Influence of solution concentration on controlled crystallization of calcium phosphate

Abstract

To investigate the influence of solution concentration on controlled crystallization of calcium phosphate, controlled crystallization in the presence of stearic acid monolayer from solutions of hydroxyapatite with different [Ca2+] have been studied by SEM, TEM with ED, IR, XRD. When [Ca2+] is 0.4 mM, octacalcium phosphate (OCP) which is a thermodynamically undersaturated phase in this condition precipitates due to the 'concentration effect' of charged headgroup -COO- of stearic monolayer to Ca2+ in the solution; while solution is supersaturated in which [Ca2+] is 4 mM, the first precipitates phase is hydroxyapatite (HAP) with (0001) parallel to the surface of stearic monolayer. Subsequent growth results in oriented OCP crystals, and all the crystals show a white semi- globular characters; while [Ca2+] is up to 5 mM, the increasing of mineralization rate results to the rapid nucleation of HAP into some core-like structure and the later growth of platelet-like OCP as the 'shell.' Nucleation of DCPD between OCP showing a flower-like structure also found at LB film/solution interface. The mechanism of influence of concentration was discussed.