FORMATION OF BONE-LIKE APATITE ON TRICALCIUM PHOSPHATE CERAMICS IN A SOLUTION MIMICKING BODY FLUID

Bone-like apatite is defined as biologically active hydroxyapatite which has similar characters to those in bone mineral. Formation of bone-like apatite layer on materials is an essential condition to make direct bonding to living bone, i.e. to show osteoconduction. Tricalcium phosphate (TCP) ceramic is well known as a biodegradable material. TCP of alpha-phase (alpha-TCP) can transform into hydroxyapatite though hydrolysis. Therefore, one expects the formation of bone-like apatite layer on alpha-TCP under body environment, but some types of alpha-TCP ceramics does not form hone-like apatite after exposure to a simulated body fluid (SBF) proposed by Kokubo er al. Hence, we have hypothesis that the formation of bone-like apatite on alpha-TCP ceramics is dependent on their pore structure, porosity and surface roughness. In this study, alpha-TCP ceramics with different porosities were fabricated to examine their formation of bone-like apatite in SBF. Dense alpha-TCP ceramics were examined on their behavior in SBF, in comparison with those of porous alpha-TCP ceramics having different porosities ranging from 53 to 89%. Bone-like apatite formation was observed on rough surface of the dense alpha-TCP ceramics fabricated after polishing, but not on the smooth surface of as-sintered dense alpha-TCP ceramics. Formation of bone-like apatite was observed on the porous ceramics having 53 or 58% of porosity, whereas not on the specimens having 68 or 89% of porosity. These findings clarify that the porosity and surface roughness would be significant parameters to determine not only biodegradability but also the ability of osteoconduction of the alpha-TCP ceramics.