Breaking the Antifouling-Adhesion Trade-off in Zwitterionic Hydrogels via Electrostatic Hydration Modulation

Zwitterionic hydrogels are known for their outstanding antifouling properties, primarily attributed to a stable surface hydration layer formed through strong interactions with water molecules via ionic solvation. This hydration layer acts as a physical barrier that inhibits nonspecific adsorption of proteins and microorganisms, rendering zwitterionic hydrogels highly valuable in biomedical and marine applications. However, recent studies have revealed that zwitterionic hydrogels may also exhibit strong interfacial adhesion, a characteristic that appears to contradict their well-established antifouling behavior. This apparent discrepancy is hypothesized to stem from the specific hydration behavior of the zwitterionic polymer. To elucidate this paradox, we propose an adhesive-additive-free, endogenous framework that modulates the bound water layer of zwitterionic hydrogels and resolves the adhesion/antifouling trade-off by incorporating polyelectrolytes to perturb their internal electrostatic equilibrium. The results demonstrate that increasing the concentration of poly(acrylic acid) effectively diminishes the density of the hydration layer, thereby inducing a marked enhancement in adhesion strength from near zero to as high as 63.27 kPa, and an adhesion energy reaching 306.34 J/m 2 . Furthermore, the zwitterionic hydrogel in the nonhydrated state exhibits bioadhesive behavior, deviating from its typically observed antifouling properties. This study successfully reconciles the previously antagonistic relationship between the antifouling and adhesive properties of zwitterionic hydrogels by elucidating molecular-level control over surface hydration dynamics, providing a foundational framework for the development of dynamic, smart material surfaces.