Biomimetic Ceramics
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BIOMIMETIC CERAMICS PAUL CALVERT Arizona Materials Labs. 4715 E. Fort Lowell Rd, Tucson AZ 85718 ABSTRACT This paper discusses the possible advantages to be gained from a bio-mimetic approach to ceramics and reviews the work now in progress that will lead us to be able to mimic biological structures with synthetic materials. BIOLOGICAL CERAMICS There are many biological materials that can be thought of as ceramics, including tooth and shell. In general these materials are usually composites with low volume fractions of polymer present that modify the properties without detracting from the hardness ceramic. Examples that we might wish to emulate in synthetic ceramics include: (a) mammalian tooth, with a high volume fraction of hydroxyapatite rods bound together by protein to form an outer wear-resistant layer over tougher dentine [1]; (b) nacreous shell where aragonite plates are stacked in a bricks-in-wall type of structure with a thin layer of chitin and protein acting as mortar [2]; and (c) sea-urchin spine, a porous single crystal of calcium carbonate, covered with a protective polymer layer and toughened by protein entrained actually within the crystals [3]. More general arguments about why we might wish to mimic other aspects of biological materials have been given elsewhere [4]. As illustrated in table 1, we can
Table 1 Strength of Biological Ceramic Composites Mineral Enamel Whale bulla Dentine Bone Antler Nacre Alumina
92 66 48 41 31 96 100
Strength MPa 76 33 250 270 179 170 100-1000
Toughness J m-2 200 200 550 1700 6200 350-1240 50
From Vincent [13]
Mat. Res. Soc. Symp. Proc. Vol. 180.
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