Effects of Ca addition on the formation of octacalcium phosphate and apatite in solution at pH 7.4 and at 37°C

Abstract

Effects of Ca addition on formation of octacalcium phosphate (OCP) and apatite were studied in solution at pH 7.4 and at 37°C. Ca solution was added at 0.02–0.1 ml/min into reacting calcium phosphate solution with initial solution conditions of Ca: 0.55–0.91 mM; PO 4: 6.3–13.9 mM; Ca/PO 4=0.043–0.14. The ratio of OCP to apatite in the product decreased as the speed of Ca addition decreased and this tendency became prominent as the Ca/PO 4 increased. The Ca addition at an appropriate speed was crucial to maintain the degree of supersaturation to OCP (DS(OCP)) during reaction at a certain level, thereby regulated the formation and transition of OCP. The lifetime of OCP increased and the transition from OCP to apatite became slow, with an increase in the duration of Ca addition. The morphology and lattice dimension of apatites obtained by slow transition were different from those of apatite obtained by fast transition. It was inferred that in vivo crystallization of apatite and property of the resultant apatite crystal are affected, in part, by the activity of the influx of Ca 2+ ions into the calcifying region.