Physics And Chemistry Basis Of Biotechnology - De Cuyper - tiera.ru

3.4. COMPOSITE MATERIALS
Aleksey Nedoluzhko and Trevor Douglas
Proteins that have been isolated from biominerals exhibit a number of the properties
mentioned in the preceding sections such as oriented nucleation, and confined reaction
environments. The production of biocomposite ceramics is a low temperature route to
strong, lightweight materials that has not yet been fully exploited. In bone,
hydroxyapatite crystals are found in spaces within the collagen fibril. Purified collagen
serves as a matrix for calcium phosphate growth in attempts to study that process and to
create synthetic bone-like material. Matrix proteins isolated from bivalves have been
shown to mediate nucleation and growth of calcium carbonate [35-38]. These materials
are composites of microscopic crystals held together by a protein "glue" and have the
advantages of both the hardness of the inorganic material, and the flexibility of the
organic matrix. Composite materials such as these often have high fracture toughness
thought to arise from interruption, by the protein, of the cleavage planes in the
inorganic crystals. For example, the calcite crystal cleaves easily along the (104)
planes, In the sea urchin skeleton the crystal fractures conchoidaly (like glass) and not
cleanly along the (104) planes of calcite. It is suggested that this is due to the protein
that is occluded within the crystal, preventing the cleavage along the (104) plane and
thereby increasing the strength of the inorganic phase. These proteins have been
isolated and shown to produce the same conchoidal fracture in synthetic calcite crystals
grown in its presence. These materials are the inspiration for a new generation of
materials incorporating both natural and synthetic polymers.
Figure 5. Schematic representation of organised surfactant assemblies. Reprinted by
permission from Chem.Rev. [15O] copyright 1987ACS Publications.
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