Three-dimensional porous carbonate apatite with sufficient mechanical strength as a bone substitute material

In this study, three-dimensional porous carbonate apatite (CO₃Ap) materials with the chemical compositions and structures similar to cancellous bone were produced via phosphorization of porous calcite precursor in hydrothermal condition. In order to make porous calcite precursor, negative replication of polyurethane foam that named as inverse ceramic foam method was conducted. When the polyurethane template occupied within the ceramic solid walls disappeared due to burning at high temperature, interconnected hollow pathways were produced. Polyurethane foam was used as a porogen-template firstly was coated layer by layer with synthetic resin to modify morphology and enlarge thickness of struts so as to expand porous area for satisficing cellular bioactivities. Calcium hydroxide (Ca(OH)₂) slurry was then infiltrated into resin coatedpolyurethane foam. Heat treatment in atmosphere of oxygen and carbon dioxide gases was carried out to eliminate polyurethane template and induce carbonation process. Ca(OH)₂ was converted to calcite with the internal porous channel architecture simulating polyurethane foam struts network. That interconnected porous calcite was subsequently transformed to CO₃Ap with remaining the same macroporous structure through hydrothermal treatment in phosphate solution. The porous CO₃Ap materials were implanted in the tibia of Japanese male rabbits and removed after a period of 3 months. The bone formation response of the three-dimensional porous carbonate apatite in vivo has been preliminary studied using micro-computed tomography (μ-CT) scanner. The results showed that the porous implant materials have sufficient mechanical strength to provide structural support during bone remodeling and successfully bond with host bone.