Skeletal tissue engineering using embryonic stem cells

Tissue engineering aims at repairing or replacing damaged or diseased tissue. In this thesis, we investigated the potential of embryonic stem cells (ESCs) for cartilage tissue engineering. After differentiation of mouse and human ESCs into the chondrogenic and osteogenic lineage had been established, tissue engineers focused on the formation of cartilage and bone by ESCs in combination with scaffolds. Various scaffold materials have been investigated for cartilage tissue engineering, such as polymeric scaffolds and hydrogels. We established that chondrocytes and ESCs could form cartilage in a newly developed dextran-based hydrogel formed in situ via a Michael type addition reaction between a thiol-functionalized dextran (Dex-SH) and a tetra-acrylated star poly(ethylene-glycol) (PEG-4-Acr). We established some critical steps when using ESCs for cartilage tissue engineering using polymeric scaffolds and hydrogels. When we implanted cartilage formed by mouse ESCs in hydrogels in polymeric scaffolds into immuno-deficient mouse, we could retrieve some cartilage. When we implanted cartilage formed by mouse ESCs on ceramic or polymeric scaffolds, we observed that the cartilage matured, became hypertrophic, calcified and was ultimately replaced by bone tissue in the course of 21 days. Hence, the cartilage was used as a template for endochondral bone formation. This is the first report of in vivo bone formation using ESCs, both ectopically and orthotopically in a cranial defect, under controlled, reproducible conditions. Bone tissue engineering by directly differentiating embryonic stem cells (ESCs) into osteoblasts was unsuccessful so far. Even though we were able to take the first steps towards an ESC-derived cartilage implant and towards bone tissue engineering using ESCs, many challenges remain, especially for human ESCs.