Hierarchical spontaneous self-assembly of polyethylenimine-poly(propylene glycol) copolymer into cationic polyelectrolyte pH-responsive thermogel

Abstract

Temperature-responsive hydrogels, otherwise known as thermogels, are promising biomaterials which undergo phase change from liquid to a solid-like gel state when warmed. Although poly (ethylene glycol) (PEG) is employed extensively as the hydrophilic segment in thermogelling polymer design, recent years has witnessed development of new families of PEG-free thermogelling copolymers which offer new opportunities in expanding material property profiles for new biomedical applications. Herein, we study the supramolecular self-assembly process of PEG-free amphiphilic branched graft copolymer containing polyethylenimine (PEI) and poly (propylene glycol) (PPG), which shows both thermogelling ability and pH-responsive gelation behaviour. Additionally, we demonstrate the ease of post-synthetic modulation of thermogel properties by amine functionalisation on the PEI copolymer segments through convenient nucleophilic substitution and amide formation reactions. The synthetic platform offered by PEI-PPG thermogels allow facile customisation of these versatile materials for targeted biomedical applications.