INTERACTION OF PYROPHOSPHATE WITH CALCIUM PHOSPHATES

Interactions of pyrophosphate (PP) with hydroxyapatite (HAP), brushite , and calcium pyrophosphate (CaPP) have been studied using electrokine tic and ESCA measurements. PP adsorbs on HAP and brushite even when th eir surfaces are highly negatively charged. Importantly, the HAP zeta potential curves as a function of PP concentration show a precipitous drop in the low concentration range. Also, curves at different pH valu es show a progressive shift in the potential toward that of CaPP. Thes e observations suggest the formation of CaPP on HAP surface and this h as been further confirmed by ESCA studies. Thus, adsorption on HAP app ears to involve a surface precipitation or chemisorption followed by s urface precipitation or surface reaction phenomenon. It is also sugges ted that in the case of brushite the dissolved calcium from the minera l competes for the PP and in turn reduces its adsorption.