Recently, some types of cell/biomaterial composites have been fabricated to regenerate bone experimentallyand clinically. The objectives of this study were to compare the osteogenic potential of bone marrow cellsdifferentiated into osteoblast-like cell/beta-TCP composites with that of undifferentiated bone marrow cell/beta-TCP composites implanted at ectopic sites, to investigate how such bone marrow cells and osteoclasts histologicallyparticipate in the absorption of beta-TCP and bone formation, and to assess the potential use of these compositesas an alternative material for the repair of jaw bone defects.
Fischer rat bone marrow cells were cultured and divided into two different medium groups. One medium containedstandard medium plus beta-glycerophosphate, dexamethasone and ascorbic acid to induce osteoblast likecells. The other medium did not contain the additives. Porous beta-TCP blocks (OSferion (R)) were seeded withthe cells in each group; the former was designated as the differentiated group and the latter as the undifferentiatedgroup. As a negative control, beta TCP blocks without cell seeding were used. The blocks were implanted subcutaneouslyand harvested 6 weeks and 12 weeks after implantation for histological analysis.
In the differentiated group, bone extensively covered the surfaces of the pores of the beta-TCP block, andosteoblasts lined the new bone. Osteoclasts were observed on the surfaces of the pores. Twelve weeks afterimplantation, the new bone was thicker than that observed at 6 weeks, and the cement lines were also observed.In addition, a large amount of capillary ingrowth was seen in the pores. In the undifferentiated group, clusters ofround cells regarded to be marrow cells were recognized on the surfaces of the pores, and a small amount ofnewly formed bone was seen at the same site. In the control group, few cells were observed on the pore surfaces, and there was no evidence of new bone formation. The number of osteoclasts in the differentiated group was largerthan those in the other two groups.
These results showed that differentiated bone marrow cell/bate-TCP composites had a high osteogenic potentialin an ectopic environment. In contrast, undifferentiated bone marrow cell/beta-TCP composites demonstratedlittle such potential. Differentiated bone marrow cells were thus suggested to play an important role in the boneformation and induction of osteoclasts on the composites.
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