[The experimental study on the activity of rhBMP-2, coral and collagen composites inducing intramuscle bone]

To investigate the ectopic bone induction activity of the composite of coral, collagen and rhBMP-2, and the degradation of the carriers of rhBMP-2.

The composites of rhBMP-2, coral and collagen were implanted into the muscle pouches of mice. The mice were divided into the following four groups. Group H: each composite had 2 mg rhBMP-2, Group L: each composite had 0.5 mg rhBMP-2, Group J: each composite had only type I collagen, Group C: only coral was implanted in the muscle of mouse. Each group had 20 mice. Every 5 mice in each group were killed postoperatively after 1, 2, 4 and 8 weeks. The ectopic osteoinductive activity was assessed with histology and histomorphometry. The point counting method was applied to measure the formation of new bone and cartilage and the degradation of coral in the composites. The data was analyzed statistically using t test.

There was no obvious morbidity in any of the animals in this study, and no wound infection, bleeding, or feeding difficulties postoperatively. The samples were examined histologically. Cartilage and bone induction occurred in Group H and L. After 1 Week, new bone was observed in Group H, and cartilage formation occurred mainly in Group L. After 2 weeks, both cancellous bone and bone marrow elements were present in Group H and L. New bone formation was not uniform throughout the specimen. Part of the coral in the composites was not absorbed between 2 to 4 weeks postoperatively. At the 8th week, the coral in the composite was absorbed completely. While in Group J and C there was not any new cartilage or bone formation. According to the statistical analysis, bone formation occurred 2 weeks earlier in Group H than in Group L after operation. From 4 postoperative weeks, no difference of the bone formation rate was observed between Group H and Group L. The degradation rate of coral in Group C was the fastest among the four groups.

The composites of rhBMP-2, coral and collagen are degradable bone substitutes with bone induction and conduction, and induce dosedependent and time-dependent amounts of intramuscle bone in mice during limited postoperative period. The coral in the composites could be absorbed completely.