Bone tissue engineering using mesenchymal stem cells

Finding a suitable material to be used in bone transplantations is a general objective in reconstructivesurgery. Currently, autologous bone transplants are favored by most surgeons due totheir reliability, however availability and donor morbidity are considerable drawbacks of this treatment. Tissue engineering has developed into a promising alternative, because the variety of biomaterials and the expertise in stem cell research are both rapidly increasing. The ideal tissue-engineered bone graft provides biocompatibility, bone-like mechanical stability, osseointegration and formation of new bone tissue. The goal of this study was to examine scaffolds of poly D,L-lactic acid (PDLLA), polyetherketoneketone (PEKK), and (hydroxyapatite-modied) silk from silk worm Bombyx mori in combination with mesenchymal stem cells (MSC) to be used for the purpose of a tissue-engineered bone graft. The chosen materials offer individual advantages such as degradability, cost-efficient production, radiolucency and biocompatibility.MSC are adult multipotent stem cells which are capable of differentiating into osteoblasts upon stimulation. Therefore, MSC are a frequently applied cell type in bone tissue engineering. The results of the In vitro tests showed that all scaffolds supported the attachment and osteogenic differentiation of both human and ovine (sheep origin) MSC. In subsequent in vivo experiments, scaffolds were implanted either cell-free, seeded with autologous ovine MSC, or seeded with osteogenically pre-dierentiated autologous ovine MSC, into sheep calvarial defects of 10 mm diameter. After three months, the implants were examined for the volume and quality of newly formed bone. Surprisingly, the MSC seeding did not result in an enhanced bone formation in comparison to the cell-free samples. We hypothezise that the absence of the presumed enhancing effect of MSC was due to a fibrous capsule, which had formed around the scaffolds. Nevertheless, PEKK and hydroxyapatite-modied silk scaffolds supported new bone formation, either with or without MSC seeding and are thus potential scaffolds for bone tissue engineering. More basic research is needed however, to identify relevant factors for improved tissue integration of transplants, while at the same time avoiding fibrous capsule formation