Osteoinductive potential of highly purified porous β-TCP in mice.

Material-induced osteoinduction of calcium phosphate ceramics has been reported in specific animals. We previously reported that recruitment of tartrate-resistant acid phosphatase (TRAP)-positive cells might be one of the main factors responsible for the difference in the occurrence of material-induced osteoinduction between dogs and rats. In this study, we evaluated the osteoinductive potential of highly purified porous beta-tricalcium phosphate materials (HPP-β-TCP) with two different porosities, 75 and 60 % (Olympus Terumo Biomaterials, Tokyo, Japan), implanted into subcutaneous pockets of FVB and C57BL/6 mice. Twelve weeks after implantation, histological examination and gene expression analysis using reverse transcription-polymerase chain reaction were performed. We observed osteoinduction in half of the HPP-β-TCP materials with 60 % porosity implanted into FVB mice. This group of mice also exhibited the most TRAP-positive cells. Significantly more vessels were found in FVB mice than in C57BL/6 mice, but the greatest number of vessels was counted in implants from materials with 75 % porosity implanted into FVB mice, which did not show osteoinduction. These results indicate that recruitment of TRAP-positive cells is one factor responsible for osteoinduction caused by HPP-β-TCP materials in both FVB mice and dogs. Vessel formation seems to be necessary but appears to be less influential for osteoinduction than TRAP-positive cell recruitment.