Tough and Skin‐Free Porous Polyelectrolyte Complex Hydrogels via Salt‐Induced Aqueous Phase Separation

Polyelectrolyte complex (PEC) hydrogels fabricated via environmentally benign aqueous phase separation (APS) can exhibit porous architectures attractive for tissue engineering, drug delivery, and soft bioelectronics. The microstructure and mechanical properties of PEC hydrogels can be tailored by modulating salt‐induced APS processing parameters. This study elucidates the critical role of counterion exchange rates in governing microstructural features of PEC hydrogel networks, using poly(sodium 4‐styrenesulfonate) and poly(diallyldimethylammonium chloride) as model system. By systematically varying polymer concentration and coagulation bath composition, direct relationship is established between counterion exchange rate, and resulting microstructure. Rapid counterion exchange induces instantaneous phase‐separation, forming skin‐layer and macrovoids. In contrast, slow counterion exchange enables more uniform phase‐separation, promoting denser PEC network with homogeneous pores, and enhanced mechanical properties. Incorporation of additives in coagulation bath further enables formation of homogeneously porous PEC networks, yielding physical hydrogels with exceptional toughness (>10 MJ·m −3 ) and stretchability (>1000%). The PEC hydrogels are compatible with advanced processing strategies, including extrusion‐based 3D (bio)printing, enabling fabrication of homogeneously porous scaffolds. Post‐functionalization of skin‐free PEC networks with polypyrrole via oxidative chemical vapor deposition produces electrically conductive hydrogels for soft bioelectronics. These findings emphasize the importance of coagulation bath composition in designing PEC hydrogels with tough, robust, and tunable properties.