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The relationship between diet, bite performance, and tooth structure is a topic of common interest for ecologists, biologists, materials scientists, and engineers. The highly specialized group of biters found in Serrasalmidae offers a unique opportunity to explore their functional diversity. Surprisingly, the piranha, whose teeth have a predominantly cutting function and whose main diet is soft flesh, is capable of exerting a greater bite force than a similarly sized pacu, who feeds on a hard durophagous diet. Herein, we expand our understanding of diet specialization in the Serrasalmidae family by investigating the influence of elemental composition and hierarchical structure on the local mechanical properties, stress distribution, and deformation mechanics of teeth from piranha (Pygocentrus nattereri) and pacu (Colossoma macropomum). Microscopic and spectroscopic analyses combined with nanoindentation and finite element simulations are used to probe the hierarchical features to uncover the structure-property relationships in piranha and pacu teeth. We show that the pacu teeth support a durophagous diet through its broad cusped-shaped teeth, thicker-irregular enameloid, interlocking interface of the dentin-enameloid junction, and increased hardness of the cuticle layer due to the larger concentrations of iron present. Comparatively, the piranha teeth are well suited for piercing due to their conical-shape which we report as having the greatest stiffness at the tip and evenly distributed enameloid. STATEMENT OF SIGNIFICANCE: The hierarchical structure and local mechanical properties of the piranha and pacu teeth are characterized and related to their feeding habits. Finite element models of the anterior teeth are generated to map local stress distribution under compressive loading. Bioinspired designs from the DEJ interface are developed and 3D printed. The pacu teeth are hierarchically structured and have local mechanical properties more suitable to a durophagous diet than the piranha. The findings here can provide insight into the design and fabrication of layered materials with suture interfaces for applications that require compressive loading conditions.

Magnetotactic bacterium, Magnetospirillum magneticum, produces biogenic magnetic nanoparticles termed magnetosomes, which are primarily composed of a magnetite core and a surrounding lipid bilayer membrane. We have fabricated human transmembrane protein-magnetosome complexes by genetic engineering with embedding the transmembrane proteins of interest, in particular G protein-coupled receptors (GPCRs), in the magnetosome membrane. The magnetosomes provide a promising platform for high throughput ligand screening towards drug discovery, and this is a critical advantage of the magnetosome display system beyond conventional membrane platforms such as liposomes and lipid nano-discs. However, the human GPCRs expressed on the magnetosomes were not fully functionalized in bacterial membranes the most probably due to the lack of essential phospholipids such as phosphatidylcholine (PC) for GPCR functionalization. To overcome this issue, we expressed two types of PC-producing enzymes, phosphatidylcholine synthase (PCS) and phosphatidylethanolamine N-methyltransferase (PMT) in M. magneticum. As a result, generation and incorporation of PC in cell- and magnetosome-membranes were demonstrated. To the best of our knowledge, M. magneticum is the second bacterial species which had the PC-incorporated lipid membrane by genetic engineering. Subsequently, a GPCR, thyroid-stimulating hormone receptor (TSHR) and PCS were simultaneously expressed. We found that PC in the magnetosome membrane assisted the binding of TSHR and its ligand, indicating that the genetic approach demonstrated in this study is useful to enhance the function of the GPCRs displayed on the magnetosomes.

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.

Iron is an essential micronutrient for most living organisms, including cyanobacteria. These microorganisms have been found in Earth's driest polar and non-polar deserts, including the Atacama Desert, Chile. Iron-containing minerals were identified in colonized rock substrates from the Atacama Desert, however, the interactions between microorganisms and iron minerals remain unclear. In the current study, we determined that colonized gypsum rocks collected from the Atacama Desert contained both magnetite and hematite phases. A cyanobacteria isolate was cultured on substrates consisting of gypsum with embedded magnetite nanoparticles. Transmission electron microscopy imaging revealed a significant reduction in the size of magnetite nanoparticles due to their dissolution, which occurred around the microbial biofilms. Concurrently, hematite was detected, likely from the oxidation of the magnetite nanoparticles. Higher cell counts and production of siderophores were observed in cultures with magnetite nanoparticles suggesting that cyanobacteria were actively acquiring iron from the magnetite nanoparticles. Magnetite dissolution and iron acquisition by the cyanobacteria was further confirmed using large bulk magnetite crystals, uncovering a survival strategy of cyanobacteria in these extreme environments.

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.

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.

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.

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.

Chitons are herbivorous invertebrates that use rows of ultrahard magnetite-based teeth connected to a flexible belt (radula) to rasp away algal deposits growing on and within rocky outcrops along coastlines around the world. Each tooth is attached to the radula by an organic structure (stylus) that provides mechanical support during feeding. However, the underlying structures within the stylus, and their subsequent function within the chiton have yet to be investigated. Here, we investigate the macrostructural architecture, the regional material and elemental distribution and subsequent nano-mechanical properties of the stylus from the Northern Pacific dwelling Cryptochiton stelleri. Using a combination of μ-CT imaging, optical and electron microscopy, as well as elemental analysis, we reveal that the stylus is a highly contoured tube, mainly composed of alpha-chitin fibers, with a complex density distribution. Nanoindentation reveals regiospecific and graded mechanical properties that can be correlated with both the elemental composition and material distribution. Finite element modeling shows that the unique macroscale architecture, material distribution and elemental gradients have been optimized to preserve the structural stability of this flexible, yet robust functionally-graded fiber-reinforced composite tube, providing effective function during rasping. Understanding these complex fiber-based structures offers promising blueprints for lightweight, multifunctional and integrated materials.

This study investigates UV irradiation-induced cell settling, followed by cell aggregation, of the oleaginous diatom Fistulifera solaris. Cell settling was observed after 24 h of cultivation following UV irradiation. The highest cell settling rate was obtained at a light intensity of 10 mJ/cm2. The cell settling was induced by irradiating with UV (254 nm), but was ineffective with light of other wavelengths (474 or 620 nm). The settling response was not observed in other microalgae, such as Chlamydomonas reinhardtii and Phaeodactylum tricornutum, with the same treatment, suggesting that this response was specific to F. solaris. The optical and SEM images revealed the occurrence of cell aggregation with the UV treatment, resulting in the subsequent cell settling. Although there was no significant change in the lipid, protein, and sugar content, secreted acidic polysaccharide was found in the F. solaris cell culture following UV irradiation. Therefore, this polysaccharide was considered likely to be the cell aggregation-inducing factor. The energy consumption of this UV-induced cell settling for cell recovery method was estimated to be approximately 0.77 × 10−1 kWh/m3, which is lower than the energy consumption of existing methods. Therefore, this method could be applied for harvesting F. solaris cells from large-scale cultures.

Wave propagation was investigated in the Bouligand-like structure from within the dactyl club of the Stomatopod, a crustacean that is known to smash their heavily shelled preys with high accelerations. We incorporate the layered nature in a unitary material cell through the propagator matrix formalism while the periodic nature of the material is considered via Bloch boundary conditions as applied in the theory of solid state physics. Our results show that these materials exhibit bandgaps at frequencies related to the stress pulse generated by the impact of the dactyl club to its prey, and therefore exhibiting wave filtering in addition to the already known mechanisms of macroscopic isotropic behavior and toughness., 19 pages, 7 figures, In press, Acta Biomaterialia (2015)

Many biomineralized organisms have evolved highly oriented nanostructures to perform specific functions. One key example is the abrasion-resistant rod-like microstructure found in the radular teeth of Chitons (Cryptochiton stelleri), a large mollusk. The teeth consist of a soft core and a hard shell that is abrasion resistant under extreme mechanical loads with which they are subjected during the scraping process. Such remarkable mechanical properties are achieved through a hierarchical arrangement of nanostructured magnetite rods surrounded with α-chitin. We present a combined biomimetic approach in which designs were analyzed with additive manufacturing, experiments, analytical and computational models to gain insights into the abrasion resistance and toughness of rod-like microstructures. Staggered configurations of hard hexagonal rods surrounded by thin weak interfacial material were printed, and mechanically characterized with a cube-corner indenter. Experimental results demonstrate a higher contact resistance and stiffness for the staggered alignments compared to randomly distributed fibrous materials. Moreover, we reveal an optimal rod aspect ratio that lead to an increase in the site-specific properties measured by indentation. Anisotropy has a significant effect (up to 50%) on the Young's modulus in directions parallel and perpendicular to the longitudinal axis of the rods, and 30% on hardness and fracture toughness. Optical microscopy suggests that energy is dissipated in the form of median cracks when the load is parallel to the rods and lateral cracks when the load is perpendicular to the rods. Computational models suggest that inelastic deformation of the rods at early stages of indentation can vary the resistance to penetration. As such, we found that the mechanical behavior of the system is influenced by interfacial shear strain which influences the lateral load transfer and therefore the spread of damage. This new methodology can help to elucidate the evolutionary designs of biomineralized microstructures and understand the tolerance to fracture and damage of chiton radular teeth.

There has been significant progress in recent years aimed at pushing the spatial resolution limits of scanning electron microscopes. Many of these endeavours have been driven by advances in the field of nanotechnology and the need to investigate the morphological features of sub-micron size materials. While scanning electron microscopy is indeed a powerful tool for investigating objects at length-scales that are prohibitive using standard optical microscopy techniques, SEMs are equally useful in characterizing the micro- and macro-scale architectures of transparent, highly reflective, or morphologically complex materials. Despite this great potential, until recently, the maximum feature sizes that could be successfully imaged in a scanning electron microscope were on the order of a few millimeters and the thought of routinely imaging objects on the order of 10s of centimeters in a single dimension, in a single image seemed unimaginable. New advances in SEM column design, however, are beginning to change all of this.

Recent analyses of the ultrastructural and mechanical properties of mineralized biological materials have demonstrated some common architectural features that can help explain their observed damage tolerance. Nature has accomplished this feat through the precise control of anisotropic crystal nucleation and growth processes in conjunction with nanoscale control over the self-assembly of spatially distinct organic and inorganic phases, resulting in effective inhibition of crack propagation through these materials. One such example is found in the hyper-mineralized and abrasion resistant radular teeth of the chitons, a group of herbivorous marine mollusks who have the surprising capacity to erode away the rocky substrates on which they graze 1-4 . Through the use of modern microscopy and nanomechanical characterization techniques, we describe the architectural and mechanical properties of the radular teeth from Cryptochiton stelleri. Chiton teeth are shown to exhibit the largest hardness and stiffness of any biominerals reported to date, being notably as much as three-fold harder than human enamel and the calcium carbonate-based shells of mollusks. We explain how the unique multi-phasic design of these materials contributes not only to their functionality, but also highlights some interesting design principles that might be applied to the fabrication of synthetic composites.

Wurtzite GaN nanocrystals were produced by the pyrolysis and crystallization of two different precursors, gallium dimethyl amide (GDA) and gallium isopropoxide (GIP), in an ammonia atmosphere between 600°C and 1200°C. Ammonia reacted with GDA at room temperature by transamination, followed by deamination of the amorphous precursor at higher temperatures. After crystallization to wurtzite GaN, grain growth occurred and was dominated by evaporation–condensation. Low-temperature pyrolysis of GIP in an ammonia atmosphere yielded gallium oxynitride nanocrystals. Higher processing temperatures transformed the nanocrystalline powders to wurtzite GaN. GaN powders exhibited the room temperature photoluminescence characteristic of wurtzite GaN. Nitrogen vacancies present in the powder appear to be potential candidates for the yellow luminescence.

Gallium nitride thin films on sapphire substrates were produced from a gallium dimethylamide-based liquid precursor by chemical solution deposition. After pyrolysis in ammonia atmosphere, films obtained from precursors with low polymer content consisted of an irregular and facetted epitaxial GaN interface layer covered by a thin layer of polycrystalline grains, whereas precursors of higher polymer concentration lead to entirely polycrystalline GaN films. At an intermediate growth stage, the formation of a gallium oxide nitride phase was observed. Epitaxial GaN growth is discussed with respect to possible material transport paths, including vapor phase transport.

A polymeric Ga-containing liquid precursor was used for the first time to prepare a buffer layer for the growth of GaN by metalorganic chemical vapor deposition. The buffer layer was prepared by chemical solution deposition (CSD), i.e. spincoating the precursor on a sapphire substrate followed by pyrolysis in ammonia. The GaN films were characterized by optical and electron microscopy, XRD rocking curves, photoluminescence and Hall measurements. The CSD-buffered GaN films showed a significantly better crystal quality than unbuffered films and came close to the quality of conventionally buffered ones.

Barium titanate (BaTiO 3 ) fine particles were coated with silica via the sol-gel reactions of tetraethyl orthosilicate. The solgel silica coating significantly stabilizes the BaTiO 3 particles in acidic solutions and changes the zeta potential of the particles to that similar to pure silica.