21. Structure and Mechanical Properties of Nacre

Many biological organisms exhibit unique chemical and physical properties (Lowenstam and Werner 1989). They often use components that contain both inorganic and organic compounds with complex structures, and are often hierarchically organized, ranging from nano- to meso-levels. The hierarchical structure provides a high tolerance against defects at all length scales. Most biological materials are multifunctional and often tend to have self-healing abilities (Vincent 1991; Ratner and Bryant 2004). In two-component biological materials, such as bones, teeth, and abalone shells, the mineral component provides high mechanical strength and the organic component hinders crack propagation, which increases fracture toughness responsible for high durability (Meyers et al. 2006). A biomineral system, which has been much investigated, is the inner layer of abalone, called nacre.