Preparation of hydroxyapatite-based composites by colloidal process

Hydroxyapatite (HAp)-based bioceramics composed of HAp, calcium-deficient hydroxyapatite (DAp) and alpha-tricalcium phosphate (alpha-TCP) were prepared by colloidal process. The HAp-based composites consist of two layers: one is composed of dense HAp-40 mass% DAp composite with high strength, the other porous HAp-40 mass% alpha-TCP with good biocompatibility. Dense HAp/DAp composite was obtained by suitable colloidal process followed by hot pressing. Microstructure and bending strength of HAp/DAp composite depended strongly on quantity of polymer dispersant in the colloidal process. The good dispersion of HAp and DAp powder at an optimum quantity of dispersant resulted in high relative density of HAp/DAp composite with homogeneous microstructure. Moreover, HAp/DAp composite was found to exhibit higher bending strength than stoichiometric HAp alone. On the other hand, porous HAp/alpha-TCP composite was prepared by mixing polymeric powder which was burned out during sintering. The porosity of the composite could be easily controlled by changing the volume fraction of polymeric powder. The bending strength of HAp/alpha-TCP composite depended strongly on the porosity; the strength decreased exponentially with increasing the porosity. The mixture of dense HAp/DAp and porous HAp/alpha-TCP is expected to result in high strength and good biocompatibility of the composites.