CONTROLLED OCCLUSION OF PROTEINS - A TOOL FOR MODULATING THE PROPERTIES OF SKELETAL ELEMENTS

Composite materials in which the organic host is stiffened by guest pa rticles, are widely used in nature and are produced synthetically by m an. Organisms also produce a different type of composite in which the host is a crystal and the guests are macromolecules occluded in an ord erly fashion within the crystal. The best studied examples, to date, a re biogenic calcite crystals, and in particular those formed by the ec hinoderms. In vitro experiments with calcite crystals grown in the pre sence of echinoderm intracrystalline proteins, show that these macromo lecules are occluded inside the crystal on specific planes, and their presence alters the mechanical properties of the crystal host. Further more, the proteins also influence the crystal textural properties. Mod el studies using crystals of dicarboxylic acid salts grown in the pres ence of intracrystalline proteins show that the coherence length is re duced in directions perpendicular to the planes on which the proteins adsorb. We found anisotropic effects in almost all the biogenic calcit e crystals we examined. Furthermore, we noted an interesting relations hip between the variations in coherence length in the different crysta llographic directions and the gross morphology of the single crystal e lements, suggesting that these proteins may also function in determini ng the morphology of the crystal during growth. These novel single cry stal-protein composites may be just one example of strategies used in nature for producing materials with special properties.