ORIENTED CRYSTALLIZATION OF VATERITE IN COLLAGENOUS MATRICES

The influence of high supersaturation on kinetic control and the impor tance of the polypeptide structure in the crystallization of calcium c arbonate polymorphs were studied in crosslinked gelatin films containi ng high concentrations of the polypeptides poly-L-aspartate and poly-L -glutamate. Oriented crystallization of vaterite occurs in uniaxially deformed gelatin films containing poly-L-aspartate at concentations gr eater than 100 mg per gram of gelatin. The fact that no orientation of the mineral phase was observed with entrapped poly-L-glutamate at the same concentrations suggests that the oriented crystallization is con trolled by the beta sheet structure assumed by poly-L-aspartate in the presence of calcium ions. These results indicate that local supersatu ration in the microenvironment in which nucleation and growth occur pl ays an important role in controlling the deposition of vaterite in cro ss-linked gelatin films. However, collagen bundles se and the ordered and oriented polypeptide chains of poly-L-aspartate can contribute to the control of polymorphism by inducing the formation of a specific ph ase by epitaxial crystallization, as suggested by the preferentially o riented deposition of vaterite and aragonite. This is of potential sig nificance in biomineralization processes and in materials science.