The role of pharmacologically active microcarriers releasing TGF-β3 in cartilage formation in vivo by mesenchymal stem cells

Cartilage engineering using mesenchymal stem cells (MSC) will require the use of a scaffold which will act as a support for cell adhesion keeping the cells in the cartilage defect. Optimally, a tissue engineered construct should allow sustained delivery of bioactive factors capable of inducing MSC differentiation into chondrocytes and should be easily injected inside the cartilage lesions to avoid surgical operations. We therefore developed pharmacologically active microcarriers (PAM) made of poly-lactic-co-glycolic acid (PLGA) produced using an oil-in-water (o/w) emulsion method. The microspheres were coated with a biomimetic surface of fibronectin (FN) and engineered to release TGF-β3 as a chondrogenic differentiation factor. When human MSCs were incubated in vitro with TGF-β3 releasing FN-coated PAMs in chondrogenic medium, they firmly adhered onto the surface of PAMs rapidly forming cell aggregates. After 3 weeks, strong up-regulation of cartilage-specific markers was observed both at the mRNA and protein level whereas osteogenic or adipogenic genes could not be detected. Importantly, implantation of MSC/TGF-β3 releasing PAM complexes in SCID mice resulted in the formation of histologically resembling cartilage which stained positive for chondrocyte markers, collagen II and aggrecan. The present study demonstrated that functionalized PLGA-based microparticles can provide an appropriate environment for chondrogenic differentiation of MSCs and should contribute to injectable biomedical device development improving in vivo cartilage engineering.