Controllable synthesis of spherical hydroxyapatite nanoparticles using inverse microemulsion method

Spherical nanosized hydroxyapatite (HA) was successfully synthesized via a water-in-oil microemulsion route at room temperature in short time. The effect of water-to-oil and water-to-surfactant ratios on the stability of microemulsion system was investigated to establish a stable reaction system, with span-80, cyclohexane and Ca(NO 3 ) 2 ·4H 2 O((NH 4 ) 2 HPO 4 ) solution as surfactant, oil phase, and water phase, respectively. Size and morphology change of obtained HA under optimal microemulsion system were further studied under various reaction time and temperature, and a possible growth mechanism was proposed. A moderate reaction temperature of 25 °C and reaction time of 5 h facilitated the formation of spherical HA particles in the dimension of 70 nm with good uniformity and regularity, which served as a great candidate in biomedical applications.