Stephen Weiner

▪ Abstract The term bone refers to a family of materials, all of which are built up of mineralized collagen fibrils. They have highly complex structures, described in terms of up to 7 hierarchical levels of organization. These materials have evolved to fulfill a variety of mechanical functions, for which the structures are presumably fine-tuned. Matching structure to function is a challenge. Here we review the structure-mechanical relations at each of the hierarchical levels of organization, highlighting wherever possible both underlying strategies and gaps in our knowledge. The insights gained from the study of these fascinating materials are not only important biologically, but may well provide novel ideas that can be applied to the design of synthetic materials.

Focusing on the basic principles of mineral formation by organisms, this comprehensive volume explores questions that relate to a wide variety of fields, from biology and biochemistry, to paleontology, geology, and medical research. Preserved fossils are used to date geological deposits and archaeological artifacts. Materials scientists investigate mineralized tissues to determine the design principles used by organisms to form strong materials. Many medical problems are also associated with normal and pathological mineralization. Lowenstam, the pioneer researcher in biomineralization, and Weiner discuss the basic principles of mineral formation by organisms and compare various mineralization processes. Reference tables listing all known cases in which organisms form minerals are included.

Acidic matrix macromolecules are intimately involved in biological crystal growth. In vitro experiments, in which crystals of calcium dicarboxylate salts were grown in the presence of aspartic acid-rich proteins, revealed a stereochemical property common to all the interacting faces. Calcite crystals are nucleated on stereochemically analogous faces when proteins are adsorbed onto a rigid substrate. The importance of this property in biomineralization is discussed.

Organisms have been producing mineralized skeletons for the past 550 million years. They have evolved many different strategies for improving these materials at almost all hierarchical levels from Ångstroms to millimetres. Key components of biological materials are the macromolecules, which are intimately involved in controlling nucleation, growth, shaping and adapting mechanical properties of the mineral phase to function. One interesting tendency that we have noted is that organisms have developed several strategies to produce materials that have more isotropic properties. Much can still be learned from studying the principles of structure–function relations of biological materials. Some of this information may also provide new ideas for improved design of synthetic materials.