Reverse micelle mediated synthesis, processing, mechanical and biological characterization of hydroxyapatite nanopowders for bone graft application

Hydroxyapatite (HA) is the most widely used bioceramic material in bone graft applications because of its compositional similarity with natural bone. However, synthetic HA does not show similar mechanical and biological properties to the inorganic component of bone. Properties of ceramic material depend on starting materials, processing techniques, densification and microstructure of the final product. The objective of this research was to process HA whisker reinforced HA composite using HA nanopowders and whiskers.; HA nanopowders with different length scale and morphology were synthesized by reverse micelle system using NP5 and NP12 as surfactants and cyclohexane as organic solvent. The lowest average aspect ratio was 1.357+/-0.39 with average particle size of 66 nm and the highest average aspect ratio was 7.277+/-3.227 with average length of 150 nm and width of 20 nm, were synthesized. Micron sized HA whiskers with aspect ratio between 20 and 50, average particle length of 15 mum and width of 400 nm was synthesized using urea as a precipitating agent. Desired microstructure was obtained after sintering with spherical HA nanopowder and whiskers along with dopants. Addition of whiskers decreased density of the sintered compacts. However, at 10 wt% whisker content sample showed microhardness and fracture toughness of 3.6 GPa and 1.5 MPa.m1/2, respectively, and a compressive strength of 80 MPa was obtained. Mineralization study in simulated body fluid (SBF) showed formation of apatite layer on the dense HA compacts indicating a good tendency of bond formation with natural bone. Cytotoxicity results showed excellent cell attachment on the HA surface.; In the Appendices, 3 journal articles have been attached which describe synthesis, processing and characterization of undoped and doped PZT nanopowders. Free standing and agglomerated PZT nanopowders were synthesized by the sucrose templated method and the citrate nitrate autocombustion method. Particle size in the range of 50 to 90 nm was obtained. The effect of dopants on sintering and dielectric properties was studied by varying the amount of ZnO, SrO and La2O3 addition in PZT nanopowders. Sintering temperature of the bulk PZT was reduced to 900°C compared to the conventional sintering temperature of 1285°C and the highest dielectric constant of about 2100 was obtained.