Chitosan-polycaprolactone copolymer microspheres for transforming growth factor-β1 delivery

Chitosan-polycaprolactone (CPC) copolymer microspheres loaded with transforming growth factor-β1 (TGF-β1) were fabricated with an emulsification method using sodium tripolyphosphate as crosslinker. They were found to be dense and had regular sphericity with various diameters changing from several hundred nanometers to a few micrometers. Their loading efficiency could be regulated by both the amount of crosslinker and the composition of CPCs, and some microspheres showed their loading efficiency higher than 80%. It was observed that in neutral PBS media, the composition of CPCs predominantly governed swelling behavior and release profiles of the microspheres while the effect of crosslinker on the swelling and release behavior was limited. The initial fast releases of TGF-β1 from different microspheres could be significantly decreased with increasing polycaprolactone content in CPCs, and some microspheres were able to maintain sustained releases of TGF-β1 by mainly controlling their composition. In addition, in a simulated acidic environment (pH 6.5) for cartilage lesions, release patterns of the microspheres were notably modulated by pH but some selected microspheres could still well administrate the release of TGF-β1 in a sustained way without severe burst features.