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(NO3)2·4H2O((NH4)2HPO4) 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.