A Cephalopod‐Inspired Zwitterionic Hydrogel With Salt‐Responsive Mechanical, Volumetric and Optical Properties

Despite their intrinsic salt responsiveness, the application of zwitterionic hydrogels in smart devices is often limited by weak response contrast and restricted responsive modes. Inspired by cephalopods, we developed a zwitterionic poly(4‐vinyl‐1‐(3‐sulfopropyl) pyridinium betaine) (pVPPS) hydrogel that integrates salt‐responsive changes in mechanics, fluorescence, volume, and transparency. By incorporating intrinsically fluorescent aromatic pyridine moieties directly into the zwitterionic side groups, the functions of strengthening interchain associations and generating fluorescence are unified within a single structural motif. This integration endows the gel with synchronized multi‐property responses upon exposure to salt stimulus. Specifically, in 0.01 m NaCl solution, Cl − ions compete with the polymer for water and promote chain aggregation, yielding an opaque, tough, and strongly fluorescent hydrogel. Conversely, in 1 m NaCl solution, abundant Cl − ions penetrate the interchain spaces and screen interchain electrostatic interactions, resulting in a transparent, swollen, and non‐fluorescent hydrogel. These pronounced and reversible multi‐property contrasts endow the pVPPS hydrogel with potential for information encryption, soft actuation, and ion sensing.