Preparation of Porous Hydroxyapatite Materials with a Continuous Porosity Profile by Use of a Filtration Method

A preparation method, which can smoothly vary the porosity profile of a sintered material, was proposed. A packing method based on semi-batchwise filtration operation of two suspensions was applied. A suspension of ceramic particles was put into a mixing tank, followed by the filtration of the suspension. Then, a suspension of carbonaceous particles was fed in continuously to the tank. The composition profile of the filter cake was found to vary smoothly in the direction of cake thickness. After drying and consolidation, the cake was sintered in an oxidizing atmosphere, resulting in a porous sintered material. A porosity profile of the material can be designed based on the filtration theory, assuming that sedimentation of particles is negligible. Effect of sedimentation can be evaluated by making a Ruth plot. It was concluded that in packing fine particles by semi-batchwise filtration, an easy-to-filter-material should be selected as one component of the binary mixture. The fabrication of porous hydroxyapatite was tried for use as an artificial bone or an artificial tooth-root. To improve the mechanical strength of porous hydroxyapatite, the capsule-free HIP sintering was conducted. Although the hardness of porous hydroxyapatite increased after the treatment, it was still lower than those of natural bones or tooth-roots. Addition of another component seemed to be essential to further improvements of the mechanical properties of the porous hydroxyapatite.