Polyelectrolyte Complex-Covalent Interpenetrating Polymer Network Hydrogels

Polyelectrolyte complex (PEC) hydrogels possess rich microstructural diversity and tunability of the shear response, self-healing attributes, and pH- and salt-responsiveness. Yet, their utility in biotechnology and biomedicine has been limited, owing to their weak mechanical strength and uncontrolled swelling. Here, we introduce a strategy to overcome these drawbacks of PEC hydrogels by interlacing the electrostatically crosslinked PEC network with a covalently crosslinked polymer network, creating polyelectrolyte complex-covalent interpenetrating polymer network (PEC-IPN) hydrogels. Structural and material characterizations of model PEC-IPN hydrogels composed of oppositely charged ABA triblock copolymers and photocrosslinkable 4-arm poly­(ethylene oxide) (PEO) highlight the key advantages of our approach. Upon initial mixing of the three constituents, the PEC network self-assembles swiftly in aqueous environs, providing structural rigidity and serving as protective scaffoldings for the covalently crosslinkable PEO precursors. Photocrosslinking of the PEO chains creates a covalent network, providing structural reinforcement to the PEC network. The resulting PEC-IPN hydrogels possess significantly improved shear and tensile strengths, swelling characteristics, and mechanical stability in saline environments while preserving the intrinsic mesoscale structure of the PEC network and its salt-responsiveness. We envision that our approach to fabricating PEC-based IPN hydrogels will pave the way for the creation of self-assembled hybrid materials that harness the unique attributes of electrostatic self-assembly pathways, with broad applications in biomedicine.