L. Addadi et al., CONTROLLED OCCLUSION OF PROTEINS - A TOOL FOR MODULATING THE PROPERTIES OF SKELETAL ELEMENTS, Molecular crystals and liquid crystals science and technology. Section A, Molecular crystals and liquid crystals, 248, 1994, pp. 185-198
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.