An ultratough, stretchable and thermo-responsive hydrogel for dynamic information encryption-decryption and high-fidelity seafood freshness monitoring

While food safety, including spoilage and adulteration, concerns millions, developing a system to address both challenges is challenging. We present a mechanically robust, thermally responsive hydrogel with dual modes for advanced information encryption and smart food freshness monitoring. Composed of a poly(acrylamide -co- 2-(dimethylamino)ethyl methacrylate) network and a calcium alginate network, the hydrogel exhibits impressive mechanical properties, including a breaking elongation of 1402 % and toughness of 249.8 kJ/m 3 , far surpassing existing hydrogel indicators which typically exhibit < 800 % strain and < 100 kJ/m 3 toughness. It also shows excellent fatigue, tearing resistance, and repeatable adhesiveness, withstanding 10 cycles of loading-unloading and achieving tearing energy of 1.12 kJ/m 2 , outperforming current hydrogel indicators, exhibiting tearing energy of < 0.5 kJ/m 2 . The hydrogel features a tunable lower critical solution temperature from 31 °C to 43 °C by adjusting acrylamide content, enabling dynamic thermo-responsive opacity transitions. This property allows it to serve as an anti-counterfeiting platform where information can be hidden or revealed with temperature changes. By integrating the pH-sensitive dye curcumin, the hydrogel effectively monitors food freshness, with strong correlation to TVB-N levels (R² > 0.937), outperforming current polymer film indicators (R² < 0.70). This work introduces a superior hydrogel system that combines advanced anti-counterfeiting and intelligent packaging, enhancing supply chain integrity and consumer safety.