BMP-2 release and dose-response studies in hydroxyapatite and β-tricalcium phosphate

The purpose of this study is to compare in vivo retention of BMP-2 and bone induction in HAp (porosity: 60-80%, pore size: 100-600 μm, sintering temperature: 800°C, surface area: 1 m²/g) and β-TCP (porosity: 75%, pore size: 100-400 μm, sintering temperature: 1050°C, surface area: 4 m²/g). We estimated the in vivo release profile of ¹²⁵I-labeled BMP-2 and bone induction of hard tissues histologically. The amount of BMP-2 remaining in the β-TCP at 1 day after implantation was 49.6%, while the amount was 34.0% in the HAp. Furthermore, the HAp and β-TCP containing 0.0, 0.05, 0.1, 0.3, 0.5, 1.0, 5.0 μg of BMP-2 were implanted into the back subcutis of 4-week old Wistar rats. At 3 weeks after implantation, the ceramics were explanted and evaluated histologically. The HAp/BMP-2 (5.0 μg) system showed 3.0% in the total volume of bone at 3 weeks, while only in the β-TCP/BMP-2 (5.0 μg) system showed 32.5%. These results indicate that the absorbable β-TCP block may be an effective bioceramic for bone induction to deliver BMP-2 to the site of action.