Biomimetics: Materials fabrication through biology

Many multicellular organisms produce hard tissues such as bones, teeth, shells, skeletal units, and spicules (1). These hard tissues are biocomposites and incorporate both structural macromolecules (lipids, proteins, and polysaccharides) and minerals of, perhaps, 60 different kinds, including hydroxyapatite, calcium carbonate, and silica. A number of single-celled organisms (bacteria and algae) also produce inorganic materials either intracellularly or extracellularly (2). Examples include magnetotactic bacteria, which synthesize magnetite (3); chrysophytes (4), diatoms, and actinopoda (radiolarians; ref. 5), which synthesize siliceous materials; and S layer bacteria that have gypsum and calcium carbonate surface layers (6). Normally, hard tissues are mechanical devices (e.g., skeletal, cutting, grinding), or they serve a physical function (e.g., magnetic, optical, piezoelectric). Bioinorganics are also ion sources that are vital for physiological activities and, therefore, integral parts of the organisms (1, 2).