Toward a Detailed Understanding of Magnesium Ions on Hydroxyapatite Crystallization Inhibition

Abstract

Magnesium ions (Mg2+) are widely present in biological fluids, and they are suggested as the vital factors that inhibit spontaneous hydroxyapatite (HAP) precipitation in nature. However, the regulation mechanisms of Mg2+ on HAP crystallization are still under intensive debates. We find that a typical precipitation of HAP from supersaturated solutions should include five stages: s1, formation of ion clusters and amorphous calcium phosphate (ACP); s2, stabilization of ACP; s3, transformation from ACP to HAP via dissolution and crystallization; s4, classical crystal growth of HAP; s5, HAP aging under a near equilibrium state. Actually, Mg2+ ions exhibit different inhibitory effects on these stages. The ions have a negligible influence on the kinetics of initial ACP formation in solutions (s1) and final aging of crystals (s5). Rather, the ions can either adsorb onto or incorporate into the ACP precursor particles during s1. In s2, the lifetime of ACP in solution is extended significantly by both two types of ...