Rheological characteristics of slurry controlling the microstructure and the compressive strength behavior of biomimetic hydroxyapatite

The sponge impregnation of water-based suspensions of hydroxyapatite powders synthesized by the coprecipitation method was investigated. The powder characteristics and slurry properties were correlated with the porosity and mechanical properties of the porous bodies obtained. The theological characterization in the continuous flow condition revealed a strong dependence of the rheological behavior on the solid loadings particularly with high specific surface area powder. The behavior changed from newtonian to plastic, with pronounced hysteresis effects due to time dependency, by increasing the solids loading from 10 to 18 vol%. The morphology and distribution of the macropores could be related to the starting powder crystallinity and morphology as well as to the rheological properties of the suspensions. The compressive strength of the materials was strongly influenced by the porosity, while there was almost no dependence on the crystallinity of the powder. From a statistical viewpoint, the microporosity better explained the behavior of the mechanical strength than the total porosity.