Incorporation Of Chitosan Microspheres Into Chitosan-polycaprolactone Scaffolds For Controlled Release Of Transforming Growth Factor-β1

In this study, chitosan-g-polycaprolactone (CS-PCL) copolymers were successfullysynthesized via a group-protection method which involves a ring-opening polymerizationroute and the polycaprolactone side chains were grafted onto C-6sites of phthaloylchitosan. By using stannous octoate as a catalyst, copolymers with grafting percentage ofaround70%or higher were achieved. The physical properties and chemical structures ofCS-PCL were detected through Magnetic resonance spectra and Fourier-transforminfrared.Chitosan microspheres loaded with transforming growth factor-β1(TGF-β1) werefirst prepared with an emulsification method using genipin as a crosslinker. The sizes andshapes of microspheres were viewed under scanning electron microscope and theaverage size was determined using a computed image analysis system by measuring thediameters of100microspheres at100different lattices in a SEM image for eachspecimen. The resulting microspheres were spherical with a smooth surface and themicrospheres with a diameter less than45μm were selected. It was found that the loadingefficiency of chitosan microspheres could be higher than80%if they were crosslinkedproperly.The microspheres were then embedded into porous scaffolds built bychitosan-polycaprolactone. It was found that by changing the compositional proportion ofCH–PCLs and manipulating the structure parameters of the scaffold, the scaffolds wouldhave tunable mechanical strength and required degradation rates. PCL percentages in theCH–PCLs at around42wt.%showed well-defined mechanical and degradation properties.Some optimized chitosan-polycaprolactone scaffolds with porosity higher than80%andhaving an initial TGF-β1load of around3ng(TGF-β1)/mg(dry scaffold) were capable ofmaintaining sustained release of TGF-β1in a simulant in vivo environment at controlledrates over a period of time longer than four weeks without severely initial burst. Theseresults suggest that they have potential in the application of cartilage repair.