Synthesis, Processing, Mechanical, and Biological Property Characterization of Hydroxyapatite Whisker-Reinforced Hydroxyapatite Composites

Effects of hydroxyapatite (HA) whiskers addition on densification, mechanical, and biological properties of HA compacts were studied for their use as an implant material for orthopedic and dental applications. HA nanopowder was synthesized using reverse micelle as template system, and urea hydrolysis synthesis route was used to prepare micrometer-sized HA whiskers. Poly (oxyethylene)(12) nonylphenol ether (NP12) and cyclohexane were used as surfactant and organic solvent, respectively, for the reverse micelle microemulsion system. Desired microstructure in sintered HA composite was obtained by mixing Mg2+ as a dopant in HA nanopowders, and Al3+ as a dopant in HA whiskers. Compacts were processed using pressureless sintering. With an increase in whisker content from 0 to 10 wt%, the average compressive strength of HA compacts decreased from 120 to 90 MPa. HA composite processed with 10 wt% HA whisker showed a microhardness of 3.6 GPa and an average indentation fracture toughness of 1.5 MPa.m(1/2). Mineralization study in simulated body fluid showed deposition of octacalcium phosphate on sintered HA compacts. In vitro cytotoxicity tests with human osteoprecursor cell line confirmed excellent osteoblast cell attachment and growth on the sintered HA compacts with 0, 10, and 20 wt% HA whiskers.