MIMICKING MOTHER-OF-PEARL

Abstract

MOTHER NATURE has mastered how to make tough hybrid materials that resist fracture, such as bone and shell, using comparatively weak starting materials. Now, researchers at Lawrence Berkeley National Laboratory have made a composite that is structurally similar to mother-of-pearl and exhibits resistance to fracturing that rivals that of aluminum alloys such as those used in aerospace engineering ( Science 2008, 322 , 1516). Natural mother-of-pearl, also known as nacre, has a brick-and-mortar structure: Layers of “bricks” made from a calcium carbonate mineral are held together by thin films of a biopolymer “mortar” such as chitin. To make the nacrelike structure, the Berkeley team used ice templates to create layers of the ceramic aluminum oxide, pressed and sintered the layers to make the bricks, and filled the voids with polymethyl methacrylate mortar. “We used the freezing properties of ice to specifically control the ceramic layer thickness and surface roughness,” says team leader Robert O. Ritchie, wh...