Crystal growth of calcium phosphates from aqueous solutions in the presence of strontium

Abstract

In the present work, the effect of the presence of strontium ions in supersaturated calcium phosphate solutions on the rates of crystal growth of octacalcium phosphate (Ca8H2(PO4)6·5H2O, OCP) and of hydroxyapatite (Ca5(PO4)3OH, HAP) was investigated at 37°C and at constant solution supersaturation. The presence of strontium reduced crystal growth rates of both calcium phosphate phases. The reduction of the OCP crystal growth was ca. 40% for strontium concentration of 1mM while for HAP was significantly higher, reaching 70% for the same concentration of strontium in the solution. Higher retardation of the rates of HAP crystal growth was achieved at higher supersaturations in the presence of 1mM strontium concentration. Moreover, strontium ions were shown to stabilize or delay the transformation of the unstable OCP that tends to hydrolyze to the thermodynamically more stable HAP. Strontium ions were incorporated into both OCP and HAP growing on the respective seed crystals.