Phase formation and morphology of calcium phosphate–gelatine-composites grown by double diffusion technique: the influence of fluoride

Abstract

Calcium phosphate–gelatine-composites are grown by double diffusion of calcium- and phosphate/fluoride-solutions into a tube filled with gelatine gel. The composite aggregates appear within periodic growth areas (Liesegang bands). Growth time and temperature were kept constant (three weeks, 25 °C), the fluoride concentration in the solutions was varied (molar ratios Ca∶P∶F = 5∶3∶y; 0 ≤ y ≤ 1). Crystalline solids (octacalcium phosphate (OCP) and apatite (AP)) were identified by X-ray powder diffraction (incl. x for (OH_1−xF_x)). The distribution of crystalline phases over the Liesegang bands was determined. Changes in surface morphologies of OCP- and AP-spheres were investigated by SEM. In case of the AP composite an increasing fluoride content of the (OH_1−xF_x) position increases the rigidity of the needle-like surface individuals. The inner architecture of OCP-spheres is dominated by core/shell-assemblies and radial structures. In case of fluoride-rich AP composites the central part of the spheres is characterised by a torus-shaped cavity generated by the fractal growth mechanism. The hexagonal shape of the cross-section of the cavity strongly supports the fractal growth.