Phase Transformations and Structural Developments in the Radular Teeth of Cryptochiton Stelleri

Abstract

During mineralization, the hard outer magnetite‐containing shell of the radular teeth of Cryptochiton stelleri undergoes four distinct stages of structural and phase transformations: (i) the formation of a crystalline α‐chitin organic matrix that forms the structural framework of the non‐mineralized teeth, (ii) the templated synthesis of ferrihydrite crystal aggregates along these organic fibers, (iii) subsequent solid state phase transformation from ferrihydrite to magnetite, and (iv) progressive magnetite crystal growth to form continuous parallel rods within the mature teeth. The underlying α‐chitin organic matrix appears to influence magnetite crystal aggregate density and the diameter and curvature of the resulting rods, both of which likely play critical roles in determining the local mechanical properties of the mature radular teeth.

From Bacteria to Mollusks: The Principles Underlying the Biomineralization of Iron Oxide Materials

“…[120] It thus appears very likely that protein-coated chitin fibers act as nucleating agents for heterogeneous nucleation of ferrihydrite.T his idea was in turn supported by the observation that the crystal aggregates are smaller and the density is larger in the leading edge than in the trailing edge of mature teeth of C. stellari. [116] At the same time,t he organic fibers are also more densely packed in the leading edge,which according to the above view,corresponds to ah igher density of nucleation sites. [116] This situation indicates av ery high degree of control over mineralization.…”

Structure and mechanical properties of selected protective systems in marine organisms

“…Fe 3 O 4 is rarely employed as a broad structural material in organisms, but rather within individual organs for a specific function. However, it is present as a structural material in the teeth of chitons, where it is employed in order to increase hardness [89]. Given the magnetic properties of Fe 3 O 4 , it is most often employed as a bio-compass allowing marine organisms such as lobsters and sea turtles to orient themselves to the earth's magnetic field and travel without other sensory cues [84,85,88,90].…”

“…Of additional interest, the chiton Cryptochiton stelleri has adapted to produce extremely hard and wear-resistant teeth of Fe 3 O 4 and α-chitin to scrape algae off of rocks (Fig. 12b) [89,114,115]. The teeth themselves mineralize in a four-step process: (1) forming a pure chitin scaffold tooth, (2) precipitating crystals of an intermediate and Adapted from: (a) [118], (b) [79], (c) [124].…”

“…[127], (c) [128]. metastable iron oxide (ferrihydrite), (3) transforming the ferrihydrate into Fe 3 O 4 and (4) allowing for Fe 3 O 4 crystal growth [89,116]. This mineralization process is driven by acidic macromolecules that pattern the chitin scaffold [116].…”

Oblique plies for steering through-thickness delamination migration in fibre reinforced polymers

“…Other examples from nature where the orientation of stiff laminar phases, comparable to the fibre direction of FRP plies, is used to control damage progression include the equine hoof wall 16 and the radula of snails 17 . In these cases the stiff laminar phases are oriented obliquely to the expected direction of damage propagation, redirecting the damage away from critical areas, such as soft tissue.…”