Symposium BM6 : Fabrication, Characterization and Applications of Bioinspired Nanostructured Materials

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 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 nonaqueous fluids, and its subsequent quantitative detection of Rhodamine 6G (R6G) down to ∼75 fM level (10⁻¹⁵ mol/L). Our platform, termed slippery liquid-infused porous surface-enhanced Raman scattering (SLIPSERS), is based on a slippery, omniphobic substrate that enables the complete concentration of analytes and SERS substrates (e.g., Au nanoparticles) within an evaporating liquid droplet. Combining our SLIPSERS platform with a SERS mapping technique, we have systematically quantified the probability, p(c), of detecting R6G molecules at concentrations c ranging from 750 fM (p > 90%) down to 75 aM (10⁻¹⁸ mol/L) levels (p ≤ 1.4%). The ability to detect analytes down to attomolar level is the lowest limit of detection for any SERS-based detection reported thus far. We have shown that analytes present in liquid, solid, or air phases can be extracted using a suitable liquid solvent and subsequently detected through SLIPSERS. Based on this platform, we have further demonstrated ultrasensitive detection of chemical and biological molecules as well as environmental contaminants within a broad range of common fluids for potential applications related to analytical chemistry, molecular diagnostics, environmental monitoring, and national security.

Keywords: SERS | slippery surfaces | nanoparticles

References
1. S. M. Nie & S. P. Emory, Probing single molecules and single nanoparticles by surface enhanced Raman scattering. Science 275, 1102 – 1106 (1997).
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, 443 – 447 (2011).
3. S. Yang, X. Dai, B. B. Stogin, & T.-S. Wong, Ultrasensitive surface-enhanced Raman scattering detection in common fluids. Proc. Natl. Acad. Sci. USA 113, 268 – 273 (2016).

Nature-inspired liquid-repellent surfaces are primarily modeled after two classes of biological surfaces – leaves of lotus¹ and pitcher plant². Lotus leaves rely on air-infused textured surfaces to repel impinging liquid droplets¹; while the leaves of pitcher plant utilize liquid-infused textured surface to maintain a highly slippery interface³. Natural and synthetic surfaces that can switch between these two liquid-repellent states are rare due to the distinctive repellent mechanisms. Here, we demonstrated a magnetically shape-shifting surface that can reversibly transform the liquid-repellent states between the modes of lotus leaves and pitcher plant. The surface property change can be programmed on-demand by external magnetic field. The ability to alter surface interfacial properties dynamically will open up new opportunities for smart liquid-repellent skin, programmable fluid control and transport, adaptive drag reduction, and controlled-release devices.

References
1. Barthlott, W. & Neinhuis, C. Purity of the sacred lotus, or escape from contamination in biological surfaces. Planta 202, 1-8, doi:DOI 10.1007/s004250050096 (1997).
2. 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 USA 101, 14138-14143, doi:10.1073/pnas.0405885101 (2004).
3. Wong, T. S. et al. Bioinspired self-repairing slippery surfaces with pressure-stable omniphobicity. Nature 477, 443-447, doi:10.1038/nature10447 (2011).

To a certain degree, it is possible to control the macroscopic wetting properties of a surface by its nano- and microstructure. In particular, super liquid-repellant-surfaces have received interest due to their many potential applications, such as anti-fouling for for example. Super liquid-repellency can be achieved by nano- and microstructuring a low energy surface in a way, that the structure can entrap air underneath
the liquid. The common criteria for super liquid-repellency are a high apparent advancing contact angle and a low contact angle hysteresis.
For a better understanding of how a drop advances and recedes on such a structured surface, we imaged the motion of a water drop on a superhydrophobic array of micropillars by laser scanning confocal microscopy (LSCM). With LSCM, we imaged an advancing water front on a superhydrophobic surface at a resolution of 1 µm. The results give a qualitatively new picture of how water advances on the microscopic
scale. We demonstrate that in contrast to traditional goniometer measurements, the advancing contact angle is close to 180° or even higher.
In contrast, the apparent receding contact angle is determined by the strength of pinning. We propose that the apparent receding contact angle should be used for characterizing super liquid-repellent surfaces [1,2].

[1] F. Schellenberger et al., Phys. Rev. Lett. 116, 096101 (2016)
[2] P. Ball, Nature Materials 15, 376 (2016)

Multiscale hierarchical structures show engineered interfacial properties that are important for controlled wetting, structural color, and selective filtration. In particular, bioinspired three-dimensional (3D) substrates have achieved such properties with superior mechanical stability over large areas (>cm² ). The fabrication of 3D patterns with length scales spanning several orders of magnitude (e.g., nm to μm), however, is usually done with complex top-down processes such as multistep photolithography or imprinting. Moreover, these tools cannot easily manipulate order/disorder of multiscale features over large areas. Here we found that memory-based, sequential wrinkling process can transform flat polystyrene (PS) sheets into bioinspired, three-dimensional hierarchical textures. Multiple cycles of plasma-mediated skin growth followed by directional strain relief of the substrate resulted in hierarchical architectures with characteristic generational (G) features. Independent control over wrinkle wavelength and wrinkle orientation for each G was achieved by tuning plasma treatment time and strain-relief direction for each cycle. As a practical application, we demonstrated stretchable superhydrophobicity on elastomeric hierarchical wrinkles monolithically formed by high fidelity pattern trasfer of PS templates designed by the sequential wrinkling. The poly(dimethysiloxane) (PDMS) wrinkles consisting of three different length scales showed wetting properties characteristic of static superhydrophobicity with water contact angles (>160°) and very low contact angle hysteresis (<5°). To examine how superhydrophobicity was maintained as the substrate was stretched, we investigated the dynamic wetting behavior of bouncing and splashing upon droplet impact with the surface. The substrate remained superhydrophobic up to 100% stretching with no structural defects after 1000 cycles of stretching and releasing. Stretchable superhydrophobicity was possible because of the monolithic nature of the hierarchical wrinkles as well as partial preservation of nanoscale structures under stretching.

The ability to control the repellent properties of bio-inspired immobilized liquid layers is of interest for a wide range of applications. Liquid layers created using infused polydimethyl siloxane (PDMS) polymers offer a potentially simple way of accomplishing this goal through the adjustment of nanoscale parameters such as cross-linker ratio and infused oil viscosity. In this work, we examine how tuning these parameters affects the material properties of the infused polymer, the stability of the liquid overlayer, and finally the overall performance of this system against bacterial adhesion and biofilm formation. We find that cross-linker density appears to have the greatest impact on the system, with a lower cross-linker:base ratio resulting in both an increased liquid overlayer stability and improved performance against bacteria. We further demonstrate how this finding may be exploited to produce patterns of slippery/sticky areas on the surface of the infused polymers for controlling the spatial arrangement of proteins and bacteria. These results demonstrate a new degree of control over immobilized liquid layers and may help facilitate their use in new applications.

Tree and torrent frogs are able to adhere and move about their wet or even flooded environments without falling. The secret of their outstanding adhesive performance is the complex hierarchical structure of their attachment pads, including microchannels of different length scales, anisotropically fiber-reinforced micropillars and different constitutional materials. Understanding the design principles behind this original surface design opens the door to novel adhesion strategies for reversible attachment in artificial systems. Over the last years, strategies to prepare frog-like microstructured surfaces of different soft materials have been reported [1-4]. However, hybrid structured surfaces with oriented fibers embedded in soft microstructures represent a fabrication challenge. I will present new fabrication strategies to obtain hierarchical, microstructured surfaces containing aligned nanofibers. The role of the anisotropic morphology in mechanical stabilisation, adhesion/friction properties and detachment will be described. Our results will clarify the role that oriented keratin fibers might have for directional and reversible attachment of frogs in wet environments.

Torrent-frog inspired adhesives: attachment to flooded surfaces. J. Iturri, L. Xue, M. Kappl, L. García-Fernández, W.J.P. Barnes, H.J. Butt, A. del Campo. Adv. Funct. Mater. 2015, 25(10), 1499-1505
Morphological studies of the toe pads of the rock frog, staurois parvus (family: Ranidae) and their relevance to the development of new biomimetically inspired reversible adhesives. D.M. Drotlef, E. Appel, H. Peisker, K. Dening, A. del Campo, S.N. Gorb, W.J.P. Barnes, Interface Focus 2015, 5(1), 1-11
Bioinspired orientation dependent friction. L. Xue, J. Iturri, M. Kappl, H.J. Butt, A. del Campo*. Langmuir 2014, 30(37), 11175–11182
Insights into the adhesive mechanisms of tree-frogs using artificial mimics. D.-M. Drotlef, L. Stepien, M. Kappl, W. J. P. Barnes, H.-J. Butt, A. del Campo. Adv. Funct. Mater. 2013, 23(9), 1137-1146

Many natural surfaces such as butterfly wings, beetles’ backs, and rice leaves exhibit directional liquid adhesion or transport; this is of fundamental interest as well as for applications including self-cleaning surfaces, microfluidic devices, and phase change energy conversion. For example, the intricate scales on the wings of the Morpho aega give rise to hydrophobicity and anisotropic droplet roll-off behavior. Previous studies have explained anisotropic roll-off, for example, via the directionality of a rigid rachet surface or the re-arrangement of nanoscale tips. Inspired by the butterfly wing, we demonstrate the fabrication of flexible synthetic scale surfaces from arrays of thin carbon nanotube (CNT) microstructures. Uniform centimeter-scale arrays of CNT scales are synthesized by a strain-engineered chemical vapor deposition (CVD) technique, using an offset-patterned catalyst layer that imparts a spatial gradient in the CNT growth rate, causing the scales to curve during growth. The scale height and curvature is controlled via the CNT growth parameters. After growth, the scales are conformally coated by a thin ceramic layer (i.e., Al₂O₃, by atomic layer deposition) followed by a hydrophobic polymer (divinylbenzene, by CVD) to tune their compliance and surface wettability. We demonstrate that the CNT scales exhibit anisotropic droplet roll-off, and via high-resolution optical imaging we observe how the droplet pinning and motion are influenced by the scale geometry and flexibility. The electrical conductivity and mechanical robustness of the CNTs, and the ability to fabricate complex multi-directional patterns, suggest further opportunities to create engineered scale surfaces.

The term biofouling describes the agglomeration of microorganisms on surfaces mainly in contact with liquid [1]. Free-floating cells freely swim and approach surfaces until they undergo irreversible attachment. At this point, thanks to the quorum sensing effect a bacterial colony will start to grow and disseminate along the surface. These bacterial layers can be found on pipelines, hulls of boats or food packaging, leading to corrosion, increase on fuel consumption due to friction and food poisoning [2]. Furthermore, when they form in medical devices nosocomial infections and failure due to clogging arise. Accounting to the economical losses and mortality related to biofilm formation [3], new approaches battling this field have been proposed in the past years. However, the increased resistance (up to a factor of 1000) of enclosed bacteria compared to free-floating cells as well as the possibility to restore films within hours inspired me to focus on hindering or delaying the first adhesion events.
On this behalf, we focused on super-liquid repellent surfaces as a platform to prevent biofilm formation. Candle-soot based superamphiphobic coatings were proved to prevent wetting by both water and low surface tension liquids thanks to the existence of a mobile air layer (Cassie state) between solid features and liquid [4,5]. By means of X-ray photoelectron spectroscopy (XPS) and time-of-flight secondary ion mass spectrometry (ToF-SIMS) we confirmed an adsorption of proteins (bovine serum albumin and human serum plasma) below the instrument detection limit of 2 ng/cm², provided by the synergy between topography in the nano-scale and chemistry [6]. Furthermore the stability of the air layer and ability to hinder bacterial adhesion was visualized by the study through laser scanning confocal microscopy (LSCM) of E. coli (GFP expressed) biofilm formation.
[1] Costerton, J. W.; Stewart, P. S.; Greenberg, E. P. Science 284, 1318-1322, 1999.
[2] Klevens, R. M. et al.; Public Health Rep 122, 160-166, 2007.
[3] Davies D. Nat. Rev. Drug Discov. 2, 114, 2003.
[4] Deng X., Mammen L., Butt H.-J., Vollmer D., Science 335, 67-70, 2012.
[5] Paven M., Papadopoulos P., Schöttler S., Deng X., Mailänder V., Vollmer D., Butt H.-J., Nature Communication 4, 2013.
[6] Schmüser L., Encinas N., Paven M., Graham D., Castner D.G., Vollmer D., Butt H.-J., Weidner T. (submitted ).

Semiaquatic water bugs and plants efficiently move and breathe while submerged underwater due to an air film retained on their superhydrophobic hair-covered surfaces. Air entrapped between the hairs forms a shear-free air-water interface, resulting in a non-zero velocity and reduced drag at such surfaces. Artificial polymeric nanofur covered with dense layer of nano- and microhairs is fabricated using a hot pulling technique in which softened polymer is locally elongated during separation from a heated sandblasted steel plate [1]. Similarly to natural surfaces, artificial bioinspired superhydrophobic polymeric nanofur film submerged underwater traps air between its hairs, forming a fixed air film on the surface. The trapped air significantly reduces the pressure drop across the microchannels lined with bioinspired polycarbonate nanofur compared to unstructured flat polymer, indicating reduction in fluid drag. Additionally, high stability of the retained air film under external stimuli is required for underwater applications. The robustness of the underwater retained air film on the bioinspired nanofur against pressure was estimated by analyzing the air-water-interface at different applied pressures. Furthermore, by perforating the nanofur and applying additional pressure to support the air-water interface, we demonstrate a fourfold increase of the air layer stability against pressure. The response of the air-water-interface to varying pressure difference between the hydrostatic pressure and the pressure of the retained air layer was analyzed in order to estimate the stability of the nanofur under pressure fluctuations. Moreover, we observed a significant increase in lifetime of the air-water interface retained by the perforated nanofur under different hydrostatic pressures.
[1] Kavalenka et al., ACS Appl. Mater. & Interfaces 7, 1065 (2015)

Antimicrobial surfaces have been critical for many areas including medical and industry. There are two main strategies for antimicrobial surfaces; to reduce bacterial adhesion or kill them by using antibacterial agents. Bioinspired soft polydimethylsiloxane (PDMS) shark skin structures show reduced bacterial attachment due to highly rough microstructured surface design. However, they wear off by the time and are not good enough to prevent bacterial adhesion in the long term. Herein, we combine antibacterial and antifouling properties by incorporating antibacterial titanium dioxide (TiO2) nanocomposite material with shark skin structure. We demonstrated that shark skin patterns prevented bacterial attachment and also induced 80-95% bacteria death in an hour. Improved mechanical properties help them to be durable in the long term. Our method is solution processable, robust and roll to roll compatible method.

Mother nature provides the ultimate inspiration for various topologically ordered patterns, structures, and flexible motion from one-dimensional (1D) linear structures such as actin filaments and muscle fibers, two-dimensional (2D) arrayed compound eyes of insects, Morpho butterfly wings composed of three-dimensional (3D) hierarchical complex structures, etc. With self-assembly and self-organization, which are the driving principles in the formation of these natural structures, a number of biologically inspired artificial materials have been prepared.
Surface wrinkling is an inventive and unconventional technique that is also fast and inexpensive for various types of surface patterning involving sinusoids (ripples), herringbones, labyrinthine designs, etc. It is especially suited for large-area surfaces of poly(dimethylsiloxane) (PDMS) elastomers based on mechanical (buckling) instability. This self-organization buckling phenomenon is widely observed in natural systems such as humanskin, brain cortex, fruits, and plants. Owing to the periodic structure and dynamically tunable wrinkles, it has been used in many applications.
Previously, we have succeeded in fabricating ultrasmall attoliter-sized (10⁻¹⁸ L) 1D metallic nanocup arrays embedded in PDMS films by colloidal soft-lithography and wrinkle processing (H. Endo et al., Langmuir 2013, 29, 15058). Moreover, we described the fabrication of various topological 1D colloidal arrays, including single, helical, zigzag, triple-line, and random arrays integrated in sinusoidal wrinkle grooves, through simple spin-coating (H. Endo et al., Coll. Surf. A 2014, 443, 576). The particles in these arrays can be connected using plasma etching, forming beaded, robust, and long (>100 mm) colloidal chains.
In this study, we succeeded in the fabrication of a large-area ultra-water-repellent film on which water drops can be flexibly controlled by utilizing original 3D-streching method. 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. In addition, we propose fabrication of 3D microobjects using controlled folding/bending of wrinkled-thin films besed on elastocapillary force toward new type of 3D-imprinting technology.

Combining high optical transmission with self-cleaning and water-repellency is of great interest for optical systems, especially for those operating in outdoor conditions such as solar cells. Natural surfaces of water plants Salvinia Cucullata and Pistia Stratiotes combine these functionalities in a transparent layer of dense microhairs. This layer renders their surface superhydrophobic without affecting the absorption of sunlight necessary for photosynthesis. Inspired by these natural surfaces, we introduce superhydrophobic flexible thin nanofur films made from optical grade polycarbonate, which can be used as a transparent coating on optoelectronic devices. Thin nanofur films are fabricated using a highly scalable cost-effective hot pulling technique, in which heated sandblasted steel plates are used to locally elongate softened polymer resulting in a surface covered in microcavities surrounded by randomly distributed high aspect ratio micro- and nanohairs. The superhydrophobic nanofur exhibits high water contact angles (166±6°), low sliding angles (< 6°) and is self-cleaning against various contaminants. Additionally, subjecting the nanofur to argon plasma reverses the film wettability to underwater superoleophobic, enabling its use as an underwater oil-repelling coating.

The thin nanofur exhibits transmission values above 85% with high forward scattering when used as a translucent self-standing film and reflection values of less than 4% for the visible spectrum when used as a coating on a polymer substrate. Those properties make it suitable for light extraction in organic light emitting diodes (OLEDs). We demonstrate a 10% relative increase of luminous efficacy for a nanofur coated OLED with respect to a bare device. Lastly, thin nanofur coatings can be used as light-collecting and -diffusing elements for enhancing absorption in solar cells. We report on the optical coupling of the thin nanofur film to a multi-crystalline silicon solar cell, which results in a relative gain of 5.8% in photogenerated current compared to a bare photovoltaic device.

Cephalopods (squid, octopuses, and cuttlefish) are known as the chameleons of the sea – these animals can alter their skin’s coloration, patterning, and texture to blend into the surrounding environment. These remarkable capabilities are enabled by unique proteins and self-assembled nanostructures found within cephalopod skin. I will discuss our work on new types of photonic and protonic devices fabricated from cephalopod-inspired materials. Our findings hold implications for the next generation of infrared stealth, renewable energy, and bioelectronics technologies.

Understanding the structure-function relationships of pigment based nanostructures can provide insight into the molecular mechanisms behind biological signaling, camouflage, or communication experienced in many species. In squid Doryteuthis pealeii, combinations of phenoxazone-based pigments are identified as the source of visible color within the nanostructured granules that populate dermal chromatophore organs. In the absence of the pigments, granules experience a reduction in diameter with the loss of visible color, suggesting important structural and functional features. Energy gaps are estimated from electronic absorption spectra, revealing HOMO-LUMO energies that are dependent on the varying carboxylated states of the pigment. These results implicate a hierarchical mechanism for the bulk coloration in cephalopods originating from the molecular components confined within in the nanostructured granules of chromatophore organs.

In nature, some marine organisms, such as Vogtia and Cephalopods, have evolved to possess camouflage traits by dynamically and reversibly altering their transparency, fluorescence, and coloration via muscle controlled surface structures and morphologies. To mimic this display tactics, we designed similar deformation controlled surface engineering via strain-dependent cracks and folds to realize four types of novel mechanochromic devices: (1) transparency change mechanochromism (TCM), (2) luminescent mechanochromism (LM), (3) color alteration mechanochromism (CAM), and (4) encryption mechanochromism (EM), based on a simple bilayer system containing a rigid thin film and a soft substrate. These devices exhibit a wide scope of mechanochromic response with excellent sensitivity and reversibility. The TCM device can reversibly and instantly switch between transparent and opaque state upon stretching and releasing. The LM can emit intensive fluorescence as stretched with an ultrahigh strain sensitivity in comparison to strain sensors based on electrical resistance change. The CAM can turn fluorescent color from green to yellow to orange as stretched within 20% strain. The EM device can reversibly reveal and conceal any desirable patterns. These novel devices are promising for applications in smart windows, dynamic optical switches, strain sensors, encryption, etc.

Vivid, saturated structural colors such as many violet, blue and green hues provide a conspicuous and important aspect of the appearance of many animals^1,2,3. In birds, butterflies, beetles, bees and arachnids, both iridescent and isotropic colors are produced by constructive interference from a staggering diversity of biophotonic nanostructures. The nanostructures in arthropods, in particular, span the phase space of morphologies commonly seen in block copolymer melts, lipid-water or surfactant systems but at harder to achieve optical length scales³. These nanostructures are architecturally sculpted within the arthropod scale cells by the in-folding of membranes, biologically “back-filled” with chitin, followed by cell death leaving behind chitin nanostructures in air, reminiscent of an engineering process^1,3. Whereas the amorphous or quasi-ordered biophotonic nanostructures in bird feather barbs appear to be self-assembled by a visco-elastic phase separation process followed by a dynamic self-arrest. I will summarize the structure, optical function, development, and biomimetic potential of these meso-scale biophotonic nanostructures (with a special focus on the single gyroid I4₁32), when defect-free, long-range synthetic fabrication of photonic morphologies remains challenging.
[1] Saranathan et al., Nano Letters (2015), 15, 3735–3742
[2] Saranathan et al., J. Roy. Soc. Interface (2012), 9, 2563–2580
[3] Saranathan et al., PNAS (2010), 107, 11676–11681

There have been significant efforts on developing novel ways to efficiently transform sunlight to energy in photovoltaics and photobioreactors by using for example high refractive index materials and nanostructures. However, it remains a major challenge in harvesting solar energy to limit photodamage in low surface area devices. In a previous study, we show that Tridacnid giant clams are highly efficient “solar transformers”. The clams have evolved a layer of forward-scattering cells, or iridocytes, overlying vertically arranged algae pillars. The iridocytes redirect photosynthetically efficient wavelengths of downwelling sunlight from the top surface of the clam tissue evenly to the algae located in the narrow pillar arrays underneath. This redistribution of solar flux in forward direction seems to allow algae to achieve maximally efficient photosynthesis within their unique pillar geometries. Here, we have designed and fabricated synthetic iridocytes via the self-assembly of silica nanoparticles (120 – 300 nm in diameter) into micron-sized beads by way of Pickering emulsion. Our synthetic iridocytes show very similar phase functions (scattered light intensity per scattering angle) as the wild iridocytes. Compared to natural clam iridocytes, the synthetic ones show a similarly wide angular distribution of light in the forward-scattering direction. The ratio between the forward (0 – 50 °) and backward (120 – 165 °) scattered light intensities and the peaks of back-scattered wavelengths from the synthetic iridocytes can be tuned by varying the size of nanoparticles and microbeads. Thus, we can engineer the synthetic iridocytes that favor forward-scattering of photosynthetically efficient light while rejecting less-efficient wavelengths. We further investigate the redistribution of downwelling solar irradiance from the synthetic iridocytes in a wavelength-tunable manner for potential applications as photobioreactors.

Despite the limitation to a restricted range of organic materials, evolution has optimized the color response of many organisms to an amazing extent that often appears to surpass the physical limits of the employed organic materials. One such example are the common pierid butterflies which show bright colors ranging from white to red caused by various pterin pigments concentrated in scattering spheroidal beads in the wing scales. The final coloration arises from the interplay of absorption and scattering of light by these pigment-loaded granules. Given the sparsity of the beads in the wing scales, the high color brightness suggests a scattering strength of the beads that significantly surpasses that of chitin, from which the beads are composed of. To elucidate this apparent contradiction, we have analyzed the optical signature of the pierids’ highly saturated pigmentary colors by using Jamin-Lebedeff interference microscopy combined with Kramers-Kronig theory and light scattering modeling. Our study shows that both the shape of the beads and the unusually high complex refractive index of these pigmented granules are optimized to give rise to one of the brightest biological materials. Our results present yet another trick of evolution for optimized light scattering that might be useful for bio-inspired applications.

The history of microscopy is a history of human progress fueled by the ability to image, imagine, and then create at ever-smaller length scale. As man-made materials become more similar to the biological structures that inspire them, they increasingly combine nano-sized hard and soft, synthetic and biological components. With its unique spatial resolution and chemical sensitivity, UV laser-pulsed atom probe tomography (APT) is poised to revolutionize our understanding of such complex composites. Specifically, APT has provided unprecedented insights into the nanostructure and phase composition of biological materials such as bone, dentin, and enamel, but also ferritin protein nanocages and even cells.
For any given organism, the hardest materials are typically used to protect the surface of teeth. Optimized to withstand the forces of mastication, they are hierarchically structured, organic/inorganic nanocomposite materials. For example, the radula teeth of the chiton are capped with a composite made from magnetite (Fe₃O₄) and a nanofibrous chitin scaffold.^[1] The excellent hardness and wear resistance of this layer allows the chiton to abrade rocks during feeding. Human tooth enamel, on the other hand, is composed of hydroxylapatite nanowires, thousands of which are bundled into rods that are organized in a three-dimensional weave; this provides great fracture resistance and a much enhanced fatigue life.^[2] It has long been known that the susceptibility of enamel to caries, i.e. acid corrosion, is greatly dependent on the presence of magnesium, carbonate, and fluoride ions. I will discuss our recent insights into the chemistry of organic/inorganic interfaces, and the role of magnesium, fluoride, and iron at grain boundaries, and in amorphous intergranular phases that are integral to the mechanical properties of teeth and their resistance to corrosion. ^[3]
[1] D. Joester, L. R. Brooker, in Iron Oxides: From Nature to Applications (Ed.: D. Faivre), Wiley-VCH Verlag GmbH & Co. KGaA, 2016, pp. 177-205.
[2] A. Nanci, Ten Cate's Oral Histology: Development, Structure, and Function, 8 ed., C.V. Mosby Co., 2012.
[3] a) L. M. Gordon, D. Joester, Nature 2011, 469, 194-197. "Nanoscale chemical tomography of buried organic-inorganic interfaces in the chiton tooth"; b) L. M. Gordon, L. Tran, D. Joester, ACS nano 2012, 6, 10667-10675. "Atom probe tomography of apatites and bone-type mineralized tissues"; c) L. M. Gordon, M. J. Cohen, K. W. MacRenaris, J. D. Pasteris, T. Seda, D. Joester, Science 2015, 347, 746-750. "Amorphous intergranular phases control the properties of rodent tooth enamel."; d) L. M. Gordon, D. Joester, Frontiers in Physiology 2015, 6. "Mapping residual organics and carbonate at grain boundaries and in the amorphous interphase in mouse incisor enamel".

Cellulose is the most abundant natural polymer produced in the biosphere. Renewable, nontoxic, and inexpensive cellulose is expected to be a highly relevant source for the development of sustainable functional materials due to its intrinsic biocompatibility and biodegradability. In nature, cellulose is found in fibers of microfibrils made by individual chains of β-(poly-1,4-D-glucose). Each microfibril consists of amorphous and crystalline domains, and a complex network of hydrogen bonds is formed. Acidic treatment of bulk cellulose selectively hydrolyzes amorphous regions of the biopolymer, thereby leaving rod-shaped cellulose nanocrystals (CNCs) that are hundreds of nanometers in length.
One of the most prominent features of CNCs is their ability to self-assemble into a chiral nematic structure where the unidirectional CNC layers are organized in a long-range helical structure with periodic rotation. This chiral nematic structure, which can be seen throughout nature in plant cell walls and exocuticles of many beetles, is frequently referred to as one-dimensional photonic crystals, selectively reflecting wavelengths of light corresponding with the helical pitch. Moreover, the light reflected from the structure is circularly polarized with a handedness that is determined by the helical orientation. As for the CNC films, the wavelength of light reflected can be tuned over the entire visible region with brilliant coloration, but the handedness of reflected light has been uncontrollable thus far. CNC films are fixed in a left-handed helical orientation which leads to the reflection of left-handed circularly polarized light (CPL). However, there are some exceptions in nature which demonstrate the reflection of both left and right-handed CPL despite having similar components to CNC films. For example, the exocuticles of Plusiotis resplendens mainly composed of chitin is known to reflect both handed CPL due to the coexistence of half-wave retarder sandwiched between two left-handed helical layers. Another renowned example is found in the cell walls of Pollia condensate, based mainly on cellulose; the mechanism has not been clarified to date.
With inspiration from such unique examples found in nature, we thought that it may be possible to convert CNC films composed of cellulose into right-handed CPL reflective materials. We have explored the possibility for controlling the handedness of reflected CPL through the fabrication of many CNC films under varying conditions. These experiments are characterized based on UV-Vis transmission measurements with CPL filters and scanning electron microscopy measurements. In conclusion, it was found that a specific arrangement of CNCs can force the film to reflect right-handed CPL.

Aliphatic amine microcapsules are desirable components for bio-inspired smart materials such as self-healing and self-reporting systems. However, the highly reactive nature of amines excludes traditional microencapsulation methods. In this work, we report an innovative approach to prepare mechanically robust and thermally stable microcapsules containing high loading of aliphatic amines. With designed chemical modification, the reactivity of the targeting amines is masked. The protected amines are thereafter encapsulated via a developed emulsification condensation polymerization method. In order to achieve on-demand activity of the sequestered amines, we incorporated nanoparticles into the microcapsules, which facilitates a stimuli-triggered in capsule deprotection to restore the aliphatic amine functionality. We integrate these microcapsules in polymer coatings and bulk polymer matrices and demonstrate that the recovered amines are fully functional to implement programmed self-healing and self-reporting abilities. With the ready availability of diverse protecting chemistries, this novel microencapsulation strategy establishes a versatile platform to encapsulate a wide range of highly reactive chemicals.

Electrospinning is a favorable technique to prepare artificial architecture mimicking extracellular matrix (ECM) structure. Cell cultivation on the electrospun meshes is often restricted to 2-D cultivation because cells cannot easily penetrate into nanoporous structures of the meshes. Instead of solid ground for depositing nanofiber, liquid ground and ball shape ground were introduced and showed low density of sponge nanofiber mesh. Hydrophilic polymer, however, is limited to use independently that the nanofiber rapidly dissolved out in water without further crosslinking process. Herein, we prepared hydrophilic alginate nanofibrous mesh by co-axial electrospinning with etching polymeric shells, which enables electrospinning of inner alginate and maintains fibrous structure of the alginate core during calcium-dependent crosslinking. Electrospun alginate nanofiber covered with poly (e-caprolactone) (PCL) (Mw 43-50K) shell using co-axial nozzle. Alginate and PCL were injected through inner and outer nozzle with 0.5 and 2ml/h, respectively. The nanofiber was subsequently immersed in various concentration of CaCl₂ solution for alginate crosslinking. After peeling off the PCL shell in chloroform, calcium cross-linked alginate gel nanofiber suspension was finally harvested. Alginate nanofiber was characterized for morphology, water swelling ratio, elastic modulus of single nanofiber, thermal property, and crystallization property. NIH3T3 cells were seeded on the top of the mesh and evaluated cell proliferation rate and cell migration according to calcium crosslinking density of the alginate nanofiber. The morphology of alginate nanofiber with/without PCL shell was confirmed by TEM and SEM that the diameter was changed from around 700nm to 100nm. According to different calcium-crosslinking density from the range, 2wt% (AL NF_high) and 0.02wt% (AL NF_low) showed different pore distribution in the mesh and water swollen ratio. Completely removed PCL was confirmed by disappearance of PCL melting peak at 60°C by DSC. NIH3T3 were seeded on the alginate nanofiber and proliferated for 28 days. At day 3, cells were stained with MTT reagent and AL NF_low showed higher cell proliferation rate than AL NF_high. Phalloidin and nucleus were fluorescently stained and observed by Z-stacking image of confocal laser scanning microscope. As lower calcium concentration, cells migrated into the mesh more deeply. In conclusion, 3-D alginate mesh by shell etching of core-shell electrospun nanofibers was developed for 3D culture scaffold. In future study, these results developed to tissue engineering to fill the defect site based on its mechanical strength.

The hierarchical structure of wood constitutes an ideal scaffold for creating functionalized renewable biomaterials. Here the in situ synthesis of ferri- and ferromagnetic mineral phases in the intrinsically anisotropic cell anatomy yields hybrid wood materials with highly directional magnetic properties, which have been characterized by hysteresis curves parallel and perpendicular to the cell axis and by magnetic susceptibility tensors. ¹ Through a detailed characterization of the embedded magnetic phases using light and scanning electron microscopy, Raman mapping, and X-ray diffraction, it is possible to relate the nanocrystal composition, shape and size to the macroscopic magnetization of the modified wood samples. A variation of the chemical synthesis allows for tailoring the nano-crystallinity and aggregation state of the magnetic particles, as well as for their deeper insertion into the cell walls, resulting in higher degrees of magnetic anisotropy compared to previous studies. Based on the results, we envision the application of these magnetic hybrids as light-weight magnetic actuators.

1. Merk, V.; Chanana, M.; Gierlinger, N.; Hirt, A. M.; Burgert, I., Hybrid Wood Materials with Magnetic Anisotropy Dictated by the Hierarchical Cell Structure. ACS Appl. Mater. Interfaces 2014, 6 (12), 9760-9767.

Micro-scale optical components play a crucial role in imaging and display technology, biosensing, beam shaping, optical switching, wavefront-analysis, and device miniaturization. Bi-phase emulsion droplets synthesized from immiscible hydro- and fluorocarbons form liquid compound micro-lenses with a tunable droplet-internal optical interface. Adjustments in interfacial tensions between the constituent liquids and the surrounding medium are used to control the curvature of the internal interface of the droplet based microlenses. This allows the microlenses to be reconfigured to focus or scatter light, form real or virtual images, and allow for a wide tuning range of their focal length. Finite Difference Time Domain and Raytracing simulations were used to predict the lensing and scattering behavior of the droplets. Experiments using the droplets as lenses show their imaging capabilities, and selective tuning of the drops show that the scattering behavior can be observed macroscopically. A wide variety of stimuli can be used to manipulate the shape and orientation of the droplets including altering the chemical environment, light, and heat.

Radula, a rasping organ for feeding, is a characteristic feature for mollusks. Depending on species, the morphology and chemical composition of radula teeth vary largely. Much work has been focused on radula teeth of chitons, marine mollusks known to scrape rocks for food, as a model for biomineralization process. Meanwhile, little is known about the radula teeth of terrestrial mollusks. Banana slugs are terrestrial gastropods in the genus Ariolimax. It is native to North America and some individuals are bright yellow like a ripe banana. Here we use the banana slug radula as an example, and report the morphology and organic-inorganic hierarchical interface of the micro-teeth for the first time. The slug radula is a conveyor-belt like structure. It is comprised of transverse rows of teeth with files pointing in longitudinal directions. Each tooth is a unique natural nanocomposite that is mainly composed of an organic chitin matrix with trace amount of minerals. Unlike the chiton, with only one pair of teeth on each row, there are dozens of teeth on each row for banana slug radula. Interestingly, depending on their specific position, teeth on the same row are in three forms – medial, lateral and marginal. We found that such shape variation results in a slight change in chemical compositions, enabling the distinctive feeding function of each tooth. In addition, during the tooth maturation process, along with the morphological change, an increase in mineral composition is observed which leads to an increase in stiffness. Our findings serve as a first-of-its-kind detailed characterization of terrestrial mollusk radula teeth, and provide insights on correlations from teeth morphology, chemical composition and structural hierarchy, to mechanical behavior and feeding functions.

The structural integrity of bioinspired particles such as red blood cells and bacteria under flow conditions is dependent upon their ability to adapt their shape. Our goal is to examine the role of the composition of bioinspired vesicles on their shape during their flow through in a channel. Via the Dissipative Particle Dynamics simulation technique, we apply laminar flow in a cylindrical channel and investigate the shape transition of a bio-inspired four-component lipid vesicle encompassing DPPC, DMPC, glycolipids and cholesterol, and a hairy vesicle composed of phospholipids and pegylated lipids. We vary the channel dimensions, flow rate and composition to study their impact on the shape of the cell-mimetic and hairy vesicles. We will also characterize the critical flow rate at which the vesicles are ruptured. Our results could be potentially used to accelerate the design of smart particles with the ability to adaptive their shape under diverse flow conditions.

Achieving strong bonding between hydrogels and non-porous rigid surfaces and understanding the interface between the materials is crucial for the development of stretchable electronics, and soft microfluidics and biomedical devices. Here, we present a method to bond hydrogels to rigid substrates with tunable interfacial toughness values ranging from 10 J/m² to 1800 J/m² by controlled treatment of such substrates with functional silanes. To study the source of the large variations (three orders or magnitude) in interfacial toughness, we analyzed the peeled samples with surface characterization techniques such as scanning electron microscopy (SEM) and x-ray photoelectron spectroscopy (XPS) to identify interfacial chemical compositions and morphology. We discovered that hydrogel polymers were present on the substrate surface of strongly-bonded systems due to the presence of nitrogen and carbon signals. Moreover, the amount of polymer residue increased with increasing interfacial toughness, indicating a relationship between interfacial toughness and microscopic residues at the interface of the hydrogel-substrate bonded structure.

Colorimetric assay represents a class of simple and convenient technique for in-vitro cancer diagnostics, which is particularly suitable for resource-constrained scenarios. The bottleneck of colorimetric assay is the relatively low detection sensitivity as confined by current mechanisms of color signal generation. In this work, we break such bottleneck by developing a novel system based on heat-triggered release of Pd-Ir nanoparticles from plasmonic vesicles. Significantly enhanced color signal for the new system is achieved through: i) the use of Pd-Ir nanoparticles as enzyme mimics that possess much higher catalytic efficiency relative to natural enzymes, ii) the utilization of plasmonic vesicle interiors that enlarges the loading amount of Pd-Ir nanoparticles, and iii) the well dispersed Pd-Ir nanoparticles in reaction solution that maximizes their catalytic activity. On the basis of this new system, an ultrasensitive colorimetric assay was developed which could detect prostate surface antigen as a model cancer biomarker at the femtogram/mL level, rivaling the limits of fluorescence and plasmonics based techniques.

One of the most fascinating natural phenomena is the ability of some surfaces to repel water drops. Since the discovery of lotus leaf surface structure, several attempts of artificial, biomimetic superhydrophobic surfaces (SHS) have been made. Nowadays, we know that superhydrophobicity arises from a combination of surface morphology and chemical composition. However, different surfaces can display analogous wetting properties in static conditions (e.g. similar contact angles) but radically divergent drop impact output. Thus, drop impact studies provide enhanced insight on surface wetting properties in dynamic conditions.
We fabricated SHS with different morphology and/or chemical composition. Namely, surface S had a flower-like alumina structure with nanoscale cavities (as observed with FESEM), chemically modified with fluorosilanes; surfaces LAU and FAS had a terrace-like alumina structure with micro-cavities, modified with lauric acid or fluorosilanes, respectively. Then, we assessed their quasi-static wetting properties (e.g. advancing contact angle θ_A, receding contact angle θ_R and contact angle hysteresis Δθ) and drop impact behavior in a range of Weber number 1<We<650 with two different liquids, namely water and hexadecane, to study the effect of surface tension σ on drop impact output. All surfaces were superhydrophobic (e.g. θ_R>135°, Δθ<10°), but while S and FAS had θ_R>120° with hexadecane, LAU was oleophilic (θ_R≈0).
In water drop impacts, S surfaces always produced a rebound, indicating a stable Cassie-Baxter wetting state. Meanwhile, for LAU and FAS a Cassie-to-Wenzel transition (CWT) was observed at high We, with partial rebound as an output. Such behavior is consistent with results in literature: nano-cavities on S surface cause high capillary pressure P_C against wetting, while micro-cavities on LAU and FAS were penetrated by drops when wetting pressures (i.e. effective water hammer pressure P_EWH and gas layer pressure P_GL) exceeded P_C. Significantly, CWT occurred at higher We for LAU than for FAS, notwithstanding their identical surface structure and water contact angles. This result hints at a role of surface chemistry in drop impact behavior, a phenomenon that has never been reported before and certainly deserves further studies.
On the other hand, hexadecane drops never rebounded, even on S and FAS surfaces. Antonini et al. (Langmuir 2013) defined θ_R>100° as a criterion for water drop rebound. However, this does not hold for hexadecane: P_C is lower when s is smaller, thus causing CWT even if the surface is oleophobic in static conditions.
In conclusion, the results highlight that it is not possible to easily correlate contact angles and drop impact dynamics of low- and high-surface-tension liquids on different surfaces, as CWT can be observed even on statically repellent surfaces. Thus, an accurate design of surface properties must be pursued in the future research towards dynamically amphiphobic, biomimetic surfaces.

Spherical structures, such as particles, capsules, lipid vesicles and dendrimers, are commonly used in biomedical, pharmaceutical or food industries for delivering of drugs, nutrients or other substances into a target environment. The detailed knowledge of the releasing mechanism is relevant not only for improving the efficiency of the delivering process, when a benefic effect is aimed, but also helps to prevent unwanted damages, such as the excess of drug or even toxicity. Biodegradable polymers have been extensively used for drug delivery systems and chitosan, among them, is of major importance. The use of nanoparticles has also been proposed for the treatment of different diseases and in particular silver nanoparticles (AgNPs) have attracted attention due to their well-known antimicrobial effect. Whereas plenty of models are found in literature for drug release, few works deal with the release of silver nanoparticles in aqueous media. In this work the kinetics of AgNPs release from chitosan spheres is addressed experimentally and theoretically. From the experimental viewpoint, the study of AgNPs release is preformed by measuring the time-dependent the UV-Vis spectra of solutions where spheres of CHI/AgNPs where dispersed. The presence of the AgNPs in the solution is determined by observing their characteristic surface plasmon resonance peak (at approximately 420nm), whose intensity reflects the concentration of dissolved particles. Despite simple expressions for drug release are found in the literature, as those yielding a dependence on the square root of time for the amount of released drug, a proper modeling requires the solution of the diffusion (partial differential) equation with initial and boundary conditions that take into account: the initial distribution of AgNPs in the chitosan sphere, the presence of stagnant layers, porosity and dissolution of the matrix, percolation effects, the accumulation of particles in the medium, among others. Different solutions obtained using finite element method are explored in this work and compared with the experimental data.

In living tissues, the complex extracellular matrix (ECM) provides cells multiscale architectural cues ranging from nanometers to micrometers in size. It has been reported that cell behaviors including cell morphology, migration and differentiation are regulated by nano-topographies and micro-geometries such as nano-roughness and two-dimensional (2D) micro-patterns. However, how micro-curvature solely or integrated with nano-scale cues exerts influence on cell behaviors in three-dimensional (3D) environments remains elusive. In this study, we first demonstrate that 3D concave micro-curvature inhibits cell spreading and directs cell polarization within micro-groove structures. To examine the comprehensive effects of nano- and micro- scale cues, we integrate nano-wavy patterns into micro-grooves by various angles including 0 and 90 degrees via an oxidation-wrinkling technique. Using these multiscale hierarchical structures, we find that the nano-topography instead of micro-curvature is the dominant factor for single cell orientation. But, as the cell density increases to a certain level, the micro-curvature plays the leading role in cell alignment, which could be attributed to the effect of cell-cell contacts. Besides, through a fluorescence immunostaining method, we further prove that intracellular actin filaments and focal adhesions are associated with both the contact guidance effect of nano-wavy patterns and the confinement effect of micro-curvature on cells. In sum, as cell morphology in the ECM is critical to many physiological processes such as wound healing and morphogenesis, our findings not only enrich our knowledge about the cell-ECM interactions but also have applications in tissue engineering like artificial tissue culture.

Lignocellulosic biofuels have been identified as a possible solution to contribute to the world’s demands in energy and environmental sustainability. However, the fundamental understanding of the physical and chemical traits hindering key reactions during biomass to biofuel conversion processes has been limited by the lack of suitable tools and by the large natural variability in such systems.
Reaction wood constitutes a good model system for variation of cellulose content within a sample, with the increase in cellulose content in the plant cell wall of the region of the sample under tension in the plant during growth.
In this work, we use confocal Raman mapping and advanced Atomic Force Microscopy (AFM) to explore the effect of variation in cellulose content on the structure and composition of the plant cell wall at the nanoscale. Using advanced statistical methods on Raman datasets, such as K-means clustering and principal component analysis, we show that it is possible to differentiate layers in the cell wall layers and their local chemical signature. The characteristic peaks for cellulose and lignin are analyzed to reveal changes in peak positions across the different scanned regions of the cross section. Advanced AFM is used to study local mechanical properties of the different layers of the cell wall. Our approach facilitates the correlation of structure-composition traits of the plant cell wall for a more fundamental understanding of processes involved in biofuel research.

Long persistent phosphor is a new-type of environmentally friendly photoluminescence pigment with the characters of non-toxic, innocuous, non-radioactive. This kind of light-responsive materials can absorb the sunlight at daylight and slowly emit the absorbed energy in the way of visible light. It has been widely used as emergency indication or illumination. The commonly used LPP materials are alkaline earth aluminate or silicate activated with rare-earth irons, which has poor water resistance. Its long time exposure to water especially to moistures can lead to partial hydrolysis or complete hydrolysis, which greatly limited its further applications especially under high humidity conditions. In this paper, by encapsulating the LPP materials with mixtures of micrometer and nanometer SiO₂ particles, a superhydrophobic coating with low contact angle hysteresis (CAH) was prepared, which can effectively prevent LPP from the infiltration of moistures or waterdroplets. This will be beneficial for the application of LPP under high humidity conditions.
LPP and SiO₂ nanoparticles with different diameters (mixtures of micrometers and nanometers) were successively added into unconverted PDMS (monomer, initiator and solvent hexane) and vigorously stirred, then the mixtures were spin coated on glass slide and solidified to form the uniform superhydrophobic self-illuminous coating. The addition of PDMS can not only ensure the formation of uniform coating, but also enhance the interactions between particles and the substrate, which is beneficial for the mechanical stability of coating. The coating possesses good self-illuminous property, which can emit visible light in the dark owing to the long afterglow property of LPP. Besides, after the addition of certain amount of SiO₂ nanoparticles modified by dimethyl dichlorosilane, LPP particles were gradually surrounded by SiO₂ nanoparticles, and micro/nano composite structure was formed in the coating. The coating can effectively resist the infiltration of water or moisture to LPP and the contamination of dust to the coating, which is also similar to the property of lotus leaf.

Low-cost, accessible, point-of-use technologies for water filtration have the potential to greatly reduce the global burden of waterborne illnesses. Drawing inspiration from fluidic transport in plants, we explored the possibility of using plant xylem tissue for low-cost water filtration. The xylem tissue conducts sap in plants and has evolved porous membranes that provide low resistance to flow while arresting the spread of cavitation-induced bubbles. We demonstrate that plant xylem in the sapwood of coniferous trees can be used to effectively remove E. coli bacteria from water at high flow rates. However, a major challenge associated with the use of xylem for water filtration is the drop in permeability and deterioration in rejection ability due to the structural changes induced during drying, which is crucial in the context of transportation and shelf-life. We have developed methods to preserve the structural integrity of the xylem and to minimize the negative impacts on filtration characteristics due to drying. Further, we found that the permeability after drying is a strong function of filter length and have studied ways to design the filter to achieve an optimal balance between flow rate and rejection ability. We have also demonstrated gravity-driven filtration through the xylem and conducted fouling studies to gain insights into filter lifetime and variation in flow characteristics over time. Fabrication of the filter is simple, and the wood required for fabrication of a gravity-driven filter with a flow rate exceeding 1 L/h costs less than 1 cent and weighs only 8 grams. This work suggests the potential of plant xylem for realizing inexpensive, locally-manufacturable, and disposable point-of-use water purification devices.

Liquid transport on superhydrophobic surfaces has been proposed to have great potential for heat transfer, anti-icing, self-cleaning, drag reduction and microfluidic systems. For these applications, the sliding behavior of water droplets on solid surfaces is of particular importance. In this work, the frictional behavior of water droplets sliding on superhydrophobic surfaces with micro-pillar arrays was quantitatively studied. Our experimental results show that the sliding friction of a water droplet increased with increasing solid fraction when the size of the micro-pillar was fixed. This trend can be explained by the enhanced effective work of adhesion as previously proposed. More importantly, our results also demonstrated that the friction force increased noticeably as the micro-pillar size was enlarged and sliding process could even become locally unstable with a “stick-slip” feature. Based on the analysis of the deformed configuration of the droplets and the measured force traces, we attributed this unusual behavior to the different coordination state of the de-pinning events around the rear of the triple-phase contact line. Our findings may provide a new strategy for tuning the frictional behavior of a water droplet sliding on superhydrophobic surfaces.

Biomimetics, the field of understanding principles abstracted from distinctive phenomenon in nature aimed at technological design and applications in human society, is a growing interest. Among many studies and technologies biologically inspired, controlling wettability, including superhydrophobicity, self-cleaning, fog harvesting and drag reduction in fluid flow, have attracted much attentions. In our study, a coastal animal, Ligia exotica, was set as a biological model. It has pairs of hydrophilic legs on which open-air capillary structures uptake water spontaneously to its gill using interfacial free energy. SEM observations revealed the water channels are composed of micron-sized blades oriented in parallel lines. This structure has a great potential of low-energy long distance liquid transport. We fabricated a series of water channels on silicon wafer by photolithography mimicking the structures of legs of Ligia exotica. The channels irradiated by VUV acquire similar water transport ability with their hydrophilicity. Moreover, we found out the velocity of liquid transport in vertical direction is accelerated after a quantifiable change of arrangement of blades although the surface area and number of the blades in the channels are fixed. In the rise of water on the channel, the shape of three phase contact line (TCL) was found to be drastically varied, depends on geographical parameters such as length of blades, distance between blades, and arrangements of blades on the surface. This work investigates a mechanism enhances the velocity of transport in terms of microscopic liquid wetting on several arrangement patterns of micro channels.

Biological organisms have succeeded in fabricating high performance inorganic materials using relatively simple building blocks under ambient conditions. Specialised biomolecules have been found to play a major role in the deposition and morphogenesis of complex inorganic structures. Biomolecules such as proteins and peptides fine-tune properties of inorganic material to match environmental pressure resulting in biominerals with controlled crystal size, shape, orientation and polymorph. The desire to explore protein directed synthesis of inorganic materials has led to application of directed evolution and combinatorial techniques as potential routes for selecting biomolecules tailored to fine-tune the properties of inorganic materials. The majority of the work in this area has focused on using phage display and/or cell surface display to screen short polypeptide libraries for their ability to bind material surfaces. While this is a convenient method to use, selection is based on binding ability rather than the ability to generate materials with specific properties. Using both phage and cell surface display, we aim to explore a diverse library (>10¹⁰) derived from the Adhiron protein scaffold for quantum dot and magnetic nanoparticle synthesis. In order to successfully screen for and select “active” proteins from our library we have coupled our ability to generate large diverse libraries with a new micro-droplet-based platform which has enabled us to use in vitro compartmentalisation (IVC) to evolve nanomaterials by directly selecting target properties during screening. Using droplet-based microfluidics we have developed a simple and reproducible method for generating artificial cell like compartments (double emulsions) that can be used in conjunction with fluorescence activated cell sorting (FACS) and magnetic separation. We have also employed the conventional phage display method to screen our libraries for proteins with the ability to control size, shape and polymorph selection.

This work presents an experimental study on the structural examination focusing on the tribological and mechanical testing through the joints of the katydid (Orthoptera: Tettigoniidae). The tibial and femoral articular surfaces of the katydid joints showed the nanosmooth and micro/nanotextured surface characteristics, respectively. The articular surfaces with a micro/nanoscale structural features demonstrated topographies for reducing the total number of the contact points. The micro/nanoscale periodic patterns (i.e., groove, lamellar, and hillock) with the hierarchical structures on the femoral articular surfaces which are in contact with the nanosmooth tibial articular surfaces allow enhancing the tribological properties, exhibiting considerably low friction. The friction coefficient (μ) values of 0.091 ± 0.003 (femur non-contact region) and 0.064 ± 0.006 (femur contact region) were recorded against a “tibia-attached tip” (tibia contact region), respectively, in air under dry conditions. Furthermore, the tibia and femur contact regions showed the reduced elastic modulus (E_r) ranging from 0.88 ± 0.01 GPa to 3.90 ± 0.11 GPa, whereas the tibia and femur non-contact regions showed the E_r ranging from 1.89 ± 0.03 GPa to 7.27 ± 0.03 GPa, as much as two times higher. Overall, this study can be valuable to the development of the innovative lubrication systems, energy efficient materials, and durable materials through the bioinspiration. We believe that our work will bring motivation to designing next generation tribological materials for the practical applications in the future.

Fouling by suspended solids and dissolved organic matters presents a great challenge for polymeric membranes for desalination and wastewater treatment. With superior hydrophilicity, bio-inspired zwitterionic polymers have been explored for membrane surface modification to enhance antifouling properties. However, there is a great challenge to graft these superhydrophilic materials onto the membrane surface with stability. Mussel-inspired polydopamine coating is adopted in this study. We have modified ultrafiltration (UF) membranes using a solution containing dopamine and sulfobetaine methacrylate (SBMA). The dopamine and SBMA react and form a thin film on the surface, while dopamine provides adhesion to the membrane surface and SBMA provides superhydrophilic properties. The coating enhances the surface hydrophilicity, which is confirmed by contact angle measurement. The coated membranes demonstrate better stability and higher water flux than those of dopamine-coated and uncoated ones, when tested with water containing bovine serum albumin (BSA). For instance, the membrane coated with dopamine and SBMA exhibits water permeance 65% higher than the uncoated one, after 3 hour filtration using a 3g/L BSA solution in a crossflow system. I will also present fundamental study of relationship between structure and water and salt transport properties in zwitterionic materials. Two series of zwitterionic polymers were prepared from SBMA and 2-methacryloyloxyethyl phosphorylcholine (MPC). These polymers were thoroughly characterized in terms of sol-gel fraction, density, glass transition temperature, contact angle, and water and salt transport properties. Interestingly, the zwitterionic polymers exhibit water sorption and permeability similar to non-charged poly(ethylene glycol) (PEG)-based materials. These zwitterionic polymers exhibit lower NaCl diffusivity and permeability and thus higher water/NaCl selectivity than the non-charged PEG-based materials, demonstrating their promise for membrane surface modification for desalination and wastewater treatment.

Rapid advances in the field of peptide-based materials have been motivated by a diverse range of potential applications including targeted drug delivery, cancer treatment, tissue engineering, treatment of neurodegenerative diseases, nanoelectronics and antimicrobial surfaces. Peptide dendrimers, branched molecules containing amino acid sequences, are of particular interest. In this project, a coarse-grained model is employed in conjunction with Molecular Dynamics simulations to study the aggregation behavior of dendrimers of different molecular architectures in solution. The effect of concentration and pH are explored.

Nature has evolved a wide range of structures that interweave micro- and nanoscale features to produce superhydrophobic skins. Superhydrophobicity gives plant leaves and pedals self-cleaning behavior, allows insects to walk on water, and keeps birds dry in the rain. Scalable methods for incorporating of superhydrophobic skins into structural materials will produce a new generation of materials with transformative properties. Polymer nanocomposites containing carbon nanotubes have allowed for enhanced properties of bulk materials with respect to properties such as strength, stiffness, thermal stability, and sensing ability. Here, we demonstrated that laser ablation of polypropylene nanocomposites containing between one and five weight percent carbon nanotubes produce superhydrophobic surfaces. These surfaces display outstanding superhydrophobicity with contact angles exceeding 175 degrees and self-cleaning properties. The observed superhydrophobicity is a result of intertwined micro- and nanoscale features that result from the laser ablation of the composite material. Laser ablation provides a simple, direct, and economical method for the generation of high-quality bulk materials with superhydrophobic skins and enhances structural properties.

Guided water transport has many applications in microfluidics, printing, oil–water separation, and atmospheric water harvesting. By introducing anisotropic micropatterns on a superhydrophobic surface, we demonstrate that water microdroplets can coalesce and leap over the surface spontaneously along a prescribed direction. This controlled behavior is attributed to anisotropic liquid–solid adhesion. An analysis relating the preferential leaping probability to the geometrical parameters of the system is presented with consistent experimental results. Surfaces with this rare quality demonstrate many unique characteristics, such as self-powered, and relatively long distance transport of microdroplets by “relay” coalescence induced leaping.

Viruses such as bacteriophages invade host cells efficiently and selectively with proteinaceous devices that are first and foremost recognized by their unique nanostructures. Synthetic mimicries of these nanostructures may bode well for the development of new membrane active antimicrobials, but this aspect has not been systematically examined yet. We study here well-defined spherical and rod-like polymer molecular brushes (PMBs) that mimic the two basic structural motifs of bacteriophages and reveal that: (1) amphiphilicity is not a required trait – hydrophilic PMBs can be potent membrane active antimicrobials with low toxicity; (2) nanostructured PMBs are far more powerful bacteria killers than the hydrophilic polymer branches that make up the PMBs; (3) PMBs induce a topological transition of bacterial membranes to form pores, while their individual linear chain polymer branches do not; and (4) the nanostructure of PMBs define their antimicrobial activity and selectivity. These findings differ from and expand existing wisdom on membrane active antimicrobials, suggesting that nanostructure is a critical determinant that can be judiciously controlled to give rise to synergistic multivalent interactions on remodeling bacterial membranes, which in turn helps the membrane active antimicrobials gain desirable activity and selectivity.

Rosette nanotubes (RNTs) are self-assembled from synthetic fused guanine and cytosine motifs (GΛC motif), where DNA Watson-Crick pairing takes place between the guanine side of the GΛC motifs and their cytosine side. The spatial arrangement of these arrays leads them to form a hexameric supermacrocycle with high stability as a result of the hydrogen bond system and further extensive π-π stacking interactions to form RNTs. In addition, various functional groups have been grafted to the GΛC motif using synthetic methods developed by our group, such as amino acid, peptides, and other bioactive molecules. Upon self-assembly, these functional groups are displayed on the surface of RNTs which results in tunable physical, chemical, and biological properties

Because of their established biocompatibility and low toxicity, RNTs have found numerous biomedical applications in the past decade. In order to improve their solubility in aqueous solutions, pharmacokinetics, and biodistribution, polyethylene glycol (PEG)-functionalized GΛC motif has been developed and self-assembled into PEG-RNTs. We have discovered that this material forms hydrogels consisting more than 99.8% water. Here we will present our synthetic strategy, self-assembly studies and rheology investigation as well as in vitro cytocompatibility studies.

Mats of randomly positioned nanofibers have widespread use in living organisms, and are capable to sustain a large range of functions, from the control of a crystallization process to the strengthening of a tissue, passing through the guiding of motion and the limitation of wetting. For instance, biomineralization in bone occurs within a complex arrangement of collagen fibrils; enamel is grown within a supramolecular structural framework based on amelogenin proteins; the cuticle of the Crustacea consists of a network of chitin-protein fibers in a biomineralized inorganic phase; in the interstitial extracellular matrix, collagen fibers provide structural support to the cells; and the surface of the leaves of Drosera burmannii are made of a random mat of flat-on long nanofibers of epicuticular wax.

This impressive range of functions results in a large part from the variety of biomacromolecules which are incorporated in the nanofibers, thereby providing a wealth of possible chemical interactions in addition to the common structural fibrous component. Inspired by the fabrication of "Bucky paper" and of cellulose nanopapers, which are obtained by the sedimentation of carbon nanotubes or cellulose nanofibrils, we show that it is possible to fabricate nanopapers based on nanotubes prepared by layer-by-layer assembly (LbL). The nanotubes are obtained by LbL in nanoporous templating membranes followed by membrane dissolution; then, a straightforward filtration methodology of suspensions of nanotubes leads to LbL nanopapers over centimeter square surfaces, with a volume density of nanotubes in the range of 10¹² cm^-3. Considering the versatility of the LbL technique with respect to the variety of compounds which can be integrated in the nanotubes, this methodology provides access to a virtually unlimited range of smart nanopapers.

In this communication, we present the main parameters which control the texture of the nanopapers, such as composition and rigidity of the nanotubes, and their areal density, using a variety of polyelectrolytes. We then demonstrate the fabrication of multilayered nanopapers made of stacks of different nanofibers, and the possibility to post-modify chemically the nanopapers by, e.g., silanization, leading in that specific case to strongly oleophobic superhydrophobic surfaces. We also show the inclusion of biomacromolecules in the LbL nanopapers, and thereby obtain an enzymatic 'paper' capable to degrade glucose.

The mussel byssal thread has been a source of inspiration for those interested in such applications as adhesives, coatings, and drug delivery. Yet, despite all the innovation inspired by the byssal thread’s material design, it is unclear how the structure of the thread influences its unique mechanical properties. We believe a metal-coordinate stiff coating on a soft elastomeric core models the toughness of a byssal thread, and present a synthetic composite fiber system to particularly characterize the interface between the coating and the core. We investigate how the interfacial strength is affected by such conditions as hydration, pH, and metal loading of the gel coating, thus influencing the overall toughness of the fiber. By studying these bio-inspired fiber systems and comparing them to their natural analogue, we can better understand the basis for the byssal thread’s stellar mechanical properties and thus more intelligently incorporate its design principles into novel materials engineering

Surface-enhanced Raman Spectroscopy (SERS) is one of the prominent methods to measure biomaterial properties due to its nondestructive approach. Plasmonic metal nanoparticles such as gold nanoparticles (AuNPs) and silver nanoparticles (AgNPs) that have excellent chemical stability are used to detect the Raman scattering, exhibiting a greatly enhanced Raman signal intensity via localized surface plasmon resonance (LSPR). Herein, we introduce bio-inspired polydopamines chemistry for the synthesis of three-dimensional (3D) gold-silica hybrid nanostructures within highly porous polymer templates through the reduction of gold ion precursors and silica precursors using the polydopamine functionality. Highly porous poly(ethlylene glycol dimethacrylate-co-acrylonitrile) (poly(EGDMA-co-AN) microspheres are prepared by conventional suspension polymerization and used as polymer templates. The internal surfaces of the polymer templates are coated by polydopamines via the oxidative polymerization of dopamines. Silica nanoparticles that are used to maintain the dispersion stability of AuNPs during thermal treatment are synthesized on the surface of the gold-polymer microspheres using by hydrolysis of tetraethyl orthosilicate (TEOS), and these gold-silica-polymer hybrid materials are annealed in air at 500 ^oC for 4 h to remove polydopamine layers and polymer templates. The structural properties and the surface chemistry are investigated using SEM, EDAX, TEM, XPS, XRD, and BET analysis. The SERS performance of our 3D gold-silica hybrid materials are tested using the various concentrations of Crystal Violet (CV) solution as the dye material for SERS that does not bind to gold. Several characteristic peaks of CV are detected in the Raman spectra: 204 cm^-1, 442 cm^-1, 726 cm^-1, 803 cm^-1, 1175 cm^-1, 1377 cm^-1, and 1622 cm^-1, and Raman signal intensity of these peaks is significantly increased in the CV 10^-6 M solution compared with untreated CV solution of the same concentration. Further detection of CV peaks at the lower concentration is indicated in the Raman spectra. The hybrid materials have long term stability as a powder or dispersed in ethanol before and after the analysis of SERS performance. Our bio-inspired approach that synthesizes the plasmonic metal-silica hybrid materials will lead to the further investigation of materials for SERS and their applications. This study was supported by a grant of the World Class 300 Project, Small and Medium Business Administration (SMBA), Republic of Korea (Grant no. 2341055).

A medical product comprised of device/drug is known as a combination product. There are several combination products approved by FDA such as iontophoresis system, photodynamic therapy, drug-eluting coronary stents, and absorbable collagen sponge with genetically engineered human protein. The last one can make bone formation hasten by using bone morphogenetic protein. It is expected further features by using various cytokines or growth factors; however, the binding property of such factors to collagen is not clear to achieve a controlled release. In this study, we investigated artificial periosteum-like membranes made from tilapia scale atelocollagen (Col) and hydroxyapatite (HAp) as a drug carrying support. A suspension including a single phase of low crystalline HAp was prepared with a conventional wet methods, based on a neutralization reaction using Ca(OH)₂ suspension and H₃PO₄ solution. Col solution and HAp suspension were mixed and degassed under the pH of 7.4. The HAp/Col composites with three different compositions in weight ratio of 2:8, 5:5 and 8:2 were made and kept at 28 degrees for fibrogenesis, and then completely exchanged water to ethanol by using ethanol series. The composite membranes were fabricated by evaporating ethanol only from side wall. The dose of gamma-ray radiation for the membranes soaked in phosphate buffer saline was fixed at 25 kGy. The Col fibrils were observed by scanning electron microscopy. The diameter of fibrils was 53 nm and interconnecting pores were not confirmed. The Col and HAp components in the samples were confirmed by thermogravimetry, indicating the ratio met the initial mixing ratio. The thicknesses of the membranes were increased and densities of the membranes were decreased with the increase of HAp ratio from 185 to 689 mm and from 0.90 to 0.36 mg/cm³. According to the increase of densities, the tensile strengths of the membranes without gamma-ray radiation were improved up to 42.2 MPa; however the gamma-ray irradiation apparently increased the strength at twice (83.5 MPa). The mechanical strength was stronger than those reported for other artificial periosteum made from high-density polyethylene or polylactic acid. Raman spectra showed the intensity of a Raman line assigned to phenylalanine was decreased after gamma-ray radiation. This indicates that Col fibers would be cross-linked at phenylalanine. The adsorption ability of proteins such as bovine serum albumin (BSA) or lysozyme (LSZ) on the membranes exhibited different tendency; the membranes including a lot of HAp can adsorb BSA rather than LSZ. In conclusions, we successfully fabricated the artificial periosteum-like membranes composed of tilapia scale Col and HAp with the high density and sufficient mechanical properties by using gamma-ray irradiation, which will be a promised biomedical device as combination products.

Natural and man-made materials are often designed to perform the same functions, including for structural support, robustness, or protection. Scaled skins in nature (e.g., fish and snake skins) have remarkable mechanical properties including being compliant, resistant to penetration, and lightweight, all of which is achieved within an ultrathin membrane structure. In this presentation, we will describe the mechanics in scales and scaled skins important to the design and microfabrication of a new bio-inspired material that can serve as a deformable, damage resistant, and robust protective coating. Our approach involves an integrated set of experiments and novel multiscale computational methods. Specifically, we will present (i) design principles for artificial scaled skins with mechanics comparable to those observed in nature, (ii) a microfabrication technique to produce artificial scales and scaled skins at the microscale, and (iii) direct measurements and computational modeling of the mechanics of the artificial scaled skins. The response of the materials to in-plane (i.e., stress-strain response) and flexural (i.e., bending response) deformations will be reported, as well as its resistance to puncture using nanoindentation measurements. We envision that our novel microscale fish-skin materials can be utilized as promising protective layers in applications that undergo deformation such as in flexible/stretchable electronics and microelectromechanical systems (MEMS). Surfaces treated with the microfabricated fish-skin material will also be shown to have anisotropic friction coefficients, such that directional motion of self-propelling walkers can be achieved.

Cellulose is one of the most abundant biomacromolecule on earth with renewability and biodegradability, mainly from green plants and bacteria. Cellulose and its derivatives conventionally have been applied to numerous different industrial fields, such as the textile industry, thermoplastics, packaging materials, etc. Compared with the conventional applications, cellulose nanofiber (CNF) has high potential for the design of high value-added nanomaterials due to its high aspect ratio, excellent stiffness and tailored functionalities. Recently, CNF has been studied to prepare polymer nanocomposites, tough transparent CNF film for devices, template nanomaterials, stimuli-responsive materials and so on.¹

With the respect of different CNF-based nanomaterials, the technique of controlling structure of CNF is critically significant and challenging. The orientation of CNF is one of the significant factors for achieving the better performance of CNF-based nanomaterials. Different methods of alignment of CNF have been explored, such as magnetic field, electric field, cold drawing and shearing force.² However, these methods had some disadvantages. Strong (usually over 1 T) magnetic field was required, which was energy-consuming, and mechanical techniques (cold drawing, shearing force) were restricted to the limited efficiency. Hence, it is of high importance to find the versatile and efficient method to align CNF for organized nanomaterials.

In this study, we firstly studied the alignment of CNF with nematic liquid crystal. Here, TEMPO-Oxidized Cellulose Nanofiber (TOCN), which had the uniform width of 3-4 nm and length of about 500 nm, was used. Mixture solution of TOCN and nematic liquid crystal was spin-coated on the alignment layer. By polarized optical microscopy and atomic force microscopy, the orientation of nematic liquid crystal and TOCN was confirmed. Moreover, the effects of different alignment layers, photo alignment layer and rubbed polyimide film, were investigated. In addition, order parameters of nematic liquid crystal with different amount of TOCN were measured and calculated by UV-vis spectroscopy. The results revealed the alignment of TOCN were able to be achieved with nematic liquid crystal, which offering a new versatile method of alignment of CNF for organized nanomaterials and devices.

Reference
1. Tingaut P, Zimmermann T, Sèbe G. Cellulose nanocrystals and microfibrillated cellulose as building blocks for the design of hierarchical functional materials[J]. Journal of Materials Chemistry, 2012, 22(38): 20105-20111.
2. Kadimi A, Benhamou K, Ounaies Z, et al. Electric field alignment of nanofibrillated cellulose (NFC) in silicone oil: impact on electrical properties[J]. ACS applied materials & interfaces, 2014, 6(12): 9418-9425.

We present the synthesis and discuss the properties of a new class of nanofibrilated dendrimeric polymer particles (DPPs). The DPPs are fabricated by a simple, efficient and scalable process for massive liquid-based synthesis of polymeric nanomaterials. These dendrimeric particles are hierarchically structured, with a big branched corona of nanofibers spreading out in all directions. Our results demonstrate that these dendrimeric particles could be made from numerous polymers by controlling the shear conditions and solvent quality. The DPPs’ biomimetic morphological similarity to the unique structure of gecko lizards’ setae enables their strong adhesion to almost any surface and to each other. This opens the way to making strongly adhesive coatings and new types of dry adhesives. Another unusual feature of the DPPs is high excluded volume induced from their hierarchical structures. Thanks to their efficient volume-filling ability, the DPPs readily modify the rheology of various liquids. These particles are expected to find a broad range of industrial applications, such as components of gelation agents and coating formulations.

Nano/micro-motor shows various promising applications in the areas of biomedicine, catalysis, environmental remediation.^[1-4] The precise controlling of the speed and direction are the most important issues that must be solved for the real application. Light controlling is a newly proposed hot topic in this area^[5,6]. Here we report a visible-light-driven silicon nanomotor based on core-shell p-n junction, which shows size and wavelength dependent motion behavior. Under light illumination, photoexcited carriers decompose hydrogen peroxide on p-Si and n⁺-Si surface and generate H⁺ and OH^- respectively. The localized electrophoretic field generated by unbalanced ions propels the motion of the nanomotor. The proposed self-electrophoretic mechanism was demonstrated by real-time individual motor motion and ionic strength measurement. The as-prepared motor shows instant “ON-OFF” response through switching the “ON-OFF” of PEC reaction by light illumination. The morphology of fracture surface shows crucial effect on the motion trajectory, which proves that the chemical energy to the mechanical energy is sufficient and fast even in the nanoscale level. The silicon nanomotor shows wavelength and diameter dependent motion speed, which originates from the different absorption, in line with the results of finite-difference time domain (FDTD) simulations. These results imply a promising prospect for novel design of individually light-controlled nano/micro machines.


References
1. Wang W.; Li S.; Mair L.; Ahmed .; Huang T.; Mallouk T. Angew. Chem. Int. Ed. 201, 53, 3201–3204.
2. Wang J.; Gao W. ACS Nano 2012, 6, 5745-5751.
3. Moo J.; Pumera M. Chem. Eur. J. 2014, 20, 1-16.
4. Li, J.; Gao W.; Dong R.; Pei A.; Sattayasamitsathit S.; Wang J. Nat Commun 2014, 5, 1-7.
5. Liu M.; Zentgraf T.; Liu Y.; Bartal G.; Zhang X. Nat Nanotech 2010, 5, 570–573.
6. Hasman E. Nat Nanotech 2010, 5, 563–564.

Controlling dropwise condensation is fundamental to water-harvesting systems, desalination, thermal power generation, air conditioning, distillation towers, and numerous other applications. For any of these, it is essential to design materials that enable droplets to grow rapidly and to be shed as quickly as possible. However, approaches based on microscale, nanoscale or molecular-scale textures suffer from intrinsic trade-offs that make it difficult to optimize both growth and transport at once. I will present a conceptually different design approach—based on principles derived from desert beetles, cacti and pitcher plants—that synergistically combines these aspects of condensation and substantially outperforms other synthetic surfaces. Inspired by an unconventional interpretation of the role of the beetle’s bumpy surface geometry in promoting condensation, and using theoretical modelling, we show how to maximize vapor diffusion flux by optimizing the geometry of convex millimetric bumps. Integrating the apex geometry with an asymmetric slope, analogous to cactus spines, directly couples facilitated droplet growth with fast directional transport. This coupling is further enhanced by a slippery, pitcher-plant-inspired, friction-free nanocoating. We observe an unprecedented sixfold-higher exponent of growth rate, faster onset, higher steady-state turnover rate, and a greater volume of water collected compared to other surfaces. We envision that this fundamental understanding and rational design strategy can be applied to a wide range of water-harvesting and phase-change heat-transfer applications.

Smart Materials have captivated the world of science and technologies for decades. The idea that a man-made material could sense the environment and respond to external stimuli such as light, temperature, or damage in an autonomous and programmed way is fascinating and, at the same time, closer than anticipated. Bioinspiration is a path to achieve all of these functionalities at the same time, as natural materials such as skin or bone, show symultaneously self-healing capabilities, and act as mechanosensors and damage sensors.

In this presentation we describe an approach for the fabrication of bioinspired adaptive composite materials able to self-repair autonomously, sense mechanical stimuli such as pressure or flexion, self-monitor their structural integrity and change their shape in response to external stimuli. These smart materials are based on the controlled integration of microscopic electrically conductive networks within polymeric matrices having self-healing or shape-memory capabilities. To realize this concept, we have taken advantage of the 2D nature of graphene combined with new processing techniques to design minimally-invasive networks able to provide a platform for inducing electrical stimuli in the composites. Superlight electrically conductive carbon-based networks with microscopic porosity obtained by freeze-casting, have been infiltrated with a second polymeric phase. The networks are tailored to provide controlled and localized joule heating at relatively low voltages in order to stimulate the desired response in the polymeric matrix (healing or shaping). The resulting materials have graphene contents below 0.5 wt.%. Their mechanical response (strength and toughness) is evaluated and related to their microstructure.
Their healing ability is quantified in terms of recovery of these mechanical properties after damage. In parallel, their shape changing and mechanical sensing capabilities in response to electrical currents are also tested. Preliminary results on shape-memory compositions show strengths up to 60 MPa and complete shape recovery through joule heating in 10 seconds. Furthermore, the composites are able to record, through a conductivity change, the initiation and progression of a crack, providing damage monitoring capabilities.

The work brings together the fields of construction, materials science, robotics, energy and bioengineering in an innovative way, opening new paths for the design of smart actuators and adaptive composites.

Manipulating materials at the nanometer scale has been consistently proposed as a grand challenge of science. An effective path towards this goal is biomaterials research, taking advantage of the results of millions of years of evolution. One promising example in this context is diatoms. These microscopic algae have intricate porous shell morphologies and features ranging from the nanometer to the micrometer scale, which have been proposed as templates for drug delivery carriers, optical devices, and metamaterials design. Several studies have found diatom shells show unique mechanical properties such as high specific strength and resilience. One hypothesis is that these properties stem from the structural arrangement of the material at the nanometer and micrometer length scales, challenging the concept between what constitutes a “material” versus a “structure”. To date, there is no robust model reported that can validate such hypothesis. In this work, we have conducted a systematic simulation-prototyping study to shed light on the mechanics of diatom-inspired hierarchical microstructures. The Finite Element Method (FEM) was used to replicate three-dimensional diatom shells under compressive forces. Geometric non-linear behavior was considered and the intricate hierarchical structure observed in nature was reproduced in detail. A FEM frustule model was created based on the available natural samples of the Coscinodiscus species, and the resulting mechanical response was compared to measurements to create a benchmark. The simulation parameters were selected so as to reproduce standard nanoindentation experiments, with a compressive load localized at the top of the diatom shell and fixed constraints at the base to simulate electrostatic adhesion to the substrate. A frustule diameter of 50 mm was used with pore diameter sizes ranging from 0.25 to 1.2 mm across different layers. After this initial step, similar designs were created with pore morphologies that depart from those observed in nature to elucidate the relation between morphology and mechanical properties. In all cases, the mechanical response to compression was used as a criterion to compare different alternatives. Additionally, select designs were prototyped using Direct Laser Writing (DLW) to evaluate the feasibility of manufacturing diatom-inspired devices at the micro-scale. Overall results from this study indicate there are distinct correlations between each morphology parameter and the overall mechanical response of the diatom shell. The DLW prototypes exhibit similar level of intricate morphological traits observed in real diatoms, thus opening the door to a simulation-based process for the design and fabrication of diatom-inspired microdevices. This research contributes to improving understanding of the mechanical response of biomaterials, and it represents a step toward the design and manufacture of emerging metamaterials and microarchitectures.

We use 3D computational modeling to study mechanically-induced changes in the structure of networks formed from polymer-grafted nanoparticles (PGNs). The nanoparticles’ rigid cores are decorated with a corona of grafted polymers, which contain reactive functional groups at the chain ends. With the overlap of the grafted polymers, these reactive groups can form labile bonds, which can reform after breakage. These PGN networks consist of two types of nanoparticles, which differ in the reactive functional groups at the chain ends. The energy of the labile bonds that are formed depends the nature of these reactive groups. We demonstrate that the application of a rotational deformation results in a controllable reconfiguration of the network. Depending on the labile bond energies, the PGN networks are shown to exhibit a deformation-induced phase separation or a mixing. The restructuring process can be controlled by the deformation protocol and boundary conditions. Our results provide guidelines for designing mechano-mutable PGN-based materials whose structures can be controllably changed under an applied mechanical action.

Nature provides a huge range of biological materials with various smart functions over millions of years of evolution, and serves as a big source of bio-inspiration for biomimetic materials. Ion channels existed in living organisms play a significant role in maintaining balanced physiological conditions and serve as “smart” gates to ensure selective ionic transport. Inspired by ion channels, various smart artificial nanochannel systems have been developed [1]. Pore and channels are everywhere on different scales, ranging from biological ion channels to large oil pipelines [2]. The problems with such channels center on energy saving, anti-block, anti-fouling and anti-corrosion. Currently, we are focusing on the development of bio-inspired liquid-based gating system, which is a smart gating membrane. The reconfigurable fluid gate is able to reconcile the competing demands of responsive control, complex multiphase selectivity, and clogging prevention in a single integrated mechanism [3]. For each transport substance, the gating threshold can be rationally tuned over a wide pressure range. This system allows gas-liquid sorting in a microfluidic flow and separates a three-phase air-water-oil mixture with an antifouling behavior. This bio-inspired system could be used in a variety of pore structures, material chemistries, and micro/macroscale systems, providing opportunities for complex sorting in fuel, environmental, microfluidics, biomedical, 3D-printing, and other applications.

1. X. Hou, Design, Fabrication, Properties and Applications of Smart and Advanced Materials. (CRC Press, 2016) ISBN:978-1-4987-2248-3.
2. X. Hou, Smart Gating Multi-Scale Pore/Channel-Based Membranes. Advanced Materials, (2016) doi:10.1002/adma.201600797.
3. X. Hou, Y. H. Hu, A. Grinthal, M. Khan, J. Aizenberg, Liquid-Based Gating Mechanism with Tunable Multiphase Selectivity and Antifouling Behaviour. Nature 519, 70-73 (2015).

Motivated by the persistent desire to develop new materials, which offer currently unavailable functions, research focused on the creation of polymers with tailored stimuli-responsive properties has evolved into an important field at the interface of chemistry, materials science, physics, and other disciplines. Due to their dynamic, stimuli-responsive nature, non-covalent interactions represent a versatile design element for the creation of stimuli-responsive polymers with unusual functions. This general approach is also widely used in Nature. The exploitation of specific nanostructures is another design element that has emerged in Nature to achieve specific functions. Several types of materials that rely on these general design approaches will be discussed in this presentation. Interactions that will be discussed include hydrogen-bonds, pi-pi stacking, and metal-ligand binding. Such motifs were used to assemble small molecules, supramolecular polymers, nanoparticles, and combinations of these building blocks to create mechanically mechanically adaptive and adapting, healable and other responsive polymeric materials that mimic function and/or design approaches encountered in Nature’s materials.

Despite the long history of wood science research, wood continues to provide new inspiration for biomimetic materials. The cell walls of wood are nanofiber reinforced composites with semi-crystalline cellulose microfibrils embedded in a hemicelluloses and lignin matrix. Our recent discoveries include that wood cell walls possess shape memory capabilities and are stimuli-responsive materials for chemical transport. Both the shape memory effect and cell wall chemical transport result from the complex cell wall nanostructure and are controlled by moisture. Shape memory effects in wood cell walls were studied by observing the moisture-induced recovery of nanoindent impressions in wood cell walls. Additionally, using the high spatial resolution and sensitivity of synchrotron-based X-ray fluorescence microscopy we recently discovered and studied moisture thresholds for ionic diffusion in wood cell walls. We propose that both the shape memory effect and the threshold for chemical transport are controlled by the nanostructure of the hemicelluloses and their passing through a moisture-dependent glass transition at approximately 80% relative humidity. Mechanical damping of the wood cell walls measured using nanoindentation-base mechanical spectroscopy also support the presence of the moisture-dependent glass transition at approximately 80% relative humidity. The nanoindentation results also revealed that there was no obvious softening in cell wall mechanical properties around the hemicelluloses’ glass transition. This is an advantage over typical synthetic stimuli-responsive polymers that undergo drastic mechanical softening during the thermal transitions that control their stimuli-responsive behavior. The nanostructures of lignin and semi-crystalline cellulose are most likely responsible for the sustained mechanical properties of the wood cell walls. Simple models of the cell wall nanostructure that can be used to inspire new biomimetic stimuli-responsive materials will also be presented and discussed.

Hemicelluloses are polysaccharides in plant microstructure that play an important biological role in strengthening the plant cell wall by interacting with cellulose, and with lignin in some secondary cell walls. A deep understanding of the structure and the properties of hemicellulose can contribute to the investigation of the cell wall mechanics and plant behaviors at macroscale. However, a proper description and modeling of the hemicellulose structure at the mesoscale remains elusive, particularly because of its configurational complexity and structural variety. Here, a set of coarse-grained force field parameters for the molecular dynamics simulation of hemicellulose is derived. The developed model of hemicellulose possesses mechanical properties close to experimental measurements. By developing the coarse-grained hemicellulose model, it facilitates relatively large-scale simulation of plant cell wall that can be used for understanding the bulk plant behaviors. In addition, such model can be used to enhance the material design process of bio-inspired composites.

The cellular architecture of wood is designed to provide optimum conditions for the tree, using a minimum of material. On the nanometer scale, the arrangement of cellulose fibrils fairly parallel to each other plays a crucial role in determining the mechanical properties of the trees. These cellulose nanofibrils (CNF) have the prospective of being a building block for future high-performance materials, due to their exceptional mechanical properties (modulus upto 140 GPa in its crystalline form). However, the mechanical properties obtained till date, are far from the maximum potential values speculated for individual CNF and it can be hypothesized that the fibrils have to be aligned and assembled in a controlled manner in order to make full use of the potential of CNF.

Therefore, inspired from the arrangement of CNF into the trees, here we made an attempt to utilize its potential for the fabrication of strong and stiff filaments. We have utilized the benefits of flow focusing approach to align the CNF, present in the form of 0.3 wt% colloidal dispersions in water with the help of elongational flow field followed by the solidification using solidifying agents or molecules. The in-situ study regarding the alignment of CNF into the channel is carried out using small-angle X-ray scattering technique and the structure of solid-filaments obtained is characterized with wide-angle X-ray scattering. With the current approach, we have managed to fabricate filaments with a modulus of 60 GPa and strength at break of around 850 MPa, which is the highest obtained value for CNF-based filaments or fibers, as of now.

We have developed a green, bottom-up approach for synthesizing flexible, organic, semi-conducting nanocomposite films based on cellulose nanocrystals (CNCs) and polyaniline (PANI) through aqueous emulsion polymerization. Dodecylbenzene sulfonic acid (DBSA) was used as surfactant and dopant for the emulsion. CNCs and DBSA micelle concentrations, their structural organization and alignment with the monomer in the emulsion have a significant effect on the physical and mechanical properties of the resulting nanocomposite films with electrical conductivity reaching as high as 5.29 x 10^-1 S.cm^-1 which falls in the electrical conductivity range of Germanium (2.24 x 10^-2 S.cm^-1) and Silicon (0.43 x 10^-5 S.cm^-1) [S. L, Kakani, Electronics Theory and Applications, New Age International, 23-24, 2005.]. The CNCs-PANI-DBSA nanocomposite films show a maximum tensile stress and strain values of 22 MPa and 0.89 %, respectively and are significantly stronger and more flexible films than those obtained with, for instance, graphene/polyaniline composite paper or graphene paper, where it has been reported in the literature that the tensile strengths were 12.6 and 8.8 MPa, and maximum strains, 0.11 and 0.08 %, respectively [Wang et al., ACS Nano, 2009, 3, 1745].

CNCs, which can be regarded as strong acid polyelectrolytes, and the micelles formed by DBSA have both been shown to act as effective templates for aniline before initiation of the polymerization process. A stable suspension of CNCs-PANI-DBSA nanocomposite can be obtained depending on the micellar concentration of the surfactant used, and by changing CNCs and DBSA concentrations we could fine-tune the mechanical and electrical properties of the final nanocomposite films. Further doping with HCl has shown to alter the structural organization of CNCs in the nanocomposite film due to high ionic strength. However, enhancement in the mechanical properties attributed to CNCs as well as the electrical conductivity can be maintained. It is possible, of course, to use different dopants and produce flexible, organic semi-conducting films that retain chiral, nematic organization.

Our work shows that the mechanical and conductive properties can be tailored to suit the desired end-use application. This development provides promising sustainable organic materials for use in electronic and opto-electronic applications. Our in-depth investigation helps provide strong insights into the structure-property interrelationships of the sustainable, organic semi-conducting films.

Controlled self-assembly of colloidal particles upon drying can lead to crystalline solids where colloids are periodically distributed in space. However, the high order obtained is usually limited to specific crystalline domains, separated by weak boundaries where cracks can easily propagate [1].

Cellulose nanocrystals (CNCs) are naturally biosourced nanorods (length 100-200 nm and width 5-15 nm for cotton) that form stable colloidal suspensions in water and exhibit at high concentration a cholesteric liquid crystalline structure that can be retained in the dry state [2-3]. Such self-assembly generally leads to a porous, permeable but brittle membrane, showing intense and bright coloration.

In this work, we explored the co-assembly conditions of CNCs with Silk Fibroin (SF) to obtain flexible colored films, as it combines excellent biocompatibility, mechanical properties with optical transparency [4]. Importantly, we show that pH and silk/cellulose ratio adjustments are the key factors that enabled us to produce homogeneous films displaying structural colors and with enhanced mechanical properties. The natural ability for cellulose and silk to form an effective oxygen barrier, as recently reported, opens possibilities in bio-friendly, colorful, comestible and protective food packaging [5].


[1]. A. van Blaaderen and P. Wiltzius, Growing large, well-oriented colloidal crystals, Adv. Mat. 9 (10) 833 (1997).
[2]. J.-F. Revol, L. Godbout, and D.G. Gray, Solid self-assembled films of cellulose with chiral nematic order and optically variable properties. J. Pulp Pap. Sci. 24, 146–149 (1998).
[3]. A. G. Dumanli, G. Kamita, J. Landman, H. van der Kooij, B. J. Glover, J. J. Baumberg, U. Steiner and S. Vignolini, Controlled, Bio-inspired Self-Assembly of Cellulose-Based Chiral Reflectors, Adv. Optical Mater. 2014, 2, 646–650.
[4]. S. Kim, A. N. Mitropoulos, J. D. Spitzberg, H. Tao, D. L. Kaplan and F. G. Omenetto, Nature Photonics, (6) 818 (2012)
[5]. B. Marelli, M. A. Brenckle, D. L. Kaplan and F. G. Omenetto, Silk Fibroin as Edible Coating for Perishable Food Preservation, Scientific Reports, 6:25263 (2016)

The fovea centralis is a closely-packed vertical array of inverted-cone photoreceptor cells located in the retina that is responsible for high acuity binocular vision. The cones are operational in well-lit environments and are responsible for trapping the impinging illumination. We present the vertical light-funnel silicon array as a light-trapping technique for photovoltaic applications that is bio-inspired by the properties of the fovea centralis. We use opto-electronic simulations to evaluate the performance of light-funnel solar cell arrays. Light-funnel arrays present ~65% absorption enhancement compared to a silicon film of identical thickness and exhibit power conversion efficiencies that are 60% higher than those of optimized nanowire arrays of the same thickness although nanowire arrays consist of more than 2.3 times the amount of silicon. We demonstrate the superior absorption of the light-funnel arrays as compared with recent advancements in the field. Fabrication of silicon light-funnel arrays using low-cost processing techniques is demonstrated.

According to the reports provided by the National Centers for Environmental Information, almost 30% of the energy that is generated is used in the building sector, as a source of light. With the increase in population, there is an increase in the demand for energy consumption and generation. Therefore, it is highly important that we significantly reduce the energy consumption in the building sector. One way to reduce the energy consumption is by utilizing natural light using environmental friendly resources such as wood. Lignin accounts for almost 1/3^rd of the wood composition and gives color to the wood. Removing the lignin followed by impregnating environmentally friendly polymers whose refractive index matches the refractive index of the cell wall helps in obtaining transparent wood. The transparent wood is a potential candidate material for light transmitting building materials and transparent solar cell windows. Therefore, in this presentation we will be reporting a simple and low cost method of fabricating transparent wood from beech wood while retaining its 3-dimensional structure. The surface morphology of the synthesized transparent wood was studied by using scanning electron microscopy (SEM). Brunauer Emmet Teller (BET) measurements were carried out to determine the pore size distribution in the transparent wood template. Optical transmittance of the transparent wood was studied using UV-Visible spectroscopy. Hardness and tensile strength of the transparent wood were then examined to understand its mechanical properties. Detailed analysis will be discussed in the presentation.

Biomimetics based on photonic structures found in nature inspires unconventional design principles to create unique and highly functional dielectric-based nanophotonics [1]. On the other hand, plasmonic metasurfaces break the diffraction limits and localize light into subwavelength dimensions by coupling light with electron oscillations in metals with the aid of nanoscale metal-dielectric architectures [2]. Here, we combine a biomimetic design of random nanoholes with plasmonics to create a large scale flexible metal-dielectric metasurfaces for biosensing applications.

The plasmonic metasurface consists of densely and randomly distributed light-scattering aluminium (Al) nanohole-disk pairs that are fabricated by spin-coating a polymer blend, selectively performing chemical etches, and subsequently evaporating an Al layer. We studied the optical properties of the metasurface, including their dependence on its geometry to understand and demonstrate the tunability and versatility of their light-scattering and field-confining capabilities. We chose aluminium as our metal because of its low cost, easy fabrication and integration, and desirable optical response over the broad range of near-UV to near-IR wavelengths [3]. Moreover, the scatterers were engineered to have randomly distributed sizes on a single substrate. When this property was combined with the subwavelength field confinement, it allowed us to excite the scatterers using a broad range of tuneable excitation wavelengths and generate strong, enhanced fluorescence and Raman emissions. Using this metasurface, we have also demonstrated biomolecule sensing based on surface-enhanced fluorescence and Raman spectroscopy. Our promising results show that the metasurface with a unique bio-inspired architecture can serve as an inexpensive and versatile tool for in vitro as well as potentially in vivo biomolecule detection and characterizations.


References
[1] Vukusic, P., & Sambles, J. R. (2003). Photonic structures in biology. Nature, 424(6950), 852-855.
[2] Kildishev, A. V., Boltasseva, A., & Shalaev, V. M. (2013). Planar photonics with metasurfaces. Science, 339(6125), 1232009.
[3] Knight, M. W., King, N. S., Liu, L., Everitt, H. O., Nordlander, P., & Halas, N. J. (2013). Aluminum for plasmonics. ACS nano, 8(1), 834-840.

The formation of color is one of the most direct physical observations, that can easily made by eye and without laboratory equipment. The origin of color though can be manifold ranging from luminescence, fluorescence, strong and normal interference to structural color typical for biological systems. A prominent example of structural color in nature is the coloring of bird feathers, whose color does not originate from pigments but from the wavelength-selective interaction of light with network-based nanostructures on the feather barbs. In this work, we design and characterize a hybrid metamaterial, combining dealloyed subwavelength metallic networks with loss-less ultrathin dielectrics coatings. Using theory and experiments, we show how a sub-wavelength dielectric coating can be used to control the resonant coupling of light to localized plasmonic modes of the underlying nanomaterial. The designed metamaterial acts as a tunable highly efficient light trap in the visible, manifesting in the formation of structural color. The network-like architecture of the nanomaterial allows for efficient absorption of light even at angles above 50°, and is characterized by a remarkable scratch resistance.

In this contribution we will go into the possibilities offered by nano structured elastomers and other types of polymers to realize micro meter scale optical responsive actuators, and active photonic materials. In particular, we will go into the realization of photonic robotic structures that respond to light and obtain their energy entirely from optical sources. Also we will look into the possibilities that nature offers to create photonic responses that are based on sophisticated structures and patterns.

R. Middleton, G. Guidetti, B. Frka-Petesic, E. Moyroud, P. Rudall, B. Glover, S. Vignolini


Structural colour is a widespread phenomenon in nature, especially well known for producing dazzling colours in insects and feathers. The intensely bright coloration in the fruit of the Pollia genus comes from helicoidally structured cellulose in the cell wall which acts as a circularly polarised multilayer reflector [1].


This natural phenomenon suggests the tantalising prospect of replacing many traditional pigments with brilliantly reflecting nanostructured cellulose.Furthermore, cellulose nanocrystals can be extracted from natural sources such as cotton or woodpulp, and when dried from suspension in water self-assemble to form structurally coloured films very similar to the Pollia cell walls [2]. This has demonstrated cellulose films to be a promising viable future optical material [3].


Further to the nanostructure replicated in these biomimetic films, the fruit exhibits a hierarchical cell structure on the micron scale. Each cell in the exterior of a Pollia fruit reflects a single colour thanks to the ellipsoidal shape of the cell walls. A bright stripe or spot of a single colour is reflected from the central region of the cell. I present my research developing the artificial multilayer to perform new optical responses mimicking the microstructure of the Pollia fruit. This technique offers a a way to extend this nascent optical material beyond its current scope.


1 S. Vignolini, P. J. Rudall, A. V Rowland, A. Reed, E. Moyroud, R. B. Faden, J. J. Baumberg, B. J. Glover and U. Steiner, Proc. Natl. Acad. Sci. U. S. A., 2012, 109, 15712–5.


2 J. F. Revol, H. Bradford, J. Giasson, R. H. Marchessault and D. G. Gray, Int. J. Biol. Macromol., 1992, 14, 170–172.


3 A. Gumrah Dumanli, H. M. van der Kooij, G. Kamita, E. Reisner, J. J. Baumberg, Ullrich Steiner, S. Vignolini, ACS Appl. Mater. Interfaces, 2014, 6 (15), pp 12302-12306.

Compression therapy, in which bandages, wraps, or stockings are used to apply controlled pressure to a patient’s limb, is used to treat a number of maladies, most notably venous leg ulcers. Billions of dollars are spent annually on this type of therapy. It has been demonstrated that compression therapy is very effective, as long as applied pressures lie within a particular range (typically between 30 and 40 mmHg). Unfortunately, it is difficult to consistently achieve ideal levels of pressure, even for highly trained and experienced medical personnel. The resulting inefficiency prolongs treatment duration and is estimated to be responsible for the waste of up to $15 billion per year in the United States.
Recently developed elastomeric photonic fibers that demonstrate a shift in their reflected color with applied strain could form the basis for a simple colorimetric pressure indicator. By incorporating these fibers into bandages used in compression therapy, we enable the facile determination of local strain levels along the length of the bandage. Furthermore, we demonstrate that the strain in a compression therapy bandage is correlated to the pressure being applied to a patient’s limb. Combining these effects, we find that the incorporation of fibers into compression therapy bandages creates a simple method to determine applied pressure levels based on observed fiber color, consequently allowing for better control of pressure levels applied to patients’ limbs.
Current lab-scale procedures, based on rolling a spin-coated bilayer of transparent elastomers with different refractive indices around an opaque elastomer fiber core, limit the length of the resulting color-tunable fibers to about ten centimeters. Scaling of fiber manufacture is crucial to enabling translation of this promising technology into applications such as the colorimetric pressure indicators discussed above. We report on progress in scaling the length of manufactured fibers, having developed a novel technique to create longer fibers, which are meters or kilometers in length, with the same useful optical and mechanical properties as their shorter predecessors.
Our efforts will permit the manufacture on a commercial scale of bandages, wraps, and stockings for compression therapy that have fully integrated, predictable, repeatable, and easy-to-read colorimetric pressure gauges. Greater ease of use, shorter treatment durations, and the transition of the ability to monitor and adjust the treatment to patients will greatly reduce the cost of, and increase the effectiveness of, compression therapy.

Morpho butterflies display pronounced blue color using 1-dimensional (1D) photonic bandgap structure on their wings. Inspired by the Morpho, various 1D photonic crystals have been designed for structural color pigments, sensors, and photonic components. For example, angle-independent 1D photonic film can be fabricated by directionally depositing dielectric layers of silica and titania on monolayer of polydisperse silica nanoparticles which makes both the vertical and the horizontal disordered. However, most of 1D structures have been prepared in a film format which restricts the additional processing. Furthermore, each film has single periodicity, thereby developing single color. Thus, using 1D photonic structure as particle or granular format which can display multiple color is promising in various applications.
In this work, we report a simple, but robust method to create new type of photonic Janus ball on which the thickness of 1D photonic film stacked decreases depending on their orientation. This gradual decrease of the thickness causes blue shift and displays multi-coloration. To design the thickness gradient of 1D photonic film, alternating layers of silica and titania are stacked on black microspheres using sputtering deposition. The sputtering deposition enables dielectric materials to be deposited on surface with high directionality and creates thickness gradient on curved spherical surface. Also, the high directionality of physical deposition makes 1D photonic film stacked only on upper hemisphere of microsphere which makes them anisotropy. Additionally, to give magneto-responsive property on Janus ball, iron layer is deposited between the dielectric layers and microspheres. Ferromagnetic property of iron film enables Janus ball to be manipulated exquisitely under external magnetic field. Therefore, the structural color of the Janus ball is tunable by rotating Janus ball with magnet. This method only employs a layer-by-layer deposition technique which is highly controllable and prevents the defect formations. Moreover, directional deposition on the curved surface results in the gradient change of structural color which is otherwise very difficult to create in Janus microspheres.

Forming macroscopic three-dimensional materials with feature sizes on the order of hundreds of nanometers remains a technological challenge. Colloidal self-assembly is a promising tool to approach this problem. DNA-functionalized colloidal systems are of particular interest, since the free energy of DNA hybridization introduces an additional parameter to control the interaction potential between colloids in a highly selective and widely tunable fashion^{1, 2}. We have shown that DNA mediated colloidal self-assembly can be used to fabricate percolating gels with controlled feature sizes in the micron range for in both single and multicomponent systems^{3, 4}.

Here, we demonstrate that this approach can be scaled to create materials with feature sizes of hundreds of nanometers by decreasing the size of the colloidal building blocks in a novel materials system. A simple two-step process is introduced to functionalize silica nanoparticles using only covalent bonds. The method is applied to silica colloids spanning an order of magnitude in diameter. Percolating DNA-silica gels are demonstrated in a range of volume fractions and colloid diameters, and the gels are studied using confocal microscopy and image structural analysis techniques. This study is then extended to fabricate silica gels with pore sizes that interact with visible light and show angle independent structural color. Unlike many recently demonstrated colloidal routes to structural color, the color in this system arises from structure factor of the gels rather than the form factor of the individual building blocks, which can be ten to a hundred times smaller than the resulting pores.


1. C. A. Mirkin, R. L. Letsinger, R. C. Mucic and J. J. Storhoff, Nature, 1996, 382, 607-609.
2. A. P. Alivisatos, K. P. Johnsson, X. Peng, T. E. Wilson, C. J. Loweth, M. P. Bruchez and P. G. Schultz, Nature, 1996, 382, 609-611.
3. L. Di Michele, F. Varrato, J. Kotar, S. H. Nathan, G. Foffi and E. Eiser, Nature communications, 2013, 4, 2007.
4. Z. Ruff, S. H. Nathan, R. R. Unwin, M. Zupkauskas, D. Joshi, G. P. C. Salmond, C. P. Grey and E. Eiser, Faraday Discussions, 2015, DOI: 10.1039/C5FD00120J.

Growing evidence supports a critical role of metal-coordination complex crosslinking in soft biological material properties such as underwater adhesion and self-healing. Given their exploitation in such desirable material applications in nature, bio-inspired metal-coordinate complex crosslinking no doubt provides unique possibilities to further advance synthetic polymer materials engineering. Using bio-inspired metal-binding polymers, initial efforts to mimic these material properties have shown promise. In addition, novel opportunities for new fundamental insights on how polymer network mechanics can be strongly coupled to supramolecular crosslink dynamics are also emerging. Early lessons from studies of these supramolecular chemo-mechanical couplings will be presented.

Nature uses metal binding amino acids to engineer mechanical properties. An example of this engineering can be found in the mussel byssal thread. This acellular thread contains reversible intermolecular protein-metal bonds, which allows the mussel to robustly anchor to rocks, while withstanding the mechanically demanding intertidal environment. Inspired by this metal-binding material, we present a synthetic hydrogel designed to mimic this bonding behavior. The mechanical properties of this hydrogel can be controlled independently by manipulating the amount of metal relative to the metal binding ligand, and the gel’s pH. Here we report how high metal to ligand ratios and low pH can be used to induce the formation of a strong, slow relaxing gels. This gel has potential applications as an energy dissipating material, and furthers our understanding of the bio-inspired engineering techniques that are used to design viscoelastic soft materials.

Structural materials and stiff structures capable of showing large adaptability of properties for load carrying applications remain scarce in contemporary engineering systems. Shape memory alloys heavily reliant on nanometric properties to produce shape adaptability are a rare such example [1], however, these type of materials have restricted structural manufacturability, very slow adaptive response and limited environmental. Different types of self-shaping materials have been proposed mostly benefiting from the compliance of a soft matrix and the peculiar behaviour of its components [2]. In contrast, natural composites have evolved to develop hierarchical architectures yields specific properties. Those systems typically show remarkable adaptation upon environmental stimuli [3]. Incorporating natural design principles in synthetic composite plates, we demonstrate that fast movement and change in shape is feasible in stiff systems and for complex shapes. To achieve such behaviour, we exploit the response of micron-sized platelets to rotating magnetic fields of different orientations to build bistable plates exhibiting fast snap-through between two stable states in less than 200 ms and for curvatures up to 10 m^-1 [4]. Using a combination of platelets with different magnetization responses, we can in addition implement a structural actuation lead by static magnetic fields. In addition, functionalities inherent to the properties of the reinforcements are demonstrated through incorporation of anisotropic electrical conductivity through out the composite. These new structural hierarchically constructed composites, complemented with simulation models that effectively predict their behaviour, open the door to a large range of applications where external actuation is needed to yield a large and fast shape change. The fields of architecture, robotics, but also bio and tissue engineering and rehabilitation, machineries are anticipated to benefit from these structural composites.

Bibliography
[1] A. Lendlein and S. Kelch, "Shape-Memory Effect From permanent shape," Angewandte Chemie, vol. 41, no. 12, pp. 2034-2057, 2002.

[2] A. R. Studart, "Biologically Inspired Dynamic Material Systems," Angewandte Chemie International Edition, vol. 54, no. 11, p. 3400–3416, 2015.

[3] R. M. Erb, R. Libanori, N. Rothfuchs and A. R. Studart, "Composites reinforced in three dimensions by using low magnetic fields," Science, vol. 335, no. 6065, pp. 199-204, 2012.

[4] J. U. Schmied, H. L. Ferrand, P. Ermanni, A. R. Studart and A. F. Arrieta, "Programmable matter magnetically micro-reinforced multi-stable shells," in submission process, 2016.

Many of the physical properties of biogenic crystals originate from the presence of intracrystalline organic molecules within individual inorganic crystalline hosts. The presence of these molecules has been shown to strongly influence the crystalline host microstructure and structure to (anisotropic lattice distortions). Recently, by applying a bio-inspired approach, we have shown that similar microstructures and lattice distortions can be achieved in synthetic calcium carbonate crystals grown in the presence of organic molecules¹. However, no similar approach has been performed on non-calcium carbonate crystals. In this work, we utilize this bio-inspired approach so as to modify the crystal properties of functional semiconductor material^2,3.
We will show that amino acids can get incorporated into the crystal lattice of semiconductor hosts, similar to the process observed for calcium carbonate. Moreover, not only that such incorporation exists; the resulting lattice distortions are accompanied by a significant band-gap energy shift of the semiconductor host (in some cases up to 17%).
We will discuss possible mechanisms for this phenomenon and show that such bio-inspired organic/inorganic interfaces have much potential for the manipulation of not only structural properties of different crystalline hosts but rather of a variety of functional properties. Moreover, we believe that this research may open a new bio-inspired route for tuning the band-gaps of semiconductors in addition to the ones known and utilized to date.

¹ Borukhin S, Bloch L, Radlauer T, Hill AH, Fitch AN, Pokroy B. Screening the Incorporation of Amino Acids into an Inorganic Crystalline Host: the Case of Calcite. Advanced Functional Materials 2012;22:4216.
² Brif A, Ankonina G, Drathen C, Pokroy B. Bio-inspired Band Gap Engineering of Zinc Oxide by Intracrystalline Incorporation of Amino Acids. Advanced Materials 2014;26: 477.
³ Brif A, Pokroy B. Bio-inspired Engineering of Zinc Oxide/Amino Acid composite: Synchrotron Microstructure Study. CrystEngComm 2014;16: 3268.

Plant nanobionics aims to engineer living plants with non-native functions by interfacing plants with specifically designed and targeted nanoparticles. Herein, we design and demonstrate living spinach plants (Spinacia oleracea) as new materials and functional devices that serve as self-powered auto-samplers and pre-concentrators of analytes within ambient groundwater, detectors of the organic molecules contained therein, and infrared (IR) communication platforms that can send this information to a user’s smart phone. The design employs a pair of near infrared (nIR) fluorescent nanosensors embedded within the plant leaf mesophyll. One nanosensor is engineered through the Corona Phase Molecular Recognition (CoPhMoRe) technique using single walled carbon nanotubes (SWCNTs) conjugated to the peptide Bombolitin II to recognize nitroaromatics via IR fluorescent emission at > 1100 nm with a response time of 5-15 mins after introducing 400 μM of picric acid to the roots. The second IR channel is a polyvinyl alcohol (PVA) functionalized SWCNT that acts as an invariant reference signal. As contaminant nitroaromatics or dopamine in solution are transported up the roots and stem into the leaf tissues, they accumulate in the mesophyll where the pair of SWCNT sensors are embedded. This results in relative changes in the intensity of SWCNT emission, with a response rate that is mathematically described using a whole plant residence time model. The real-time monitoring of embedded SWCNT sensors also allows residence times in the roots, stems and leaves to be estimated, calculated to be 8.3 min (combined residence times of root and stem) and 1.9 min/mm leaf, respectively. We further show that this system is generalizable to the detection of other analytes, such as dopamine which is known to effect physiological changes in plants. These results demonstrate the ability of living, wild-type plants to function as chemical monitors of groundwater and communication devices to external electronics at standoff distances.

Access to biologically relevant signals provides significant challenges given the difficulties encountered when integrating technology with living tissue and wearable substrates. The challenges presented by the biotic/abiotic interface impose restrictions and limitations for the extraction of meaningful signals that represent physiological parameters and health states. A particular opportunity is offered by the use of naturally derived materials to generate devices that operate seamlessly at the interface of the biological and technological worlds. Silk fibroin is a very attractive biopolymer for use as the starting point for nanostructure optical materials and thin-film electronics. Devices such as silk-based photonic crystals, random lasers, fuel cells, wireless antennas and resorbable electronics will be described as some examples of the possibilities that this water-processed, biocompatible material offers.

Among many bioinspired materials, spider silk has attracted great attention from relevant scientists due to its unique and excellent properties arising from the combination of extreme toughness, great extensibility and biocompatibility. Production of spider silk by gene engineering pathway enables mass production as well as monitoring certain structure/morphology as desired. Thus recombinant spider silk can be applied in a wide range of applications, from medical to structural materials. To date, science has relative successes on synthesis of spider silk with similar molecular and higher-order structures but still suffers from its low stability under high temperature and humidity. The degradation of spider silk under critical conditions has not been clearly understood, mainly due to the complex nature from the molecular level to the higher hierarchical structure of spidroin, consequently leads to challenges in providing any stabilization strategy. In this study, recombinant spider silk was subjected to thermal degradation and the subsequent changes in structure and morphology were studied. By applying a series of characterizations in a systematic way, we are able to explain the major role of oxidation in spider silk degradation. The detailed results will be discussed in term of chemiluminescence analysis (CLA), thermogravimetric analysis (TGA), nuclear magnetic resonance spectroscopy (NMR), infrared spectroscopy (IR), X-ray photoelectron spectroscopy (XPS), and X-ray diffraction (XRD) techniques. Furthermore, correlation coefficient spectra were built to provide an entire picture of the thermo-oxidative degradation process of recombinant spider silk. The results revealed that the thermal degradation of spider silk includes preferential decomposition in the amorphous region, discoloration due to Tyrosine dimerization and formation of carbonyl due to oxidation.

The brown recluse spider (Loxosceles) spins high-aspect ratio silk ribbons unlike any other natural or synthetic polymer fiber. The ribbons are 6–8 μm wide and only 40–50 nm thin, corresponding to only a few molecular layers of protein. These dimensions thus approach the case of a “2-D protein material”, giving rise to a unique combination of properties. In terms of stiffness and strength, these ribbons rival the highest-performing silks previously reported. However, due to their extreme thinness, these ribbons can bend and wrinkle easily, which facilitates surface conformation to contacted objects and thus introduces exceptionally strong adhesion.
Using a unique spinning mechanism, the recluse spider uses this combination of properties to organize these 2-D silk ribbons into a 1-D metastructure of serial loops. The loop junctions based on self-adhesion of the ribbon can sustain extremely high forces but open non-destructively. The opening of such a sacrificial loop bond releases hidden length, relaxes the fiber, and restarts the stress–strain curve. This "strain cycling" can substantially increase the toughness of the material and change its tensile characteristics. We theoretically investigated the limits of this kind of stress–strain engineering via metastructure for both elastic and plasic materials and found that manifold toughness enhancements are possible. We demonstrated this kind toughness enhancement in a synthetic, bio-inspired looped ribbon design and found the measured performance in line with our predictions.

Nature’s materials display unique mechanical properties not only due to their composition, but also their complex nano- and microarchitectures. Nacre, with its complex layered architecture, is one such example. Many bio-mimicking approaches aim to reproduce nacre’s impressive mechanical properties, especially in terms of toughness. By designing the local morphologies of bacterially-produced, patterned organic-inorganic composites and inorganic samples, we can locally control their mechanical properties, such as stiffness, as well as the deformation modes, crack propagation and energy dissipation.

We have used bacteria to produce an organic-inorganic composite, with a layered microstructure resembling that of nacre. To mimic the stiff inorganic layer of nacre, we have used the bacterium Sporosarcina pasteurii to deposit a layer of calcium carbonate crystals (approx. 6 µm thick) onto a substrate. To mimic the ductile organic layer, we have used Bacillus licheniformis to produce a nanolayer made of polyglutamic acid. By alternating deposition of inorganic and organic layers, we have produced biomimetic nanocomposite materials, as well as control samples consisting of bacterially-produced calcium carbonate.

To evaluate the mechanical properties of our composites, we have used microindentation. Mechanical testing protocols involved load-controlled indentations with shallow depths (final indentation depth of 1.5 µm) and deeper indents, aimed at homogenising the mechanical behaviour of a few adjacent layers, taking into account load redistribution, crack deflection between layers and delamination (final depth of 6 µm). The samples’ stiffness (indentation moduli) and the relative amounts of dissipated energy in the indentation process, as well as the elastic energy recovered during unloading were quantified and compared for the bacterial organic-inorganic composites and the inorganic control samples.

The organic-inorganic composite samples tested were on average stiffer as compared to the inorganic control samples. Although no significant difference in the total energy of deformation was obtained, significantly more elastic energy was recovered in the unloading process in the layered composite samples. In contrast, more energy was dissipated during the deformation of the inorganic controls, as compared to the organic-inorganic composites. These data suggest that the organic layers in the composites may allow recovering higher fractions of the elastic energy of deformation by allowing for the relief of locally high stresses in the ductile organic layers.

This study shows the opportunities for designing materials, that can locally recover/dissipate deformation energy, by biologically mimicking the complex architectures of natural nacre. This approach will allow the fabrication of strong and tough materials in a green, economical and simple manner using bacteria.

Bacteria biohybrids employ the motility and power of swimming bacteria to carry and maneuver micro and nanoscale particles. They have the potential to perform drug and cargo deliver in vivo, but have been limited by poor design, reducing swimming capabilities and impeding functionality. To address this challenge, motile Escherichia coli (E. coli), were captured inside electropolymerized microtubes, exhibiting the first report of a bacteria microswimmer that does not utilize a spherical particle chassis. Single bacterium became partially trapped within the tube and became a bioengine to push the microtube though biological media at an average velocity of 5 µm s^-1. Microtubes were modified with 'smart' material properties for motion control, including a bacteria-attractant polydopamine inner nanolayer, addition of magnetic components for external guidance, and a biochemical kill trigger to cease bacterium swimming on demand. Swimming dynamics of the bacteria-microtube biohybrid were extensively quantified and compared to previous work using bacteria-microbead systems. The multifunctional microtubular swimmers present a new generation of biocompatible micromotors towards future micro-biorobots and minimally invasive medical applications.

Looking into the Nature, hair has numerous functions such as to provide warmth, adhesion, locomotion, sensing, a sense of touch, as well as it’s well known aesthetic qualities. This work presents a computational method of 3D printing hair structures using commercially available stereolithography machine. It allows us to design and generate super dense hair geometry at 50 micrometer resolution and assign various functionalities to the hairy surface. The ability to rapidly fabricate customized hair structures enables us to create fine surface texture; mechanical adhesion property; new passive actuators and touch sensors on a 3D printed artifact. As the resolution of 3D printing machine is improving rapidly, we believe this method can be easily scaled up to design and fabricate new functional material surfaces with tunable properties.

By controlling structure across multiple length scales, new architected ceramics with unique properties can be created. Specifically, we explore the ability to fabricate ultra-lightweight ceramics via 3D printing. We will first describe the development of novel ceramic inks that enable printing of hierarchically designed materials. We will then demonstrate the fabrication of architected ceramics over a broad range of densities with hierarchical features. Finally, we will characterize their mechanical properties and establish a correlation between their composition, geometry, and characteristic feature/cell sizes.

Biological composites, like nacre and bone, have captured the interest of the scientific community for their outstanding ability to amalgamate a host of properties such as stiffness, strength, toughness, and impact resistance. Nacre which is composed of 95 wt.% mineral content and 5 wt.% soft polymeric matrix has a toughness orders of magnitude great than its mineral phase while having to sacrifice very little in stiffness. As a result, researchers aim to mimic the structure of nacre composites and showed excellent material properties compared to its base materials. However, most of the simulations and experiments of nacre-like composites are confined to simple tension or compression loadings. We hypothesize that nacre-like composites have superior impact performance compared to their monolithic stiff phase. Here, we studied nacre-like designs using two base materials that are vastly different in properties and structured them in a ply with a nacre-like architecture. These plies are then stacked in different sequences and repeated to generate a laminate. Impact test of 3D-printed designs were conducted in a drop tower setup and a finite element model is also created to compare to experiments and understand underlying mechanisms seen during impact. Our experimental and simulation results show that nacre-like designs outperform its bulk materials in impact resistance. This study demonstrates that the emerging 3D-printing technology can enable rapid prototype towards hierarchical polymer composite designs with optimal impact-resistant properties, viable for future expeditionary materials-on-demand of lightweight structural components, including but are not limited to emerging helmet and body armor designs.

The engineering and construction of tissue mimics continues to be a primary challenge in synthetic biology. The development of synthetic tissues, form entirely artificial components, presents an innovative methodology to rebuild the functions of life within artificial materials. While a substantial effort has been invested in the design of artificial cells and cell membranes, assemblies of interacting protocells, to construct tissues, have been lightly explored, and thus, the presented work is an advance in this direction. Achievement of functional droplet-based tissues is dependent on (1) the ability to mass produce robust and durable aqueous droplets, (2) and the ability to connect the compartments and to allow them to interact. Mass production may be achieved via three-dimensional printing, and therefore, the development of a 3D printer capable of printing a large number of aqueous droplets in oil, is needed.

In this work, we present the development and design of a 3D printer for the automated production of droplet-based 2D and 3D materials. This is achieved by modification of the commercially available 3D printer. The tool head, that comes with the printer, is replaced with a piezoelectric droplet generator, which is be designed and built in the lab. The droplet generator consists of an acrylic chamber capable of containing a certain volume of an aqueous solution. On one side of the chamber a piezoelectric transducer will be glued. On the other side of the chamber, and opposing to the transducer, a rubber adapter is fitted through a small hole, and into the adapter a pulled glass capillary is inserted. The aqueous solution, contained within the chamber, travels through the glass capillary due to capillary action. The water, however, stops at the tip, which is 100 µm in diameter, due to surface tension. To generate a droplet, a pulse is applied to the droplet generator and due to vibrational shocks in the aqueous solution, micron-sized droplets are released into bulk oil. Upon release of the aqueous droplets in the oil reservoir, containing DPhPC lipids, a lipid monolayer forms at the water-oil interface of each droplet. Neighboring droplets are connected by means of lipid bilayers, which could also host various types of biomolecules. A ten-by-ten-by-three array of aqueous droplets is printed in a bath of temperature-sensitive organogel formed from silicon oil, hexadecane, and SEBS triblock copolymer. Upon cooling, the organogel solidifies to form a liquid-in-gel, tissue-like material. To study the functionality of the material, alamethicin peptides are incorporated within the lipid bilayers, and activated through application of electrical potential.

Taking clues from nature, we are interested in understanding the design rules employed by nature and applying these strategies to the development of mechanically-enhanced and tunable materials. Fiber constructs are prevalent in natural systems, from collagen fiber networks in tendon to tough spider silk fibers. With these bio-inspired cues, we are intrigued by the impact of synthetic fiber orientation, nanostructure, alignment, manufacturing, and reinforcement on mechanics and functionality.

Recent innovations in multilayer co-extrusion technology have translated to the fabrication of melt-extruded polymeric rectangular fiber mats and composites. Distinct advantages of this modular approach over other traditional fiber processing techniques include scalability, environmentally-friendly conditions, and the ability to obtain cross-sectional dimensions on the nanoscale. Here, we describe the mechanics and structural features of biologically-relevant, high surface area, and functional fiber mats. We also focus on this fiber technology as a new platform for the development of reinforced hydrogels via an in situ approach. This manufacturing strategy allows for exquisite control of hydrogel architecture, fiber alignment and loading, compressive stability and stiffness. Promising results related to cell adherence, growth, and differentiation are highlighted for these extruded hydrogel scaffolds.

Self-assembly was first conceptualized in the field of molecular chemistry, but has since expanded to the bottom-up design and construction of nano- and micro- meter scaled structures. Today, self-assembled morphologies are ubiquitous in microelectronics, nano- and even bio- technologies. Despite extensive research progress, scales of assembly continue to be limited by material dimensions and requirements for localized inputs of energy. To overcome such limitations, we drew inspiration from the Mimosa (Mimosa pudica)’s ability to dynamically respond to a distinct pinpoint stimulus. Contact stimulus in the Mimosa plant triggers electrical potentials and cascading waves of osmotic pressure driven motion, resulting in large-scale shape transformation. Here, we present the Mimosa-Origami Effect, which demonstrates the rapidly cascading self-organization of soft materials into centimeter-scale 3D geometries. To achieve this, we designed and integrated highly surface active soft materials with enhanced surface areas (SSA). This culminated in the synthesis of physically distinct superhydrophilic-superhydrophobic Janus nanofibrous bilayers. The optimally developed material is highly wetting-responsive, readily liberating surface energies for the on-demand triggering of mechanical motion. Further geometrical optimization bestowed capabilities for the dynamic propagation of a single pinpoint water stimulus along a predetermined axis. In this design, the rapid axial transmission of the pinpoint stimulus occurs alongside cascading orthogonal local material responses. The axial motion is attributed to capillary/Laplace pressure, which occurs sequentially with local shape reconfiguration, driven by enhanced elastocapillary folding. These rapid axial responses (2.5 cm s^-1), coupled with its ability for centimeter-length (ca. 10 cm) self-assembly, is reminiscent of the Mimosa’s shape transformations upon stimulation. These SSA-enhanced material responses are strong enough to navigate right-angled corners, T-junctions and tapered curves. To the best of our knowledge, the Mimosa-Origami Effect represents the first macroscopically-scaled self-assembly of soft materials, powered by Laplace-elastocapillary coupling along a predetermined path. This on-demand directed self-organization behavior holds immense potential for sensing, micro-robotics and microfluidic technologies.

Curli nanofibers produced by E. coli represent a versatile scaffold for displaying a variety of affinity tags, binding domains, catalytic sites, and other functional protein domains. Naturally part of E. coli biofilms, curli nanofibers are tens or hundreds of microns in length by only a few nanometers in diameter and are extremely resistant to harsh environments. While they can be engineered as part of biofilms to produce living materials, curli nanofibers can also be extracted from biofilms and purified as fibrous nanomaterials. Producing such versatile biologically-derived materials could be useful for several biomedical and biotechnological applications, but traditional protein purification methods do not allow for the isolation of sufficient quantities of protein nanofibers. Here, we report the development of a novel filtration-based process for isolating quantities of curli protein nanofibers from E. coli biofilms, and the use of these purified nanofibers to assemble various macroscopic materials including thin coatings, free-standing films, hydrogels and aerogels.
E. coli bacteria were engineered to produce curli nanofibers that can be directly secreted in the culture medium, and that spontaneously aggregate to form large fibrous structures. These large nanofiber aggregates can be separated from bacteria and other debris via size exclusion using vacuum filtration. This filtration purification process allows for the production of tens to hundreds of milligrams of curli nanofibers per liter of bacterial culture. The resulting purified fibers can be used directly on filter membranes or collected to assemble novel curli-based materials. Examples of fibrous materials fabricated using this process include free-standing curli fiber films obtained after dissolving the filter membrane support, hydrogels containing engineered curli fiber proteins capable of forming crosslinks or entanglements, and dried aerogels or paper-like films that can be used to imprint nanoscale surface features. Since several functional tags or proteins domains were observed to remain active throughout the purification and materials assembly process, potential applications are broad for curli-based materials.

Natural structural materials such as insect cuticles, crustacean shells and mollusk nacres often owe their remarkable mechanical properties to the highly ordered organization of chitin nanofiber network embedded within a protein matrix. This hierarchical structure involves several length scales, from the chitin molecular chain alignment, protein wrapped chitin fibrils, sheets of branching network of fiber bundles, to plywood structure composed of these stacked sheets. We have previously shown that chitin nanofibers self-assemble inside a silk matrix yielding a biocomposite, which mimics, on the molecular level, the organic phase of the insect cuticles and the exoskeleton of crustaceans. Here, we expanded our work by exploring the use of electric field-directed assembly of chitin-silk materials to design anisotropic biocomposites. A combination of scanning electron microscopy and polarized optical microscopy was used to confirm the anisotropy of the chitin-silk biocomposites. In addition, our biomimetic composite demonstrates stiffness dependence on the direction of the stress applied with respect to the nanofiber alignment direction. Together, these results suggest that electric field-directed assembly of chitin-silk biocomposites may be used as a technique to fabricate mechanically robust, anisotropic biocomposites as a closer mimic to its nature counterpart.

This study focuses on the structure-properties relation of a new class of sustainable bio-composites with matrix made from fungal mycelium. The mycelium, which consists of a random network of bio-filaments, binds randomly distributed reinforcements such as agricultural waste particles to form the bio-composite. We aim to identify the system parameters that control the mechanical behavior of these materials and to develop relevant material design rules. To this end we have characterized the density, degree of cross-linking and filament branching density of the network and observed the dependence of these parameters on the mycelium growth conditions. Further, we developed models of the network to relate its structure to the mechanical properties. The model predictions were compared with mechanical test data to conclude that the mycelium matrix behaves similar to open cell foams. Moving up to the scale of the bio-composite, we performed mechanical tests and used the results to validate a continuum-level model of the composite. Further, the multiscale model has been used to perform a parametric study in order to identify the key structural parameters that can be used to control the macroscale material performance.

For patients who suffer from sensorineural hearing loss (SNHL) by damaged or loss of hair cells in the cochlea, biomimetic artificial cochleae to overcome the disadvantages of existing implant systems have been widely studied. In this work, a novel concept of flexible inorganic-based piezoelectric acoustic nanosensor (iPANS) for the purpose of a biomimetic artificial hair cell to mimic the functions of the original human hair cells is introduced. A trapezoidal silicon-based membrane (SM) mimics the function of the natural basilar membrane for frequency selectivity, and a flexible iPANS is fabricated on the SM utilizing a laser lift-off technique to overcome the brittle nature of the inorganic piezoelectric materials. The vibration amplitude vs piezoelectric sensing signals are theoretically examined based on the experimental conditions by finite element analysis method. The SM is successful at separating the audible frequency range of incoming sound, vibrating distinctively according to varying locations of different sound frequencies, thus allowing iPANS to convert tiny vibration displacement of ≈15 nm into an electrical sensing output of ≈55 μV, which is close to the simulation result. This conceptual iPANS of flexible inorganic piezoelectric materials could open the new fields of nature-inspired biomimetic systems using inherently high piezoelectric charge constants than those of organic polymer-based piezoelectric materials.

Inspired by the marine mussel strategy of adhesion in aqueous environments, catechol-functionalized polysiloxane (CFPS) was synthesized and further used as a platform to adhere silver nanoparticles (AgNP) and applied for Surface enhanced Raman scattering (SERS). Four functional 1,3,5,7-tetramethyl-cyclotetrasiloxane (TMCS) and two functional 1,3-divinyltetramethylsiloxane (DTMS) were first polymerized into linearly structured polymers by controlling the monomer feeding ratio and were subsequently functionalized with vinyl-terminated catecholic derivatives. Because both condensation and functionalization processes are based on hydrosilylation reaction, the entire synthesis procedure can be completed simply in a one-pot reaction. The polymerized TMCS in each repeating unit has two remaining silicon hydrogen bonds, thereby ensuring a high concentration of catechol units which results in a strong adhesion force to anchor silver nanoparticles (AgNPs) toughly. At the same time, nice biocompatibility of polysiloxane makes it a perfect polymer backbone to serve as a SERS substrate which is a powerful bio-analytical method.
It is more interesting that CFPS affords versatile coating on numerous substrates not only on the solid substrates like glass slide or quartz but also on flexible polymer substrates e.g. PMMA, PI, and PET with a finely controlled film thickness and surface roughness. This makes preparation of flexible SERS substrate possible, which is under highly demand for the in-situ testing that detects directly on the irregular shaped fruits vegetables or animal skins. More importantly, as a polymer binder, CFPS may anchor AgNP on its surface strongly thus generates an ultra-stable surface. In the experiment we used a transparent 3M Scotch Tape® to peel off the surface of AgNP/CFPS repeatedly, not even a little AgNP can be peeled off during the whole procedure. This property ensures in-situ SERS substrates made by our method could be repeatedly used.
Moreover, the surface number density of AgNPs can be tuned easily by changing the AgNP dispersion concentration. It has been well studied that SERS effect is mainly caused by localized surface plasmon resonance: the SERS signal is generated by the roughed silver structure, for instance, a gap between highly attached AgNPs. These structures are commonly called as “hot spot”. Resulting from a tunable concentration of AgNPs, the hotspot concentration of CFPS/AgNP assembly may also controllable. Thus it is also an enhancement tunable SERS substrate. The enhancement factor of the CFPS/AgNP assembly SERS substrate reached as high as 7.89×10⁷ with a sensitive detection limit of 10^-10 M using PATP as probe molecular. An in-situ testing on an apple skin was also conducted. The work demonstrates the design of a flexible polymer binder that enables to prepare a truly useful SERS substrate with a facile method.

Objective: To determine the optimal nacre-like geometry to promote toughness and crack resistance in 3D printed composite materials, and to create a geometry that is, like nacre, tougher than each of the constituent materials alone.

Abstract: Nacre is a naturally occurring material in seashells that garners interest for its high toughness and resistance to crack propagation. Nacre’s geometry occurs on the order of microns in nature as a brick-and-mortar structure that is replicated into a large patterned arrangement. This experimental study mimicked the geometry on a larger scale, using additive manufacturing with plastic polymers, to determine if the toughening mechanism still exists. Variations on nacre's geometry were studied using a stiff and soft 3D-printed polymer in place of nacre’s aragonite and biopolymer, respectively.

The two parameters tested were the volume fraction of stiff material and the presence of mineral bridges across the material's soft interface. The specimens were then tested for strength and toughness in tensile fracture tests. Preliminary results show a positive correlation between stiff volume fraction and strength, while maximum toughness occurs at a volume fraction between the two extremes. Additionally, the presence of mineral bridges significantly increases the strength of the material, without sacrificing significant flexibility or elasticity. Further results and simulations show which combination of these variables optimizes the material's performance.

3D printing is a fast and cost-effective way to build composite specimens from computer-generated designs for experimentation. This method allows for a complete picture of crack propagation and failure that cannot be achieved by computer simulation alone. Simply by changing the architecture of the constituent materials, these results could yield benefits in producing high-quality composites from low-cost components.

Our group is exploring the use of biological phenols and polyphenols as building blocks in the design of advanced materials with unusual dynamic and responsive physical properties. The use of biological phenols/polyphenols is also attractive because of their diverse and interesting biological properties such as antiproliferative, antiviral and anti- inflammatory activities. Here, we aim to employ polyphenols such as tannic acid, ellagic acid, and nordihydroguaiaretic acid as linkers in dynamic polymer networks formed by complexation with boronic acid containing polymers. The dynamic covalent boronate ester (BE) bonds formed between o-dihydroxyphenyl functional groups of multivalent phenols/polyphenols and boronic acid polymers produce hydrogels with interesting physical properties. Mixing of branched boronic acid terminated poly(ethylene glycol) (PEG) mixed with polyphenol cross-linker resulted in self-healing hydrogels due to the dynamic nature of BE bonds. The chemical composition of the boronic acid strongly influenced the physical properties and physiologic stability of the gels. BE linked hydrogels are stable under physiological conditions, however they dissociate at mild acidic conditions due to the pH dependence of BE bond stability, offering an opportunity to achieve pH-dependent release of biologically active polyphenol compounds.

It is well known that nanostructures with certain refractive index are periodically arranged to produce a structural color, which is called photonic crystals (PhCs). Structural coloration has been attractive due to their high reproducibility, mechanical stability, and economic feasibility compared to pigments-derived coloration. In this work, we report on a technique for generation of structural color which is implemented by tuning the periodicity of TiO₂ nanobowl arrays (TNAs).
TNA has appropriate refractive index to produce a structural color, as well as it is cheap and offers high controllability. Prepared TNAs show distinct structural colors from indigo to red resulting from increase in diameter from 41 nm to 106 nm. The morphology and size of the resulting films were characterized by a field emission scanning electron microscope. The reflectance spectra were obtained by an ultraviolet-visible diffuse reflectance spectroscopy.
Bragg diffraction theory, derived from the constructive interference, is used to predict structural color of TNAs. It shows that the structural color of TNAs strongly depends on the structural parameters rather than a refractive index of TiO₂. In order to investigate scalable application, large-scale color printing was achieved on a thin metal substrate. A reproduced Mondrian painting with centimeter scales shows high reflectivity and stability under the sunlight irradiation and toxic solvents. Consequently, color printing technique thorough TNAs indicates a potential alternative method for practical applications for color display, barcode, and anti-counterfeit tags.

Superhydrophobic surfaces biomimicking lotus leaves have been extensively studied and applied for various fields for a long time. In recent years, the non-wetting property of superhydrophobic surfaces submerged in water has attracted much attention because it has potential applications in drag reduction, anti-fouling anti-corrosion, water proof devices, microchannels, anti icing and other non-wetting related application. Drag reduction, one of the applied field, has become a serious issue in terms of energy conservation and environmental protection. Among diverse approaches for drag reduction, superhydrophobic surfaces have been mainly researched due to their high drag reducing efficiency. In superhydrophobic surfaces, it is known that the presence of an air (or gas) interlayer on the submerged surface causes the non-wetting behavior, and thus, stability of underwater superhydrophobicity is determined by the life time of the air interlayer. However, the air interlayer is highly unstable with limited life time due to the diffusion of the air gases into water. According to previous researches, the gas diffusion rates are mainly determined by surface characteristics (surface morphology and surface energy) and hydrostatic pressure. Various surface structures such as mesoporous structures, nanowire arrays, and micro/nano hierarchical structures, have been reported to enhance the lifetime of the air interlayer. However, despite those diverse studies, they could not overcome the impermanence of the air interlayer. This work presents a breakthrough in improving the underwater stability of superhydrophobic surfaces by optimizing nanoscale surface structures using SiC/Si interlocked structures. The effects of the surface structures on the stability of the underwater superhydrophobicity were investigated by measuring the lifetime of the air interlayer for three different structures: SiC nanowire arrays, Si micropost arrays and SiC/Si hierarchical structures. SiC/Si hierarchical structures have an unequaled stability of underwater superhydrophobicity with a lifetime of plastron over 18 days. To evaluate the drag reduction properties of the superhydrophobic SiC/Si hierarchical structures and their SLIPS samples, double sided superhydrophobic surfaces immersed in water to move along the tilted water filled tank. By changing the angle of water tank to change the velocity of samples, drag reduction ratio is 56% in maximum velocity. Furthermore, through photoelectrochemical water splitting on a hierarchical SiC/Si nanostructure surface, the limited lifetime problem of air pockets was overcome by refilling the escaping gas layer, which also provides continuous drag reduction effects.

Drop-on-demand (DOD) inkjet technology refers to delivering microdroplets on a desired location and has several distinguished advantages for fabrication of micro patterns over the conventional method. Thus, this has come into spotlight as a fabrication tool with functional materials. In DOD inkjet printing systems, droplet formation frequency is a primary parameter because high throughput formation of microdroplets is directly linked with high productivity. In this work, the droplet frequency of our previously developed pneumatic DOD printing system is improved by the application of a superhydrophobic surface at the nozzle. The superhydrophobic surface was obtained by a metal-assisted chemical etching technique.
In our printing head, applied pressures deflect a flexible membrane between rigid parts to squeeze a liquid chamber. A negative pressure opens the chamber for liquid filling. Instantly, a positive pressure is applied to close the chamber and eject the liquid. A bump structure of the chamber stops an undesired backflow. The head composes of silicon, glass, and PDMS layers fabricated by micromachining techniques. The droplet formation process was captured by high speed camera to analyze the droplet formation.
To fabricate a superhydrophobic nozzle, silver nano-ink was deposited by spin-coating on the silicon part including the nozzle (65 µm in diameter). After sintering, nanoscaled clusters were formed on the silicon surface. The silicon part was immersed in the etching solution: a mixture of water, hydrofluoric acid (HF), and hydrogen peroxide (H₂O₂). The silicon under coated clusters was dissolved with the help of silver catalyst and numerous nanoscaled pores with height of 1 mm were covered. To remove silver clusters, it was dipped in a diluted nitric acid (HNO₃). The nanostructured surface attained superhydrophobicity (contact angle > 170°) after self-assembled monolayer (SAM) coating. Two printing heads were prepared with the nanostructured nozzle and the bare nozzle. A 60% glycerol solution containing 0.14 gL^-1 Triton-X surfactant was used as a printing liquid.
During a droplet formation, most time is taken to retract a residual liquid into the nozzle after pinch-off from a stretched liquid filament. In droplet formation process with the bare nozzle, 80% of a total formation time was consumed to retract the residual liquid. The averaged required time to form a droplet was 9.9 ms and the maximum allowable frequency was 100 Hz. By the application of the nanostructured nozzle, the retraction time decreases up to 70%. The averaged required time to form a droplet and the maximum allowable frequency were 7.2 ms and 138 Hz, which is 18.5% increment compared to the bare nozzle.
This research was supported by a grant of the Korea Health Technology R&D Project through the Korea Health Industry Development Institute (KHIDI), funded by the Ministry of Health & Welfare, Republic of Korea (grant number : HI15C0001).

In nature, control of the heterogeneous nucleation and growth of water droplets on a surface has been crucial for survival and proliferation of the bioorganisms. For example, in extremely arid habitat such as the Namib Desert, beetles Stenocara sp. capture and collect water from the early morning fog on their backs, consisting of hydrophilic/hydrophobic wettability pattern. Since the free energy barrier for the droplet formation and nucleation rate are strongly governed by the intrinsic wettability of surface, wettability contrast between different regions plays a critical role in determining where droplet nucleation and growth occur selectively. In order to realize such wettability pattern, we fabricate hierarchical polymer pillar arrays templated from a hierarchically porous anodized aluminum oxide (AAO) membrane. First, a microporous epoxy membrane (pore diameter of 10 - 100 μm) is placed on an aluminum plate as the anodization mask to direct AAO nanopore (300 nm in diameter) formation within the micropores. The hierarchical AAO template is then replica molded into polyurethane acrylate and epoxy. The combination of micro-and nanostructures dramatically increases the wettability contrast and surface roughness vs. the non-patterned regions. On such surfaces, water droplets are found to nucleate and grow selectively in the grooves between the microposts as the vapor pressure increases. In contrast, surfaces consisting of microposts or nanopillars only do not show such selectivity. Since the roughness of nanopillars is much smaller than the initial water droplet condensed from atmosphere (~1 - 40 μm), they can prevent the nucleation of water droplets within or on top of nanopillars. In addition, because the nanopillars sit only on top of the microstructures, thus, they are isolated from each other, which further prevent water nucleation. Importantly, the spatial selectivity of water nucleation and growth demonstrated here is achieved solely by structural hierarchy on a chemically homogeneous surface.

Creating artificial biomimetic materials with multiple functions similar to those of living bodies is an important frontier for advanced society in near future. Electromechanical coupling is one of the important functional properties of several classes of organic and bioorganic materials and is one of the essential features of biological and living systems. It is based on the complex dipolar properties and dipole-dipole interactions conjugated with hydrogen bonds network in biomolecular systems with different levels of self-assembly and hierarchy. Among these systems, amino acids are the most important ones as they are used as building blocks for proteins and peptides. It has been long known that α-glycine crystals are centrosymmetric and thus do not exhibit any property described by the 3^rd rank tensor, such as piezoelectricity or second harmonic generation (SHG). On the contrary, γ- and β-glycine polymorphs are strongly noncentrosymmetric and, therefore, can be used as biocompatible nonlinear optical and piezoelectric materials. In addition, recently observed room-temperature ferroelectricity in glycine [1] opens up new perspectives of using this material in biocompatible electronic devices.

In this work, we study the formation and properties of β-glycine nanoislands prepared by spin-coating. Self-assembly of these nanoislands occurs under the influence of centrifugal force with concomitant increase of the stability of ferroelectric β phase and apparent piezoelectric and ferroelectric properties. Piezoresponse Force Microscopy studies have shown electrical switchability of the β-glycine nanoislands. The microRaman studies were conducted to confirm the orientation and formation of the β-phase. It is shown that spin-coating can be used for the nanopatterning of organic ferroelectrics grown from solution and that their functional properties can withstand miniaturization without notable size effects.
The work has been funded by the Portuguese-NSF grant FLAD 299/2015 and RFBR, according to the research project No. 16-32-60188 mol_a_dk.
[1] A. Heredia et al, Adv. Func. Mater. 22, 2996 (2012)

Layered double hydroxide (LDH) are hydrotalcite-like minerals which have potential for fabricating bioinspired nanocomposites. In the present study, LDH nanomaterials containing calcium ions in the framework (Ca-LDH) were synthesized and their surface was further coated with enteric polymer, Eudragit®L 100 in order to protect nanomaterials against acidic gastric condition. The X-ray diffraction patterns, Fourier transform infrared spectroscopy, and transmission electron microscopy revealed that hydrocalumite-structured Ca-LDH was well prepared and that the polymer effectively coated the surface of Ca-LDH without inducing structural change. Thermal analysis demonstrated that less than 1% of polymer was coated on the Ca-LDH, however, its metal dissolution property significantly decreased upon polymer coating in simulated gastric and enteric fluids. Intracellular calcium concentration significantly increased in human intestinal cells after Ca-LDH treatment without causing cytotoxicity up to 1000 μg/ml. Pharmacokinetic study showed oral absorption efficiency of polymer coated Ca-LDH in rats. Furthermore, Ca-LDH did not exhibit acute toxicity in rats after single-dose oral administration up to the highest dose tested. These findings suggest the great potential of LDH nanomaterials as mineral supplements.

Preparation of cellulose/chitin nanowhiskers, which have been gaining much more attention as reinforcing fillers because of its large resource, superior physical properties with light density, large aspect ratio rarely found in mineral substances and so on, essentially depends on aqueous conditions including acid hydrolysis and subsequent homogenization in water. The obtained nanowhiskers indicate strong cornification (keratinization) on drying to form an irreversibly aggregated solid film. With this state, it is very difficult to apply cellulose nanowhisker to a promising functional filler for polymer materials.
In contrast to the conventional aqueous preparation scheme, the authors have developed a non-aqueous route to disaggregative fine powders of nanowhiskers. The process modification we have added is quite simple, that is solvent exchanging after acid catalyzed hydrolysis of cellulose form water to low dielectric organic solvents. The aims of solvent switching are below.
1. to reduce cohesive force (capillary force) on drying.
2. to utilize friction triboelectric charging in dielectric medium for repulsive force between nanowhiskers.
3. less heat of evaporation and high concentration process therefore the process is energy efficient.
The sample could be obtained via a homogenization of cellulose hydrolysate in, for example, toluene to give a slurry-like suspension, which remained a fine powder containing nanowhiskers even after a simple air-drying. The suspension is also useful for further surface modification of nanowhiskers such as controlled radical polymerizations with particles (CRPwP). These newly developed nano-cellulose can be a promising fillers for polymers. And of course the powder cellulose nanowhisker is convenient for food nad medical purposes because no surfactant and dispersant was added.

Many marine organisms employ organic additives to direct the synthesis of a wide range of calcium carbonate structures vital for survival in their environments. These structures vary from amorphous calcium carbonate (ACC) composites all the way to hierarchical crystalline structures with fascinating mechanical properties. These organisms exploit the versatility of ACC’s interactions with the organic matrices to assemble, shape and crystallize calcium carbonate on-demand. Understanding the complex interactions between the mineral and organic phases, and their effect on the mechanical properties of these structures, is vital for the development of new bioinspired materials.
In this work, the influence of the organic matrix on the stability and nanomechanical properties of ACC composites is studied through a suite of calorimetric and spectroscopic techniques, as well as nanoindentation tests. ACC composites are synthesized and stabilized in solution using biomimetic polymers rich in carboxylic groups. The ACC composites exhibit remarkable stability both in solution, as well as in a dry state, depending on the polymer content. The mechanical properties of the ACC composite are tested by growing films on a template surface using a continuous flow cell. Extensive characterization of these films reveal a strong interaction between the polymer and mineral phase and a strong correlation between the polymer content and the degree of amorphization of the composite. Our approach aims to provide new insights into the mechanism through which marine organisms exploit the versatile nature of ACC to fabricate tunable calcium carbonate products.

Tunneling and charge hopping are two well-understood mechanisms of short-range electron transport and transfer in biological systems, but long-range electron transport is rare in biology. Such long-range conduction has been observed in extracellular appendages, known as pili, produced by the anaerobic exoelectrogenic bacteria genus, Geobacter. Electronic transport through pili potentially represents a novel mechanism for conduction through proteins. To better understand this conduction paradigm, we have designed bioinspired, repeat-unit peptides that self-assemble into coiled-coil oligomers and higher order nanostructures. The sequence tunability of these peptides makes them an ideal experimental platform for studying the structure-function relationships in electronically conductive, amino acid-based materials.
The designed de novo alpha-helical peptides self-assemble into an antiparallel hexamer, which further stack end-to-end by electrostatic interactions into pilus-like nanofibers. At higher concentrations, the peptides are driven by non-specific hydrophobic interactions to formbranched hydrogel networks. Solid state I-V characteristics and electrochemical gating measurements show that these peptide fibers are conductive over a range of pH and ionic strength, demonstrating physiologically robust electron transport. Conductivity through fiber networks increases with decreasing temperature, a trend opposite to that expected for charge hopping, yet charge is carried over several microns, orders of magnitude further than distances associated with tunneling. Electronic measurements reveal that hydrogel networks formed from the peptide are also conductive, though the conductivity does not scale monotonically with peptide wt%, suggesting the importance of peptide packing in determining electron transport. These bioinspired peptides and their fiber and gel morphologies serve as a promising platform for understanding mechanisms of long-range electron transport in nature and as potential building blocks of bioelectronic devices.

Although hydrogels have superior characteristics over other supports for enzymes, including high water contents and 3D microstructure, their weak mechanical properties and/or harsh preparation conditions make their use as supports limited. In the present work, tough and stable hydrogel as protective reaction matrix for enzyme, m-ngCA-silk hydrogel, was developed through bioinspired dual-crosslinking, photochemical dityrosine crosslinking and dehydration-mediated physical crosslinking (β-sheets formation), of silk fibroin and carbonic anhydrase from Neisseria gonorrhoeae (ngCA). Through bioinspired and rapid dual-crosslinking strategy, up to 1800 μg ngCA was immobilized within 10% (w/v) silk hydrogel, and m-ngCA-silk hydrogel retained ~50% p-nitrophenyl acetate hydrolysis activity of free ngCA. Mechanical properties of m-ngCA-silk hydrogel were remarkable, showing high elasticity and flexibility, compressive modulus of ~1.3 MPa and ~11 MPa for 20% and 40% strain, and constant compression strength with an energy dissipation of ~5 kJ m^-3 at 20% strain during 20 cycles. In addition to good thermal stability, the m-ngCA-silk hydrogel exhibited outstanding multi-use stability with ~97% of initial activity after 6^th reuse and excellent storage stability without reduction in activity after stored at 30 °C for 35 days. Finally, we also demonstrated that the ability of m-ngCA-silk hydrogel to the sequestration of CO₂ in carbonate mineral. The m-ngCA-silk hydrogel exhibited ~56% of CO₂ sequestration ability of free enzyme, which is expected to be the maximal ability of the immobilized ngCA. Thus, this enzyme-immobilized hydrogel synthesized via bioinspired dual-crosslinking can be successfully used in environment-friendly CO₂ sequestration, demonstrating that the applicability of hydrogel as robust support for enzyme.

A pure continuous montmorillonite (MMT) film was fabricated by casting exfoliated clay nanosheets. Polyvinylidene fluoride (PVDF) was subsequently coated on the MMT film surface via a facile dipping process. The PVDF both uniformly covered the surface and penetrated into the orientated MMT layers. The characterization results showed that the PVDF coated MMT film exhibited excellent mechanical and barrier properties thanks to the highly oriented MMT sheets and the strong interfacial interactions between PVDF and MMT. This polymer-incorporated clay-based film may find applications in packaging.

Natural materials or naturally-derived materials for organic electronics have received increasing attention in recent years because of ecological advantages and overall sustainability. Organic field effect transistors (OFETs) represent one promising component for modern electronic devices, and examples where they have been fabricated by using either natural or natural-derived materials as semiconductors, substrates and dielectrics have begun to appear. In this work, natural rice, obtained from a local market and used without further purification, was selected as a precursor for the dielectric layer in OFETs. After set of simple treatments, a high-quality transparent dielectric film was formed on the semiconductor layer via low temperature and low cost solution processing. The natural rice based transparent dielectric film has a cross-linked structure, is insoluble in common organic solvents, has low roughness surface and a high dielectric constant. More importantly, the OFETs fabricated with the natural rice insulator show good performance and stability under ambient conditions. Given its performance attributes, low cost and simple fabrication processes, natural rice may represent be an ideal dielectric material candidate for the next generation of bio-integrated electronic devices.

The mechanical properties of cells are increasingly suggested as a promising label-free biomarker indicative of various intracellular changes associated with disease processes. Stiffness is especially of importance as many studies have linked the changes in stiffness to the invasiveness of cancers, red blood cell diseases and infections. Since the basic structure of liposomes is the same as that of biomembranes, they have been chosen in this study to serve as model systems mimicking the properties of real biomembranes. In a free-flowing microchannel, an ultrasonic standing wave is designed to yield a pressure node at the center, and two low-pressure zones at the walls of the channel. Giant liposomes between 1-10 μm in diameter were prepared from two phosphatidylcholines containing linear saturated fatty acyl chains using a modified solvent-injection method. The label-free separation of these liposomes based on their composition was investigated under free-flow conditions. It was shown that the separation performance of the liposomes in a standing-wave depended chiefly on the compressibility of their membranes, which is inversely proportional to stiffness. The results of this study suggest that this approach can be applied for the separation of diseased cells in which the cellular stiffness is affected during the different phases of the disease.

Diatoms are unicellular microorganisms that play a key role in the aquatic ecosystem and in the advancement of nanotechnology. These photosynthetic algae display a wide range of patterns and shapes only visible at the micron scale. Efforts have been made to replicate the diatom’s intricate structure to design nanoscale systems and devices from sensors and nanotemplates to dye-sensitive solar cells and nanostructured battery electrodes. The correlation between diatom morphology and its mechanical properties continues to provoke debate. Some studies have proposed that this correlation is based on the variance in mechanical properties, microfluidics behavior and light diffraction seen at different diatom sizes. To perform a systematic study of diatoms, it is increasingly important to sort them by size quickly and reliably to facilitate sample preparation and reduce time. In this work, we have investigated different diatom sample preparation methods, selected the most suitable one for centric diatoms, specifically the Coscinodiscus sp., fabricated a low-cost diatom sorter system, and tested its performance. The outer shells of these diatoms (frustule) vary largely in diameter size ranging from 50 to 300 microns. The motivation herein is to propose a velocious technique for sorting diatoms by size. Currently the most commonly used method involves light microscopy and is highly favored for sorting diatoms due to its well-magnified and detailed images. Unfortunately the setbacks include extensive amount of time to conduct sorting of diatoms and the need of specialized equipment to execute the experiments. This makes the method unpractical for sorting large amounts of diatoms in a short period of time. The state of the art methods reviewed in this work were found to illustrate different perspectives on the separation and characterization of the diatom frustule sizes. The methods included field-flow fractionation (FFF), fabrication of gold nanostructures, and biovolume calculations. The selected applications compared in terms of technique, performance, and level of difficulty vary greatly from one another, and upon further analysis it was found that FFF is the most suitable method for separating the diatom sizes. Field flow fractionation is classified as one of the most adaptable family of separation techniques, which uniquely characterizes a massive assortment of particles and substances with a high success rate. Consequently, we have designed a diatom sorter system using FFF with a specific asymmetric flow cell for the separation of diluted Coscinodiscus sp. frustules. A FFF CAD model with dimensions suitable for such frustules was created and subsequently used for the fabrication and testing of a diatom sorter system. This designed sorter system has resulted in a practical prototype to evaluate the FFF model. This research contributes to improving diatom sample preparation by designing and implementing diatom-specific sorters.

Nature has developed simple, highly functional structures such as the Venus flytrap, which takes advantage of its bistable leaf to rapidly capture prey in a smooth motion. As the leaf switches between two minimum energy positions, it undergoes a shape change termed “snap-through.” This two-stage actuation procedure enables the flytrap to use minimal energy input to produce large rapid motion. Such bistable structures are attractive for functional devices because they require an impulse input for only a short time to switch states and are able to maintain either state indefinitely. Mimicking such structures informs hardware designs with intelligent characteristics for use in energy applications, such as storage and harvesting.

Dielectric elastomers (DE) have emerged as a promising candidate for use as a soft actuator material to actuate complex deformation. Under application of an electric field, DEs exhibit large deformation, high energy density, and fast response. These properties have led to the incorporation of DEs into biologically inspired structures such as bistable mechanisms found in the Venus flytrap. Nonetheless, current research in programming DEs to achieve bistability is limited by the need for bulky structures required to provide the bistability mechanism and to support prestretched elastomers, resulting in reduced energy density. To overcome this drawback, this work achieves programmable bistable deformation that harnesses snap-through instabilities with minimal structures, thus increasing energy density. Compared to previous bistable actuators that typically involve uniaxial bending, this work presents the bistable actuation of elastic passive structures with varying Gaussian curvatures; zero Gaussian curvature metal plates and positive Gaussian curvature elastomer shells. Since the structures require a unique deformation path for switching, designs of suitable patterned elastomer actuators are developed such that the areal deformation from the DE active layers can be used to actuate the structure. The functionality of this bistable device is derived from detailed structural patterning of the elastomer shell, inspired by microstructures found in nature. Relationships between actuation parameters, geometry of the passive element structure, and resulting deformation are presented based on experimental works. Further, energy-harvesting properties of this device are demonstrated. This new bistable soft materials design has the potential to open opportunities for simple bistable actuation and applications in bioinspired energy storage and harvesting.

Within cells, the cytoskeleton orchestrates functions such as motility, the organization of chromatin, and directed cellular transport. A relatively small set of filament components and proteins that organize filaments form a diverse array of structures because different spatiotemporally controlled processes of assembly and disassembly can produce a variety of assembled structures. The decision about which architecture to form within a cell is made by signal transduction pathways and gene expression programs that sense chemical and physical inputs and produce outputs that control the abundance and activity of cytoskeletal building materials, thereby controlling what assembles.

We are developing programmable active materials made from synthetic DNA components using the cytoskeleton as a model. The architectures we build are formed from DNA nanotubes assembled from small tile monomers and are semi-flexible polymer fibers with a persistence length similar to actin fibers and a structure similar to microtubules. DNA origami structures organize nanotubes into functional architectures, and nucleic acid based molecular circuits that sense inputs and produce outputs that in turn direct the assembly and disassembly of these nanotube arrangements. The ability to program the assembly state and architecture of synthetic fibers could make it possible to create a toolkit of components that form many structures in different environments and to build materials that self-heal or metamorphose.

An increase in the demand for clean and sustainable energy storage with the importance of high power density, along with a long cyclic life time has made supercapacitors as an emerging energy storage device. However, one of the main challenges of today’s world is to develop energy storage devices which are environmentally friendly, cost effective, and which possess an excellent storage capacity. Therefore, in this presentation we will be reporting a facile way to synthesize nickel/carbon nanocomposites from wood as a novel electrode material for supercapacitors. The electrode i.e. nickel/carbon nanocomposites from wood was synthesized by carbonizing the nickel nitrate impregnated wood at 900°C for an hour. The concentration of nickel nanoparticles in the carbonized wood was varied by changing the concentration of nickel nitrate solution. Subsequent X-ray diffraction (XRD) results for the synthesized electrodes showed that that after a high-temperature carbonization process, wood is converted into graphitic carbon and nickel nitrate is reduced to nickel nanoparticles. Later, the surface morphology of the as-prepared electrodes was studied using scanning electron microscopy (SEM) which indicated that the nickel nanoparticles were evenly distributed within the three dimensional structure of the wood. Electrochemical measurements such as cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS) and galvanostatic charge-discharge measurements were conducted. CV measurements showed the presence of redox peaks demonstrating a typical psuedocapacitive behavior of the electrode. Moreover, the galvanostatic charge-discharge measurements also showed a non-linear charge-discharge curves indicating that the redox charge transformation is reversible. The composite electrode exhibited an enhanced specific capacitance of 3616 F/g along with a high power density of 30 KW/kg and an energy density of 125.5 Wh/kg. Furthermore, the nickel/carbon nanocomposite electrodes displayed an excellent specific capacitance retention of greater than 89% after 5000 charge-discharge cycles. This tremendous performance of nickel/carbon nanocomposite electrodes synthesized from wood demonstrates an outstanding potential to be utilized for future application in fabricating environmentally friendly supercapacitors.

We report that water repellency of polymeric film surfaces can be simply tuned by pressing softened polystyrene (PS) films into a monolithic porous anodized aluminum oxide (AAO) mold. Highly-dense nano-pillars and nano–hairs on the PS film surfaces were reproduced via physically or chemically separating the AAO mold from the surface-pressed PS films. The resulting nano-textures on PS showed various aspect ratios (AR) of height to cross-sectional diameter from 2 to 120, depending on the viscoelastic response of the polymer chains during hot AAO pressing and subsequent separation. Contact angle values for water droplets on the nano-textured PS films considerably changed from 91° to 160° with an increase in AR. Using hot pressing and physical detaching of a porous AAO-covered Al cylinder bar, we successfully demonstrated the fabrication of one-pot large-area nano-textured PS films with superhydrophobic character similar to that of rose petals and lotus leaves.

The design and discovery of advanced ceramics has led to ceramics becoming a staple material in modern life. Modern electronics for example, utilise ceramics with properties that encompass a myriad of electrical properties such as piezoelectricity, semi-conductivity and superconductivity, as well as an array of impressive magnetic properties. Furthermore, the catalytic activity of materials such as iron carbide, in reactions such as the oxygen reduction reaction, mean that there is scope for replacement of costly noble metal catalysts with economically viable, earth abundant materials. Yet, in order to further enhance many of these properties the frontier of morphological control needs to be explored.
Controlling the morphology of ceramic materials such as transition metal carbides is a complex problem, the crux of which relates to the high temperatures required during carbide syntheses. Temperatures in excess of 1000^oC are not uncommon. At these temperatures sintering occurs. In fact, sintering is a key step in the formation of a ceramic in which individual particles fuse together to produce a strong, hard, dense material. Problems arise however, when trying to exert fine control over the morphology of said materials, particularly at the micro and nano-scales, as the fusing of particles results in the loss of structural information and the formation of agglomerates, as well of shrinkages of anywhere between 10-40%.
Our group is investigating two key areas aimed at addressing these issues. The first aims to address the issue of uncontrolled sintering. The key approach being explored in this regard is the use of micro-structured cast materials such as porous alkaline earth metal oxides that are capable of immobilising Prussian Blue nanoparticles during calcination, to give a phase pure, nano-particulate, iron carbide decomposition product.
The second area of investigation builds on the first by introducing further complexity into ceramic material morphologies. This is principally approached by combining the previously described cast concept with bio templating. Bio-templating exploits the tendency of smaller basic building blocks such as transition metals to self-assemble at the surface of natural organic templates, commonly rich in polysaccharides that have a high affinity for metal cations. The template itself can therefore also be used as a carbon source in synthesis. Ordinarily, once coated, the template is then removed by calcination or chemical etching leaving behind a free standing, inorganic structural replica. The clear advantage to this technique is that through millions of years of natural selection, nature has amassed a wide assortment of small structures with unique morphologies and topologies, capable of an eclectic variety of functions. Mimicking these properties is therefore an attractive proposition for materials chemists.

Bacterial biofilms are ubiquitous in nature and potentially important substrates for the production of renewable biomaterials. They are composed of bacterial cells in an extracellular matrix usually containing protein-based fibers, polysaccharides and DNA. Here we employ an engineered, light-sensing strain of Escherichia coli to pattern functionalized biofilm proteins in two dimensions. We engineered E. coli to sense different wavelengths of light and respond uniquely to each wavelength by producing different variants of curli fibers, the major component of E. coli biofilms. By controlling the pattern, wavelength, and intensity of the light incident on a stationary culture of our engineered strains, we are able to precisely control the density, composition, and shape of the resulting biofilm to a resolution of 1 mm on any substrate and in under three hours. Furthermore, the protein building block of curli fibers can be fused to functional peptides through genetic modification. Different strains producing different versions of the fibers can be mixed in culture and stoechiometrically controlled by varrying wavelengths and intensity. The resulting patterned bacterial film can sense signals and produce outputs. This type of live bacterial “bioprinting” represents an advance in employing engineered strains of bacteria to produce complex living materials. This work lays a foundation for synthesizing, patterning, and controlling functional composite materials with living cells.

By understanding and redesigning nature’s building blocks and directing their assembly into complex geometries, we aim to develop 4D materials and techniques for growing lightweight highly damage tolerant armour systems. Current conventional armour has proven challenging to replace, however with its low specific strength and lack of flexibility there is significant room for improvement. Diatoms, ceramic marine eukaryotes, offer incredible strength and energy dissipation, with the highest specific strength of any known biological material¹ whilst cohesively combining inorganic and organic matter.

A two part bio-ink was developed to hold live cell cultures providing biocompatibility and stable structure with continued cell growth of human mesenchymal stem cells for up to 35 days². This ink has been adapted to print diatom cultures in 3 dimensional architectures. Stereolithography printing has shown that the ink developed can successfully cross-link and withstand movement whilst diatom laden. Microscopic analysis has shown an even distribution of diatoms within the ink has been achieved, with ordered directionality in alignment with the direction of extrusion. Printed extant cultures of diatoms will provide information on cellular growth within a limited intricately structured 3D architecture. Once printed, analysis of flow alignment of the diatoms within the bio-ink will enable understanding of shear forces to which the diatoms are exposed and are therefore able to withstand. Rheological testing of whole structure demonstrates alteration to the physical properties that the diatoms bring to printed structures.

3D printing will continue to be used to provide complex architectures, culminating in the creation of 4D high strength composite structures, utilising live diatoms for optimised performance and tailored growth between the print pathways.

1. Aitken ZH, Luo S, Reynolds SN, Thaulow C, Greer JR. Microstructure provides insights into evolutionary design and resilience of Coscinodiscus sp. frustule. Proc Natl Acad Sci U S A. 2016;113(8):2017-2022. doi:10.1073/pnas.1519790113.

2. Armstrong JPK, Burke M, Carter BM, Davis SA, Perriman AW. 3D Bioprinting Using a Templated Porous Bioink. Adv Healthc Mater. April 2016. doi:10.1002/adhm.201600022.

Introduction: The extracellular matrix (ECM) is a complex network composed of collagen, fibronectin and other macromolecules that not only provides structural support but also relays crucial biochemical and biomechanical signals. It dictates how cells attach, behave and interact with one another, thus, it plays a key role in tissue morphogenesis, differentiation and repair. In this context, the construction of artificial matrices that mimic the structure of the naturally occurring ECM and display biological signals might prove to be highly promising in controlling tissue regeneration. DNA has emerged as one of the most promising building blocks for such nanoconstruction due to its programmability and modularity. In the present study, DNA nanotubes were constructed based on double-crossover motifs and were further covalently functionalized with a BMP-7 derived peptide. The structure of the nanotubes was inspired by collagen with similar size , and the BMP-7 derived peptide was selected because of its role in regulating the proliferation, differentiation and apoptosis of bone cells. The objective of the present study was to develop an extracellular microenvironment that can mimic the structural and regulatory characteristics of natural ECMs. Results showed that the DNA nanotube coated glass coverslips possessed a tangled network of fiber-like materials that resemble the morphology of the natural ECM, suggesting DNA-peptide nanotubes could be a promising candidate as artificial ECM. Further experiments are still need to fully investigate their effects on osteoblast cell proliferation and stem cell differentiation.
Results and Discussion: TEM images confirmed that the rationally designed DNA tiles can self-assemble and form long tubelike structures about 10-12 nm in diameter and often many micrometers in length. Incorporating BMP-7 derived peptide into one of the strands yields an almost indistinguishable structure. This offers the largest advantage of this system over other alternatives in that there is potential to vary the biological epitope without affecting the core structure. Stability of the nanotubes and nanotube-peptide hybrids against temperature, cation depletion and nuclease degradation were shown to be better than DNA double helices using TEM. The fibrillar morphology of the coating resembles that of ECM, indicating the potential of these DNA nanotubes to act as mimics of a native ECM. Finally, these nanotubes were shown to have no toxic effect on osteoblast cells at a concentration of up to 5 µM. Conversely, at low concentrations, specifically 1.25 and 2.5 µM, increases in cell density were observed.
Conclusions: Through above experiments, DNA nanotubes self-assembled from DNA tiles were successfully designed, constructed and characterized. The ECM-like fibrillar morphology and the minimal toxicity to osteoblast cells indicated their potential to be used as improved artificial extracellular matrices.

Biological materials, such as peptides, can undergo self-assembly due to their complex structures, hydrogen bonding, electrostatic or hydrophobic interactions between different molecules and sometimes due to the presence of their complementary sequences. There are different ways by which peptides undergo self-assembly, the most common one is in aqueous solutions. There are also other methods for self-assembly, such as exposure to a plasma stream, or electrostatic forces. One way of utilizing electrostatic forces for self-assembly is the electrospinning for the synthesis of nanofibers. Electrospun nanofibers have been of much interest in the field of biomedical engineering for applications in tissue engineering and drug delivery.In this study, we have investigated the synthesis of biodegradable nanofibers and nanospheres composed of short aromaticpeptides self-assembled using electrospinning or electrospraying conditions.By using specific peptides, the composition and the properties of the resultant fibers can be tuned for a specific applications. Aromatic cyclic and linear peptides with varying composition such as phenylalanine-tyrosine,tryptophan-tyrosine, cyclic tryptophan-tyrosine and triphenylalanine peptides have been studied to understand their behavior under optimized electrospinning conditions. The different parameters which influence the final structure of the electrospun fibers, such as; solution concentration, type of solvent, needle to collector distance, voltage, flow meter were modified to obtain required morphology of the fibers. Interestingly, under specific conditions, changing these parameters lead to the formation of spheres instead of fibers. In this case, the process conditions were similar to electrospraying. Peptides which self-assemble to form spheres, such as tri-phenylalanine were investigated using the electrospraying procedure.
The morphology of the structures were studied using the scanning electron microscope (SEM) and the conditions were further modified to obtain continuous bead-free fibers or spheres from the aforementioned dipeptides. In order to analyze the characteristic properties of the self-assembled structures, FTIR, Raman and UV-vis were performed on the resulted fibers and spheres. We have compared the structure and characteristics of the fibers and spheres obtained from the electrospinning procedure to the ones obtained by other methods of self-assembly of peptides, both in aqueous solutions and via vapor deposition. Finally we have analyzed the biocompatibility of the nanofibers and nanospheres for biomedical applications such as tissue scaffolds and drug delivery.

Recently, hybrid structures have been prepared aiming at different applications in the field of biomimetic, bioinspired engineering and biomaterials [1], particularly the use of fungi, which has showed to be versatile templates for the organization of advanced functional materials[2]. In these structures, the combination of biological material and properties of inorganic nanoparticles, such as electrical conductivity or optical activity, can lead to construction of hybrid macrostructures with high technological applications [3]. In this context, we are interested in the use of fungi as biotemplate to obtain self-assembled systems of gold nanoparticles forming stable mesostructures with potential use for sensors and biosensors via surface-enhanced Raman scattering (SERS). We also presented a facile route for self-organization of colloidal gold nanoparticles on living filamentous fungi as natural architecture to construct microtubules. The structured material was prepared by adding the spores of the filamentous fungus Cladosporium sphaerospermum in the colloidal dispersion of gold nanoparticles. During two months, fungi grew consuming the unreacted citrate ion remaining in the medium and gold nanoparticles adhered to the cell wall, covering it in multiple layers which resulted in an uniform gold microtubules with controlled thickness. Gold nanoparticles and microtubules were characterized by X-ray diffraction, UV-Vis spectroscopy, scanning electron microscopy (SEM) and SERS. UV-Vis spectrum of the gold nanoparticles showed the plasmom band in 520 nm, well characterized for spherical nanoparticles. The diffractogram confirmed the face-centered cubic structure. SEM images showed a good uniformity related to the distribution of the nanoparticles on the hyphae of the fungus, with average size around 20 nm. Gold microtubules had a good improvement in the SERS signal in 632,8 nm using benzenetiol. Therefore, structured materials obtained by biotemplates and self-organization of colloidal nanoparticles were prepared with controlled size and good uniformity.

[1] N. L. Rosi, C. S. Thaxton, C. A. Mirkin. Angew. Chem. Int. Ed., 2004, 43, 5500-5503.
[2] N. C. Bigall, M. Reitzig, W. Naumann, P. Simon, K.-H. van Pée, A. Eychmüller. Angew. Chem. Int. Ed., 2008, 47, 7876-7879.
[3] a) A. Sugunan, P. Melin, J. Schnurer, J. G. Hilborn, J. Dutta. Adv. Mater., 2007, 19 (1), 77-81. b) Sharma, S., Srivastava, S. Biosensors and Bioelectronics, 2013, 50, 174–179.

This work was supported by CAPES, FAPESP, CNPq, and CDMF/CEPID.

Recently, a flexible and stretchable artificial electronic skin (E-skin) has attracted considerable attention for its various applications such as wearable devices, artificial robot arms, and health monitoring systems. To develop the E-skin which imitates the function of human skin, sensitive response for external mechanical stimulation is required. Over the few years, piezoelectric, piezoresistive, optical and capacitive type of flexible pressure sensors have been explored as excellent candidates for variety of applications in E-skin. Among these pressure sensors, the capacitive pressure sensors have lots of strength like its low power consumption, simple design and high sensitivity. To achieve the further improvement of the capacitive pressure sensors, morphologies and structures of natural living things are able to be utilized in sensor structure. In nature, there are microscale porous structures with reversible compressibility such as diatoms, mushrooms and spongia officinalis. These superb abilities of natural structures can enhance the performances of capacitive type pressure sensor.
In this research, we demonstrated a facile approach to fabricate a highly sensitive capacitive pressure sensor using a sponge-like structure of polydimethylsiloxane(PDMS) thin-film. The morphology of porous dielectric layer in pressure sensors were effectively controlled by changing the pore sizes. This highly sensitive pressure sensor successfully detected sophisticated pressure stimulus lower than 1kPa. The obtained pressure sensor achieved real-time tactile array sensing and also distinguished varying applied pressures. The developed flexible pressure sensor may give a chance to proceed advanced wearable health monitoring or human-machine interfaces and various robotic sensor system.

Single-biomolecule function detection is one of the recent interests. In order to detect and understand single-molecular functions, the detection and/or monitoring of their structural behaviors is the first step. We have proposed a methodology for tunnel-current based single-molecule identification. Based on differences in the electrical conductivity, we have discriminated the characteristic chemical species in the biopolymers just passing through the sensing electrode at single-molecular level. In this study, we applied this methodology for detecting the structural differences of biopolymers. We developed the thermal-controllable unit integrated tunnel-current measurement systems. By using this system, we investigated the thermal effect on the DNA duplexes. As the sample nucleotide, we measured GTGTATG and its complementary sequences nucleotides, and found that the DNA duplex have characteristic conductance-peaks in the histogram, which are probably due to the G:C and A:T pair. This suggested that the thermal control system is worked for the discrimination of DNA duplex and single-stranded DNA. This methodology can detect the single-molecule structural behaviors around the sensing electrodes.

Lotus leaf exhibits a superhydrophobic character with a water contact angle higher than 160° and sliding angle lower than 5°, resulting from the convergence of the surface micro/nanostructures and the hydrophobic wax layers. Furthermore nanostructured smart materials with surface properties that switch in response to external stimuli play an important role in a variety of applications in nano/microsystems, materials science, biotechnology, and medicine. In particular, multi-scale surface nanostructures with a large surface-to-volume ratio are an essential prerequisite for maximizing the performance of such smart devices and systems. In this study, we demonstrated multifunctional electrospun polyelectrolyte fabrics with switchable superhydrophobicity as well as oleophobicity. To produce this smart fabric, we used a strategy that combines electrospinning to fabricate nanofibrous templates with nanopores and a simple coating of the polyelectrolyte that can exchange counterions with various hydration energies. The ion exchange of polyelectrolyte embedded in nanoporous fibrous webs leads to switchable wetting behavior in water and oil. This electrospun fabric was also utilized as chemical filters for the efficient removal of sulfur dioxide (SO₂) from waste gas streams. This kind of electrospun polyelectrolyte fabric might provide a valuable solution in functional filters, membranes, and templates in a wide range of applications such as the desalination of seawater, demineralization, and decontamination.

We develop a transparent and tough inorganic and organic composite material inspired by the cornea that is a transparent portion of an eye ball. The transparency is explained from the structure color development from the aggregations of colloidal particles and fibers. The structure color from the aggregations is produced by diffraction and interference of the scattered light. Opal is one of the typical example of the aggregations where fine silica particles form a crystal structure. The scattered light of the specific wavelength is selectively emphasized because of the uniform distance between the fine silica particles. The emphasized scattered light varies according to a point of view by Bragg's law. As a result, the opal becomes the brilliant appearance. The crystal structure is a sufficient condition for displaying structure color, but is not a requirement. Mandrill is known for its blue cheek whose color does not depend on viewing and light illumination angles. Collagen fibers existing under the skin of the mandrill are arranged only with short-range order with about 200 nm apart. The scattered light of approximately 400 nm is emphasized in all directions due to the presence of the short-range order, whereas other scattered light in visual light range cancels each other. If the short-range order of the aggregations is shorter than 200 nm, the wavelength of the emphasized scattered light becomes shorter than that of the visible light. As a result, the aggregations become colorless and transparent. The example is cornea. As for the human corneas, collagen fibers are arranged only with short-range order in mucopolysaccharides gel. Because the average distance between the fibers is 50 nm, in this case, the wavelength of the emphasized scattered light is approximately 100 nm: the scattering light can be vacuum ultraviolet. Therefore, the cornea is a colorless and transparent material. In this study, we tried to prepare the transparent composite material where fine silica particles form the aggregation with short-range order, and transparent flexible polymer gel fills the interstices between the particles. The average diameter of the fine silica particles is 110 nm. When the concentration of the fine silica particles to the polymer gel is lower than 9.5 vol%, the randomly-arranged fine silica particles induced incoherent scattering. Consequently, the composite material becomes cloudy. With increasing the concentration of the fine silica particles, however, the transparence of the composite material becomes higher because of the order formation of the fine silica particles. The order distance and the structure of the fine silica particles can be controlled by adjusting these concentration. Moreover, we found that the transparent composite material has also high mechanical strength which combines flexibility of the gel and high elasticity of the silica fine particles. Such material is expected to find wide application as biomimetics materials.

Ice accretion remains a costly, hazardous hindrance worldwide. Current methods for ice removal are extremely energy intensive due to the strong adhesion between ice and most surfaces. Structural materials like aluminum or steel display extremely high ice adhesion strengths, τ_ice (τ_ice ≈ 1600 and 1400 kPa, respectively). However, to passively remove ice with no external energy input, such as on airplane wings, power lines, or boat hulls, extremely low ice adhesion strengths (τ_ice < 25 kPa) are required. Thus, the challenge of developing materials that facilitate the facile removal of ice remains critically important, yet unsolved.
To date, the lowest ice adhesion values have only been reported using lubricant-infused surfaces or lubricated gels. However, the low ice adhesion observed for lubricated surfaces (τ_ice ≈ 1–2 kPa) drastically increases once the oil is displaced and removed by water droplets, frost, or during the removal of accreted ice. There have been no reports of durable icephobic surfaces that can maintain τ_ice < 20 kPa.
In this talk I discuss our recent work on the ice adhesion of elastomers. Elastomers are viscoelastic, meaning they display both solid-like and liquid-like properties. We control the viscoelastic nature of our elastomers in two ways. First, we modify the crosslink density, ρ^CL, of our elastomers to alter their physical stiffness. We observe that the ice adhesion strength of elastomers depends on ρ^CL in a manner consistent with the detachment process of interfacial cavitation. Utilizing interfacial cavitation, some of our low-ρ^CL elastomers exhibit a non-increasing τ_ice ≈ 10 kPa.
Second, we alter the no-slip boundary condition at the ice-elastomer interface through the addition of uncrosslinked, polymeric chains. If the polymeric chains within an elastomer are sufficiently mobile, slippage (i.e. a non-zero slip velocity) can occur at the solid-solid interface. When a hard surface slides over a soft elastomer, such as during interfacial slippage, the observed shear stress should be linearly proportional to ρ^CL, which we verified for a wide range of elastomers spanning multiple chemistries. By tailoring ρ^CL for different elastomeric coatings, and by additionally embedding miscible, polymeric chains to enable interfacial slippage, I will show that it is possible to systematically design durable icephobic coatings with extremely low ice adhesion strengths (τ_ice < 0.2 kPa). Utilizing these two mechanisms allows for the rational design of icephobic coatings with virtually any desired ice adhesion strength, irrespective of surface chemistry. As such, we fabricate extremely durable coatings that maintain τ_ice < 10 kPa after severe mechanical abrasion, acid/base exposure, 100 icing/de-icing cycles, thermal cycling, accelerated corrosion, and exposure to Michigan wintery conditions over several months.
This work was published in Science Advances, highlighted in Science and has been featured in over 100 news stories worldwide.

Associating polymer networks have been utilized in the design of tough hydrogels that are also capable of self-healing. The dynamic nature of the association allows for it to act as sacrificial bonds under mechanical stress, which when relaxed then lets the system re-associate, conferring the material its self-healing ability. While this has been documented using mechanical testing data showing the material regaining most of its original stiffness after a recovery period, such data provides no information on the molecular level processes occurring as the network is damaged, and subsequently as it heals.
A luminescent hydrogel, crosslinked with dynamic metal-ligand coordinate complexes has been developed. Through this system, there is an opportunity to visualize and hence analyze these molecular level processes, as the optical and mechanical properties of the gel are inherently coupled. The hydrogel consists of terpyridyl-end capped 4-arm poly(ethylene) glycol polymer, such that on addition of lanthanide ions, metal-coordination crosslinks are formed. On sonication, a gel-sol transition is observed, due to partial dissociation of the complexes, and the fluid phase appears to emit blue light, seen in the emission spectra as a broadband emission centered at 425nm, that was also observed in the “free” polymer. Thus the relative intensity of the emission in the 400-475nm range, as the hydrogel is stressed, is a measure of the degree of dissociation and re-association of the complexes. In this work, we further developed the system for the study of the molecular processes occurring as the metal-coordinate gel is deformed. For greater control over the applied mechanical stress, the hydrogel is deformed using a tensile tester that is mounted onto a fluorescence microscope. Through this experimental setup, simultaneous application of the tensile stress and collection of the optical signal can be achieved.

Increasingly frequent petroleum contamination in oceans continue to threaten our ecosystem, which lacks efficient and safe remediation tactics on both macro and nanoscales. Current nanomaterial and dispersant remediation methods neglect to investigate their adverse environmental and biological impact, which can lead to a synergistic chemical imbalance. In response to this rising threat, a highly efficient, bio-inspired and biocompatible nano-dispersant has been developed comprising a multi-shelled nanoparticle termed ‘Nano-CarboScavengers’ (NCS) with native properties for facile recovery via booms and mesh tools. Bushy extensions of milkweeds with water repellent properties inspired us to generate hydrophobic extensions using amphiphilic polymers around crosslinked agave nector based carbon core during synthesis of NCS. NCS were able to treat different forms of petroleum oil (raw and distillate form) with remarkable efficiency (80% and 91% respectively) utilizing sequestration and dispersion abilities in tandem with a 9.9:1 (oil:NCS) loading capacity. In major contrast with chemical dispersants, the NCS was found to be remarkably benign in in vitro and in vivo assays. Additionally, the carboneous nature of NCS broke down via human myeloperoxidase and horseradish peroxidase enzymes, revealing that incidental biological uptake can enzymatically digest the sugar based core.

Bioinspired and biologically-based water-responsive materials are promising as powerful actuators^1,2. Recent works have shown that Bacillus spores have high energy densities and can be utilized as micro-meter scale locomotive elements. However, development of macroscopic actuators that maintain the high energy density of spore building blocks has been challenging. Although the water-soluble adhesives offer a simple fabrication of spore film based actuators ², the requirement for water evaporation is time consuming. Furthermore, the resulting spore films did not exhibit as high energy density as individual spores. To enhance the actuation capabilities of the spore layer, we carried out systematic studies with UV-curable adhesives with varying adhesion and mechanical characteristics. The mechanical properties of the adhesive in the spore suspension play an essential role on performance, durability, and the fabrication complexity of the actuators. In order to transmit the high mechanical force from one spore to another, spores should adhere each other with a stiff and ductile material. Otherwise, the adhesive would absorb energy and be damaged irreversibly. Moreover, curing time and type of the adhesive itself define the length and the complexity of the fabrication process. The novel method we developed enables the production of humidity-responsive actuators with high energy density and scalable fabrication scheme. In this work, we use UV curable optical adhesives with Young’s Modulus’ in 1-2 GPa range and durability under high elongation (up to 35%). UV curing enables rapid fabrication of the actuators within seconds which can be important for large scale manufacturing. We investigated the performance of these adhesives with different mechanical characteristics. Our analysis shows that energy densities up to 1 MJ/m³ are achievable with a rapid, simple fabrication process. Our process may facilitate development of biologically-based actuators for applications including energy harvesting, construction of complicated 3D folding structures, and soft robotic applications.

1. Chen, X., Mahadevan, L., Driks, A. & Sahin, O. Bacillus spores as building blocks for stimuli-responsive materials and nanogenerators. Nat Nanotechnol 9, 137-141 (2014).
2. Chen, X. et al. Scaling up nanoscale water-driven energy conversion into evaporation-driven engines and generators. Nature communications 6, 7346 (2015).

The advantage of biopolymer composite’s biodegradable, sustainable, hierarchical structure has attracted much attention from materials scientist recently. Investigating the mechanical and physical response of biopolymer in cell wall level is essential for better understanding the mechanism and expanding its application fields. In this research, we investigated the nanomechanical behaviors of wood based biopolymer composite by advanced instrumented indentation technique (NanoBlitz 3D) from Nanomechanics, Inc. By this powerful technique, we generated mechanical-properties maps of wood cell wall which distinguishes modulus, hardness and stiffness properties among different phases.

Periodic laminated structures are recurrent in nature where they provide exceptional functionalities such as structural colouring [1] or attenuation and dissipation of mechanical energy [2]. Magnetically-assisted slip casting [3], a versatile technology that combines an aqueous-based ceramic process with magnetically-directed microplatelet assembly, enables the translation of natural hierarchical periodic microstructures into man-made composites. By understanding the underlying mechanisms involved during the platelet alignment under dynamically varying rotating magnetic fields and fluid flow, we demonstrate that control of the periodic microstructure can be achieved at each hierarchical level, from the platelet angle, the monoaligned layer thickness to the macroscopic pitch. Using platelets of varying aspect ratios, structures with pitches as small as 50 µm could be achieved. Additionally, for periods in the micrometer range, periodic assemblies are expected to interact with stress waves and provide a phononic bandgap, hence preventing certain frequencies of stress waves to be transmitted throughout the structure [2]. We therefore developed a method to densify these periodic constructs into dense ceramics. Based on an analytical model, we explore the influence of different periodic architectures on the propagation of stress waves, the presence of bandgaps resulting in energy dissipation, demonstrating the feasibility to fabricate periodic ceramic with on-demand energy dissipation properties for high-velocity impact protection.

Highly specific and sensitive platforms for detection of clinically relevant biomarkers are critical for accurate disease diagnosis. Pathogens such as Vibro cholerae continue to cause significant mortality in resource-limited areas, where low cost, point-of-care (POC) diagnosis is ideal. While standard tools such as an enzyme linked immunosorbant assay (ELISA) meet diagnostic specificity and sensitivity needs, they cannot be utilized outside a clinical setting, at the site of the patient. To fill this unmet need for specific and sensitive disease detection with POC accessibility, we propose to use a novel nanoarchitecture for electrochemical sensing, the extended core coax (ECC). Each ECC is a vertically oriented nanocoax comprised of an extended inner metal core and an outer metal shield, separated by a dielectric annulus. The inner core, comprised of gold, acts as a working electrode which extends ~200 nm above the chrome counter electrode. Arrays with a base area of ~2000 μm² each contain ~2000 individual ECCs connected in parallel. The extended gold core provides a substrate that allows for protein biofunctionalization, making the ECC an attractive candidate for development as a fully lab-on-a-chip biosensor for electrochemical detection of infectious disease biomarkers such as cholera toxin.

Organic electrochemical transistor, so-called OECT, is the best candidate for sensor in a bio-system. Since an OECT consist of a channel, that is usually made of a conjugated polymer, and is in direct contact with electrolyte, these direct system generates high transconductance that is related to signal amplification and sensitivity. Moreover, choosing biocompatible materials as components, a bio-compatible OECT can be achieved easily. Therefore, an OECT is usually used for super-sensitive bio-sensor, such as mineral sensor, DNA sensor, glucose sensor, and so on.
Conventional OECT channels are Poly(3,4-ethylenedioxythiophene): poly(styrene sulfonate) (PEDOT:PSS) film because, in addition to its biocompatibility, PEDOT:PSS performs huge change in electrical conductivity up to 4600 S/cm, environmental stability, mechanical flexibility and easy processibility. In spite of these advantages, however, PEDOT:PSS has some critical limits. First, it easily dissolves in aqueous system and, therefore, loses sustainability, and the resistance increases. Second, it is hard to be fabricated as nanofiber which has a higher surface area to volume ratio (SA/V) and higher sensitivity than film.
Here, we demonstrate the PEDOT:PSS/Polyacrylamide (PAAm) nanofiber with high water stability for OECT channel. To solve the water stability and fabrication issues, PAAm was selected as a binder. PAAm is usually used as a gel matrix, due to its mechanical and chemical stability as well as hydrophilicity. To make entanglement between PAAm chains for enhancing physical cross-linking, PAAm was polymerized to form long chains while the concentration of initiator was controlled. After polymerization, we mixed PAAm with PEDOT:PSS in solution and fabricated nanofiber by electrospinning. Then we soaked the nanofiber in DMSO and heat treated to improve the crystallinity of PEDOT, which resulted in huge rise in conductivity.
PEDOT:PSS/PAAm nanofibers have extremely large water-stability compared to PEDOT:PSS film. After dipping in de-ionized (DI) water, resistance of PEDOT:PSS film increased 5 times bigger after 200sec, while resistance of PEDOT:PSS/PAAm nanofibers just increased 2 times bigger after 31hrs. It shows PEDOT:PSS/PAAm nanofibers have almost 7200 fold higher stability than PEDOT:PSS pristine film. SA/V also increases. SA/V of PEDOT:PSS film is about 10 μm^-1,while PEDOT:PSS/PAAm nanofiber is about 20~40 μm^-1, which is about 2~4 fold higher. If considering composition of nanofiber, the effective SA/V can be more increased and it can strongly enhance sensitivity.
We successfully applied PEDOT:PSS/PAAm nanofiber to OECT channel. Before sensing, we purified it in DI water to eliminate impurities in nanofiber. On low drain bias(0.1V) and gate bias(0.5V), it detects Na⁺ ions up to 10nM, the sensitivity of which is almost 100 times higher than the conventional OECT ion sensors.

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 how microfluidic systems can be used to investigate crystallisation within constrained volumes. Crystals are precipitated within individual droplets in segmented-flow devices, and we also incorporate a “pico-injector” into our devices such that additives can be introduced into the droplets at different time-points in the reaction. A novel “crystal hotel” is additionally described which comprises a series of “rooms”, each of which offers an independent, structured reaction environment. These “hotels” exhibit many features including flow, confinement and the possibility of changing reaction conditions with time that are common to biological systems. 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.

Oriented crystallization in complex biomaterials is one of the most exciting topics discussed in the field of biomineralization. While glycoproteins are known to be involved in controlling crystallization processes, the role of carbohydrates is less clear. As previously shown for the minerals calcium carbonate ^{1 2} or iron oxide ³, natural wood constitutes an intriguing scaffold for building mineral phases in situ. Scanning electron microscopy, Raman spectroscopic imaging and synchrotron-based wide-angle X-ray scattering (WAXS) allow to characterize the deposition pattern, morphology, and texture of barium sulfate at the cellular interface and in the sub-microporous cell wall. Scanning WAXS-measurements reveal a crystallographic co-orientation of barite crystals and cellulose microfibrils. The experimental findings help understanding inorganic crystallization in confinement. Moreover, the presented mineralization approaches are highly promising for templated crystal engineering and bio-inspired materials design.

References

1. Merk, V.; Chanana, M.; Keplinger, T.; Gaan, S.; Burgert, I., Hybrid wood materials with improved fire retardance by bio-inspired mineralisation on the nano- and submicron level. Green Chem. 2015, 17 (3), 1423-1428.
2. Merk, V.; Chanana, M.; Gaan, S.; Burgert, I., Mineralization of wood by calcium carbonate insertion for improved flame retardancy. In Holzforschung, 2016; online
3. Merk, V.; Chanana, M.; Gierlinger, N.; Hirt, A. M.; Burgert, I., Hybrid Wood Materials with Magnetic Anisotropy Dictated by the Hierarchical Cell Structure. ACS Appl. Mater. Interfaces 2014, 6 (12), 9760-9767.

Solid solution strengthening is a classical method for enhancing the mechanical properties of materials through lattice strain from disparate ionic radii. Traditional solid solutions are typically equilibrium compositions of two components whose radii differ by less than 15% (Hume-Rothery criterion), otherwise excess strain leads to phase separation into secondary precipitates. This heuristic also generally applies to carbonate minerals, out of which many organisms form their skeletons, shells, and/or teeth. However, organisms are also able to produce and maintain non-equilibrium compositions, e.g., high-magnesian calcite (Ca_1-xMg_xCO₃) in the sea urchin tooth. In this study, we demonstrate a bioinspired method for generating highly non-equilibrium solid solutions from ions of vastly different radii using amorphous precursors. Barium-substituted calcites (“balcite”, Ca_1-xBa_xCO₃, 9-fold coordination) rather than calcite (CaCO₃, 6-fold) form from amorphous calcium barium carbonate (ACBC) precursors. This non-equilibrium structural rearrangement allows balcite to contain up to 50 times more barium than calcite can accommodate at equilibrium. The effects of Ba²⁺ substitution for Ca²⁺ in the calcite lattice appear to be analogous to those observed during the carbonate disordering phase transition in pure calcite above T_c=970°C, and balcite was confirmed to have the same R-3m symmetry as high temperature calcite. Energetic pathways between these metastable states were investigated with a combined MD/DFT simulation approach, which confirmed the downhill nature of crystallization from ACBC → balcite → calcite+witherite. As expected, the hardness and strength of these materials is significantly improved over pure calcite. This synthesis pathway improves our understanding of biomineral synthesis, and describes mechanisms to generate non-equilibrium but long-lived solid solutions.

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 have developed a rheological technique to study mineral nucleation and growth events by measuring the modulations in mechanical properties of a hydrogel system during mineralization. Although the structure and formation of natural CaCO₃ materials have been intensely studied, questions regarding the mineralization pathways and early thermodynamics and kinetics of nucleation and growth still remain. Given its suitability for use with hydrated samples, rheology is a useful tool to study these hard-soft viscoelastic systems to try to capture early mineralization kinetics, which are difficult to study using traditional microscopy techniques. Our 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 and relaxation modulus of the system. We have found that gels with grown minerals exhibit higher storage and loss moduli than those without minerals and minerals simply mixed in and relax on longer timescales with additional modes of relaxation. We believe these differences are results of interactions between the CaCO₃ and gelatin interfaces and may indicate evidence of gel incorporation. By learning how these mechanical signatures are linked to the physical and chemical interactions of the system, we will be able to use nondestructive rheological characterization to understand how modulations in the gel result in changes in the grown mineral. Exploiting this new knowledge, we strive 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.

The mechanical properties of tissues play a crucial role in tissue function and disease. However, investigation of tissue mechanics requires special needs for the underlying culture scaffold. Organotypic tissue preservation and good adhesion of the tissue explant to the substrate are prerequisites. As we have shown previously, nanostructured TiO₂ substrates are ideal scaffolds to achieve these goals and adult neuronal tissues such as the retina can be long-term cultured for at least 2 weeks [1]. Here we present that these substrates can be employed as vibrating reed to investigate the mechanical properties of adult mammalian retinae at the nanometer, viz. protein level. Within a self-designed mechanical spectroscopy setup, the reed with the retina on top is excited to perform free damped oscillations. The detected oscillation parameters represent a fingerprint of the frequency-dependent mechanical tissue properties that are derived in combination with sandwich beam analysis and finite element calculations [2]. We found that the Young’s modulus of the retina is of the order of a few GPa, much higher than values obtained from experiments in which tissue response is investigated on micrometer length scales. In our study, polymers and proteins on the photoreceptor side of the retina in contact with the nanostructured reed are stretched and compressed during vibration of the underlying scaffold and the acting intramolecular forces are probed at the protein level. In fact, the Young’s moduli of proteins from serum – a major component of the used tissue culture medium – are about 16 times higher compared to the modulus of the TiO₂ nanostructure when probed at the nanoscale (38 GPa vs. 2 GPa). To this end, our mechanical spectroscopy approach offers new perspectives in probing mechanical response of individual proteins within the tissue for studying tissue mechanics, diseases and the effect of drugs.
[1] V. Dallacasagrande, M. Zink, S. Huth, A. Jakob, M. Müller, A. Reichenbach, J.A. Käs, S.G. Mayr. Adv. Mater. 24, 2399–2403 (2012)
[2] S.M. Rahman, A. Reichenbach, M. Zink, S. Mayr. Soft Matter 12, 3431 – 3441 (2016)

Diatoms are single-cell algae characterized by nanopatterned microscopic silica shells (frustules), which exhibit intriguing mechanical and photonic properties. The possibility to use these biosilica microstructures as multifunctional scaffolds by chemical modifications opens up the way to biotechnologically-produced nanomaterials with applications ranging from bio-medicine to photonics¹.
We used two approaches for the functionalization of diatoms biosilica with several organic molecules such as fluorophores, stable organic radicals. The first is based on covalent attachment of the dye molecules on the silica shells (after the removal of the organic cellular matrix) by condensation reactions of a triethoxysilyl groups with the frustules’ silica surfaces. The second approach is based on in vivo incorporation of the molecules into the biosilica during the cell growth.
The lecture will discuss two examples of nanomaterials for different applications obtained by chemical functionalization of biosilica from diatoms microalgae. In the first case in vivo incorporation of several classes of ad hoc synthesized light emitting molecules (fluorescent conjugated compounds or phosphorescent organometallic complexes) in living Thalassiosira weissflogii and Coscinodiscus wailesii diatoms results in nanostructured light emitting materials. The second example will present functionalization of biosilica from Thalassiosira weissflogii with 2,6,6-tetramethylpiperidine-N-oxyl (TEMPO), an efficient scavenger of reactive oxygen species (ROS) in biological systems. Drug delivery properties of the TEMPO-biosilica for Ciprofloxacin, an antimicrobial against orthopedic implant related infections, will be discussed. The TEMPO-biosilica, combining Ciprofloxacin drug delivery with anti-oxidant properties, is demonstrated to be a suitable material for osteoblast-like cells growth².
We disclose biosilica from diatoms microalgae as a multifunctional material for nanotechnology and regenerative medicine. Our studies point out at the combination of biotechnological production and chemical modification as a convenient approach to the synthesis of functional nanostructured materials.

References
W. Yang, P. J. Lopez, G. Rosengarten Analyst, 2011, 136, 42
S. R. Cicco, D. Vona, E. De Giglio, S. Cometa, M. Mattioli Belmonte, F. Palumbo, R. Ragni, G. M. Farinola ChemPlusChem, 2015, 80, 1063

On-demand, ultra-high precision delivery of molecules and cells assisted by scaffold is a pivotal theme in the field of controlled release, but it remains extremely challenging for ceramic-based macroporous scaffolds that are prevalently used in regenerative medicine. Sea sponges (phylum Porifera), whose bodies possess hierarchical pores or channels and organic/inorganic composite structures, can delicately control water intake/circulation, achieving high precision mass transportation of food, oxygen and wastes. Inspired by leuconoid sponge, we designed and fabricated a biomimetic macroporous ceramic composite sponge (CCS) for high precision logic delivery of molecules and cells regulated by mechanical stimulus. The CCS reveals unique on-demand AND logic release behaviors in response to dual-gates of moisture and pressure (or strain) and, more importantly, 1 cm³ volume of CCS achieves unprecedentedly delivery precision of ~100 nanograms per cycle for hydrophobic or hydrophilic molecules and~1400 cells per cycle for fibroblasts, respectively.

In this work, we report an innovative type of rotary bio-micromachines by using diatom frustules as integrated active components and their applications in microfluidic systems for mixing. Diatom frustules are porous cell walls of diatoms made of silica. They are remarkably abundant in nature, highly biocompatible, and have unique embedded nanostructures. Our micromotors use diatom frustules as rotors and patterned micromagnets as bearings, which are facilely manipulated and assembled into working devices in electric fields. They can be integrated into ordered arrays and rotated with controlled orientation and speed up to ~3000 rpm, one of the fastest biomaterial-based rotary micromotors. By exploiting the distinct electro-mechanical properties of diatom frustules and metallic nanowires, we further developed the first reconfigurable micro/nanomotor arrays each of which can be controlled individually. Finally, the diatom frustule micromachines are successfully assembled in microfluidic systems and demonstrated active microfluidic mixing. The outcome of this work would be an important advance in low-cost and biocompatible micro/nanoelectromechanical systems (MEMS/NEMS) and lab-on-a-chip architectures and inspire a new type of devices made of naturally existing biomaterials.

Nature never ceases to amaze by its variety of shapes, flavors and colors, offering elegant solutions approved by evolution. Very bright blue and green colors, for example, are achieved by the interplay of light with periodic and/or quasi-periodic nanostructures found in butterflies. Highly disordered photonic structures in the scales of the white beetles on the other hand produce high brightness white with a surprisingly low-mass-per-unit-area [1].
Here, we introduce a fabrication method to engineer ultrathin white films inspired by these beetles based on saturation with supercritical carbon dioxide. As a result of the saturation, dense nanopores are formed inside thin films of poly(methyl methacrylate) (PMMA). The morphology of scattering media can be well controlled through the parameters of the saturation process which we optimized in terms of bright whiteness. The obtained films have an exceptional whiteness for their thickness, showing 95% reflectance for a 50 µm thin film and still 60% reflectance for 9 µm thick foil. The transport mean free path of light of our thin films is 3.5 - 4 µm being close to photonic glass (2.9 µm) and white beetles (1.47 – 2.1 µm) [1].
Our approach allows scaling up and the ultrathin white films can be post processed and transformed to various shapes by standard procedures like thermo-molding without affecting their pore morphology. Furthermore, the method is not limited to PMMA and can be applied to various thermoplasts including biodegradable ones.

[1] M. Buresi et al., Sci. Rep. 4, 6075 (2014).

The precise control over the interaction between cells and the surface of materials plays a crucial role in optimizing the integration of biomaterials for implants. In this regard, the physico-chemical properties of a given surface play a key role in the overall cell behavior and therefore the final osseointegration of the implant. In this work, femtosecond (fs) laser micro/nano machining technology was used to control cell adhesion, migration, and proliferation over the surface of stainless steel. More specifically, we exploited the fact that nanopatterns generated by fs Laser Induced Periodical Surface Structures (LIPSS) are defined perpendicular to laser polarization and therefore their orientation can be precisely controlled. Cell culture experiments were performed with human mesenchymal stem cells (hMSCs). Our experimental results demonstrate that cell distribution, shape, and migration can be controlled by changing the geometry and orientation of the surface micro/nanopatterns. Our surface-patterning approach, which does not involve chemical treatments and is performed in a one single step, can be applied to most metallic materials, thus representing a simple, clean, and scalable method to control cell behavior.

Technology for solar fuel production is now waiting for major breakthroughs in materials science. Metal oxides play an important role as photoelectrode materials for solar water splitting and CO₂ reduction in photoelectrochemical cells because of their environmentally benign nature and low cost and high abundance. Iron oxide is a highly controversial material for that purpose, because its conductivity in the bulk and at the surface are rather limited.

We have found a way around this limitation by designing a self-assembled electrode architecture based on spheroidal shaped heterostructures from iron oxide and tungsten oxide. Specifically, with a vesicle formation process we synthesize tungsten oxide spheroidal cores with sub-micrometer size and coat them with a nano-sized ultrathin film iron oxide. This electrode architecture has enhanced conductivity. Moreover, it has photonic properties with which allow us to tune its optical absorption by simple processing parameters, such as the spin coating speed.

It turns out that our electrode works similar to the moth eyes in nature [1,2]. The practical outcome is that the photocurrent density is doubled alone by the mesoscale structuring.

We present a complete experimental and computational analysis of the synthesis, property and functionality of this device.

[1] F. Boudoire, R. Toth, J. Heier, A. Braun, E. C. Constable, Photonic light trapping in self-organized all-oxide microspheroids impacts photoelectrochemical water splitting, Energy Environ. Sci., 2014, 7, 2680-2688.
[2] F. Boudoire, A. Braun, E.C. Constable, J. Heier, R. Toth, A World Disrupted - The Leading Global Thinkers of 2014, Innovators For Capturing The Power in Moth Eyes, FP Foreign Policy Magazine Nov/Dec 2014, 75-76.

Bio-Molecular self-assembly is one kind of crucial processes to the growth, survival and evolution of nature life. It underlies the construction of functional quaternary structures, like proteins in living organisms; and that is the requirement to the appropriate functions of proteins and cells. Interface cannot be neglected in the research of protein self-assembly; as in a number of cases, interface involves into the molecular self-assembly of proteins. Exploring the interaction between proteins and interfaces, not only does contribute to people’s knowledge of nature life, but also benefits to a number of bio-engineer applications.
In this presentation, I explore the self-assembly behaviors of the designed helical repeat protein (DHR10-mica18) via atomic force microscopy (AFM). It is one kind of artificial protein with tandem repeating a simple helix–loop–helix–loop structural motif.[1] It has been modified to attach to mica surface with certain orientation by attaching to negative charged mica surface. AFM records the self-assembly process and proves the concept of the design. The results further prove it is the combination of classical and two-step nucleation. Such formed protein self-assembly layer may be used as template for further crystal nucleation and growth.

1. Brunette, T.J., et al., Exploring the repeat protein universe through computational protein design. Nature, 2015. 528(7583): p. 580-584.

Atomic force microscopy (AFM) is an enabling tool for nanoscience due to its ability to image surfaces with sub nanometer resolution. However, the lithographic processes used to fabricate conventional AFM probes impose restrictions on the materials and architectures that can be constructed, limiting the ability of researchers to choose the properties of the probe to best image samples of interest. In contrast with AFM cantilevers that are largely 2D, nature is filled with complex and multiscalar 3D structures composed of diverse substances. Analogous to advances in rapid prototyping that allow researchers to better leverage inspiration from natural systems in macroscopic manufacturing, nanoscale 3D printing can in principle be used to fabricate AFM probes in a manner that allows important properties such as stiffness and vibrational resonance frequency to be rationally chosen. Moreover, since it is possible to fully specify the 3D structure of a probe, other properties such as resonance frequencies of higher order vibrational modes, deflection sensitivity, and non-linearities in the force-distance relationship can be independently adjusted as well.

Here, we demonstrate that functioning AFM cantilevers that are compatible with commercial AFM systems can be 3D printed and used for imaging. In particular, a series of polymeric bisegmented probes with uniquely specified varied cross-sectional geometries were designed using finite element simulation, printed with direct laser writing, and evaluated using an AFM. These studies revealed that probe properties can indeed be rationally designed for specified properties. Furthermore, this technique can provide mechanical information about the polymers used in the writing process whose properties are otherwise poorly characterized and highly process dependent. Additionally, we found that the second harmonic mode could be tuned to an integer multiple of the principle harmonic in a manner that could resonantly enhance multi-harmonic imaging, which is particularly useful for investigating biotic surfaces. Not only does this technique provide access to previously inaccessible probe architectures, 3D printed probes can investigate a larger spectrum of soft and biologically relevant samples. This work opens the door for complex non-rectilinear cantilevers that provide uniquely tuned force-distance relationships or harmonic behavior for bio-inspired sensing and actuation applications.

Micro- and nano-scale sensors are important components of small, highly integrated lab-on-a-chip systems. Yet, as the size of sensors becoming smaller, the probability for the analyte to reach the sensing area, especially in dilute solution or gas, becomes reduced, resulting in a “needle in a haystack” problem. Here, inspired by the chemotaxis behavior of bacteria, we constructed a radially symmetric chemical potential gradient to direct the analyte to a micro-scale area. The chemical potential gradient was fabricated in polyacrylamide (PAAm) hydrogel by E-jet printing a concentration gradient of a hydrolysis solution over an 100 ± 10 µm diameter area on PAAm, followed by coupling with a tertiary amine molecule. We observed that this micro-scale cationic gradient could accumulate the anionic analyte with 50-fold concentration enhancement to a micro-scale area with a diameter of 100 ± 10 µm. By comparing the collection behavior with larger gradients of diameter in the millimeter scale, we also found that the analyte concentration enhancement could be remarkably improved by minimizing the gradient size. We envision that both the sensitivity and the response time of the micro-, nano-scale sensors would be improved by applying a micro-scale chemical gradient potential to them.

Current processes for making particles are quite wasteful of energy and material resources. Most complex particles are made in top-down fashion, requiring expensive lithographic and other equipment with relatively low throughput. By contrast in biology intricate, complex, hierarchical materials are assembled bottom-up with multiple functions, at room temperature. I will overview recent discoveries we have made with the groups of several collaborators, where bioinspired principles were applied to the design and growth of artificial multi-functional materials.

We show examples of engineering the symmetry breaking and dynamics for multiple structures and processes, on multiple lengthscales – from nanometers to centimeters. We demonstrate the formation of Janus and other asymmetric particles, which form as a result of coupling of chemical reactions to non-linear mechanical properties of materials[1,2]. We also demonstrate the opposite effects – how mechanical deformations and molecular interactions can help one simplify chemical syntheses[3].Further, we also demonstrate that even without reactions, the material properties and geometry alone could cause symmetry breaking. We show instabilities and symmetry breaking, both static and dynamic, in some of the simplest known structures spherical cap and cone shells.

We combine geometrical approaches with chemistry to achieve multifunctionality.[4] Instead of designing all the desired functions in a single molecule with unpredictable chemistry approach, we use controlled internal phase separation in a material to introduce existing materials with already optimized functions, and interweave them into one. This route to combining existing syntheses results in over 8000 3-function combinatorial possibilities from just 20 different functions. We have demonstrated the incorporation of ionic actuation, shape memory, and electrical conductivity, as well as emerging effects, to create the first bottom up programmable movement material.

Finally, we describe bottom-up molecular mechanisms we have discovered for growing particles of multiple shapes liquid droplets. They rely only on transformations inside the droplets and, without any external applied fields, are able to generate a number of regular geometric shapes, including octahedra, hexagons, rhomboids, triangles and fibers. We explain the transitions between these shapes and methods to control them in both the liquid and solid state. This scalable process is a molecularly based method for symmetry breaking on various scales.[5] I will outline a number of implications for further fundamental discoveries and for potential applied explorations we are pursuing in symmetry breaking, manufacturing and nanoscience.
[4] Khaldi A, Plesse C, Vidal F, Smoukov SK, Adv. Mater. 27 (30), 4418–4422 (2015) DOI: 10.1002/adma.201500209
[5] Denkov N, Tcholakova S, Lesov I, Cholakova D, Smoukov SK, NATURE 528, 392–395 (2015), DOI: 10.1038/nature16189

In materials synthesis, structure dictates function; complete control over the physical properties of a material necessitates complete control over material structure at all length scales. While chemistry can be used to dictate structure at the atomic level, and various manufacturing techniques can control macroscopic material form, manipulation of structure at the nanometer to micron length scale presents a more difficult challenge. Recent advances in DNA-directed nanoparticle assembly have significantly increased the diversity and precision achievable via bottom-up syntheses, as programmable base-pairing between DNA-grafted nanoparticles can direct the formation of ordered superlattices with a multitude of different crystallographic arrangements. However, DNA-based particle assembly currently lacks a simple method to specify arbitrary crystallite sizes or shapes, or defect positions within the crystals, preventing it from achieving complete control over material structure. In this work, we demonstrate how the combination of bottom-up, DNA-based self-assembly and top-down nanolithography can be used to circumvent the limitations associated with each individual method of nanoscale materials synthesis. An array of gold posts is first fabricated with e-beam lithography, and subsequently functionalized with DNA, allowing DNA-grafted particles to be epitaxially deposited onto this post array in a manner analogous to atomic thin film deposition techniques. By modulating the crystallographic arrangement of the lithographically defined posts, we can grow multi-layer lattices with precise control over lattice size, shape, and orientation. Additionally, we demonstrate how fundamental concepts that govern atomic thin film deposition can be used to understand this nanoscale assembly process, and conversely how this unique materials synthesis method can be used to explore basic concepts in thin film growth that are not easily examined in atomic systems. The templated growth of nanoparticle superlattices therefore enables both fundamental understanding of thin film growth methods, as well as the synthesis of nanoparticle-based materials with complete control over material structure across all length scales.

Mimicking features of a natural material is not a trivial undertaking. Natural particles such as pathogens (esp. viruses) are highly optimized for their specific functions, in vivo, and possess features that are most desirable in drug delivery carriers. Considering their characteristics, we will be able to satisfy the central dogma of drug delivery, which is to design bio-inspired vehicles that target tissues and cells with maximal therapeutic efficacy. HIV is one of the most professional biological hijackers. It has been reported that immature HIV particles are more than 14-fold stiffer than mature ones. Moreover, there is a striking correlation between the softness of HIV viruses during maturation and their ability to enter cells.
Based on these findings, it is logical to expect that the Young’s modulus of nanoparticles (NPs) is one of the cornerstones determining their pharmacokinetics, tumoral distribution pattern, cellular uptake rate and their mechanism of internalization. Therefore, this calls for the studies aimed at evaluating the effect of elastic deformation of NPs on their biological behavior.
Here we present an engineering strategy to enhance the efficacy of cancer nanotherapeutics by controlling their physicochemical properties. The objective of this paper is to show how we can tailor mechanical properties of self-assembled polymeric NPs, inspired from viruses. As a robust synthesis tool, we have used microfluidics platforms, benefiting from a controlled mixing regime, to provide monodisperse NPs with adjustable physicochemical properties. Our results confirm the possibility of controlling main physical and biological characteristics. The possibility of having control over size (50-250 nm), Zeta potential (1-14 mV), drug loading efficiency (>95% for Paclitaxel anticancer drug at 15wt% of initial loading), ligand density (10-200×10⁶#RGD.um^-2) and sustained release profile (2×10^-22 m².s^-1) of NPs has been demonstrated in this study. By playing with polymer composition, as well as flow characteristics (flow rates and microchannel design) we were able to tune the Young’s modulus of chitosan-based NPs between 200 MPa and 1.5 GPa. And based on in vitro and in vivo studies, we can conclude our outcomes are as: (i) soft NPs will have a longer circulation half-lives compared to stiffer ones, and this can be used to increase targeting to certain tissues; (ii) this increased circulation time for soft NPs can be correlated to the attenuated level of the macrophage-NPs interactions; (iii) stiffer NPs are endocytosed much more rapidly and in higher amounts than softer NPs by both of immune cells (macrophages) and cancer cells.
Based on the findings, mechanical properties of NPs, which is often ignored in nano-bio interface, will affect their therapeutic efficacies significantly. The rationale for this work is that it will establish a robust approach to build a new avenue in cell-nanomaterials interactions for the next generation of nanomedicine.

The use of bio-design concepts is a promising strategy to fabricate nanostructured hybrid materials, because have the variety available of biomelecules which can be used in self asembly of structures enables several innovative alternatives to overcome the limitations of conventional self assembly methods. In this context we use the biotechnology with materials chemistry for propose the use of design concept of biomimetic to establish a protocol to fabricate self-organized systems of metal nanoparticles on surfaces with the composition, structure and morphology controlled in the shape of plates, wires, tubes using among other metals, ceramics and polymers. The inducing agent of self assembly were biomolecules than produced by fungi Penicillium brasilianum, which were added in systems containing surfaces to be coated with metal nanoparticles. We showed than the deposition of the nanoparticles layer is the resulting in a self-assembly effect induced by biomolecules produced by micellar fungi than act directly on the stability of the nanoparticles in the colloidal suspension, favoring the formation of successive layers of nanoparticles surfaces. The concentration of metabolites and pH values of solution have directly affects the stability and self assembly of the nanoparticles.

Optical reflectors made by photonic materials with brilliant structural colors have great impacts in applications such as reflective displays, sensing, detection and smart windows. Although high quality photonic structures could be fabricated through well designed manufacturing or assembly procedures, current materials are lack of the capability to recover or partially restore function from mechanical damages. In this work, we report durable optical reflectors made from supramolecular nanocomposites with angle-independent structural colors and fast healing properties. The relationship between the material composition and the optical and mechanical performance of the materials are also discussed.