Bone as a ceramic composite material

Bone is the primary structural material used to carry major loads in an enormous variety of vertebrate animals. To fulfill this role, nature has devised an extremely interesting ceramic composite whose components are primarily collagen and hydroxyapatite, but whose complex structure contains a wealth of mechanically relevant detail. It is a composite in several different senses, being a porous material, a polymer-ceramic mixture, a lamellar material, and a fiber-matrix material. Its mechanical properties depend on each of these aspects of composition and structure. Variations in porosity and mineralization serve to adapt bone's mechanical properties to suit a great variety of conditions. Lamellar and fiber-matrix interfaces limit the growth of cracks and fatigue damage. Through the actions of remodeling by cells, bone's composite structure repairs fatigue damage and continuously adapts to changes in mechanical usage.