Biomimetic Ceramics: What, Why and How?
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BIOMIMETIC CERAMICS: WHAT, WHY AND HOW? PAUL CALVERT Arizona Materials Laboratories, 4715 E. Fort Lowell Rd., Tucson, AZ 85712 ABSTRACT The role of biomimetic approaches in materials engineering is reviewed. In the case of ceramics, close parallels in structure and function can be seen between synthetic and biological materials. Biological ceramics have resolved difficulties which are limiting the application of synthetic materials, particularly in the need for greater toughness. The enhanced toughness of materials such as shell and tooth enamel can be attributed to microstructural factors. Both natural materials contain a small amount of polymer. If this is essential, then any synthetic mimetic material would be limited by the temperature resistance of the polymer. In fact, much of the toughness is dependent on the elongated particle morphology and does not require polymer. Routes to forming ceramics with such elongated particles are discussed. INTRODUCTION Biomimetic materials have recently become the focus of much interest. Most of this attention has been on ceramics and stems from the conjunction of a number of developments. One motivating force has been that the major research effort to develop strong ceramics by the processing of monodisperse, sub-micron powders, has achieved significant improvements but has run out of momentum. It has become clear that the goal of very high and reproducible strength cannot be reached simply by making flaw-free materials. This has focussed attention back onto ways of improving the toughness of ceramics by controlling the microstructure. In this context, the structures of biological ceramics such as tooth and shell look very impressive and do seem to show very good toughness. A second reason for this interest is that biotechnology has advanced to where polymers are being produced by bacterial fermentation. Genetic manipulation will allow the range of polymers made by bacteria to be broadened. This raises the possibility of other materials, including inorganic materials, being produced in the same way. In addition tissue culture methods are approaching the point where bone will be formed in vitro. This has obvious implications for surgery but might also provide a route for growing complex synthetic components. A third thread is that the mechanisms of control of biological mineralization are being elucidated by work on invertebrates. As we understand how interacting control systems allow complex structures to be formed from solution, we can hope to start developing similar methods for the growth of synthetic components.
Mat. Res. Soc. Symp. Proc. Vol. 249. 01992 Materials Research Society
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EARLY USE OF BIOLOGICAL MATERIALS One thousand years ago most of the materials in daily life were of biological origin. Even today biological materials such as wood, cotton and leather form a large fraction of what we actually use. The major contributions by mankind to the range of available materials came from thermal processing for firing ceramics and smelting metals. As we contemplat
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