Molecularly Engineered Zwitterionic Hydrogels with High Toughness and Self-Healing Capacity for Soft Electronics Applications

Zwitterionic hydrogels have attracted tremendous interest due to their densely charged network, ultralow fouling characteristics, and excellent biocompatibility. However, the unsatisfactory mechanical performance of the zwitterionic gels limits their practical applications. Here, we developed a new class of zwitterionic hydrogels from a structurally ameliorated sulfobetaine monomer, 3-(1-(4-vinylbenzyl)-1H-imidazol-3-ium-3-yl)propane-1-sulfonate (VBIPS). The incorporated benzene and imidazole greatly enhance the tensile toughness and fracture toughness of the gel, which are 40 and 60 times higher than those of the conventional zwitterionic hydrogel, respectively. An obvious crack blunting occurs during the crack extension. In situ microscopic observation reveals that the outstanding toughness originates from the formation of a two-phase structure at room temperature, with an obvious contrast of the association energy. The mechanical properties of the gel can be well-tuned by changing the pH, and self-healing is achieved with an acid treatment. The VBIPS gel also possesses excellent short-term antifouling properties and the attached bacteria in a longer timescale can be easily released via salt treatment. To expand the application potentials, a VBIPS ionogel is prepared by soaking the gel in ionic liquids, which is flexible, antifreezing, and can be used as a strain sensor. This work provides a molecular strategy to toughen zwitterionic hydrogels, which should broaden their applications in diverse fields.