Regulation of hydroxyapatite formation by gelatin and type I collagen gels.

Calcium and phosphate were allowed to diffuse into gelatin and Type I collagen gels which were then cut into slices and analyzed for ion concentrations. Solutions of calcium and phosphate were then prepared, with ion concentrations equivalent to the highest levels in the slices, and mixed together, whereupon a rapid and copious precipitation of hydroxyapatite (HA) was observed. In contrast, HA bands were not visible in the gels until 1 to 2 1/2 days after analysis. These results indicate that Type I collagen exerts a considerable inhibitory effect on HA proliferation, probably by steric blockage of nuclei and crystal formation and growth. It thus appears that Type I collagen should be added to the list of agents that perform a regulatory role in bone mineral formation.