Synthesis, Characterization and Self-assembly Behavior of Chitosan-graftpolylactide Copolymers

Amphiphilic chitosan-graft-polylactide copolymers (CS-g-PLA) were synthesized via coupling reaction of monocarboxyl-ended polylactide with the amine group of chitosan in the presence of 1-ethyl-3-(3-dimethylaminopropyl) carbodiimide hydrochloride and N-hydroxysuccinimide. The composition of CS-g-PLA copolymers was confirmed by 1H NMR and FTIR. Self-assembled micelles were prepared by direct dissolution of the copolymers in aqueous medium. TEM and DLS were used to determine the morphology and size distribution of micelles. The average diameter of micelles determined by DLS was in the range of 100-120nm, which is much larger than that estimated by TEM. The stereocomplexation between CS-g-PLLA and CS-g-PDLA seemed to enhance the stability of mixed micelles. Paclitaxel was loaded inside micelles by stirring for two days in the micellar solution. Release properties were examined by using high performance liquid chromatography. Micelles with lower initial drug load exhibited faster release rate. After 15 days, the cumulative release percentages from micelles with 5% and 10% initial drug loads reached 11% and 6%, respectively.