.; Shenk, M. A.; Gorodetsky, A. A. J. Mater. Chem. C.2015, Advance Article, DOI: 10.1039/C5TC00125K.

Photonic fibers are playing a significant role in many applications where the manipulation of light is crucial, including biomedical sensing and imaging, laser surgery, white light laser devices, or communication and information processing technology. Conventional photonic fibers are fabricated by thermal drawing. This process imposes stringent requirements on the constituent materials&’ thermal and mechanical properties, thereby severely limiting the library of suitable components and ultimately restraining the resulting fiber&’s functional scope. Here, we present a novel approach for the formation of elastic, mechano-sensitive, color-tunable photonic fibers that are mimicking the structural aspects of a biological photonic system found in the blue seed coat of a tropical plant. The photonic fibers consist of an elastomeric multilayer cladding, rolled onto a stretchable core fiber at room temperature. The fibers show up to 95% transverse reflectivity. The fiber&’s reflection band can be tuned by applying an axial strain or a lateral compression. An axial elongation of initially red fibers to about twice their original length results in a shift of the reflected color via orange, yellow, and green to blue. This phenomenon is reversible and persists even after several thousand deformation cycles. Applications for the mechano-responsive, color-tunable photonic fibers include the optical sensing of mechanical deformations and stress distributions in medical and civil engineering applications, solvent vapor analyzers, dynamic textiles, and components for fiber-optic signal processing.