Enhancing strength in mineralized collagen

Living organisms build an assortment of mineralized tissues by combining biopolymers and minerals. Mineralization is fundamental to many biological functions, ranging from mechanical shock protection by shells, mastication by teeth, linear acceleration detection by otoconia in the inner ear, and body support by skeletons. Scientists have been investigating the material properties of these biominerals with the focus on the combination of organic and inorganic phases and on the organization of microscopic building blocks across several length scales. Bone, which consists of nanocrystalline calcium phosphate in the form of hydroxyapatite embedded within collagen fibrils (1), is one of the most extensively studied biominerals. Fracture resistance of bones is generally attributed to the mineralized collagen fibril (2). On page 188 of this issue, Ping et al. (3) report that mineral growth inside collagen generates a fibril that is under tension, similar to prestressed concrete.