Effect of Molecular Structures on Entanglements and Mechanics of Zwitterionic Hydrogels

Zwitterionic hydrogels have great potential as implant materials due to their excellent resistance to protein adsorption. However, it remains a great challenge to toughen these gels owing to the ultrastrong hydration capability of polyzwitterions, which leads to weak associations between hydrated chains. Herein, a zwitterionic hydrogel with integration of toughness and protein resistance was developed by programming the benzene–methylene–imidazolium motif into the zwitterionic moiety and regulating its association behavior. It was found that the benzene and imidazolium did not interfere with the hydration of the anionic group, yet they changed the water coordination shell around the cationic group to allow the formation of compact zwitterion pairs. Taking advantage of 1H NMR technology and MD simulation, all of the benzene, imidazolium, and methylene between them were revealed as key moieties that facilitate the associations, especially at high monomer concentrations. Among them, the imidazolium was proven to be the predominant factor. Then, the densely associated monomers were conducive to polymerizing into a highly entangled network, contributing to simultaneous improvements in Young’s modulus, toughness, and resilience. Meanwhile, the typical characteristics of a zwitterionic gel were not sacrificed, showing high resistance to protein adsorption. This work provides new insights into the chemical and mechanical design of the zwitterionic gels.