Figure 2.

Hierarchical structures of bone and nacre

(A) Osteons have a lamellar structure, with individual lamella consisting of fibers arranged in geometrical patterns. The fibers comprise several mineralized collagen fibrils, composed of collagen protein molecules (tropocollagen) formed from three chains of amino acids and nanocrystals of hydroxyapatite, and linked by an organic phase to form fibril arrays.

(B) Nacre is a brick-and-mortar structure of CaCO₃ mineral platelets (aragonite), which provide strength and proteins, which allow for ductility and toughness. Adapted with permission from Wegst et al. (2015). Copyright 2014, Springer Nature.