Control of the architectural assembly of octacalcium phosphate crystals in denatured collagenous matrices

Xerogels, obtained by evaporating a water solution of gelatin, were used as templates for the growth of crystal assemblies of calcium phosphate. Octacalcium phosphate (OCP) crystals were grown inside the gelatin xerogel by diffusion of solutions of calcium and phosphate ions into the gelatin films from opposite ends. The structure, morphology and orientation of the crystals grown on the surfaces and inside the gelatin films were studied by optical and scanning electron microscopy and X-ray diffraction. OCP was the unique detectable crystalline phase. The crystals preferentially grew as thin plates elongated along their c axes with large {100} faces parallel to the sheets of gelatin films. When the gelatin films were uniaxially deformed the OCP crystals grew with their c axes almost parallel to the direction of deformation. According to a mechanism of templated nucleation, a structural model for the ordered growth of OCP on the portions of triple helical collagen molecules has been proposed.