Hierarchical structures of molluscan bioceramic shells: Mechanics and biomimetics

Over millions of years of natural evolution, molluscan bioceramic shells have developed highly ordered, hierarchical structures that simultaneously achieve exceptional strength and toughness. These structural features confer robust resistance to environmental erosion and predatory attacks, thereby preserving both the structural integrity and physiological homeostasis of the underlying soft tissues. A rigorous mechanistic understanding of the mechanical behaviors and underlying strengthening and toughening mechanisms in these natural bioceramics shells offers not only fundamental theoretical insights but also valuable biomimetic principles for the rational design of advanced structural materials. In this review, we provide a comprehensive overview of the development in the mechanics and biomimetics of two archetypal molluscan shells: the brick-and-mortar structure of nacreous shells and hierarchical crossed-lamellar structure of conch shells. First, we discuss the hierarchical structural features, mechanical properties, and associated strengthening and toughening mechanisms of two molluscan shells. Second, we synthesize progress in the development of multiscale mechanical models and biomimetic structural materials. Finally, we identify the main challenges and future trends in the mechanics and biomimetics of two molluscan shells. This review aims to stimulate further research on the mechanics and biomimetics of molluscan bioceramic shells, promoting the transition of this field from fundamental mechanism exploration to practical engineering applications.