Biologically inspired and impact-resistant composites

There is an increasing need for the development of multifunctional lightweight materials with high strength and toughness. Natural systems have evolved efficient strategies, exemplified in the biological tissues of numerous animal and plant species, to synthesize and construct composites from a limited selection of available starting materials that often exhibit exceptional mechanical properties that are similar, and frequently superior to, mechanical properties exhibited by many engineering materials. These biological systems have accomplished this feat by establishing controlled synthesis and hierarchical assembly of nano- to micro-scaled building blocks. This controlled synthesis and assembly require organic that is used to transport mineral precursors to organic scaffolds, which not only precisely guide the formation and phase development of minerals, but also significantly improve the mechanical performance of otherwise brittle materials. However, Nature goes one step further, often producing materials with that display multi-functionality in order to provide organisms with a unique ecological advantage to ensure survival. In this work, we investigate a few organisms that have taken advantage of hundreds of millions of years of evolutionary changes to derive structures, which are not only strong and tough, but also demonstrate multifunctional features dependent on the underlying organic-inorganic components. We discuss, for example, (i) the hyper-mineralized combative dactyl club of the stomatopods, a group of highly aggressive marine crustaceans, (ii) an elytra from an impact resistant beetle and (iii) an ultrahard and light diffusing shell of a bioluminescent gastropod that uses its thick shell not only for protection but also to ward off predation through illumination. Many of these tissues include both fibrous organic components that improve toughness as well as, in many cases, guide mineral growth. Spider silks are renowned as high-performance materials and compare favorably with the best manmade fibers in strength and toughness. Thus, we also highlight some recent work on spider silks, investigating fundamental ultrastructure-property relationships in thermally annealed silks, which are utilized via bio-inspired designs in mimetic composites

Shear wave filtering in the Mantis Shrimp’s dactyl club

We propose that the presence of Bouligand-like structure in the dactyl club of the stomatopod lead the material to exhibit wave filtering in addition to the already known mechanisms of macroscopic isotropy behavior and toughness. We use a propagator matrix approach, earlier introduced to study layered materials to simplify the treatment of the boundary value problem. The periodic nature of the material is then considered in terms of frequency dependent dispersion relations, which are found using Floquet–Bloch boundary conditions for a typical elementary cell. These curves provide as a main result, frequency band-gaps which are then compared with the amplitude spectra for a typical impact sustained by the dactyl-club in the mantis-shrimp. This comparison directly yields fractions of transmitted energy against different parameters of the layered composite

Improved neuron culture using scaffolds made of three-dimensional PDMS micro-lattices

Tissue engineering strives to create functional components of organs with different cell types in vitro. One of the challenges is to fabricate scaffolds for three-dimensional (3D) cell culture under physiological conditions. Of particular interesting is to investigate the morphology and function of the central nervous system (CNS) cultured using such scaffolds. Here, we used an elastomer, polydimethylsiloxane (PDMS), to produce lattice-type scaffolds from a photolithography defined template. The photomask with antidot arrays was spin-coated by a thick layer of resist and downward mounted on a rotating stage at angle of 45\ub0. After exposure for three or more times keeping the same exposure plan but rotated by the same angle, the photoresist was developed to produce a 3D porous template. Afterward, a pre-polymer mixture of PDMS was poured in and cured, followed by a resist etch, resulting in lattice-type PDMS features. Before cell culture, the PDMS lattices were surface functionalized. Culture test has been done using NIH-3T3 cells and primary hippocampal cells from rats, showing homogenously cell infiltration and 3D attachment. As expected, a much higher cell number was found in 3D PDMS lattices than in 2D culture. We also found a higher neuron to astrocyte ratio and a higher degree of cell ramification in 3D culture compared to 2D culture, due to the change of scaffold topography and the elastic properties of the PDMS micro-lattices. Our results demonstrate that the 3D PDMS micro-lattices improve the survival and growth of cells as well as the network formation of neurons. We believe that such an enabling technology is useful for research and clinical applications including disease modeling, regenerative medicine, and drug discovery/drug cytotoxicity studies

Direct Ink Write Printing of Chitin-Based Gel Fibers with Customizable Fibril Alignment, Porosity, and Mechanical Properties for Biomedical Applications

A fine control over different dimensional scales is a challenging target for material science since it could grant control over many properties of the final material. In this study, we developed a multivariable additive manufacturing process, direct ink write printing, to control different architectural features from the nano- to the millimeter scale during extrusion. Chitin-based gel fibers with a water content of around 1500% were obtained extruding a polymeric solution of chitin into a counter solvent, water, inducing instant solidification of the material. A certain degree of fibrillar alignment was achieved basing on the shear stress induced by the nozzle. In this study we took into account a single variable, the nozzle's internal diameter (NID). In fact, a positive correlation between NID, fibril alignment, and mechanical resistance was observed. A negative correlation with NID was observed with porosity, exposed surface, and lightly with water content. No correlation was observed with maximum elongation (similar to 50%), and the scaffold's excellent biocompatibility, which appeared unaltered. Overall, a single variable allowed a customization of different material features, which could be further tuned, adding control over other aspects of the synthetic process. Moreover, this manufacturing could be potentially applied to any polymer

Integrated transcriptomic and proteomic analyses of a molecular mechanism of radular teeth biomineralization in Cryptochiton stelleri

　Many species of chiton are known to deposit magnetite (Fe3O4) within the cusps of their heavily mineralized and ultrahard radular teeth. Recently, much attention has been paid to the ultrastructural design and superior mechanical properties of these radular teeth, providing a promising model for the development of novel abrasion resistant materials. Here, we constructed de novo assembled transcripts from the radular tissue of C. stelleri that were used for transcriptome and proteome analysis. Transcriptomic analysis revealed that the top 20 most highly expressed transcripts in the non-mineralized teeth region include the transcripts encoding ferritin, while those in the mineralized teeth region contain a high proportion of mitochondrial respiratory chain proteins. Proteomic analysis identified 22 proteins that were specifically expressed in the mineralized cusp. These specific proteins include a novel protein that we term radular teeth matrix protein1 (RTMP1), globins, peroxidasins, antioxidant enzymes and a ferroxidase protein. This study reports the first de novo transcriptome assembly from C. stelleri, providing a broad overview of radular teeth mineralization. This new transcriptomic resource and the proteomic profiles of mineralized cusp are valuable for further investigation of the molecular mechanisms of radular teeth mineralization in chitons

Hierarchical Growth of ZnO Particles by a Hydrothermal Route

The crystallization of ZnO microrods by hydrothermal treatment of a suspension formed from reaction of zinc acetate and sodium hydroxide has been examined using scanning and transmission electron microscopy. Polycrystalline hexagonal ZnO microrods first appeared after 0.5 h reaction time at 120°C. These early stage rods were composed of stacks of hexagonal layers, each ~50 nm in thickness containing closely aligned assemblies of nanocrystallites <20 nm in size. Further growth of the microrods involved columns of nanoparticles extending from the basal layers of the preformed hexagonal stacks. Re-crystallization produced single-crystal microrods, many of which existed as twin particles

Controllable synthesis of mesostructures from TiO2 hollow to porous nanospheres with superior rate performance for lithium ion batteries

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

Ecologically driven ultrastructural and hydrodynamic designs in stomatopod cuticles

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.Facultad de Ingenierí