The Chemistry of Form

The emergence of complex form in living and nonliving systems remains a deep question for scientists attempting to understand the origins and development of shape and structure. In recent years, biologists and physicists have made significant advances in explaining fundamental problems in fields such as morphogenesis and pattern formation. Chemists, on the other hand, are only just beginning to contemplate the possibility of preparing manmade materials with lifelike form. This review traces a route to the direct synthesis of inorganic structures with biomimetic form, beginning from an understanding of crystal morphology and biomineralization. The equilibrium form of crystals can be modified by surface-active additives but only within limits dictated by the symmetry of the unit cell. In contrast, biological minerals, such as shells, bones, and teeth, are distinguished by a complexity of form that bears little resemblance to the underlying order of their inorganic crystals. By understanding the constructional processes that give rise to the inorganic structures of life it should be possible to develop a chemistry of form in the laboratory. For example, complex small-scale inorganic architectures are produced at room temperature by undertaking precipitation reactions in self-assembled organic media, such as surfactant micelles, block copolymer aggregates and microemulsion droplets. Unusual inorganic forms emerge when these reaction fields are subjected to instability thresholds and synthesis and self-assembly can be coupled to produce materials with higher-order organization. Like their biological counterparts, these hard inorganic structures represent new forms of organized matter which originate from soft chemistry.