In vitro crystallization of octacalcium phosphate on type I collagen: influence of serum albumin

The heterogeneous crystallization of octacalcium phosphate (OCP, Ca8H2(PO4) (6) . 5H(2)O) on demineralized Type I collagen has been studied from metast able supersaturated solutions, at 37 degrees C and pH = 6.50, using the con stant composition crystal growth technique. The induction period, before OC P crystal growth, varied markedly with the deg ree of supersaturation of th e solution. The data obtained allowed us to determine the apparent order fo r the precipitation and the growth mechanism of OCP on Type I collagen. Inf rared spectroscopy analyses indicated the progressive mineralization of col lagen and observations by scanning electron microscopy confirmed the develo pment of OCP crystals on the collagen surface. The influence of bovine seru m albumin on both the kinetics of OCP nucleation and growth has also been i nvestigated. Because this protein was adsorbed on calcium phosphate nuclei, it exhibited two distinct effects as a function of its concentration in so lution. We proposed a mechanism explaining the interaction between albumin and calcium phosphate nuclei or crystals and its incidence on the OCP cryst allization kinetics. Observations by scanning electron microscopy revealed a modification of the size and the appearance of crystals grown on collagen due to the adsorption of albumin on the crystal surface. (C) 1999 Kluwer A cademic Publishers.