1999 年 12 巻 2 号 p. 206-212
IBM (insoluble bone matrix) delivery system as an effective carrier of rhBMP-2 (recombinant human bone morphogenetic protein-2) is well acknowledged, but the mechanism is unclear. The long-term results of rhBMP-2, in IBM particle implants, were examined by heterotopic bone formation in rats. The purpose of this study was to evaluate the delivery system for finding a suitable carrier which can be applied clinically.
Chondroblast cells conforming to the shape of lacunae with the basophilic matrix were observed at one and two weeks after implantation. The chondroid tissue was partially absorbed at two weeks after implantation. Bone formation and remodelling were noticed from two weeks. Both endochondral and intramembranous ossification were observed, and the former was predominant at two weeks. A bone marrow-like structure was observed at three weeks and fat marrow was found from four weeks.New bone formation and absorption were not active from seven weeks after implantation. IBM particles were covered by new bone in a stable state. By the end of nine weeks mature bone tissue was still present. Thus rhBMP-2 and IBM composites have high osteoinductive ability, and the newly-formed bone was relatively stable for a long time.This result suggested that IBM provides an excellent immobilization system of rhBMP-2 in the early period of rhBMP-2 induced bone formation. After remodeling the new bone, IBM seems to become part of the new bone matrix.