The effect of high-molecular hyaluronan on osteoinduction process in allogeneic bone grafting

Min, Seung Ki; Song, Jong Min

Abstract

Hyaluronan(HA) is an essential component of extracellular matrices. Early in embryogenesis mesenchymal cells migrate, proliferate and differentiate, in part, because of the influence of hyaluronan. Since the features of embryogenesis are revisited during wound healing, including bone fracture repair, this study was initiated to evaluate whether hyaluronan has an effect on osteogenesis in early stage of wound healing. Grafting bone chip was applied on the two squared shaped bone defects on the total 60 rat calvarium about 7x7 mm size which were made with electric drill intentionally, the right side was grafted with allogeneic bone and the left side was autogenous bone grafting. In experimental groups, grafting materials were hydrated with 1.0 mg/ml concentration of hyaluronan solution before surgery for 30 minutes. The calvarial bone defects were covered with layer suture. In order to evaluate initial bone formation process, total experimental rats were sacrificed and evaluated under light microscope with routine HandE, and toluidine blue stain and found initial osteogenesis under electric microscope at postoperative 1 day, 4 days, 1 week, and 2 weeks. There were fixed grafted bone chip with fibrosis and not inflammed grafted site on autogenous and allogeneic bone grafting groups grossly, but more stabled bone chip particles in experimental HA group at 1 week. At 2 weeks, similar new bone formation was seen on both grafted sites. In postoperative 1 and 2 weeks, inflammatory changes in the wound sites were more prominent in bones to which hyaluronan had been applied. But, new bone formation had been induced by day 7 on both peri- and endosteal surfaces of the grafted areas. Newly formed trabecular bones were filled in grafted wound. Electromicroscopic findings of allogeneic bone grafting at 1 week showed small group of rER and mitochondria in control group, but relative abundant mitochondria and rER in cell and dense connection in experimental group. There was few difference between autogenic and allogeneic group. At 2 weeks, increased mitochondria in cell and newly formed bone was incorporated into the grafted allogeneic bone in control group, but more prominent cellular activity in experimental allogeneic bone group. These results suggested that high-molecular hyaluronan is capable of accelerating new bone formation in initial bone formation process through mesenchymal cell differentiation in bone grafting.