Mechanical properties and in vitro cell compatibility of hydroxyapatite ceramics with graded pore structure

In order to improve the mechanical strength of hydroxyapatite (HA) ceramics used as osteoimplants and to enhance cellular penetration functionally graded ceramics with a transition in porosity from the surface towards the centre were designed. The multilayer structures were prepared by multiple tape casting based on an aqueous HA slurry containing polybutylmethacrylate (PBMA) spheres with diameters ranging from 100 to 300 microns. After burning out the PBMA, pores of 70-200 microns were generated. The pore-graded laminates were sintered at temperatures between 1250 degrees C and 1450 degrees C. Bending strength of the pore-graded ceramics was approximately 50% higher as compared to HA of the same pore volume fraction but without gradient structure. The materials were tested in vitro for attachment and activity of osteoblast-like MC3T3-E1 cells over a period of 3 weeks. Cells formed confluent layers on the ceramic surface, penetrated into the graded porosity ranging from 100-150 microns to 250-300 microns in size and showed increasing alkaline phosphatase activity over 3 weeks. The results demonstrated initial in vitro cell compatibility of the functionally graded HA materials and their potential as osteoimplants.