From sol-gel processing to bio-inspired materials synthesis

The improvement of materials performance and their respective processing routes ever has been the driving force for material science and engineering. For the preparation of non-metallic inorganic materials the synthesis from chemical precursors is a field of steadily increasing scientific and industrial importance: Products in a broad variety of compositions can be obtained by sol-gel techniques. The shaping of intermediates allows the specific preparation of many microarchitectural configurations such as powders, fibers, thin films and aerogels. For purely inorganic products the sintering temperatures are low compared to conventional mixed-oxide ceramic processing which enables e.g. the coating of glasses and metals. Hybrid inorganic-organic compositions combine some advantages of polymers and ceramics. Nature has found amazing alternative ways to produce high-performance inorganic-organic composites at ambient temperatures under physiological conditions: Teeth, bone and nacre are self-evident examples for the capability of biomineralization processes. Even though many aspects of the related mechanisms in vivo are not yet fully understood, the utilization of the basic strategies of natural biomineralization has become a challenge to material scientist in an interdisciplinary approach. In this paper the strong points of sol-gel processing are highlighted, its limitations are discussed and related to the unique characteristics of natural biomineralization. Subsequently biomimetic and biologically-inspired material syntheses routes are reviewed which try to compensate the shortcomings of sol-gel techniques.