Abstract
The objective of this study is to discuss the thermo responsiveness properties of methoxy poly(ethylene glycol)-polyesters (mPEG-PLGA, mPEG-PCLA) diblock copolymers. Without changing the hydrophilic/hydrophobic segment ratio of the copolymer, the molar ratio of ester monomers was adjusted to obtain better formulation for a thermal-sensitive hydrogel. Diblock copolymers were synthesized using ring-opening polymerization. For the mPEG-PLGA series, L10, L8G2, L6G4, L4G6, L2G8, and G10 were prepared corresponding to LA/GA ratios of 100/0, 80/20, 60/40, 20/80, and 0/100, respectively. For the mPEG-PCLA series, L10, L8C2,L6C4, L4C6, L2C8, and C10 were prepared corresponding to LA/CL ratios of 100/0, 80/20, 60/40, 20/80, and 0/100 respectively. Results showed that L10, L4G6, L2G8, L2C8, C10 and G10 were insoluble in water due to high crystallinity and hydrophobicity. L8G2, L6G4, L8C2, L6C4, and L4C6 formed nanoparticles with sizes under 100 nm and critical micelle concentrations below 0.1 mg/mL in aqueous solution. Also, it was observed that 15 wt% (w/v) mPEG-PLGA displayed a wide gelation window in water. Adjusting the molar ratio of monomers in mPEG-PLGA did not significantly alter the gelation window while decreasing the LA units in mPEG-PCLA narrowed the gelation window. In degradation test, mPEG-PCLA series showed slower degradation rate, L4C6 and L6C4 both degraded less than 40% of their original weight after 30 days. In brief, L6C4 hydrogel has optimal ratio, which shows good biocompatibility in cytotoxicity test. Also, L6C4 is a promising drug delivery carrier in cartilage defect regeneration model. These results demonstrate some diblock copolymers of mPEG-PLGA and mPEG-PCLA can be used as in situ gelling drug delivery systems.