Symposium SM07—Bioinspired Materials—From Basic Discovery to Biomimicry

The wet adhesion of mussels, although incompletely understood, has inspired numerous translational studies seeking to capture its strength, toughness and versatility. Given the Dopa-rich interfacial proteins in mussel adhesion, most translations depend on adopting Dopa or catechol functionalities for a variety of synthetic backbone chemistries. Although notable short-term successes have been reported, a robust and durable adhesive formulation based on catechol or Dopa has yet to emerge. The reason for this is fairly obvious: catechols including Dopa are prone to oxidation. Although oxidation products such as quinones have some use in promoting cohesion as cross-linking agents, they have poor adhesion on most surfaces.
Despite the very oxidizing influence of seawater, catechol-mediated mussel adhesion does not succumb to this limitation. Indeed, adhesive plaque interfaces remain reducing after months of service in the sea. Current evidence supports that mfp-5 with >25 mole % Dopa deposited as a 10-20 nm thick film is the functional adhesive bound to surfaces by its Dopa and lysine functionalities. On top of this, sits an mfp-3 rich hydrogel about 100-200 nm deep. Mass spectrometry reveals that the Dopa in mfp-3 remains intact despite the ambient oxidizing environment. As mfp-3 variants coacervate during deposition there is conjecture that coacervates are insulating Dopa but the mechanism for this is not yet understood. Certainly, mfp-3 in aqueous solution at pH8 undergoes spontaneous oxidation.
Segregation of different redox-active proteins into specific compartments resembles a battery. The mfp-5 containing adhesive film is one compartment; mfp-3 and mfp-6-containing coacervate droplets is another. These two share a common but immiscible interface for redox exchange. Assuming that the film of mfp-5 is vulnerable to oxidative damage and given that mfp-3/6 within coacervate droplets is shielded from oxidation, the reservoir of reduced mfp-3 should offer electrons and protons to restore damaged Dopa in mfp-5 until mfp-3 and -6 are depleted.
The significance of this to translational studies is clear: if the aim is to make synthetic adhesives based on Dopa, then the adhesive has to be engineered to include a redox reservoir or battery that will maintain the surface-bound catechols against oxidative damage.

The microstructures of natural surfaces, such as plant leaves, reptile skin and ciliated tissues can be actuated to provide dynamic, adaptive properties of wetting, transport, and adhesion [1]. Examples include the gecko and the octopus, which can reversibly switch their adhesion to a wide variety of opposing surfaces. Yet, most synthetic surface structures are static, lacking an ability to change dynamically in response to their environment or an applied signal. This work explores how adhesion, friction, and wetting can all be controlled through bio-inspired dynamic surfaces. By engineering the shape, scale, and spacing of surface microtopography on silicone layers, interfacial contact and interaction can be modified. Our dynamic microtopography devices will show droplet wetting transition from Cassie-Baxter to Wenzel, switchable adhesion to structured or flat surfaces and tunable friction capable of >50% change in peak frictional force. [1] Gorb S. Functional surfaces in biology: mechanisms and applications. CRC Press; 2006. p. 381-97.

Macrofouling organisms have plagued mariners and scientists alike since the sailing of the first ships in the ocean. Even today, combating fouling is a global challenge with great economic burden on the world’s navies and maritime operations. Over the last year, our team has applied modern bioinformatic approaches to produce a new, more comprehensive picture of the specialized proteins found in the adhesive of one of the most tenacious fouling organisms in the ocean: the acorn barnacle. Barnacles produce a micron-thick layer of ordered amyloid-like nanofibers from proteins that function as a permanent wet adhesive. Recent proteomic sequencing of the dissolved barnacle glue reveals that, like in other fibrous biomaterials such as silks and elastin, small and flexible amino acids play a key role in forming the mesh-like adhesive. Their well-defined, modular, nature result in novel biomaterials that serve many purposes: adhesion, durability, bacterial resistance, and even potent enzymatic activity. Fibers are shaped by a highly conserved domain alternating between short 20-residue low complexity sequences (Gly/Ser/Thr/Ala residues) and regions with alternating charged and non-charged side chains, with more than 80 such domains in just five proteins. The adhesive properties of these unique sequences and their function in an amyloid-like structure remain unclear.
To develop the sequence basis of cement formation, we design short synthetic peptides from homologous cement proteins. Short synthetic peptides demonstrate that materials are formed through a set of patterned sequences that exert specific control over polymerization, curing, and adhesion using recognition mechanisms similar to how globular proteins recognize each other, i.e., structure-based recognition. Specifically, we find that patterned charge domains recognize and activate otherwise dormant peptides through recognition of a unique anti-parallel beta sheet structure as measured by FTIR. While charged domains favor an anti-parallel structure, sequences without charged domains switch fibril assembly to parallel beta sheet aggregates. Our work demonstrates that the structures produced by patterned cement sequences, and the progression of domain interactions, are critical in polymerizing materials that resemble the natural adhesive. Finally, to understand whole protein self-assembly, we demonstrate that emergent platforms such as engineered bacterial biofilms are a viable route for the growth of recombinant cement materials as well as for mapping protein and peptide interactions. Synthetic and recombinant adhesive materials provide a route to scale up and study a scarce but potent class of multifunctional adhesive nanostructures produced by one of the oldest adversaries of naval and maritime technologies.

We will report how coatings and nonwovens with outstanding superhydrophobic and icephobic properties can be made from novel types of polymer particles with controlled morphologies and interactions. First, we will introduce the synthesis of a new class of particles named soft dendritic colloids (SDCs). These particles are hierarchically structured, with a branched corona of nanofibers spreading out in all directions. They are nanomanufactured by multiphasic polymer precipitation under intensive shear. The nanofiber corona around these "gecko leg" particles endows them with extraordinary strong adhesion to almost any surface and to each other, and enables unique structure-forming abilities. These particles exhibit the phenomenon of “contact splitting”, which is displayed in the remarkable adhesion of gecko feet. The morphological similarity of the SDCs to the gecko lizards’ setae endows the SDCs with excellent dry adhesion and cohesion properties. The hierarchical surface roughness resulting from the overlapping SDC micro- and nanofibers allows the facile formation of superhydrophobic and superhydrophilic coatings depending on the properties of the polymer used. The adhesion of SDC coatings to substrates can be further improved both through the addition of a poly(dimethyl) siloxane (PDMS) binder and by creating bicontinuous networks of SDCs composed of different polymers. The addition of a PDMS binder and formation of bicontinuous SDC networks modify the surface roughness and contact angle of the SDC coatings and lead to improvements in durability, wettability, and anti-icing properties, including increased ice nucleation time and decreased ice adhesion strength when compared to uncoated and SDC coated substrates. The new functional coatings can find applications in numerous industrial and consumer products.

Gecko-inspired fibrillar adhesives have become increasingly prevalent over the past two decades because of the multifunctional behavior exhibited in gecko adhesive toepads, including self-cleaning, controlled releasability, and reversibility. Many challenges remain in replicating this multifunctionality, a major one being understanding the role of the complex morphology: microscopic hierarchy of the adhesive setae and their macroscopic patterning across the toepad. Deconvolution of the structural effects in producing the desired properties remains daunting, because setal structure is very complex. However, fibrillar adhesion has been independently evolved by Anolis lizards, and these lack the hierarchical branching of their setae. Thus, anole setae more closely resemble the theoretical models used to explore the principles of fibrillar adhesion and the synthetic seta-like fibrils that have been employed in the generation of synthetic adhesives. In this study, we employ scanning electron microscopy to examine the setal dimensions and patterning of Anolis lizards across the toepad and compare our findings with the attributes of the fibrillar adhesives of geckos. Detailed morphological characterization of Anolis adhesive setae provides information which can be used to understand the potential emergent properties of hierarchical complexity and patterning of lizard fibrillar adhesives.

A successful biomedical adhesive must be biocompatible, set in a wet environment, match the mechanical properties of the surrounding tissue, and have proper adhesive and cohesive properties. Current technologies do not meet these needs. We developed bioinspired protein-based adhesives that combine adhesion from DOPA residues found in mussel adhesive proteins with the mechanical properties of elastin, which can also coacervate in response to the environment. We demonstrated that these proteins are cytocompatible, provide the strongest bonds of any rationally designed protein when used completely underwater, and can be easily applied underwater because they coacervate in physiological conditions. Recently, we investigated different formulations in physiologically relevant environments by using pig skin substrates and curing in a warm, humid environment.

We present a new class of bioinspired nanomaterials that are stabilized by a combination of covalent and hydrogen bonds. Prior work by others has shown that cyclic peptides can self-assemble to form supramolecular assemblies through backbone-backbone hydrogen bonding. To improve upon this molecular architecture, we develop a synthesis route to polymerize cyclic peptides and form a linear polymer chain that can transition between a rigid nanorod and a “soft” unfolded conformation. For a cyclic peptide polymer containing amine-terminated side chains on each ring, we demonstrate that self-assembly can be triggered in aqueous solutions by varying the pH. We measure the elastic modulus of the rigid nanorods to be ca. 50 GPa, which is comparable to our molecular dynamics (MD) prediction (ca. 64 GPa). Our results highlight the uniqueness of our molecular architecture, namely their exemplary toughness (up to 3 GJ m^-3), in comparison to other cyclic peptide-based assemblies. Finally, we demonstrate that the amphiphilic cyclic peptide nanopores are capable of inserting into the membrane of both gram-negative and gram-positive bacteria, and causing their deaths by disrupting their osmotic pressure.

Self-assembly of molecules is an attractive materials construction strategy due to its simplicity in application. By considering peptidic molecules in the bottom-up materials self-assembly design process, one can take advantage of inherently biomolecular attributes; intramolecular folding events, secondary structure, and electrostatic interactions; in addition to more traditional self-assembling molecular attributes such as amphiphilicty, to define hierarchical material structure and consequent properties. A new solution assembled system comprised of theoretically designed coiled coil bundle motifs will be introduced. The molecules and nanostructures are not natural sequences and provide opportunity for arbitrary nanostructure creation with peptides. With control of the display of all amino acid side chains (both natural and non-natural) throughout the peptide bundles, desired physical and covalent (through appropriate “click” chemistry) interactions have been designed to produce one and two-dimensional nanostructures. One-dimensional nanostructures span exotically rigid rod molecules that produce a wide variety of liquid crystal phases to semi-flexible chains, the flexibility of which are controlled by the interbundle linking chemistry. The two dimensional nanostructure is formed by physical interactions and are nanostructures not observed in nature. All of the assemblies are responsive to temperature since the individual bundle building blocks are physically stabilized coiled coil bundles that can be melted and reformed with temperature. Additional, novel nanostructures to be discussed include uniform nanotubes as well as the templated growth of metallic nanoparticle on and in peptide nanostructures. Included in the discussion will be molecule design, hierarchical assembly pathway design and control, click chemistry reactions, and the characterization of nanostructure as well as inherent material properties (e.g. extreme stiffness, responsiveness to temperature and pH, stability in aqueous and organic solvents).

Silk fibers produced by silkworms and spiders are protein-based biomaterials with a combination of excellent mechanical properties and biocompatibility. Due to these attributes, silk-based biomaterials are useful for fabricating bio-devices with important functional performance. Considerable effort has been made in developing techniques to process native silk fiber materials into silk solutions, including aqueous and solvent systems. These solutions can then be processed to generate a variety of regenerated silk materials such as films, foams, sponges and tubes. However, the tendency of silk fibroin to self assemble in solution can result in some limitations in terms of process control windows. To overcome these potential limitations and offer additional processing options for silk materials, new solution-free methods based on lyophilized silk powders help. Further improvements could be attained by using silk as a raw material from the start, avoiding the complexities of processing windows and also the addition of lyophilization steps. Such processes could lead to new silk-based materials such as for films, plates, screws, bricks, and sponges prepared with tunable mechanical properties. Such a new approach should impact the field of silk device fabrication by providing new processing routes for the protein and avoiding some of the challenges with more traditional options.

Natural materials have been widely explored and applied in various fields, especially for biomedical applications. Nowadays, problems of energy crises and climate change pose a threat to human living. The consumption of the energy leads to greenhouse gas emission, which causes global warming. Therefore, developing eco-friendly cooling systems is the significant issue that people are still working on. However, most of the current cooling methods needs energy to carry heat away. Radiative cooling is a passive cooling method which can lower the temperature without any energy consumption. It means that the heat can radiate to outer space through a transparency window of the atmosphere between 8-13 μm. In the past, radiative cooling during nighttime has been studied. Radiative cooling during daytime, however, is more difficult to achieve because the cooler needs to have not only high emissivity in the atmosphere windows but high reflectivity in the solar spectrum. Recently several methods have been applied to daytime radiative cooling. For example, photonic solar reflector and thermal emitter, such as HfOs, or SiO₂ and metamaterial film, can reflect incident sunlight while emitting in the atmosphere windows. However, nanophotonic approaches require complicated fabrication and high cost, which is difficult to scale up to meet the requirements of commercial applications. While the radiative cooling technology based on natural materials is still not well studied, natural materials may have the great potential for applying on daytime radiative cooling devices.

Herein, we studied different kinds of natural materials, such as seashell, wood, bamboo and cocoon. All samples were cut into 2 x 2 cm² for optical measurements. Interestingly, all of them displayed very high absorption (i.e., high emissivity, > 80%) in broadband IR wavelength range (8-25 μm), which were mainly attributed to their intrinsic chemical composition, such as proteins, cellulose, minerals and some small molecules due to their vibrational transitions. Noteworthily, compared to the typically narrow IR emissivity peaks of artificial daytime cooling materials, the extremely broadband emissivity peak of the natural materials could cover two atmospheric windows (8-13 μm and 16-25μm). The result means they could transfer more heat to outer space via thermal radiation and consequently are able to more efficiently lower the temperature. Among the natural materials, silk cocoon was chosen for further investigation because of its 90% absorption at IR wavelengths and the simple, well-studied fabrication process for different morphologies. We fabricated silk fibroin (SF) thin films from natural cocoon through the reported protocol. By adjusting the concentration of SF solution, the thin films with different thickness of 10 and 20 μm could be obtained for optical measurements. We observed that the 20-μm SF film shows a higher average emissivity of 70 % in the atmosphere windows region than the average emissivity of 50 % for the 10-μm SF film, indicating that the film thickness is a key factor. Thus, we performed a thin-film optical simulation to find the optimal thickness for the SF film. Finally, we found that the emissivity gradually increased with thickness and reached a maximum value of 95% as the thickness of 100 μm. Further optical analyses and cooling temperature measurements for the optimized SF films are in progress and will be reported at the conference. Also, other natural materials and their optical properties as well as cooling capacity evaluations will be reported.

Elastomeric proteins function as molecular springs in their biological settings to establish elastic connections, and provide mechanical strength, elasticity and extensibility. To fulfill their biological functions, elastomeric proteins have evolved to assume different structures, from simple random coil-like structure to more sophisticated beads-on-a-string conformation, and exhibit distinct mechanical properties. The development of single molecule force spectroscopy techniques has made it possible to directly probe the mechanical properties of such elastomeric proteins at the single molecule level and allowed to understand molecular design principles of these complex protein polymers. This knowledge has enabled us to engineer novel elastomeric proteins to achieve tailored and well-defined nanomechanical properties. Going a step further, we have started to employ these novel elastomeric proteins as building blocks to construct protein-based biomaterials, which in turn provide an ideal system to understand how single molecule nanomechanical features are translated into biomechanical properties of macroscopic materials. These studies will pave the way to utilizing proteins as building blocks to engineer new generations of protein-based biomaterials for diverse applications in biomedical engineering as well as material sciences.

Supramolecular filaments, such as microtubules (MTs), are key elements behind many of the dynamic and responsive behaviors in biological systems. In particular, MTs enable key processes ranging from intracellular cargo manipulation or changing the shape of a cell to separating genetic materials during cell division. MTs undergo a remarkably dynamic, often cyclic, assembly and disassembly process, known as dynamic instability. Key to the dynamics of the MT system is the balance between the driving forces behind MT assembly and the destabilizing influences that lead to MT depolymerization. While MT assembly is driven by a complex series of intermolecular attractive forces that bring together the tubulin heterodimer building blocks, destabilization of these attractive forces by changes in tubulin molecular shape, variations in temperature, or molecular interference with tubulin binding will cause the MTs to disassemble. Here, we explore how these concepts affect supramolecular assembly of synthetic peptides, based on the tubule-forming dipeptide, di(phenylalanine) (FF). We specifically discuss how this system mimics biological concepts of inherent supramolecular instability. We further show how the systematic incorporation of light-responsive, shape-changing azobenzene derivatives enables the use of variable molecular morphology to controllably change to both the stability and morphology of self-assembling peptide nanostructures. Through microscopic and spectroscopic characterization of systematically-modified FF peptide assemblies, we explore the mechanisms behind this dynamic behavior. Taking inspiration from such natural systems, we can learn to control critical, competitive molecular influences that regulate dynamic materials assembly. Understanding these processes will advance the development of new classes of adaptive and reconfigurable materials.

Sandia National Laboratories is a multi-mission laboratory managed and operated by National Technology and Engineering Solutions of Sandia, LLC., a wholly owned subsidiary of Honeywell International, Inc., for the U.S. Department of Energy’s National Nuclear Security Administration under contract DE-NA0003525.

The origin of spider silk’s superior mechanical properties has been intensively studied for several decades. It is widely accepted that such appealing properties originate from the hierarchical structure of silk threads. Although the protein sequence and macroscopic morphology of the silk fiber are well known, our understanding regarding structural organization for length scales in between is still limited. Nanofibrils have been suggested as an important building block in this intermediate length scale. However, no consensus model regarding their concentration in spider silk fibers or even their dimensions has emerged, which has hindered a systematic analysis of these materials.
We study the silk ribbons (major ampullate (MA) silk) of the recluse (Loxosceles) spider, which entirely consist of 20-nm thin nanofibrils. This much simpler silk system thus provides an excellent opportunity to study its structure-property relations. Having performed polarized Fourier transform infrared (FTIR) and polarized Raman spectroscopy on single fibers of this silk, we know that the spectra stem solely from nanofibrils. This has allowed us to quantitatively determine the relative orientation and volumetric percentage of β-sheets vs. other types of protein secondary structures directly. Hence, our approach provides a path toward a significantly improved understanding of the structure of this protein-based material and useful insights towards replicating its merits in synthetic fibers.

Surfactants and lipids are used in a broad range of applications from basic science to industrial cosmetics, hygiene, and food products. Here, we report on the structure and phase behavior of a system of two fatty alcohols (FA) and a monovalent cationic surfactant (CS) mixed with water. At low to intermediate surface charge density (σ), the shape of these lipids generally promotes the formation of chain-ordered bilayer membranes. In this study, we use synchrotron x-ray scattering and polarized optical microscopy to characterize the phase behavior of this ternary system, with special focus on the effects of water content and the CS:FA ratio. Remarkably, as a function of increasing σ, we observe that high water-content mixtures (d=interlayer spacing >> δ=bilayer thickness) undergo an abrupt transition from a chain-ordered lamellar phase (L_CO) to a chain-melted lamellar phase (L_CM) in coexistence with a fiber-like phase of tubular morphology, which grows stronger with increasing σ. Unexpectedly, the chain-melted lamellar phase exhibits a new length scale (2π/q*≈160Å) associated with the bilayer structure that is not seen in conventional lamellar L_α phases of fluid biological membranes. Further, the interlayer spacing in this phase is constant at more than 10nm smaller than in the L_CO phase, even though the two-phase system occurs at a higher CS:FA ratio in the phase diagram. Also of interest is the role of common additives, such as the preservative EDTA (a chelator of metal ions), which we have found to have a significant effect on the nanostructure of the lamellar phases. These findings are particularly important because the microstructure of these materials underlies the viscoelastic properties of interest in application.

Self-assembly, involves assembly of molecules into ordered structures to various structures based on different conditions. Self-assembly of structures using biomolecules such as aromatic dipeptides, give rise to functional and biocompatible nanostructures of various forms and biomedical applications. We have synthesized nanotubes using solution-phase self-assembly (SPSA) and plasma enhanced chemical vapor deposition (PECVD), an eco-friendly technique. Quantum chemical computational methods at different levels of theories like dispersion-corrected density functional and Moller-Plesset perturbation were employed to draw insights into the self-assembly process and forces involved.

The biophysicochemical surface properties of SPSA and PECVD nanotubes were examined using various techniques. Confocal, scanning electron and transmission electron microscopy were used to know the morphological features of these nanostructures. Thermal characterization was carried out using differential scanning calorimetry and thermogravimetric analysis, whereas the chemical characterization was done using Fourier transform infrared spectroscopy, Raman scattering, liquid chromatography-mass spectroscopy, and nuclear magnetic resonance, and circular dichroism spectroscopy, and powder x-ray diffraction. The rat adrenal pheochromocytoma (PC-12), human bone marrow neuroblasts (SH-SY5Y) and neural progenitor cells were used for cytotoxicity studies with MTT (3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide), real-time polymerase chain reaction (q-PCR), and dopamine-enzyme linked immunosorbent assay. The differences in proliferation and expression of the cells on various samples were observed.

Mechanically guided assembly is considered as a facile and scalable methodology for fabrication of three-dimensional (3D) structures. However, most of the previous methods require multistep processes for bonding bi- or multi-layers and only result in non-freestanding 3D structures due to usage of a supporting elastomer substrate. Herein, we report a functional elastomer composite that can be transformed to a freestanding and monolithic 3D structure driven by the mechanically guided assembly. Photolithography can be used to selectively tune the mechanical properties of UV exposed regions which exhibit enhanced elasticity compared with the non-exposed regions. Thus, a gradient of the residual strain in the thickness direction makes the films assemble into 3D structures. These 3D structures are also predicted by our computational models using finite element simulations, which yields a reasonable agreement with the experiments. The systematically designed 2D structures with varied patterns can be transformed to various 3D structures with the control of the residual strain gradient, via key processing parameters including pre-strain, film thickness, and UV exposure time. By integrating different active electronic components on the fabricated 3D structures, potential applications of this 3D platform in electronics were demonstrated. This study offers a unique capability in constructing monolithic and freestanding 3D assembly, paving new routes to many applications such as wearable electronics, smart textiles, soft robotics, and structural health monitoring.

Metal ion recovery from industrial wastewater and electronic waste has attracted increasing attention to recycle precious metals and inhibit emission of hazardous heavy metals. The recovery of the precious metals has been particularly emphasized with a concept of urban mining, which aims to recover precious metals from waste resources. However, current technologies for metal recovery are not cost-effective and environmentally friendly. Recently, bioinspired coating materials have been actively investigated as metal adsorbents. In particular, polyphenols can easily produce excellent coating layers at a low cost and form coordination complexes with various metal ions, which can be used to recover precious metals from the waste. Here, we report a porous bioinspired polyphenolic adsorbent for gold recovery enhanced by light illumination. Mesoporous polymer microspheres were employed as a porous substrate providing high specific surface area enough to efficiently adsorb gold ions. The polymer substrate was coated with tannic acid via hydrogen bonding, which leads to the coordination of gold ions with galloyl moieties and subsequent photochemical reduction of gold ions. Metal selectivity of the tannin-coated microspheres was investigated using an aqueous mixture of various metal ions. The light-enhanced adsorption and reduction of gold ions were investigated under 1 sun-simulated illumination using adsorption isotherm models. The light-enhanced adsorption and reduction of gold ions was initiated by ligand-to-metal charge transfer mainly due to UV light absorption by tannic acid, and then visible light absorption by the surface plasmon resonance of metallic gold nuclei created additional driving force for the selective reduction of gold ions. This work suggests a new design of environmentally friendly metal adsorbents for efficient noble metal recovery with a low cost by harnessing the solar energy and bioinspired coatings.

Fresh water collecting technology from fog that known as fog harvesting is one of the solutions to solve water shortage problem specially at desert areas. In this study, we investigate an efficient water collection on a superhydrophilic surface with patterned hydrophobic regions to mimic the stenocara beetle surface. Superhydrophilic surface is synthesized on silicon wafer by growth of vertically aligned zinc oxide (ZnO) nanowires. The contact angle of the surface of ZnO nanowires shows 0 degree that is superhydrophilic surface due to the imbibition phenomena with water. To make the hydrophobic surface, the ZnO nanowire patterned surface is dipped into 0.1M of AgNO₃ solution in distilled water. Then, the dipped surface is exposed by ultra violet (UV) that generates electron-hole pairs at the ZnO surface. The excited electrons reduce Ag ions in the AgNO₃ solution to Ag nanoparticles on the ZnO nanowire surface. The contact angle of ZnO nanowire-Ag nanoparticles structure shows around 125 degree that has hydrophobic property. To divide the superhydrophilic and hydrophobic regions, patterned mask is used for selective synthesizing the Ag nanoparticles on the ZnO nanowire surface. Effects of hydrophobic patterns are investigated by collecting water from artificial fog. Hydrophobic surface without superhydrophilic region is easily draining water. However it doesn’t fast capture water due to low adhesion between water and surface. At the superhydrophilic surface patterned surface, water droplets are easily formed and roll off from surface. As a result, the hydrophobic surface with patterned hydrophobic regions makes more water collection rate of 170 mg/hcm² than superhydrophilic surface of 128 mg/hcm²

Bioinspired design develops new solutions in fields that conventionally have few connections with biology. Functional membrane developed through this design approach incorporates natural systems with inorganic compounds to display various functionalities, such as conductivity, magnetism, and hydrophobicity. Bacterial cellulose (BC) membrane produced by Gluconacetobacter species forms the skeletal framework and aids in entrapping recombinant E. coli bacteria. The recombinant E. coli bacteria containing the genetic circuit tuned to produce extracellular amyloid protein, curli, with specific functional peptides. The curli protein in the BC-curli hybrid facilitates the synthesis of magnetite nanoparticle at temperatures below 100 °C by acting as in situ nucleating sites for metal salts. The final BC-curli hybrid membrane decorated with magnetite nanoparticles shows a magnetic response. The surface morphology of the hybrid material was characterized through FESEM and distribution and shape of the nanoparticles was characterized through TEM. The chemical structure and inorganic phase were characterized by FTIR and XRD respectively. Magnetic response of the hybrid material was measured using VSM.

Biological ion channels embedded in cell membranes with multiple functions have gained attention. Bacterial outer membrane protein F (OmpF) is a multifunctional channel with ionic selectivity, ionic gating, and ionic rectification properties. Also, this plays critical roles in life processes, including maintaining intracellular acidity, keeping osmotic balance, participating in ion exchange, etc. Membranes mimicking these ion channels have important applications in materials science. For practical applications, bioinspired heterogeneous membranes, which generally refer to the composite porous membrane formed by the hybridization of two functional membranes with different chemical composition, have drawn enormous research attention because of their simplicity and potential applications in mimicking various functions of biological ion channels. With respect to maintaining high mechanical strength and promoting the functionality of the fabricated membranes, organic/inorganic hybrid heterogeneous membranes represent an ideal candidate. Here, we prepared a multifunctional heterogeneous membrane by combining a sulfonated tetrafluoroethylene based fluoropolymer-copolymer membrane, Nafion, and a porous anodic aluminum oxide membrane. Despite the morphology of the as-prepared membrane is not nearly as refined as that of the OmpF, we have demonstrated a bioinspired multifunctional heterogeneous membrane capable of achieving high ionic rectification and highly efficient cation-selective gating. We expect that greater levels of multifunctionality can be implemented by optimizing the morphology of the used Nafion, thereby opening new applications in energy conversion, filtration, desalination, etc.

Amphiphilic block copolymers can (ABC) self-assemble into bilayer or monolayer membranes on surfaces. Relatively low molecular weight ABC bio-inspired membranes have previously been reported to be fluid as monolayer but immobile as bilayer membranes. (Goertz et al.) In this study, we investigate low-molecular weight polybutadiene-b-polyacrylic acid (pBD-b-pAA) and polybutadiene-b-polyethyene oxide (pBD-b-pEO) bilayer fluidity as a function of pH. pBD-b-pAA demonstrates the ability to generate fluid bilayers while pBD-b-pPEO bilayers are immobile as previously reported. We investigate the mobility of these short chain ABCs as a function of pH and propose a mechanism for induced fluidity in ABC membranes. Fluorescence recovery after photobleaching (FRAP) and in-situ Atomic Force Microscopy (AFM) are used to characterize the membrane composites and their functional properties. We report our findings and the potential for generating mobile polymer membranes that more closely mimic fluid bilayers similar to those in biological lipid systems.

Reference:
Goertz, M.P., Marks, L.E. & Montaño, G.A. (2012) Biomimetic Monolayer and Bilayer Membranes Made From Amphiphilic Block Copolymer Micelles. ACS Nano: 6(2):1532-40.

Pectins are polysaccharides from the cell wall of dicotyledonous plants and consist of linear polymers formed mainly by galacturonic acid units linked glycosidically by α- (1,4) bonds. Traditionally, pectins are extracted from citrus peels and apple pomace, although they can also be recovered from minor sources such as sugar beet which have particular structural characteristics, like the presence of ferulic acid bound to galactose and arabinose residues, which enables oxidative coupling between polysaccharide chains. Ferulated pectin gels have become relevant in the design of matrices for the controlled release of molecules of therapeutic interest. In the present study, ferulated pectin was extracted from a sugar beet cvar. grown in Mexico, and composition and physicochemical characteristics were investigated. Pectins presented a galacturonic acid content of 63% (w/w) and residual amounts of neutral sugars (rhamnose, arabinose, xylose, mannose, galactose and glucose). The ferulic acid and diferulic acid contents were 3.5 and 0.16 µg/mg pectin, respectively. The intrinsic viscosity and molecular weight values for pectin were 2.5 dL/g and 665 kDa, respectively. Fourier Transform Infra-Red (FT-IR) spectrum of pectin showed characteristic bands confirming the molecular identity of this molecule. From FTIR analysis, methoxylation degree of pectin was estimated to be 63%, which correspond to high-methoxyl pectin. The general characteristics and specifically the ferulic acid content in pectin from sugar beet, could increase the impact of this polysaccharide in food, pharmaceutical and nutraceutical applications.

Maize processing industries generate maize bran as a by-product which is most commonly sold for livestock feeding. Maize bran contains high amounts of arabinoxylan (AX), a group of polysaccharides composed by β-(1→4) xylose residues which may be substituted with arabinose units and some of those arabinoses might have ester-linked ferulic acid (FA). In this study, AX were extracted from maize bran by using mild alkaline conditions. AX presented a high FA content (22.4 µg/mg) and an arabinose to xylose ratio of 0.6. The methylation analysis of this polysaccharide showed a substitution degree of 49% with 74% of arabinose residues in a terminal position. Deferulated AX (DAX) were chemically prepared without affecting the rest of the structure. AX solution at 1% (w/v) formed gels induced by laccase and registered a storage modulus of 530 Pa and a mechanical spectrum characteristic of a solid-like material. DAX did not present gelling capability. AX exhibited a high antioxidant capacity (208 and 160 TEAC µmol/g for ABTS and DPPH assay, respectively) which dramatically decreased in DAX (31 and 24 TEAC µmol/g for ABTS and DPPH assay, respectively). These results confirm the central role of FA in maize bran AX gelling capability and antioxidant capacity. Highly ferulated AX could be used for the reliable design of tailored gelling agents presenting concomitant antioxidant activity due to the high FA content preserved within the molecule.

Bacterial cellulose can be obtained through fermentation of sugared tea with Kombucha fungus. Kombucha drink is considered as health and therapeutic agent. Tea fungus is a symbiotic culture of acetic acid bacteria and yeasts and during fermentation acetic acid bacteria synthesize a cellulose network floating on tea surface. The cellulose mass with attached bacteria and yeasts is secondary metabolite of fermentation which can be utilized as supplement in animal feed or thrown as waste. Presented research analysis is about possibilities to use BC material obtained through Kombucha fermentation as alternative material for sustainable fashion. The effect of washing and chemical treatment on mechanical, structural and water barrier properties of bacterial cellulose material is analysed. The study concerns bacterial cellulose (BC) properties in three different states: 1. Untreated - as natural fermentation product from acetic acid bacteria Komagataeibacter xylinus; 2. Pretreated - washed with water and weak alkali (0.5 %) solution; 3. Treated with dimethylol dihydroxyethyleneurea (DMDHEU) solid. Through pretreatment washing procedure fermentation side products (acids, input materials, sugars) are removed from BC membrane therefore this process has influence on material structure and properties. The structure of washed BC material can be described as coherent three-dimensional network of nanofibers with low water vapour permeability and low hygroscopicity. The decrease of deformation and of water barrier properties is recorded after BC washing. Applied chemical treatment has positive influence on properties of BC membrane (increase of material elasticity, strength, hygroscopicity and water vapour permeability) and no influence on BC structural transformation (FTIR analysis).

Electrostatic interactions have been implicated in a wide range of biological materials, including the interactions between proteins, polysaccharides, and polynucleotides. We draw inspiration from biomolecular condensates, or membraneless organelles, which utilize liquid-liquid phase separation to create transient compartments in cells. These condensates are commonly formed due to interactions between intrinsically disordered proteins and RNA, and have been shown to selectively incorporate specific enzymes. We utilize polypeptides as model sequence-controlled polymers to study how the patterning or presentation of charges and other chemical functionalities can modulate the potential for liquid-liquid phase separation via complex coacervation. We further examine how the distribution of charge on globular proteins can be used to facilitate selective uptake into coacervate phases, and how such materials can be used to stabilize proteins against denaturation. Our experimental efforts are supported by the parallel development of computational approaches for modeling and predicting the phase behavior of patterned polymeric materials. Our goal is to establish molecular-level design rules to facilitate the tailored creation of materials based on polyelectrolyte complexation that can both illuminate self-assembly phenomena found in nature, and find utility across a wide range of real-world applications.

Tunicate, a filter-feeder in seawater, is able to accumulate high amount of metals using intracellular polymer matrices. The woven pyrogallol structures of tunichrome, a small peptide contained in tunicate’s blood cells, is believed to be responsible for selective metal sequestration in tunicates from seawater. However, the intriguing tunichrome matrix is difficult both to harvest from the tunicate and to synthesize massively due to the extreme oxidation sensitivity of the pyrogallol moiety which limits the study scope. Here, we succeeded to mimic tunichrome by conjugating two cheap and naturally occurring components: pyrogallol-5-carboxylic acid (gallic acid) and chitin nanofiber. A tunicate-mimetic infiltration matrix of surface-tailored chitin nanofibers with pyrogallol moieties (CGa) demonstrated the versatility of this strategy in generation of ingenious filtration material, especially for unprecedented fine and clean gold recovery inside of the tunicate-mimetic infiltration matrix (>99%, 533 mg gold per gram weight), which exceeds that of the presently most popular materials. Complexation between pyrogallol on the nanofiber and gold was similar to that of a tunichrome’s metal sequestration. Extended X-ray absorption fine structure (EXAFS) spectroscopy and data-fitting elucidated the decreased coordination numbers for Au–Au nearest neighbors, demonstrating that gold coordinated to pyrogallol units, followed by an intramolecular association of Au⁰. A catalytic reduction of 4-nitrophenol mediated by the tunicate-mimetic matrix with harvested gold revealed excellent recyclability up to 30 cycles (∼95% reduction), which together with methylene blue reduction and antimicrobial performances indicates the versatile characteristics of sustainable processes by the tunichrome mimetics. This strategy opens the door for fast-developing new biomimetic alternatives for precious metal recovery, which is not restricted to gold and can offer a tool for multifaceted soft/hard nanomaterials.

The extracellular matrix (ECM) is a complex hydrogel material providing multiple functions and is in this way an impressive example for integrating several functions in a material system. It still is a challenge to completely prepare ECM by synthetic methods. However specific principles for generating functions by molecular design or hierarchical organization can serve as concepts for the bioinspired design of structured hydrogels.
In this lecture a gelatin based porous hydrogel will be presented, which is prepared in a one step process integrating synthesis and shaping [1]. Its elastic properties on the micro- and the macrolevel can be tailored and cell behavior can be influenced. The hydrogel is also capable of a water induced shape-memory effect. The concept of shape-memory hydrogels [2] has been taken further to a triple-shape effect enabling two subsequent shape changes upon heating [3]. Finally, the application potential of multifunctional structured hydrogels will be outlined.

References
[1] A.T. Neffe, B. F. Pierce, G. Tronci, N. Ma, E. Pittermann, T. Gebauer, O. Frank, M. Schossig, X. Xu, B. M. Willie, M. Forner, A. Ellinghaus, J. Lienau, G. N. Duda, A. Lendlein, Adv. Mater 2015, 27, 1738-1744.
[2] C. Löwenberg, M. Balk, C. Wischke, M. Behl, A. Lendlein, Acc. Chem. Res. 2017, 50, 723-732.
[3] U. Nöchel, M. Behl, M. Balk, A. Lendlein, ACS Appl. Mater. Interfaces, 2016, 8, 28068-28076.

Liquid-liquid phase separation (LLPS) of intrinsically disordered proteins (IDPs) has been recently associated with formation of intracellular membrane-less organelles and extracellular load-bearing structures, including biocomposite materials. Although the biophysical principles of LLPS of various synthetic and natural polymer systems have been already well characterized, molecular interactions driving the phase separation of IDPs are still poorly understood.

Histidine-rich squid beak proteins (HBPs) are IDPs that are the main component of the beak of Humboldt squid D. gigas. The beak is an interesting example of a graded biocomposite material with remarkable mechanical properties exhibiting a 200-fold variation in stiffness from the soft base to the hard tip. It is exclusively made of chitin and proteins, i.e. lacks a mineral phase such as calcium carbonate or phosphate - the classical load-bearing component of a hard tissue. Thus, the beak represents a promising model of a fully organic material with load-bearing functions for bioinspired materials engineering.

It has been proposed that the HBPs have crucial role in the beak processing in nature due to their intrinsic ability to undergo LLPS (coacervation) that allows them to gradually impregnate chitin nanofibers scaffold in the beak, condense into a solid structure, and form a dense cross-linked network (final beak structure). By studying a model protein (HBP-1) we showed that phase separation of HBPs is mediated through modular repeats located in their C-terminal part. Using mutagenesis approach, we mapped essential minimal peptide sequences required for LLPS to occur and showed critical role of tyrosine residues. We also demonstrated that the morphology of separated phase (coacervates/hydrogel) is correlated with the hydrophobicity of modular repeats and can be tuned by incorporation of specific sequence motifs into a peptide sequence. Utilizing solution-state NMR, we investigated initialization of LLPS of the HBP-1 protein and HBP-derived model peptide sequence (GY-23). We demonstrated that they phase separate in a pH depended process, triggered by deprotonation of histidine residues followed by stabilization of their tautomeric state by transient hydrogen bonding with tyrosine residues. We proposed that these events lead to hydrophobic inter-molecular interactions which are the main driving force of LLPS. Subsequently, we investigated separated phase (coacervates) of GY-23 peptide using SAXS and showed that it possesses internal structure in nm range which is partly ordered. Finally, we studied the molecular features of coacervate phase with solid-state NMR and showed that tyrosine residues stabilize its structure by hydrophobic interactions. Overall, this work provides essential knowledge and guidelines for rational design of pH responsive peptides with LLPS ability for engineering of bioinspired functionally graded composite materials and other applications such as smart hydrogels and drug delivery systems.

References:
[1] A. Miserez, T. Schneberk, C. Sun, F.W. Zok and J.H. Waite, Science 319, 5871 (2008).
[2] Y.P. Tan, S. Hoon, P. A. Guerette, W. Wei, A. Ghadban, C. Hao, A. Miserez, and J. H. Waite. Nature Chemical Biology 11, 7 (2015).
[3] H. Cai, B. Gabryelczyk, M. S. S. Manimekalai,G. Grüber, S. Salentinig, and A. Miserez. Soft Matter 13, 7740 (2017).

We employed computational molecular modeling and dynamic force spectroscopy in silico accelerated on Graphics Processing Units (PGPUs) to perform the mechanical manipulations at the nanoscale on a variety of superhelical protein fragments. We utilized the atomic structures of coiled-coil motifs available from the Protein Data Bank (PDB) for myosin (PDB entry: 2FXO), chemotaxis receptor (2GUV), vimentin (1GK4), fibrin (2GHG), and phenylalanine zippers (2GUS), as suitable study systems. We used the all-atom Molecular Dynamics simulations on GPUs in the underdamped (low-friction) limit in conjunction with the Solvent Accessible Surface Area (SASA) model of implicit solvation. The coiled-coil motifs listed above vary in size as well as topology of their α-helical packing. We loaded these study systems with tension linearly increasing in time, which fully mimics the tensile testing single-molecule force-ramp experiments. When stretched along the superhelical axis, all superhelices showed elastic, plastic, and inelastic elongation regimes, and underwent a remarkable dynamic transition from the α-helices to the β-sheets, which marks the onset of plastic deformation. Hence, the soft α-to-β phase transition in coiled coils is a universal mechanism underlying the mechanical properties of filamentous α-helical proteins. We analyzed in detail the output from the simulations. Microscopically, the α-helical (β-strand) content decreases (increases) with tension, and the transformation from the α-helices to the β-sheets is a two-state transition. This transition is accompanied by redistribution of the dihedral angles φ and ψ and reconfiguration of hydrogen bonds (from the intra-chain to the inter-chain hydrogen bonds). Using Abeyaratne-Knowles formulation of phase transitions, we developed a new theory to model the mechanical and kinetic properties of protein superhelices under mechanical non-equilibrium conditions used in tensile testing assays. We also implemeted an approach to map out the free-energy landscapes of polypeptides with coiled-coil motifs, in order to resolve the critical extension and to estimate the energy difference between the α-helical state and β-sheet state per helical pitch. The developed theory was validated by directly comparing the simulated and theoretical force-strain spectra. Interestingly, we found that the coiled coils show a roughly additive contribution to the mechanical strength from α-helices, which weakly cooperate to sustain the stress. We also found that the coiled coils with parallel arrangement of their α-helices provides higher mechanical strength as compared to the coiled coils with antiparallel arrangement. The theory can be used to accurately describe dynamic transitions in wild-type and synthetic superhelical polypeptides under mechanical non-equilibrium conditions, and to model their force-strain spectra available from dynamic force manipulations in vitro and in silico. The theory can be applied to any coiled-coil superhelical polypeptide, in order to probe its mechanical and kinetic properties and to map out its free-energy landscapes. The derived scaling laws for the elastic force and the force for α-to-β transition to plastic deformation provide an analytical tool to rationally design novel synthetic biomaterials and nanomaterials with the required mechanical strength and desired balance between stiffness and plasticity.

The successful application of synthetic biomaterials lies in their ability to mimic naturally occurring biological molecules and systems. The challenge however, has always been to generate materials with hierarchical assemblies down to the atomic level that have precisely tailored chemical heterogeneities and external stimuli-responsiveness. Self-assembling peptides have recently emerged as a potential avenue for the creation of novel biomaterials because they are materials based on natural building blocks. The knowledge about their sequence-structure relationship coupled with the ability to design and synthesize de novo peptides has sparked an interest in the use of coiled-coil peptides as biomaterials in various fields; tissue engineering, drug delivery, regenerative medicine and bio-sensing to name a few. Our approach utilizes a GCN4 leucine zipper sequence-based coiled-coil trimer that has been radially functionalized with aromatic ligands to build hierarchical assemblies. These higher-order assemblies, which take the form of banded rectangular nanosheets, are formed via electrostatic and aromatic interactions. The dimensions and overall shape of these assemblies vary with the strategic placement and number of aromatic ligands on the monomer backbone. Their assembly was observed to be reversible and can be controlled by adjusting the pH of the solvent medium. Additionally, the unmodified variant of the peptide resulted in the formation of microtubes. Our work showcase how small changes in the peptide sequence can translate into distinct differences in the resulting supramolecular architecture. The possible variety of hierarchical structures make coiled-coils suitable for creating novel biomaterial scaffolds.

In mechanical testing, polymers regularly underperform compared to their theoretical calculations due to defects in the network, including dangling chains, free chains, loops, and various forms of bridge entanglements. Efforts have been made to count the number of network imperfections, however, there are no current methods for reducing defects in physically-associated polymer networks. Well-organized biological networks in cell cytoskeletons contain selective binding mechanisms and rigid-structured proteins that reduce defects, inspiring our polymer network design. In this study, a novel mechanism for reducing network defects was investigated by designing protein polymer mid-blocks with rigid and flexible components in specific ratios and module arrangements.

Protein polymers were designed with a rigid rod block and various lengths of flexible coil blocks to modulate polymer chain stiffness, which can potentially control network defects. The rigid component consists of synthetic ankyrin repeats, known for its 3D solenoid structure. The flexible component includes primary-structured polyelectrolytic protein repeats. These rod and coil protein blocks were genetically inserted into a telechelic associative construct with self-oligomerizing proteins to form hydrogels. To determine the optimal copolymer design that reduces network defects, such as self-loops and dangling chains, we investigated the mechanical properties of hydrogels containing mid-blocks with varying rigid-to-flexible length ratios, as well as symmetrical and asymmetrical block arrangements within each protein polymer. The incorporation of rigid components increased the elastic moduli compared to flexible controls, providing evidence that network defects can be reduced in telechelic associative polymers by manipulating chain flexibility.

An aortic aneurysm constitutes a local enlargement of the aorta that is identified incidentally in most patients due to absence of symptoms. Prevalence of this disease strongly depends on age, gender and distinct risk factors, including smoking, overweight, hypertension and increased level of blood lipids. In case of an increasing aneurysm diameter, rupture within the aortic wall is an acute threat, the so called aortic dissection. At worst, rupture of the entire aorta arises, the so called aortic rupture. Within an interdisciplinary approach we investigate aortic samples from patients who suffer from an aortic aneurysm and underwent a surgery with regard to their mechanical properties. In doing so, tubular aortic portions were harvested from patients and cut into rectangular shapes, originated from convex, concave and longitudinal parts of the aorta, and stretched until rupture. Clinical data of patients as age, aortic diameter, arterial hypertension, elastin and collagen content or type of aortic valve (bicuspid- or tricuspid aortic valve) were correlated with the Young's modulus to contribute to a better understanding of the role of pathological factors in mechanical properties of aorta.

Wrinkles form, when a system consisting of a hard, thin layer in strong adhesive contact with a soft, thick elastomer is subjected to in-plane compression, just like skin that wrinkles or mountain ranges that fold. The arising buckling instability can be unordered, or a highly periodic surface corrugation with well-defined wavelength and amplitude, when a defined stress-field is applied. Manifold preparation methods are known, such as metal deposition on elastomers, plasma treatment of PDMS or the adhesion of stiff polymeric layers on elastomeric sheets. However, most methods are limited in terms of material and parameter variety, only few perform with more than one elastomer or thin layer material, respectively. Also they comprise side features as cracks and line defects, which form in most wrinkling process and are not predictable yet. Furthermore, controlled wrinkling is still limited to small size ranges in the square millimeter- and centimeter-range. [1]
We demonstrate a new approach, where line defects are confined and subsequently arranged by modifying the substrate, and cracks are suppressed by the implementation of a specific elasticity gradient. [2,3] Furthermore, we show a new approach that is applicable to versatile layer and elastomer materials, and also unlimited in terms of pattern size. [4] We show the utility of both line defect- and crack-free wrinkles, and of different layer and elastomer materials for large-scale wrinkled areas. Such highly ordered, macroscopic patterns can be applied to biologically functional surfaces, like cell- and virus-repelling material for medicine, anti-fouling surfaces in large area for diverse bio-industrial applications or friction-minimizing interfaces.

[1] A. Schweikart and A. Fery: Controlled wrinkling as a novel method for the fabrication of patterned surfaces, 2009; Microchimica Acta, 165 - 3, 249-63
[2] B. A. Glatz, M. Tebbe, B. Kaoui, R. Aichele, C. Kuttner, A. E. Schedl, H.-W. Schmidt, W. Zimmermann and A. Fery: Hierarchical line-defect patterns in wrinkled surfaces, 2015, 11, 3332-3339
[3] B. A. Glatz and A. Fery: The influence of plasma treatment on the elasticity of the in-situ oxidized gradient layer in PDMS: Towards crack-free wrinkling, 2018, submitted
[4] B.A. Glatz, A. Knapp and A. Fery, 2017, European and Worldwide Patent Application

Freestanding nanopillar structures are attractive in a variety of biomedical and technological applications because of the improvement in the surface area suitable for particle trapping, the sensitivity enhancement for the analysis and detection of DNA and proteins, in tissue-engineering platforms, and for the design of antimicrobial interfaces for industrial and clinical applications. Nanopillars can be fabricated in soft materials by a diversity of nanofabrication tools, and typical methods consist in electron beam lithography and reactive ion etching, focused ion beam lithography (FIBL), chemical vapor deposition, pulsed laser deposition, and template-assisted synthesis. However, many of those technologies are still restricted by their lack of nanopattern variability, processing area, and control of surface chemistry, especially in clinically relevant polymers.
In this work, we present a method based on directed plasma nanosysntesis (DPNS) for fabricating freestanding nanopillars in a model fibrous hydrogel, i.e., bacterial cellulose (BC), with the aim of designing antimicrobial interfaces that can prevent bacterial contamination in biomedical devices. DPNS is advantageous for the large-area and short processing time as compared to FIBL and similar approaches. Nanopillars are fabricated in BC hydrogel by DPNS using argon at high fluence, normal incidence, and energies of 1 keV. BC is a natural polysaccharide formed by β−1,4−glucopyranose residues and used in biomedical applications such as wound dressing, artificial cornea, and in skin and blood vessel substitutes. The surface morphology of BC after argon plasma treatment was investigated by focused ion beam with scanning electron microscopy. Structural characterization showed that at low argon doses, the BC ribbon structure exhibited nucleation and growth of holes that progressively building-up leaving behind well-organized nanopillars at high fluences with an average height of 220 nm determined by atomic force microscopy. X-ray photoelectron spectroscopy (XPS) spectra revealed an enrichment of the C-C/C-H bonds and depletion of oxygen with the preferential removal of C-O bonds. The C-O-C/C-OH bonds also decreased drastically, whereas the C=O/O-C-O were only slightly reduced. Because oxygen atoms are responsible for linking the glucopyranose monomers and forming the ring structure in the BC, this would cause the restructuration of the polymer chains via ring opening and chain scissoring, driving nanopillar formation. The surface wettability of argon-treated BC measured within the first 24 h after treatment using the static water contact angle showed that this material was superhydrophilic. By tuning the energy, ion dose, and angle of incidence during DPNS treatment, we found that was possible to custom design the pillar height width and nanopillar density. In summary, the nanopillar structures obtained here in a fibrous hydrogel are of practical significance for the application in various fields such as biosensors, optoelectronics, and antibiofouling interfaces of industrial and clinical importance.

Overuse of antibiotics has created “superbugs” such as methicillin-resistant Staphylococcus aureus (MRSA) that pose serious threat to global health due to treatment failure and high mortality rates. The threat is further aggravated by chronic infections from biofilms, which exhibit high resistance towards both the host immune response and traditional antimicrobial therapy. Synthetic macromolecules have emerged as an alternative to conventional antibiotic therapy exhibiting broad spectrum activity against antibiotic-resistant bacteria. However, high toxicity towards mammalian cells and concomitant low therapeutic indices have limited their practical applications in clinical settings. Here, we report engineered polymers that can effectively eradicate pre-formed biofilms while maintaining a high therapeutic index against human red blood cells (RBCs). We synthesized a library of quaternary ammonium poly(oxanorborneneimides) possessing different degrees of hydrophobicity and screened their antimicrobial and hemolytic activities. These polymers form 10-15 nm nanoparticles in aqueous solution, increasing their overall cationic charge and molecular mass. We determined that increasing hydrophobicity of the alkyl chains bridging the cationic head group and polymer backbone greatly enhances toxicity against planktonic bacteria while maintaining excellent hemolytic activities towards RBCs (Therapeutic Index >5000). Additionally, polymeric nanoparticles readily penetrate and eradicate pre-formed biofilms while still maintaining high therapeutic indices (~120) relative to RBCs. Polymeric NPs demonstrated a 6-log reduction in bacterial count in a biofilm-mammalian cell coculture model. Significantly, we observed that bacteria did not develop any resistance against polymeric NPs even after 20 serial passages. Overall, our engineered polymeric nanoparticle platform shows strong potential as an infectious disease therapeutic and simultaneously provides a rational approach to design novel antimicrobials for long-term combating of bacterial infections.

[ABSTRACT]
Self-assembly of polymeric liquid crystals (LC) has emerged as a powerful technique to recreate the complex hierarchy found in nature, from simple building blocks. Evaporation is often employed as a driving force to initiate the assembly of LC domains in the solution. By tuning the conditions of drying, it is possible to gain control over their mobility and in turn on the orientation during deposition. Recently, our group reported a macrospace-partitioning phenomenon upon drying a polysaccharide aqueous LC solution from a limited evaporative interface.^1,2 Vertical membranes were deposited, bridging a millimeter-scale gap between the substrates and formed a highly oriented structure as a result of a non-equilibrium process between polymer deposition and hydration. In this study, in order to generalize this space-partitioning phenomenon and explore structural changes due to temperature variations, we have explored the drying of xanthan gum solution. It is a cholesteric LC polysaccharide commercially used in food industry, cosmetic formulations and as a viscosity enhancer. Most importantly, xanthan gum LC state is intrinsically affected by changes in temperature. By varying the conditions of temperature and initial concentration, the depositions induced in the limited space have been monitored and a comparative phase diagram prepared.³

We observed deposition of a horizontal lid-like membrane preceding the growth of vertical membrane. The restrained availability of space led to a dense layer at the drying interface which resulted in the deposition of this lid structure. To clarify the microstructures of these membranes, the lid and the vertical membrane retrieved after drying xanthan solution at 60 °C were scrutinized in three dimensions. The deposited membranes exhibited an arrangement of fibrous structures with orientations dictated by the experimental conditions and LC mobility. The SEM images showed that the membrane is composed of fibres with ∼50 nm diameter in orientation. We also prepared a phase diagram, focusing on the initial polymer concentration, C₀ and drying temperature to clarify the effect of the domain’s mobility on the bridging deposition.

Furthermore, the introduction of crosslinking points in the membranes, by annealing at a higher temperature resulted in the formation of oriented hydrogels with quick and reversible anisotropic swelling. Such hydrogels with inherent biocompatibility and fast response rate have great demand for drug delivery, tissue engineering, and biomimicking applications. The imitation of condensation by drying in this work will provide not only an understanding of the self-organization of biopolymers in living systems but also a simplified methodology to design self-assembled biomimetic materials with highly-ordered structures.

[REFERENCES]
1. K. Okeyoshi: M. K. Okajima; T. Kaneko. Scientific Reports 2017, 7, 5615.
2. K. Okeyoshi; G. Joshi; M. K. Okajima; T. Kaneko. Advanced Materials Interfaces 2018, 3, 1870013.
3. G. Joshi, K. Okeyoshi, T. Mitsumata, T. Kaneko. Submitted

[ACKNOWLEDGEMENTS]
G. J. is grateful for the JSPS DC2 Fellowship and the JSPS Kakenhi Grant Number JP18J11881.

Materials inspired by the byssal threads of mussels are of interest for their strong mechanical properties, which are based on coordination of catechol moieties with Fe³⁺ ions. A 4-arm polyethylene glycol terminated with catechols (4PEG-c) was used to investigate the chemistry and rheology of crosslinking with a set of different compositions (Fe₃O₄, CoFe₂O₄, NiFe₂O₄, Co, and Ni) and sizes (3-7 nm diameters) of NPs. A ligand exchange process was developed to prepare the samples for dispersion in water and coordination with 4PEG-c to form hydrogels. Raman spectroscopy showed less binding of 4PEG-c to Co- and Ni-based NPs than to Fe₃O₄ NPs, but rheology measurements revealed significantly slower relaxation times for Co- and Ni-based NPs than for Fe₃O₄ NPs. We attribute these results to initial binding of catechols to Co- and Ni-based NPs, which could catalyze the oxidation of catechols and drive covalent crosslinking between 4PEG-c molecules. We propose such crosslinking results in a polydopamine-like structure. Thus, Co- and Ni-based NPs can serve as catalysts, drive crosslinking, and slow the relaxation, while only weakly binding to the catechols. These results provide a foundation for incorporating other types of NPs into synthetic, physical hydrogels and highlight the potential role of Co- and Ni-based NPs in catalyzing crosslinking of catechols.

Inspired by the catechol and amine-rich adhesive proteins of mussels, polydopamine (pDA) has been widely adopted for coating solid surfaces due to the versatility and simplicity of pDA film deposition. Conformal pDA films of thickness 1~100 nanometers spontaneously form at the solid-liquid interface on nearly all types of solids by simple immersion in an aqueous alkaline solution of dopamine. Little is understood about pDA film formation except that oxidation of dopamine gives rise initially to dopamine-quinone and dihydroxyindole. An open question concerns whether the final product is a covalent polymer or a supramolecular aggregate of small molecules and oligomers. We employed single molecule force spectroscopy (SMFS) to show that pDA exhibits characteristic features of a polymer with contour lengths up to 200nm. pDA chains exhibit mostly weak interactions with oxide surfaces with occasional “sticky” points along the contour length, suggestive of a copolymer structure composed of building blocks of variable composition. Our findings provide the first direct evidence for the polymeric nature of pDA, and offer a foundation upon which to better understand and tailor its physicochemical properties.

Metal ion adsorption from electronic wastes (E-wastes) has received much attention for the elimination of heavy metals and the recovery of precious noble metals. However, cost effectiveness and metal selectivity still remain to be solved. Herein, we introduce a simple method to efficiently increase gold adsorption from metal ion mixtures using bio-inspired polyphenol chemistry under light illumination. Mesoporous poly(ethlylene glycol dimethacrylate-co-acrylonitrile) (poly(EGDMA-co-AN) microspheres were prepared by suspension polymerization and used as polymer templates. The internal surfaces of the polymer templates were coated by polydopamines via the oxidative polymerization of dopamines. The polydopamine layers served as a metal ion reductant activated by 1 sun-simulated illumination. The adsorption isotherm curves and maximum capacities of gold ions were evaluated by Langmuir, Freundlich, and BET adsorption models. The maximum amounts of chloroaurate ions adsorbed per unit mass of the adsorbents under the 1 sun-simulated light were 25 times higher than the adsorbents in the dark. The gold ions could be removed from the adsorbents in a thiourea solution. Metal ions complex solutions were used to determine the selectivity of the polydopamine-coated particles for gold ions among various metal ions. High adsorption capacity and selectivity toward gold ions at a high concentration (1.5 mM) of a metal ion mixture containing six kinds of metals (Cu, Co, Ni, Pt, Zn, and Au) was demonstrated. The structural properties and the surface chemistry were investigated using SEM, TEM, XPS, XRD, and BET analysis, and the amount of gold ions were analyzed by ICP-MS analysis. Our bio-inspired approach to photo-enhanced adsorption of gold ions using polyphenol chemistry will lead to practical applications for the recycling of the precious metals from E-wastes. This research was supported by Nano-Material Technology Development Program through the National Research Foundation of Korea (NRF) funded by the Ministry of Science, ICT and Future Planning (2017M3A7B4042235).

Self-assembly of diverse natural component is critical for biological phenomenon understanding and advanced materials development; however, self-assembly of 2D heterostructural nanosheets from 1D biocolloid is extremely challenging because of complex interactions, geometrical structure, flexibility and limited processing window. Herein, we report a simple, efficient, and universal amphiphilicity-driven self-assembly strategy to construct 1D stiff nanocellose into 2D flexible nanosheets with graphene oxide (GO) monolayer as template core. This self-assembly is facilitated by highly tunable amphiphilic interaction via tailoring the surface chemistry of GO nanosheets, resulting in unprecedentedly ultradense nanocellulose coverage. These as-obtained ultradense nanocellulose nanosheets demonstrate recorded-breaking elastic modulus cellulose nanocomposites, even comparable to single nanocellulose. Additionally, the presence of nanocellulose significantly enhance the surface wetting ability of hydrophobic rGO nanosheets, enabling the long-term stable rGO dispersion and allowing fast water transport through these hybrid thin films for dye and nanoparticles separation.

Technology for solar fuel production is now waiting for major breakthroughs in materials science. Metal oxides play an important role as photoelectrode materials for water splitting for solar hydrogen fuel production 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 found a way around this limitation by designing an 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 an 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. The practical outcome is that the photocurrent density is doubled alone by the mesoscale structuring.

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.

Fiber-reinforced compound materials are used increasingly in many high-end technical applications including aviation and space flight, automotive, but also for sports equipment and medical applications as e.g. for prostheses and orthoses. Technical fiber-reinforced compound materials share many properties with their biological counter parts and proved to be very suitable for the fabrication of innovative biomimetic products. Examples for light-weight materials with excellent mechanical load bearing properties and an benign fracture behavior include biomimetically optimized branched fibrous composite materials with gradient structure and with or without concrete filling inspired by branched stems of dragon trees (Dracaena spp.), dwarf umbrella trees (Schefflera arboricola) and columnar cacti (e.g. Myrtillocactus sp. or Pachycereus sp.). However, fiber-reinforced materials systems can do much more than stiffening as well in biology as in technology. The hierarchically structured fibrous bark of the giant sequoia (Sequoia gigantea), for example, represents not only a brilliant heat insulator and is self-extinguishing (protection against wild fires) but additionally is a very efficient and light-weight damping system (protection against rock fall). In addition, also complex motion patterns can be imprinted in the fibrous structure of fiber-reinforced plant materials systems allowing for one, two and three-phase motions. Examples include one and two phase motion patterns found in pinecone scales (Pinus spp.) and three phase motions occurring in the involucral bracts of the silver thistle (Carlina acaulis). What’s more: these organs combine sensor, actuator, reactive movable element and support structure in one materials system, are entirely passive (no energy consumption), show high level of functional integration and display extraordinary high functional resilience and robustness. The latter was proven for 11.5 to 16 million years old charcoalified conifer cone scales (Ketleeria sp.) that still show the same motion pattern in hydration/dehydration cycles as their extant counter parts. New production methods, as e.g. 3D/4D-printing or 3D-braiding pultrusion, allow to produce similar as in biology from small to big and to create a hierarchical structuring similar to that found in the biological role models. They therefore enable for the first time the transfer of many outstanding properties of the biological role models into innovative biomimetic products at reasonable costs. Based on a thorough analysis of the hierarchical structuring of the biological role models and of their scale overarching mechanical properties these production methods will allow for the development of novel sophisticated living, adaptive and energy-autonomous materials systems. This challenge is central to the new Custer of Excellence livMatS, which has started in January 2019 at the University of Freiburg and aims to come from bioinspired materials to living materials systems.

Cellular structures provide high material usage efficiency, specific strength, and energy absorption for lightweight structural materials. The mechanical properties can be maintained or increased through apposite porous and wall designs even the material selections are limited. In this research, we focused on the enhancement of lightweight structure tensile properties based on single material. Voronoi tessellation, often appears in cells and bone microstructure generation modeling, was used to partition a plane into several pores after the distribution of pore centers were calculated. Mathematical models were proposed to describe the distribution of pores in tensile specimens. The Fibonacci sequence divides planes or spaces regularly, often found in nature such as sunflowers, pinecones, etc. The Poisson-disc sampling mimics cells growth distribution in two-dimensional plane. The hexagon model is proposed to tile the plane in highly symmetric situation. The regular model and Monte Carlo sampling correspond to a completely regular and completely random distribution models. The porosity variance of specimens was controlled by changing the distribution and quantity of the porous. A series of polymer-based tensile specimens for tensile tests were produced via additive manufacturing. The numerical models were systematically simulated to verify the stress-strain behaviors under physical tensile tests. Extended finite element method cause divergence and errors by the discontinuity of the mesh boundaries and micro-cracks in cellular structures under tensile condition. In this work, lattice spring model was used to simulate micro-cracks generation and propagation. We found when the porosity is 40%, the Poisson-disc sampling and the Fibonacci sequence have higher elongation at break (20% enhancement), ultimate tensile strength (15% enhancement), and toughness (35% enhancement) than other models. Toughening mechanisms such as crack deflection/tortuosity and uncrack ligament bridging were observed and validated. This research proposes a feasible analysis of lightweight structures, tensile measurement methods, and developed bio-inspired structural materials that can be potentially applied to structural engineering, civil engineering, and aerospace technology.

Acknowledgments:
This research was supported by the Ministry of Science and Technology, Taiwan, R.O.C.
(107-2218-E-007 -049)

Bamboo achieves its mechanical efficiency in bending and compression, meaning mechanical performance per unit mass, due to its hierarchical structure. As an orthotropic tube with a higher strength and stiffness parallel to the tube axis and with a density and property gradient across the tube wall, in which fiber bundles are embedded in a porous matrix, the bamboo culm is both stiffer and stronger in bending and less prone to ovalization and catastrophic failure than an orthotropic tube without property gradient would be. Few engineered materials exist that emulate bamboo’s mechanical efficiency. The results of the study presented here demonstrate that freeze casting (ice templating) is a manufacturing process with which bamboo-inspired tubular scaffolds and with property gradients across the tube wall can be custom-made. A highly aligned, honeycomb-like porosity is generated by ice crystal growth opposite to the direction of heat flow. Using a core-shell mold, the microstructure of the tube wall material, such as the pore size, geometry, and alignment, is defined by the mold materials’ properties and applied cooling conditions. These also allow to custom-design the desired property gradient across the section. Further customization of tube gradient structure and properties is possible through the deposition of additional layers on the freeze-cast scaffolds. Characterizing the pore structures of the freeze-cast tube using X-ray microtomography, pore morphology and property gradients can be analyzed and correlated to both the processing conditions and the resulting mechanical properties determined in three-point bending and radial compression. The resulting fundamental structure-property-processing correlations support the custom design of tubular scaffolds that are ideally suited for applications that range from conduits for peripheral nerve repair to ureteral stents.

Nature provides amazing examples of high velocity, high acceleration, impulsive movements that can be repeated numerous times over the course of an organism’s lifetime. Synthetic, or engineered, devices, on the other hand, are often challenged to achieve comparable performance across a wide range of size scales. Common to nature’s examples, including mantis shrimp and trap-jaw ants, is the integration of three essential components for elasticity-assisted movement: an actuator, spring, and latch. Elasticity-assisted motion has been utilized for thousands of years to amplify the power of natural or synthetic actuators; however, the scaling physics of these multi-component systems, especially in light of materials design, have not been widely considered. Here, we discuss our group’s efforts, within a multi-university collaborative team, to lay a foundation for understanding the role that materials properties and structure play in the performance of impulsive systems in nature with an eye toward aiding the development of engineered devices that can overcome current limitations. We first discuss the mechanics of elastic recoil and a set of systematic experiments on a resilin-like synthetic material. The results from this study leads to a common framework for describing the roles of geometry and materials properties for controlling duration, velocity, and acceleration. We then introduce recent advances of using mesoscale polymers, which build upon previously introduced concepts from our group, to develop high rate, large strain, microscale actuators. Collectively, these examples highlight the integrative approach of our group and how we use bio-inspired materials mechanics to inspire new technologies and provide fundamental insight.

Shape-transformation is a prevalent function observed in living systems, from moisture responsive plants that self-disperse seeds, to muscle actuation by calcium concentration within myocytes. A number of classes of synthetic materials, which mimic this natural behavior, have been developed that use physical or chemical stimuli such as temperature or pH to cause shape changes. However, these stimuli are not specific to the material and may affect various components of the surrounding environment¹. Additionally, these materials lack the ability of living organisms to respond to specific biomolecular cues and respond accordingly. Here we use the tools of synthetic biology to create living composites capable of responding to pre-determined and very specific stimuli (e.g. biomolecules). Specifically, we present a new method to create programmable shape-morphing living composites using polyacrylamide hydrogels that encapsulate Saccharomyces cerevisiae yeast cells. Proliferation of these microorganisms is controlled to cause the macroscopic shape of the polymer matrix to change (volume expansion up to 300%). As the composite only changes shape in the presence of an appropriate growth media, composites that sense and respond to changes in glucose concentration or the presence of an essential amino acid (e.g. histidine) can be fabricated. Moreover, we utilize optogenetic tools to regulate DNA transcription upon light illumination in modified yeast strains. Shape-change of the composite and proliferation of cells can be spatially and temporally controlled using low power blue light. This extracellular cue induces protein expression in cells and can be used to pattern shape changes in the material. Additionally, the use of these tools enables precise and directional control of shape-morphing structures with potential applications in tissue engineering, sensing, and drug delivery systems.
References:

1. Aguilar, M. R., & San Roman, J. (2014). Smart Polymers and their Applications. Smart Polymers and their Applications (pp. 1–568). Elsevier Ltd.

In nature, structure, material and function are constantly evolving in tandem. This work employs polymer additive manufacturing to study the mechanical properties of new honeycomb materials inspired by disordered, hierarchical architectures in biomineralized organisms. Inorganic structural features encountered throughout biology are particularly fascinating due to their mechanical resilience and toughness, which arise despite limitations in the available molecular phases of environmental precursors. From very basic and often brittle building blocks, nature has found ways to extend material performance beyond the compositional limitations of its biomineral constituents, e.g. calcium carbonate, apatite and silica. Such improvements have been shown to rely in part on the architectural arrangement of the inorganic phase, which is often non-periodic. This is exemplified in the spongy trabecular bone of load-bearing mammalian limbs, the arrangement of aragonite platelets in the nacre system, and the cellular sandwich-core morphology of biosilica in diatom frustules. The primary aim of this work is thus to elucidate the mechanical role of structural order vs. disorder in natural cellular solids by way of a bioinspired polymer analogue. New honeycomb materials are proposed with improved damage tolerance. A mathematical Voronoi “regularity parameter” controls the degree of cell stochasticity. Uniaxial tension, compression and fracture experiments reveal significant crack path deviations and strain delocalization. These lead to enhancements in e.g. ductility and fracture toughness, K_J, between 30-90% beyond equivalent periodic hexagonal geometries. Optimal cell irregularities are suggested, revealing a relationship between damage tolerance and cell size. Conserving spatial relative density, honeycombs with members composed of hierarchical micro-trusses are also presented. Depending on design objective, a 100% increase in compressive strength and three-fold energy absorption limits (U_v) have been achieved. These results comprise novel design spaces, where disorder and hierarchy are embraced as design variables. Capitalizing on the spatial manufacturing freedom afforded by a modern MultiJet 3D printing technique, iterative tailoring of cell regularity and micro-truss architecture in the honeycomb enables new pursuits toward minimization of energetic tradeoffs. The result is a balance between high strength, light weight and damage tolerance from an otherwise brittle constituent polymer.

Biofilms from the marine bacteria, Cellulophaga lytica, have been reported to display structural, iridescent colors that were found to be both reversible and dynamic. Here we present several scientific and technological advances using micro-spectral imaging, confocal microscopy, angle- dependent reflection measurements and atomic force microscopy. To facilitate these studies, we have successfully fixed C. lytica colonies which remain stably iridescent for months. Micro- spectral imaging revealed angle-dependent reflection in the blue, green, yellow, orange and red structural color regions. Since cells displayed a similar size in all structural color regions, the different reflected colors likely came from different crystalline planes and/or periodicities. Cross- section images of C. lytica in the different colored regions demonstrated highly-ordered end-to- end assembly of hexagonal photonic crystals through crystalline planes, and the small refractive index mismatch between the bacteria and aqueous environment explains the small angle reflection peaks. Together, our studies imply that C. lytica is an excellent light scatterer that reflects different wavelengths of light through self-organization. Moreover, since our studies focused on a C. lytica strain with a known genomic sequence, future synthetic biology approaches will be aimed at producing low-cost, tunable photonic crystals based on programmable, self-assembling microorganisms for optical and sensor applications.

Freeze casting is a bioinspired technique for the fabrication of tailored, porous ceramic materials. Mimetic of the growth of mammalian bone and other biomaterials where biopolymers template the deposit of biominerals to create complex composites, freeze casting employs a template of growing ice crystals to create a complex porous microstructure in any ceramic. We propose that this bioinspired technique can be controlled through either intrinsic (those that modify from within by altering the constituents) or extrinsic (those that apply external forces or templates) means. Through these classifications, examples of extrinsic (through energized external fields) freeze cast, bioinspired structures will be discussed with a focus on providing advanced control of the final material structure and properties. Applications in energy and filtration technologies will be discussed.

Striking differences in microstructure and properties are observed, when biopolymers of different composition, structure, and form (e.g. fibrillar, crystalline) are directionally solidified, or freeze cast, into highly porous scaffolds. The resulting honeycomb-like aligned porosity and mechanical anisotropy, and the hierarchically structured scaffold architecture and cell wall material offer insights into the effects of flow and other forces on solidification, structure formation, self-assembly, and mechanical properties in freeze-cast biopolymer scaffolds. Presented will be observations made in a range of biopolymer systems composed of materials such as collagen, chitosan, and nanocellulose, and conclusions drawn from the observed microstructural features such as fibrillar bridges and cell wall ridges, and the preferential alignment of crystals and fibrils in the cell wall material parallel to the freezing direction. Rigorous structure-property-processing correlations will be provided for the different material systems tested in the dry and fully hydrated state, in tension and compression, both parallel and perpendicular to the freezing direction. Highlighted will be the promising strategies for the custom-design of new scaffolds and devices for biomedical applications that range from peripheral nerve repair to ureteral stents.

The structure of many biological materials is hierarchical in nature meeting specific needs at each length scale. This includes human bone, which has a porous structure that plays a critical mechanical role in arresting crack growth, energy absorption and providing mechanical strength in specific loading directions. In this research, a novel tri-axial nested Helmholtz coil-based freeze casting setup is used to control the fabrication of porous structures. With this setup, a magnetic field can be created in any direction which is utilized to manipulate particles to align the microstructure. The ability to control the particle alignment results in user-specific mechanical properties at user-specific locations. These structures provide a path to better mimic the mechanical characteristics seen in human bone.

Anisotropy is one of the common elements in the microstructure formation in nature, providing different mechanical properties in transversal and longitudinal directions. The tubular structure in nature exists in teeth, bamboo, trees, and horns, which possesses great impact resistance or toughness. In this research, a novel polymeric freeze-casting method is developed to fabricate scaffolds with tubular microstructure. The polymer with water-soluble and cross-linkable functional groups is essential for material selection and polyvinyl alcohol is one of the few materials that meet these requirements. The crosslinking temperature is below 453K, which does not require sintering at high temperature as in the typical freeze-casting method. The porous sizes and mechanical properties of tubular structures in PVA scaffold can be tuned by using various cooling rate, solid loading, crosslinking treatment. The porosity of this scaffold is around 66%. The ultimate compressive strengths of PVA scaffolds are measured to be 22MPa, 13MPa, 11MPa under relative humidities of 0%, 53%, 75%, respectively. In the longitudinal direction, the stress-strain curve shows ductility and exhibits series of jagged breaks after the yield strength until densification. In the transversal direction, the scaffold shows compressibility before the strain of 60%, and complete recoverability during swelling/deswelling process. The thermal conductivity in longitudinal direction is higher than transverse direction due to the tubular structure penetrating the entire scaffold. The value is 0.135-0.187W/mK, and is considered as a good thermal insulator. Anisotropic structure shows different mechanical behavior and characteristics in two directions. Composite scaffolds can be easily formed when functional ceramics are added to the initial PVA slurry, which increases the diversity of material selection and extensive potential applications. This research is funded by the Ministry of Science and Technology, Taiwan (MOST 103-2221-E-007-034-MY3).

Shahrouz Amini, Maryam Tadayon, Jun Jie Loke, Akshita Kumar, Deepankumar Kanagavel, Hortense Le Ferrand, Martial Duchamp, Manfred Raida, Shawn Hoon, Ali Miserez
[email protected]

The dactyl club of the mantis shrimp (stomatopod) is a fascinating example of a highly organized hierarchical hard composite material that combines strength and toughness. Another peculiar feature of this appendage lies in its formation process through molting cycles: as a crustacean mantis shrimps grow an entirely defect-free functional exoskeleton within just a few weeks. This feature makes the mantis shrimp an ideal model organism to monitor biomineralization processes. In this study, a protein from the club (club Mineralization Protein 1, CMP-1) was identified and sequenced using a combined transcriptomics/proteomics approach, and shown to regulate calcium phosphate mineralization of the club. After recombinantly expressing CMP-1, we show that CMP-1 can form dense organic microdroplets through liquid-liquid phase separation induced by calcium ions. Furthermore, in vitro experiments with TEM demonstrate that CMP-1 can participate in the formation of precursor-like amorphous calcium phosphate granules that subsequently grow into preferentially oriented crystalline apatite nanofibers.

This work not only corroborates recent observations made in other systems that proteins regulating biomineralization can initially undergo phase separation [3], but also provides a comprehensive picture of key steps involved the growth of a mechanically functional highly mineralized composite. The study thus offers guidelines for advanced bioinspired manufacturing methods for strong and tough ceramic-organic composites.

[1] S. Amini, M. Tadayon, S. Idapalapati, A. Miserez, The role of quasi-plasticity in the extreme contact damage tolerance of the stomatopod dactyl club, Nature Materials, 14 (2015).

[2] J. Weaver, G. Milliron, A. Miserez, K. Evans-Lutterodt, S. Herrera, I. Gallana, et al. The stomatopod dactyl club: a formidable damage-tolerant biological hammer, Science, 8 (2012).

[3] S.Y. Bahn, B.H. Jo, Y. S. Choi, H. J. Cha, Control of nacre biomineralization by Pif80 in pearl oyster, Science Advances, 3 (2017).