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The influx and efflux of water in biological structures actuates reversible deformation and recovery processes that are crucial for mechanical functions in plants and animals. These processes utilize various mechanochemical mechanisms: swelling directed by the arrangement of cellulosic microfibrils in a bilayer construct, which generates different deformation patterns; lignification gradients; hierarchical foam-like inner structures, some of which also include swelling by hygroscopic cellulose inner cell layer; turgor pressure, which is activated by osmosis and acts at the cellular level, generating reversible motions. In this Review, we present representatives of each of these four mechanisms: pine cones, wheat awns, the twisted opening of Bauhinia pods and the seed of the stork’s bill; the resurrection plant; ice plant seed capsules and carrotwood seed pod; the wilting and redressing of plant stems. Natural polymeric materials produced by animals can also exhibit hydration-driven shape and strength recovery: bird feathers and hair are prime examples. Spider silk — a non-keratinous biopolymer — also exhibits humidity-driven reversible deformation. After describing these animal-based mechanisms, we outline bioinspired applications to actuate multifunctional and biocompatible smart materials, and indicate future directions of research with potential for new bioinspired designs. The influx and efflux of water in biological structures leads to reversible deformation, which has important functions in plants (for example, in seed protection and dispersal) and animals (for example, in the recovery of the strength and shape of feathers, and for reversible changes in silk and hair). Here the authors review the main hydration-induced deformation mechanisms and highlight applications inspired by these processes.

Biologically composites offer inspiration for the design of next generation structural materials due to their hierarchical microstructure that allows for, low density, and combination of high stiffness and toughness, currently unmatched by engineering technologies. Here, we investigate biomimetic composite materials that feature the laminated helicoidal architecture of fibers characteristic of the arthropod cuticle, specific to the mantis shrimp, but utilize either glass or Kevlar fibers, with epoxy or urethane matrix materials, to examine their role in impact energy dissipation. Drop weight impact test revealed epoxy-matrix composites exhibited the highest peak load on impact and showed larger degrees of external damage such as delamination and fiber breakage as compared to the urethane-based composites. Moreover, the helicoidal panels, showed a significant reduction in dent depth and better residual compressive strength as compared to the quasi-isotropic design. These findings provide useful insight into the variation of reinforcement and matrix materials for the helicoidal architecture and how it affects the delocalization of damage and improves residual strength.

Joining dissimilar materials such as plastics and metals in engineered structures remains a challenge1. Mechanical fastening, conventional welding and adhesive bonding are examples of techniques currently used for this purpose, but each of these methods presents its own set of problems2 such as formation of stress concentrators or degradation under environmental exposure, reducing strength and causing premature failure. In the biological tissues of numerous animal and plant species, efficient strategies have evolved to synthesize, construct and integrate composites that have exceptional mechanical properties3. One impressive example is found in the exoskeletal forewings (elytra) of the diabolical ironclad beetle, Phloeodes diabolicus. Lacking the ability to fly away from predators, this desert insect has extremely impact-resistant and crush-resistant elytra, produced by complex and graded interfaces. Here, using advanced microscopy, spectroscopy and in situ mechanical testing, we identify multiscale architectural designs within the exoskeleton of this beetle, and examine the resulting mechanical response and toughening mechanisms. We highlight a series of interdigitated sutures, the ellipsoidal geometry and laminated microstructure of which provide mechanical interlocking and toughening at critical strains, while avoiding catastrophic failure. These observations could be applied in developing tough, impact- and crush-resistant materials for joining dissimilar materials. We demonstrate this by creating interlocking sutures from biomimetic composites that show a considerable increase in toughness compared with a frequently used engineering joint.

The semicrystalline protein structure and impressive mechanical properties of major ampullate (MA) spider silk make it a promising natural alternative to polyacrylonitrile (PAN) fibers for carbon fiber manufacture. However, when annealed using a similar procedure to carbon fiber production, the tensile strength and Young’s modulus of MA silk decrease. Despite this, MA silk fibers annealed at 600 °C remain stronger and tougher than similarly annealed PAN but have a lower Young’s modulus. Although MA silk and PAN graphitize to similar extents, annealing disrupts the hydrogen bonding that controls crystal alignment within MA silk. Consequently, unaligned graphite crystals form in annealed MA silk, causing it to weaken, while graphite crystals in PAN maintain alignment along the fiber axis, strengthening the fibers. These shortcomings of spider silk when annealed provide insights into the selection and design of future alternative carbon fiber precursors.

The equine hoof has been considered as an efficient energy absorption layer that protects the skeletal elements from impact when galloping. In the present study, the hierarchical structure of a fresh equine hoof wall and the energy absorption mechanisms are investigated. Tubules are found embedded in the intertubular matrix forming the hoof wall at the microscale. Both tubules and intertubular areas consist of keratin cells, in which keratin crystalline intermediate filaments (IFs) and amorphous keratin fill the cytoskeletons. Cell sizes, shapes and IF fractions are different between tubular and intertubular regions. The structural differences between tubular and intertubular areas are correlated to the mechanical behavior of this material tested in dry, fresh and fully hydrated conditions. The stiffness and hardness in the tubule areas are higher than that in the intertubular areas in the dry and fresh samples when loaded along the hoof wall; however, once the samples are fully hydrated, the intertubular areas become stiffer than the tubular areas due to higher water absorption in these regions. The compression behavior of hoof in different loading speed and directions are also examined, with the isotropy and strain-rate dependence of mechanical properties documented. In the hoof walls, mechanistically the tubules serve as a reinforcement, which act to support the entire wall and prevent catastrophic failure under compression and impact loading. Elastic buckling and cracking of the tubules are observed after compression along the hoof wall, and no shear-banding or severe cracks are found in the intertubular areas even after 60% compression, indicating the highly efficient energy absorption properties, without failure, of the hoof wall structure. STATEMENT OF SIGNIFICANCE: The equine hoof wall is found to be an efficient energy absorbent natural polymer composite. Previous studies showed the microstructure and mechanical properties of the hoof wall in some perspective. However, the hierarchical structure of equine hoof wall from nano- to macro-scale as well as the energy absorption mechanisms at different strain rates and loading orientations remains unclear. The current study provides a thorough characterization of the hierarchical structure as well as the correlation between structure and mechanical behaviors. Energy dissipation mechanisms are also identified. The findings in the current research could provide inspirations on the designs of impact resistant and energy absorbent materials.

Genetic analysis of single-cells is widely recognized as a powerful tool for understanding cellular heterogeneity and obtaining genetic information from rare populations. Recently, many kinds of single-cell isolation systems have been developed to facilitate single-cell genetic analysis. However, these systems mainly target non-adherent cells or cells in a cell suspension. Thus, it is still challenging to isolate single-adherent cells of interest from a culture dish using a microscope. We had previously developed a single-cell isolation technique termed "gel-based cell manipulation" (GCM). In GCM, single-cells could be visualized by photopolymerizable-hydrogel encapsulation that made it easier to isolate the single-cells. In this study, GCM-based isolation of single-adherent cancer cells from a culture dish was demonstrated. Single-adherent cells were encapsulated in a photopolymerizable hydrogel using a microscope and isolated with high efficiency. Furthermore, whole genome amplification and sequencing for the isolated single-adherent cell could be achieved. We propose that the GCM-based approach demonstrated in this study has the potential for efficient analysis of single-adherent cells at the genetic level.

We report the biological synthesis of titania that is integrated into the silica-based cell walls of a titanium-resistant diatom, Fistulifera solaris. Titania is deposited across the diatom cell wa...

The Bouligand structure in some arthropods is a hierarchical composite comprised of a helicoidal arrangement of strong fibers in a weak matrix. In this study, we focus on the Bouligand structure present in the dactyl club of the smashing mantis shrimp due to its exceptional capability to withstand repetitive high-energy impact without catastrophic failure. We carry out a combined computational and experimental approach to investigate the high damage resistance of the Bouligand structure through a biomimetic composite material. This is studied by performing specific fracture experiments on the helicoidal composites specimens, where it was found that crack twisting, driven by the fiber architecture, is the main fracture mechanisms. This crack twisting mechanism competes with other alternative mechanisms such as crack branching and delamination, delaying catastrophic failure. The main mechanism of crack twisting is studied through specifically designed specimens in which the crack propagation path is controlled. Further quantification of the toughening mechanisms and crack growth rate is analyzed with analytical and finite element models. The biomimetic helicoidal composites are shown to have improved fracture resistance as the crack twists mainly driven by the increase in crack surface area and fracture mode mixity. Our analysis allowed us to study the effect of crack front shape, stress distribution and energy dissipation mechanisms.

Nature assembles weak organic and inorganic constituents into sophisticated hierarchical structures, forming structural composites that demonstrate impressive combinations of strength and toughness. Two such composites are the nacre structure forming the inner layer of many mollusk shells, whose brick-and-mortar architecture has been the gold standard for biomimetic composites, and the cuticle forming the arthropod exoskeleton, whose helicoidal fiber-reinforced architecture has only recently attracted interest for structural biomimetics. In this review, we detail recent biomimetic efforts for the fabrication of strong and tough composite materials possessing the brick-and-mortar and helicoidal architectures. Techniques discussed for the fabrication of nacre- and cuticle-mimetic structures include freeze casting, layer-by-layer deposition, spray deposition, magnetically assisted slip casting, fiber-reinforced composite processing, additive manufacturing, and cholesteric self-assembly. Advantages and limitations to these processes are discussed, as well as the future outlook on the biomimetic landscape for structural composite materials.

This paper explores whether the photochromic reaction of a molecule embedded in a polymer film can affect its surface adhesion properties, as measured by shear strength and delamination in water. The adherence of polystyrene (PS) to glass was chosen as a model system. Two commercially available photochromes—a spiropyran derivative 1′,3′-dihydro-1′,3′,3′-trimethyl-6-nitrospiro[2H-1-benzopyran-2,2′-(2H)-indole]) (SP) and a diarylethene derivative 1,2-bis(2,4-dimethyl-5-phenyl-3-thienyl)-3,3,4,4,5,5-hexafluoro-1-cyclopentene (DAE)—are studied in detail. Both photochromic reactions can significantly enhance the adhesion of PS to a glass surface. The most dramatic results were obtained for PS/SP films, whose shear strength increased by a factor of 7 while the delamination rate was suppressed by at least 2 orders of magnitude after exposure to UV light. The enhanced polymer adhesion could only be partially reversed, even after extended exposure to visible light completely regenerated the UV-absorbing isomer. Na...

Gastropods shells have evolved to resist the threat of increasingly stronger predators that smash, peal, and crush their shells. Their shells are most commonly constructed from a crossed lamellar microstructure, which consists of an exquisitely architected arrangement of aragonitic mineral and organic encompassing at least four orders of hierarchy. It is this careful control of mineral and organic placement within the entire crossed lamellar structure that yields a four-order of magnitude increase in fracture toughness versus abiotic aragonite. We investigated the effect of differing microstructural orientations on their influence of inter-3rd order lamellar fracture behavior using nanoindentation from the inner layer of the Strombus gigas shell. We observed a significant influence of lamella (plank) orientation and nanoindenter probe on the mechanical properties. The ±45° arrangement of mineral planks found within biological crossed lamellar composites provides a significant enhancement of isotropic resistance to penetration by sharp objects such as jaws and claws. In addition, the ±45° arrangement is able to resist higher loads before failure. This combination of features from the crossed lamellar architecture helped enable species with this shell structure to survive predation for hundreds of millions of years and will also help provide insights into designs of future generations of composites.

Nature utilizes the available resources to construct lightweight, strong and tough materials under constrained environmental conditions. The impact surface of the fast-striking dactyl club from the mantis shrimp is an example of one such composite material; the shrimp has evolved the capability to localize damage and avoid catastrophic failure from high-speed collisions during its feeding activities. Here we report that the dactyl club of mantis shrimps contains an impact-resistant coating composed of densely packed (about 88 per cent by volume) ~65-nm bicontinuous nanoparticles of hydroxyapatite integrated within an organic matrix. These mesocrystalline hydroxyapatite nanoparticles are assembled from small, highly aligned nanocrystals. Under impacts of high strain rates (around 104 s−1), particles rotate and translate, whereas the nanocrystalline networks fracture at low-angle grain boundaries, form dislocations and undergo amorphization. The interpenetrating organic network provides additional toughening, as well as substantial damping, with a loss coefficient of around 0.02. An unusual combination of stiffness and damping is therefore achieved, outperforming many engineered materials. A coating made from densely packed hydroxyapatite particles in an organic matrix endows the dactyl club of mantis shrimps with high stiffness and energy damping.

Biological materials found in Nature such as nacre and bone are well recognized as light-weight, strong, and tough structural materials. The remarkable toughness and damage tolerance of such biological materials are conferred through hierarchical assembly of their multiscale (i.e., atomic- to macroscale) architectures and components. Herein, the toughening mechanisms of different organisms at multilength scales are identified and summarized: macromolecular deformation, chemical bond breakage, and biomineral crystal imperfections at the atomic scale; biopolymer fibril reconfiguration/deformation and biomineral nanoparticle/nanoplatelet/nanorod translation, and crack reorientation at the nanoscale; crack deflection and twisting by characteristic features such as tubules and lamellae at the microscale; and structure and morphology optimization at the macroscale. In addition, the actual loading conditions of the natural organisms are different, leading to energy dissipation occurring at different time scales. These toughening mechanisms are further illustrated by comparing the experimental results with computational modeling. Modeling methods at different length and time scales are reviewed. Examples of biomimetic designs that realize the multiscale toughening mechanisms in engineering materials are introduced. Indeed, there is still plenty of room mimicking the strong and tough biological designs at the multilength and time scale in Nature.

Nanostructured amorphous silica in rice plants (biosilica or plant opal) plays an important role in plant growth related to food production. However, the same silica has a structural supporting role as well that has not been uncovered. The current study focuses on the structural design of the two main types of biosilicas in rice plants for the improvement of their mechanical properties. One structural motif is plate-like silicas, which cover most of the surfaces of leaf blades. Another is fan-shaped silicas, which are aligned inside leaf blades, providing a stiff backbone. These biosilica structures consist of 10–100 nm diameter nanoparticles. The mechanical properties, such as hardness and Young's modulus, of the biosilicas are associated with their relative density. Thus, the rice plant mechanics is inferred to be designed by changing the packing of the nanoparticles. Silica plates consisting of loosely packed particles have relatively low density and high flexibility enabling coverage of leaf blade surfaces, while fan-shaped silicas, which consist of tightly packed nanoparticles, are rigid to support the leaf blades as a backbone.

The remarkable mechanical properties observed in biological composite materials relative to those of their individual constituents distinguish them from common engineering materials. Some naturally occurring high-performance ceramics, like the external veneer of the Chiton ( Cryptochiton stelleri ) tooth, have been shown to have superior hardness and impressive abrasion resistance properties. The mechanical performance of the chiton tooth has been attributed to a hierarchical arrangement of nanostructured magnetite rods surrounded with organic material. While nanoindentation tests provide useful information about the overall performance of this biological composite, understanding the key microstructural features and energy dissipation mechanisms at small scales remains a challenging task. We present a combined experimental/numerical approach to elucidate the role of material deformation in the rods, debonding at the rod interfaces and the influence of energy dissipation mechanisms on the ability of the microstructure to distribute damage under extreme loading conditions. We employ a 3D finite element-based micromechanical model to simulate the nanoindentation tests performed in geological magnetite and cross-sections of the chiton tooth. This proposed model is capable of capturing the inelastic deformation of the rods and the failure of their interfaces, while damage, fracture and fragmentation of the mineralized rods is assessed using a probabilistic function. Our results show that these natural materials achieve their abrasion resistant properties by controlling the interface strength between rods, alleviating the tensile stress on the rods near the indentation tip and therefore decreasing the probability of catastrophic failure without significantly sacrificing resistance to penetration. The understanding of these competing energy dissipating mechanisms provides a path to the prediction of new combination of materials. In turns, these results suggest certain guidelines for abrasion resistance rod-like microstructures in composites with high volume fraction of brittle minerals or ceramics with tailored performance for specific applications.

Uniform TiO2 nanospheres from hollow, core–shell and mesoporous structures have been synthesized using quasi-nano-sized carbonaceous spheres as templates. The TiO2 nanospheres formed after calcination at 400 °C are composed of ∼7 nm nanoparticles and the shells of the hollow TiO2 nanospheres are as thin as a single layer of nanoparticles. The ultrafine nanoparticles endow the hollow and mesoporous TiO2 nanospheres with short lithium ion diffusion paths leading to high discharge specific capacities of 211.9 and 196.0 mA h g−1 at a current rate of 1 C (167.5 mA g−1) after 100 cycles, and especially superior discharge specific capacities of 125.9 and 113.4 mA h g−1 at a high current rate of up to 20 C. The hollow and mesoporous TiO2 nanospheres also show superior cycling stability with long-term discharge capacities of 103.0 and 110.2 mA h g−1, respectively, even after 3000 cycles at a current rate of 20 C.

Woodpeckers peck at trees without any reported brain injury despite undergoing high impact loads. Amongst the adaptations allowing this is a highly functionalized impact-absorption system consisting of the head, beak, tongue and hyoid bone. This study aims to examine the anatomical structure, composition, and mechanical properties of the skull to determine its potential role in energy absorption and dissipation. An acorn woodpecker and a domestic chicken are compared through micro-computed tomography to analyze and compare two- and three-dimensional bone morphometry. Optical and scanning electron microscopy with energy dispersive X-ray spectroscopy are used to identify the structural and chemical components. Nanoindentation reveals mechanical properties along the transverse cross-section, normal to the direction of impact. Results show two different strategies: the skull bone of the woodpecker shows a relatively small but uniform level of closed porosity, a higher degree of mineralization, and a higher cortical to skull bone ratio. Conversely, the chicken skull bone shows a wide range of both open and closed porosity (volume fraction), a lower degree of mineralization, and a lower cortical to skull bone ratio. This structural difference affects the mechanical properties: the skull bones of woodpeckers are slightly stiffer than those of chickens. Furthermore, the Young's modulus of the woodpecker frontal bone is significantly higher than that of the parietal bone. These new findings may be useful to potential engineered design applications, as well as future work to understand how woodpeckers avoid brain injury.

The Bouligand structure, which is found in many biological materials, is a hierarchical architecture that features uniaxial fiber layers assembled periodically into a helicoidal pattern. Many studies have highlighted the high damage-resistant performance of natural and biomimetic Bouligand structures. One particular species that utilizes the Bouligand structure to achieve outstanding mechanical performance is the smashing Mantis Shrimp, Odontodactylus Scyllarus (or stomatopod). The mantis shrimp generates high speed, high acceleration blows using its raptorial appendage to defeat highly armored preys. The load-bearing part of this appendage, the dactyl club, contains an interior region [16] that consists of a Bouligand structure. This region is capable of developing a significant amount of nested twisting microcracks without exhibiting catastrophic failure. The development and propagation of these microcracks are a source of energy dissipation and stress relaxation that ultimately contributes to the remarkable damage tolerance properties of the dactyl club. We develop a theoretical model to provide additional insights into the local stress intensity factors at the crack front of twisting cracks formed within the Bouligand structure. Our results reveal that changes in the local fracture mode at the crack front leads to a reduction of the local strain energy release rate, hence, increasing the necessary applied energy release rate to propagate the crack, which is quantified by the local toughening factor. Ancillary 3D simulations of the asymptotic crack front field were carried out using a J-integral to validate the theoretical values of the energy release rate and the local stress intensity factors.

Atractosteus spatula has been described as a living fossil (having existed for 100 Myr), retaining morphological characteristics of early ancestors such as the ability to breathe air and survive above water for hours. Its highly effective armour consists of ganoid scales. We analyse the protective function of the scales and identify key features which lead to their resistance to failure. Microstructural features include: a twisted cross-plied mineral arrangement that inhibits crack propagation in the external ganoine layer, mineral crystals that deflect cracks in the bony region in order to activate the strength of mineralized collagen fibrils, and saw-tooth ridges along the interface between the two scale layers which direct cracks away from the intrinsically weak interface. The macroscale geometry is additionally evaluated and it is shown that the scales retain full coverage in spite of minimal overlap between adjacent scales while conforming to physiologically required strain and maintaining flexibility via a process in which adjacent rows of scales slide and concurrently reorient.

This paper explores the structure, composition, and mechanical properties of porcupine fish spines for the first time. The spine was found to be composed of nanocrystalline hydroxyapatite, protein (collagen), and water using X-ray diffraction, energy-dispersive X-ray spectroscopy, and thermogravimetric analysis. Microstructures have mineralized fibrillar sheets in the longitudinal direction and in a radial orientation in the transverse direction that were observed using light and electron microscopy. Based on the images, the hierarchical structure of the spine shows both concentric and radial reinforcement. Mechanical properties were obtained using cantilever beam and nanoindentation tests. A tapered cantilever beam model was developed and compared to that of a uniform cantilever beam. The tapered beam model showed that while the stresses experienced were similar to those of the uniform beam, the location of the maximum stress was near the distal region of the beam rather than at the base, which allows the porcupine fish to conserve energy and resources if the spine is fractured.

A fibrous herringbone-modified helicoidal architecture is identified within the exocuticle of an impact-resistant crustacean appendage. This previously unreported composite microstructure, which features highly textured apatite mineral templated by an alpha-chitin matrix, provides enhanced stress redistribution and energy absorption over the traditional helicoidal design under compressive loading. Nanoscale toughening mechanisms are also identified using high load nanoindentation and in-situ TEM picoindentation., 6 figures. Published in Advanced Materials 2016

The flying feathers of birds are keratinous appendages designed for maximum performance with a minimum weight penalty. Thus, their design contains ingenious combinations of components that optimize lift, stiffness, aerodynamics, and damage resistance. This design involves two main parts: a central shaft that prescribes stiffness and lateral vanes which allows for the capture of air. Within the feather vane, barbs branch from the shaft and barbules branch from barbs, forming a flat surface which ensures lift. Microhooks at the end of barbules hold barbs tightly together, providing the close-knit, unified structure of the feather vane and enabling a repair of the structure through the reattachment of un-hooked junctions. Both the shaft and barbs are lightweight biological structures constructed of keratin using the common motif of a solid shell and cellular interior. The cellular core increases the resistance to buckling with little added weight. Here we analyze the detailed structure of the feather barb and, for the first time, explain its flexural stiffness in terms of the mechanics of asymmetric foam-filled beams subjected to bending. The results are correlated and validated with finite element modeling. We compare the flexure of single barbs as well as arrays of barbs and find that the interlocking adherence of barbs to one another enables a more robust structure due to minimized barb rotation during deflection. Thus, the flexure behavior of the feather vane can be tailored by the adhesive hooking between barbs, creating a system that mitigates damage. A simplified three-dimensional physical model for this interlocking mechanism is constructed by additive manufacturing. The exceptional architecture of the feather vane will motivate the design of bioinspired structures with tailored and unique properties ranging from adhesives to aerospace materials. Statement of Significance Despite its importance to bird flight, literature characterizing the feather vane is extremely limited. The feather vane is composed of barbs that branch from the main shaft (rachis) and barbules that branch from barbs. In this study, the flexural behavior of the feather barb and the role of barbule connections in reinforcing the feather vane are quantitatively investigated for the first time, both experimentally and theoretically. Through the performed experiments, structure-function relationships within the feather vane are uncovered. Additionally, in the proposed model the sophisticated structure of the barbs and the interlocking mechanism of the feather vane are simplified to understand these processes in order to engineer new lightweight structures and adhesives.

Woodpeckers avoid brain injury while they peck at trees up to 20 Hz with speeds up to 7 m/s, undergoing decelerations up to 1200 g. Along with the head, beak and neck, the hyoid apparatus (tongue bone and associated soft tissues) is subjected to these high impact forces. The shape of the hyoid apparatus is unusual in woodpeckers and its structure and mechanical properties have not been reported in detail. High-resolution X-ray micro-computed tomography and scanning electron microscopy with energy dispersive X-ray spectroscopy were performed and correlated with nanoindentation mapping. The hyoid apparatus has four distinct bone sections, with three joints between these sections. Nanoindentation results on cross-sectional regions of each bone reveal a previously unreported structure consisting of a stiff core and outer, more compliant shell with moduli of up to 27.4 GPa and 8.5 GPa, respectively. The bending resistance is low at the posterior section of the hyoid bones, indicating that this region has a high degree of flexibility to absorb impact. These new structural findings can be applied to further studies on the energy dissipation of the woodpecker during its drumming behavior, and may have implications for the design of engineered impact-absorbing structures. Statement of Significance Woodpeckers avoid brain injury while they peck at trees, which results in extreme impact conditions. One common adaptation in woodpeckers is the unusual shape of the elongated tongue, also called the hyoid apparatus. The relationship between the structure and mechanical properties of the bony part of the hyoid apparatus has not been previously reported. A three dimensional model of the bony tongue was developed, and the hardness and stiffness were evaluated. A new type of bone structure, which is opposite of typical skeletal bone structure was found. The combined microstructural and mechanical property analysis indicate possible energy absorption routes for the hyoid apparatus and are applicable to the design of engineered structures.

Carbon-based nanocomposites have shown promising results in replacing commercial Pt/C as high-performance, low cost, nonprecious metal-based oxygen reduction reaction (ORR) catalysts. Developing unique nanostructures of active components (e.g., metal oxides) and carbon materials is essential for their application in next generation electrode materials for fuel cells and metal-air batteries. Herein, a general approach for the production of 1D porous nitrogen-doped graphitic carbon fibers embedded with active ORR components, (M/MOx , i.e., metal or metal oxide nanoparticles) using a facile two-step electrospinning and annealing process is reported. Metal nanoparticles/nanoclusters nucleate within the polymer nanofibers and subsequently catalyze graphitization of the surrounding polymer matrix and following oxidation, create an interconnected graphite-metal oxide framework with large pore channels, considerable active sites, and high specific surface area. The metal/metal oxide@N-doped graphitic carbon fibers, especially Co3 O4 , exhibit comparable ORR catalytic activity but superior stability and methanol tolerance versus Pt in alkaline solutions, which can be ascribed to the synergistic chemical coupling effects between Co3 O4 and robust 1D porous structures composed of interconnected N-doped graphitic nanocarbon rings. This finding provides a novel insight into the design of functional electrocatalysts using electrospun carbon nanomaterials for their application in energy storage and conversion fields.

Ecological pressures and varied feeding behaviors in a multitude of organisms have necessitated the drive for adaptation. One such change is seen in the feeding appendages of stomatopods, a group of highly predatory marine crustaceans. Stomatopods include "spearers," who ambush and snare soft bodied prey, and "smashers," who bludgeon hard-shelled prey with a heavily mineralized club. The regional substructural complexity of the stomatopod dactyl club from the smashing predator Odontodactylus scyllarus represents a model system in the study of impact tolerant biominerals. The club consists of a highly mineralized impact region, a characteristic Bouligand architecture (common to arthropods), and a unique section of the club, the striated region, composed of highly aligned sheets of mineralized fibers. Detailed ultrastructural investigations of the striated region within O. scyllarus and a related species of spearing stomatopod, Lysiosquillina maculate show consistent organization of mineral and organic, but distinct differences in macro-scale architecture. Evidence is provided for the function and substructural exaptation of the striated region, which facilitated redeployment of a raptorial feeding appendage as a biological hammer. Moreover, given the need to accelerate underwater and "grab" or "smash" their prey, the spearer and smasher appendages are specifically designed with a significantly reduced drag force.

Highly oriented epitaxial rutile titanium dioxide (TiO2) nanowire arrays have been hydrothermally grown on polycrystalline TiO2 templates with their orientation dependent on the underlying TiO2 grain. Both the diameter and areal density of the nanowires were tuned by controlling the precursor concentration, and the template surface energy and roughness. Nanowire tip sharpness was influenced by precursor solubility and diffusivity. A new secondary ion mass spectrometer technique has been developed to install additional nucleation sites in single crystal TiO2 templates and the effect on nanowire growth was probed. Using the acquired TiO2 nanowire synthesis knowhow, an assortment of nanowire arrays were installed upon the surface of undoped TiO2 photo-electrodes and assessed for their photo-electrochemical water splitting performance. The key result obtained was that the presence of short and dispersed nanowire arrays significantly improved the photocurrent when the illumination intensity was increased from 100 to 200 mW cm-2. This is attributed to the alignment of the homoepitaxially grown nanowires to the [001] direction, which provides the fastest charge transport in TiO2 and an improved pathway for photo-holes to find water molecules and undertake oxidation. This result lays a foundation for achieving efficient water splitting under conditions of concentrated solar illumination.