Persistent polyamorphism in the chiton tooth: From a new biomineral to inks for additive manufacturing

Significance Biomineralization is a highly successful strategy to create functionally graded materials with complex shape. Herein, we demonstrate that the rock-grazing molluskCryptochiton stelleri uses two amorphous, yet structurally distinct, phases in neighboring microarchitectural domains to reinforce its dentition. Nano-disperse santabarbaraite, an amorphous iron hydroxyphosphate, is present in the stylus, extending the range over which hardness and stiffness vary by at least a factor of two. Use of ferric phosphates with low iron and high water content may present a stratagem to create strong composites with low density. Indeed, we show that bio-inspired inks based on chitosan and mineral precursors allow three-dimensional printing of tunable composites strengthened by amorphous nanoparticles precipitated in situ.