Hydroxyapatite nanopowders: Synthesis, densification and cell–materials interaction

Hydroxyapatite (HA) nanopowders with different aspect ratios were synthesized using reverse micelle template system. Nanopowders were characterized using X-ray diffraction (XRD), BET specific average surface area analysis and transmission electron microscopy (TEM). It was observed that increase in aqueous to organic ratio (A/O) and pH decreased the aspect ratio of the nanopowders. HA nanopowders with the highest aspect ratio (rod-shaped) of 7.2 ± 3.2 and the lowest aspect ratio (spherical) of 1.3 ± 0.3 were synthesized for processing dense compacts. Effect of powder morphology on densification at 1250 °C was studied with different amount of rod-shaped and spherical nanopowders. It was observed that an increase in high aspect ratio powder content in the compacts decreased sintered density under pressureless sintering condition. Also, due to excessive grain growth, no nanoscale morphology could be retained in the sintered microstructure. Mineralization study in simulated body fluid (SBF) showed formation of apatite layer on the entire surface of both compacts made with spherical and rod-shaped particles. Cytotoxicity result with OPC1 human osteoblast cells showed excellent cell attachment and cell spreading on samples after 5 days in culture.