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

- “Sunflower” micelles are formed from PEG-PLA diblock/triblock copolymer mixtures.
- The micelles undergo temperature-dependent sol-gel transition.
- The terminal furan-BMG reaction induces micelle particle aggregation.
- Gel strength is enhanced to 11 kPa with the BMG-added micelle solutions.
- The gelation is controlled by both stereocomplexation and Diels-Alder coupling.

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.

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