Tissue Engineering of Multi-zonal, Osteochondral-like Constructs with Bone Marrow Stromal Cells

Articular cartilage facilitates weight bearing and movement in a synovial joint. As articular cartilage does not spontaneously heal, damaged cartilage leads to loss of cartilage and subchondral bone remodelling. In previous studies we developed biphasic constructs with articular chondrocytes and porous calcium polyphosphate (CPP) substrate that could replace both damaged cartilage and bone. However, articular chondrocytes are scarce and cannot be expanded in vitro without losing their functional attributes. Since bone marrow stromal cells (BMSCs) can be expanded to large quantities and differentiated into chondrocytes, it was hypothesized that, using BMSCs as the cell source, cartilage with a multi-zonal architecture can be formed on porous CPP substrate to produce osteochondral-like constructs with biomechanical properties that approach native articular cartilage. A protocol was devised to differentiate BMSCs on collagen-coated porous membranes and harvest the cells, which were subsequently cultured on porous CPP substrates to form biphasic constructs with high compressive mechanical properties. Implantation of BMSC-derived biphasic constructs in sheep joints revealed insufficient mechanical integration between the cartilage and the substrate. To address this limitation, a strategy was devised to generate a zone of calcified cartilage at the interface, mimicking the multi-zonal osteochondral architecture in healthy joints. A thin calcium hydroxyapatite film was formed on the surfaces of CPP using organic sol-gel processing method to limit the release of inorganic polyphosphates (polyP), which inhibit mineralization near the interface. Also, sequential seeding of BMSC-derived chondrocytes, in which only the interfacial layer was treated with triiodothyronine, yielded scaffold-free cartilage tissues on coated CPP substrates with distinct hyaline and calcified zones. The interfacial shear strength of constructs with the distinct calcified zone was significantly higher compared to non-calcified control. In vivo studies are warranted to investigate whether the multi-zonal constructs could effectively repair defects in a joint. Generation of anatomically shaped multi-zonal constructs for whole joint replacement are ongoing.Ph.D.2016-11-30 00:00:0