Controlled synthesis and transformation of nano-hydroxyapatite with tailored morphologies for biomedical applications

Hydroxyapatites (HAps) with nano-sized structures are promising materials in various biomedical areas, but the synthesis of high quality particles is still challenged by the insufficient precision of size and morphology, as well as the presence of severe agglomeration. An inadequate knowledge of the early nucleation, growth and transformation might limit our exploration and application of HAp. Here, we report a novel oil/water microemulsion-hydrothermal hybrid strategy for the preparation of highly dispersive HAps with tailored morphologies and controlled size. Through the synergetic effect of the oleic acid and microemulsion system, a well-dispersed HAp nucleus was first generated at 2 h. By tuning the ensuing hydrothermal conditions from room temperature to 140 °C, the nucleus would grow from spherical to needle-like nanoparticles. The size of the particles could be regulated by the alteration of the hydrothermal temperature. In addition, we experimentally demonstrated the complete evolution of HAp growth and transformation at a critical temperature of 90 °C by quenching the reaction at various intervals. The obtained particles were explored as potential cellular delivery carriers and polymer fillers.