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

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

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

Multiscale mechanical characterization of biobased photopolymers towards sustainable vat polymerization 3D printing

In vat polymerization (VP) 3D printing, there is an urgent need to expand characterization efforts for resins derived from natural resources to counter the increasing consumption of fossil fuels required to synthesize conventional monomers. Here, we apply multiscale mechanical characterization techniques to interrogate a 3D printed biobased copolymer along a controlled range of monomer ratios. We varied the concentration of two dissimilar monomers to derive structural information about the polymer networks. Current research primarily considers the macroscale, but recent understanding of the process-induced anisotropy in 3D printed layers suggests a multiscale approach is critical. By combining typical macroscopic techniques with micro- and nanoscale analogues, clear correlations in the processing-structure-property relationships appeared. We observed that measured moduli were always greater via surface-localized methods, but property differences between formulations were easier to identify. As researchers continue to develop novel sustainable biopolymers that match or exceed the performance of commercial resins, it is vital to understand the multiscale relationships between the VP process, the structure of the formed polymer networks, and the resultant properties

Unveiling the resistance to penetration of the radular teeth of the Cryptochiton stelleri

The tongue of the C. stelleri is provided with numerous rows of highly mineralized teeth composed of a soft organic chitin matrix and hard magnetite rods. The shell of the tooth is characterized with the highest modulus and hardness of any known biomineral. Similar to other biological materials (i.e., nacre and conch), the tooth is provided with mineral bridges, nanoscale asperities and roughness, and a microstructure composed of stiff piled rods wrapped in a matrix of soft organic material. Despite the advanced microscopic techniques used today, not much has been said about the influence of the geometrical aspects in the complex microstructure. To test the effect of the geometrical parameters in the mechanical properties measured by indentation test (Er, H), a set of biomimetic designs composed of stiff rods surrounded by weak interfaces have been manufactured. Postindented samples show that it is possible to replicate the localized damage and crack tolerance observed in the tooth with rapid prototypes. Results indicate that a variation in the aspect ratio of the rods can lead to a 50% increase in the stiffness and a 30% increase in the hardness measured. It is also observed that the rod like microstructure can mitigate catastrophic failure with interface cracking, rod failure, and material debonding. Computational models suggest that inelastic deformation of the rods at early stages of indentation can vary the resistance to penetration, in which the mechanical behavior of the system is influenced by interfacial shear strain and high plastic stresses in the rods. It is also shown that the design of the rod-like microstructure can be tailored to abrasion resistant or fracture tolerant materials. In this study, it is demonstrated that additive manufacturing is a useful technology that can be used to unveil the mechanical behavior of intrincated microstructures