Stress and Damage Mitigation from Oriented Nanostructures within the Radular Teeth of Cryptochiton stelleri

Abstract

Chiton are marine mollusks who use heavily mineralized and ultrahard teeth to feed on epilithic and endolithic algae on intertidal rocks. To fulfill this function, chiton teeth must be tough and wear‐resistant. Impressive mechanical properties are achieved in the chiton tooth through a hierarchically arranged composite structure consisting of a hard shell of organic‐encased and highly oriented nanostructured magnetite rods that surround a soft core of organic‐rich iron phosphate. Microscopic and spectroscopic analyses combined with finite element simulations are used to probe the ultrastructural features and uncover structure–mechanical property relationships in the fully mineralized teeth of the gumboot chiton Cryptochiton stelleri. By understanding the effects of the nanostructured architecture within the chiton tooth, abrasion‐resistant materials can be developed for tooling and machining applications, as well as coatings for equipment and medical implants.

A Sinusoidally Architected Helicoidal Biocomposite

“…Nanoparticulated surface coatings have been observed in other biological composite materials such as the ultra-hard teeth of the chiton, Cryptochiton stelleri, a marine mollusk. [42] These teeth feature an outermost 2 μm thick layer of densely packed sub-100 nm magnetite particles with no preferred orientation, which cover an underlying rod-like microstructure and provide abrasion resistance. [42] The incorporation of ceramic nanoparticles into epoxy polymers used as matrix materials for fiberreinforced composites has also been shown to improve the toughness as well as Young's modulus of the polymer.…”

“…[42] These teeth feature an outermost 2 μm thick layer of densely packed sub-100 nm magnetite particles with no preferred orientation, which cover an underlying rod-like microstructure and provide abrasion resistance. [42] The incorporation of ceramic nanoparticles into epoxy polymers used as matrix materials for fiberreinforced composites has also been shown to improve the toughness as well as Young's modulus of the polymer. [43][44][45] The extent of plastic deformation of the epoxy is enhanced so as to dissipate more energy in regions surrounding the crack tip.…”

Analysis of the mechanical response of biomimetic materials with highly oriented microstructures through 3D printing, mechanical testing and modeling

“…Finite element models of the tooth have shown that the leading edge is dominantly loaded in tension while the trailing edge is in compression during scraping events. Moreover, the principal directions of applied stress coincide with the natural rod alignment within the tooth [22], [30]. This difference in loading conditions accounts for the size difference in the rods, as larger diameter rods are favorable for compressive loading [31].…”

“…A recent study of the fully mineralized radular teeth of Cryptochiton stelleri has revealed insights into the abrasion resistance of the rod-like microstructure [30]. The hard magnetite shell of the tooth is reminiscent of a fiber-reinforced composite, composed of aligned hexagonal closepacked rods, surrounded by thin regions of organic α-chitin, which run parallel to the longitudinal axis of the tooth ( Figure 1C, D).…”

“…Indentation tests are therefore ideal to reproduce and examine the effects of erosive mechanical agents on the rod-like microstructure of worn teeth. It has been shown that rods on the trailing edge are approximately 30% larger in diameter (φ) than those in the leading edge [30]. However, the length, and therefore the aspect ratio of the rods remain unknown.…”