Nacre-inspired Hard and Tough Materials

Nature fabricates materials with properties that are difficult to reproduce with manmade counterparts. For example, nacre, composed of layers of CaCO₃ crystals that are interspaced with small quantities of organic components, is one of the toughest known biomaterials. To produce materials with such fascinating proper- ties, nature has established processes that offer an excellent control over their structure and local composition. Inspired by nacre, a lot of work has been devoted to the fabrication and characterization of composites with similar structures that nevertheless display distinctly different mechanical properties. The first part of this review summarizes methods used to produce nacre-inspired layered composites, their influence on the composition, structure, and mechanical properties. A key difference between the formation of nacre and that of nacre-inspired materials is the mechanism and kinetics of the formation of the inorganic components. In an endeavor to gain a better control over the mechanical properties of the inorganic platelets contained in nacre-inspired composites, the second part of this review describes methods to control the shape, structure, and orientation of CaCO₃ formed in organic scaffolds.