Polyelectrolyte Complex-Covalent Interpenetrating Polymer Network Hydrogels

Polyelectrolyte complex (PEC) hydrogels possess a rich microstructural diversity and tunability of 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. In the PEC-IPN hydrogels demonstrated here, composed of oppositely charged ABA triblock copolymers and photocrosslinkable 4-arm poly(ethylene oxide) (PEO), 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, supplying structural reinforcement to the PEC network. The resulting PEC-IPN hydrogels possess significantly improved shear and tensile strength, swelling characteristics, and mechanical stability in saline environments while preserving the intrinsic features of PEC networks, including the mesoscale network structure and salt-responsiveness. We envision that our approach to produce PEC based IPN hydrogels will pave the way for creation of self-assembled hybrid materials that harness the unique attributes of electrostatic self-assembly pathways, with broad applications in biomedicine.