Using cartilage to repair bone: an alternative approach in tissue engineering.

Materials and techniques currently used for bone replacement/repair conform to the current paradigm, relying on bone or bone products to produce bone or induce bone formation. Yet, nature forms and heals most of the skeleton by ossification of a cartilaginous model. In this study, we cultured aggregates of E10.5 or E12 mouse embryonic limb cells in the bioreactor for 3 weeks, determined the stages of cartilage differentiation attained, and assessed the ossification and bone healing potential of the spheroids by implantation adjacent to, or directly in, a skull defect. Cultured spheroids had large cartilaginous areas, sometimes with cellular arrangements characteristic of growth plate zones. Aggregates implanted for 2 weeks adjacent to a defect mineralized and ossified (histology, micro-CT). Defects with implants had a central mass of differentiated and differentiating bone, with osteoclast activity, filling the defect. Controls had considerable remodeling on the bone edges demarcating the still present defect. This study shows that cartilage, grown in the bioreactor for 3 weeks, ossified when implanted adjacent to a bone defect, and when implanted directly in a defect, contributed to its healing. Our ability to grow differentiated bone-forming cartilage for implantation is an alternative approach in the field of bone repair.