Materials design in biology

The materials formed by organisms are often the products of hundreds of millions of years of fine-tuning by evolution. They thus incorporate some neat solutions to complex structural problems. Here, we examine four different mineralized biological materials that all appear to fulfill a multipurpose function. They are the crossed lamellar structure of mollusk shells, the skeleton of sea urchins, the lamellar bone type of vertebrates, and the biogenic silica deposited by a wide variety of organisms. They all have very different structures and compositions, but are all structurally designed to reduce the extent of mechanical anisotropy. The strategies for reducing anisotropy are manifold, including features that to date have not been incorporated into synthetic materials.