The effect of pyrophosphate concentrations on calcium phosphate growth on well-crystallized octacalcium phosphate and hydroxyapatite seed crystals

Abstract

The comparative effects of 0.3, 1 and 3 μM P 2 O 4- 7 concentrations on the growth of calcium phosphate on octacalcium phosphate (OCP) and on “well-crystallized” hydroxyapatite (OHAp) seeds were studied. The control growth rates (without P 2 O 4- 7) were adjusted by weight or surface area of the seed crystals. The induction periods were longer with higher P 2 O 4- 7 concentrations a nd longer on OCP seeds than on the OHAp seeds. However, the final growth rates were about the same on both kinds of seeds when equal concentrations of P 2 O 4- 7 were used, suggesting that the same phase was growing on both kinds of seeds. The growth rates were faster when higher concentrations of OHAp seeds were used. The crystal growth on both OCP and OHAp seeds was accelerated when most of the labeled P 2 O 4- 7 disappeared from the solution. The composition of the initial phase that grew on either OCP or OHAp seed crystals appears to be OCP or partially hydrolyzed OCP. These results lead to the conclusion that apparently OCP, but not OHAp, grew on OCP and OHAp seeds in the presence of P 2 O 4- 7.