Strengthening of hydrogels made from enantiomeric block copolymers of polylactide (PLA) and poly(ethylene glycol) (PEG) by the chain extending Diels–Alder reaction at the hydrophilic PEG terminals

Abstract

Mixtures of furan (F)-terminated AB diblock copolymer of F-PEG-PLA and ABA triblock copolymer of PLA-PEG-PLA (PEG: poly(oxyethylene), PLA: poly(l-lactide) (PLLA) or poly(d-lactide) (PDLA) depending on the enantiomeric block chain) having different compositions were readily synthesized by ROP of l- and d-lactides using partially furanylated PEGs as the macro initiators. Mixed micelle solutions of the enantiomeric copolymer mixtures (F-PEG-PDLA/PDLA-PEG-PDLA + F-PEG-PLLA/PLLA-PEG-PLLA) were prepared in the presence and absence of a coupling agent 1,8-bis(maleimido)diethylene glycol (BMG). Both the BMG-free and BMG-added mixed micelle solutions underwent sol–gel transition, and in which the gel strength was found to become much higher in the BMG-added micelle solutions, reaching a level of 11 kPa. These hydrogel systems were thought to be controlled by the dual cross-linking mechanisms for the gel formation: stereocomplex formation between the enantiomeric PLA blocks and Diels–Alder coupling of the furanyl terminals on PEG blocks with BMG. These sol–gel systems producing strengthened gels are versatile for use as injectable scaffolds in the tissue engineering.