Tissue-engineered fabrication of an osteochondral composite graft using rat bone marrow-derived mesenchymal stem cells

This study tested the tissue engineering hypothesis that construction of an osteochondral composite graft could be accomplished using multipotent prog enitor cells and phenotype-specific biomaterials. Rat bone marrow-derived m esenchymal stem cells (MSCs) were culture-expanded and separately stimulate d with transforming growth factor-beta1 (TGF-beta1) for chondrogenic differ entiation or with an osteogenic supplement (OS). MSCs exposed to TGF-beta1 were loaded into a sponge composed of a hyaluronan derivative (HYAF(R)-11) for the construction of the cartilage component of the composite graft, and MSCs exposed to OS were loaded into a porous calcium phosphate ceramic com ponent for bone formation. Cell-loaded HYAFF(R)-11 sponge and ceramic were joined together with fibrin sealant, Tisseel(R), to form a composite osteoc hondral graft, which was then implanted into a subcutaneous pocket in synge neic rats. Specimens were harvested at 3 and 6 weeks after implantation, ex amined with histology for morphologic features, and stained immunohistochem ically for type I, II, and X collagen. The two-component composite graft re mained as an integrated unit after in vivo implantation and histologic proc essing. Fibrocartilage was observed in the sponge, and bone was detected in the ceramic component. Observations with polarized light indicated continu ity of collagen fibers between the ceramic and HYAFF(R)-11 components in th e 6-week specimens. Type I collagen was identified in the neo-tissue in bot h sponge and ceramic, and type II collagen in the fibrocartilage, especiall y the pericellular matrix of cells in the sponge. These data suggest that t he construction of a tissue-engineered composite osteochondral graft is pos sible with MSCs and different biomaterials and bioactive factors that suppo rt either chondrogenic or osteogenic differentiation.