EFFECTS OF SILICATE IONS ON THE FORMATION AND TRANSFORMATION OF CALCIUM PHOSPHATES IN NEUTRAL AQUEOUS-SOLUTIONS

The effects of silicate ions on calcification reactions have been investigated in neutral solutions containing calcium and phosphate ions. The results have shown that the silicate ions enhanced the precipitation of amorphous calcium phosphate (ACP) and dihydrated dicalcium phosphate (DCPD). Transformation of these precursors to hydroxyapatite (HAP), however, was inhibited by silicate ions. X-Ray photoelectron spectroscopy (XPS) results have shown that a type of silicate was formed at the surface of the precursors in the early stage of the calcification process, resulting in inhibition of the transformation. On the contrary, silica, investigated for comparison with silicate ions, was found to provide favourable sites for ACP and DCPD nucleation. Thus, silica played the role merely of substrate for the nucleation, and as a result silica did not inhibit the conversion of the precursors to HAP.