Novel bioresorbable hydrogels prepared from chitosan‐ graft ‐polylactide copolymers

A series of biodegradable chitosan‐ graft ‐polylactide (CS‐ g ‐PLA) copolymers were prepared by grafting of poly( L ‐lactide) (PLLA) or poly( D ‐lactide) (PDLA) precursor to the backbone of chitosan using N , N ′‐carbonyldiimidazole as coupling agent. The composition of the copolymers was varied by adjusting the chain length of PLA as well as the ratio of chitosan to PLA. The copolymers synthesized via this ‘graft‐onto’ method present interesting properties as shown by NMR and infrared spectroscopy, gel permeation chromatography and solubility tests. Hydrogels were prepared by mixing water‐soluble CS‐ g ‐PLLA and CS‐ g ‐PDLA solutions. Gelation was assigned to stereocomplexation between PLLA and PDLA blocks as evidenced by differential scanning calorimetry and wide‐angle X‐ray diffraction measurements. Thymopentin (TP5) was taken as a model drug to evaluate the potential of these CS‐ g ‐PLA hydrogels as drug carriers. An initial burst and a final release up to 82% of TP5 were observed from high‐performance liquid chromatography analysis.