ABSTRACT Hydrogel‐based soft sensors are gaining increasing attention for next‐generation wearable and stretchable electronics, but achieving a filler‐free material that integrates mechanical robustness, protonic conductivity, dielectric responsiveness, and environmental adaptability remains challenging. We report a green and scalable strategy for constructing a multifunctional hydrogel through a freeze‐thaw process followed by mild post‐soaking, combining polyvinyl alcohol (PVA), casein (CA), and gallic acid (GA). CA, an amphiphilic protein, forms hydrated micro‐channels that facilitate water retention and ion mobility, while GA supplies mobile protons, resulting in continuous proton‐transport pathways and enhanced dielectric behavior. Cooperative hydrogen bonding, ionic coordination, and hydrophobic interactions generate a tough supramolecular GA‐PVA/CA network with high tensile strength (1.25 MPa), fracture energy (12.6 kJ m −2 ), stretchability (287%), and toughness of 513.4 kJ m −3 at 400% strain. The hydrogel also shows a high storage modulus (∼100 kPa), a thermally induced gel–sol transition, and heat‐triggered structural recovery. When employed as a wearable strain sensor, it demonstrates stable electromechanical responses with a gauge factor of ∼0.33 for monitoring human joint motions. Additionally, a reversible pH‐responsive color transition across a pH gradient (1 → 14) provides optical functionality for visual sensing. This work offers an eco‐friendly, filler‐free hydrogel platform that bridges mechanical resilience, protonic functionality, and multimodal sensing for sustainable soft electronic devices.
Ahanger et al. (2026) studied this question.