Solubility isotherms of gradient strontium-reinforced hap by solid titration

Abstract

INTRODUCTION: Strontium plays special interest in the treatment of osteoporosis and enhancement of bone mineralization. Therefore, strontium-reinforced apatite was widely used as bone filling material. However, the dissolution behaviour, in particular the mechanism of the formation of interface between bone and material is still controversial. Therefore, the solubility study of strontium-reinforced HAp may provide basic knowledge to understand the dissolution behaviour in human body. MATERIALS AND METHODS: Solid titration, using laser-scattering end-point detection, was used to determine the solubility isotherms of gradient strontium-reinforced HAp (1%, 5%, 10% and 100%) in 100 mM KCl at 37°C. The precipitat es were respectively characterized by XRD, EDX and SEM. RESULTS AND DISCUSSIONS: 1%Sr-HAp was found significantly higher soluble than pure HAp. Meanwhile, the solubility further increased with the increase of strontium content. It is possibly due to the crystal stability of apatite decreased with the incorporation of strontium. In addition, the precipitates at equilibrium were only identified as HAp without other phases, EDX indicated that the Ca/P ratio decreased with the decrease of pH, meanwhile strontium released completely. Thus, it is clear that the formation of interface between bone and material was due to the (re)precipitation of partial dissolved strontium-reinforced HAp. The released strontium was not a crystal composition of the precipitate. CONCLUSIONS: The solubility isotherms of gradient strontium HAp were well established. The solid titration method shows excellent reliability and reproducibility in the determination of solubility; such method can be further employed to investigate other complicated system.