Osteogenesis in a rat model: use of bone marrow cells and biodegradable gelatin matrix carrier

We investigated the use of a biodegradable porcine gelatin matrix (Gelfoam) as a carrier for marrow cells that induce osteogenesis at ectopic sites in rats. Bone marrow cells obtained from the long bones of 6-week-old Sprague-Dawley rats were dissociated enzymatically and the cells reconstituted in rat serum. Twenty million cells in 0.1 mL of serum were then adsorbed into 1-cm3 pieces of gelatin matrix substrate and implanted into ectopic sites in live Sprague-Dawley rats. The implants were retrieved and analyzed histologically for bone and cartilage formation 3, 4, 6, and 8 weeks after implantation. Woven bone was seen as early as 3 weeks and persisted through 8 weeks. No cartilage was observed. Osteoclasts first appeared at 3 weeks, peaking in number at 4 weeks. By 6 and 8 weeks, only small islets of substrate remained, surrounded by dense, woven bone. Control implants, consisting only of serum adsorbed into the carrier, showed no bone formation. We conclude that biodegradable gelatin matrix can serve as a carrier for the osteogenic cells of bone marrow in rats in ectopic sites. Such a system may be further developed to augment bone healing.