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 sin tered material, was proposed. A packing method based on semi-batchwise filt ration operation of two suspensions was applied. A suspension of ceramic pa rticles was put into a mixing tank, followed by the filtration of the suspe nsion. 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 s intered material. A porosity profile of the material can be designed based on the filtration theory, assuming that sedimentation of particles is negli gible. Effect of sedimentation can be evaluated by making a Ruth plot. It w as concluded that in packing fine particles by semi-batchwise filtration, a n 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 po rous hydroxyapatite, the capsule-free HIP sintering was conducted. Although the hardness of porous hydroxyapatite increased after the treatment, it wa s still lower than those of natural bones or tooth-roots. Addition of anoth er component seemed to be essential to further improvements of the mechanic al properties of the porous hydroxyapatite.