Mesocrystalline Ordering and Phase Transformation of Iron Oxide Biominerals in the Ultrahard Teeth of Cryptochiton stelleri

Abstract

Biological organisms naturally synthesize complex, hierarchical, multifunctional materials through mineralization processes at ambient conditions and under physiological pH. One such example is the ultrahard and wear‐resistant radular teeth found in mollusks, which are used to scape against the rock to feed on algae. Herein, the biologically controlled structural development of the hard, outer magnetite‐containing shell of the chitin teeth is revealed. Specifically, the formation of a series of mesocrystalline iron oxide phases, templated by chitin‐binding proteins, is identified. The initial domains, consisting of ferrihydrite mesocrystals with a spherulite‐like morphology, undergo a solid‐state phase transformation to form magnetite while maintaining mesocrystallinity, likely via a shear‐induced solid‐state reaction, without any noticeable architectural changes. Subsequent growth via Ostwald ripening leads to nearly single‐crystalline rod‐like elements. In addition, an interpenetrating organic matrix is identified that, at early stages of tooth development, potentially contains iron‐binding proteins that guide the self‐assembly of the mesocrystalline mineral and influence the preferred orientation of the later‐formed magnetite nanorods, which ultimately determines the mechanical behavior of the mature chiton teeth.

Bioinspired Robust Mechanical Properties for Advanced Materials

“…The radulae are composed of mineralized mesocrystallines and chitin-binding organic matrix, where the minerals are mainly magnetite and iron phosphate (Figure 7I). [81][82][83] A typical core-shell architecture was identified in this ultra-hard structure. The hard shell is made of magnetite crystals embedded in nanorods parallel to the long axis, where the nanorods of the chitin organic matrix direct the formation of mineral crystals.…”

“…The investigation of the biologically controlled phase development of the hard magnetitecontaining shell of the chiton teeth revealed that a phase transition of the ultrafine nanoparticles from ferrihydrite crystals to magnetite is facilitated by an organic matrix of chitin fibrils (Figure 7J), which leads to the growth of highly aligned single-crystalline nanorods and contributes to the strength and damage tolerance at mature stages. [82]…”

Bioinspired Robust Mechanical Properties for Advanced Materials

“…The radulae are composed of mineralized mesocrystallines and chitin‐binding organic matrix, where the minerals are mainly magnetite and iron phosphate (Figure 7I). [ 81–83 ] A typical core–shell architecture was identified in this ultra‐hard structure. The hard shell is made of magnetite crystals embedded in nanorods parallel to the long axis, where the nanorods of the chitin organic matrix direct the formation of mineral crystals.…”

“…The investigation of the biologically controlled phase development of the hard magnetite‐containing shell of the chiton teeth revealed that a phase transition of the ultrafine nanoparticles from ferrihydrite crystals to magnetite is facilitated by an organic matrix of chitin fibrils (Figure 7J), which leads to the growth of highly aligned single‐crystalline nanorods and contributes to the strength and damage tolerance at mature stages. [ 82 ]…”

Adsorption of Biomineralization Protein Mms6 on Magnetite (Fe3O4) Nanoparticles

“…Nature has evolved sophisticated strategies via biomineralization processes to synthesize functional inorganic materials [ 1 , 2 , 3 , 4 , 5 , 6 , 7 , 8 , 9 , 10 ]. Most biomineralization processes occur under ambient physiological conditions, often templated or guided by proteins.…”