Abstract
Background
Tissue engineering strategies to heal critical-size bone defects through direct bone formation are limited by incomplete integration of grafts with host bone and incomplete vascularisation. An alternative strategy is the use of cartilage grafts that undergo endochondral ossification. Endochondral cartilages stimulate angiogenesis and are remodeled into bone, but are naturally found in only small quantities. We sought to develop engineered endochondral cartilage grafts using human osteoarthritic (OA) articular chondrocytes.
Methods
Study approval was obtained from our human and animal ethics review committees. Human OA cartilage was obtained from discarded tissues from total knee replacements. Scaffold-free engineered grafts were generated by pelleting primary or passaged chondrocytes, followed by culture with transforming growth factor-β1 (TGF-β1) and bone morphogenetic protein 4. Samples were transplanted into immunocompromised mice either subcutaneously or into critical-size tibial defects. Grafts derived from passaged chondrocytes from either of two patients (64 year old and 68 year old men) where implanted into tibial defects in five mice. Bone formation was assessed with histology after four weeks of implantation.
Results
Engineered cartilage grafts generated from passaged OA chondrocytes underwent endochondral ossification after implantation either subcutaneously or in bone. The grafts bridged tibial defects, integrating with bone proximally and distally in all cases. Portions of the graft were remodeled into woven bone, which spanned the defects in two animals. Unmodified OA cartilage and engineered grafts formed from primary chondrocytes did not undergo endochondral ossification in vivo.
Conclusions
Human OA chondrocytes adopt an endochondral phenotype after passaging and TGF-β superfamily treatment. Engineered endochondral cartilage grafts can integrate with host bone, undergo ossification, and heal critical-size long-bone defects in a mouse model.
Level of Evidence
Animal study.
Disclosure
A patent application on this technology has been filed.
