Oriented crystallization of vaterite in collagenous matrices

The influence of high supersaturation on kinetic control and the importance of the polypeptide structure in the crystallization of calcium carbonate polymorphs were studied in crosslinked gelatin films containing 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 greater 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 controlled by the beta sheet structure assumed by poly-L-aspartate in the presence of calcium ions. These results indicate that local supersaturation in the microenvironment in which nucleation and growth occur plays an important role in controlling the deposition of vaterite in cross-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 phase by epitaxial crystallization, as suggested by the preferentially oriented deposition of vaterite and aragonite. This is of potential significance in biomineralization processes and in materials science.