Biomimetic bilayer design of cellulose-gelatin hydrogels for environmentally stable strain sensing

Hydrogel strain sensors hold great promise for artificial intelligence field. Conventional cellulose-based hydrogels suffer from compromised mechanical and electrical performance in fluctuating humidity environments due to excessive water absorption. Herein, a novel hydrophobic-conductive synergistic bilayer hydrogel is designed via a biomimetic strategy. A hydrophilic double-network matrix, comprising dialdehyde cellulose, gelatin, and polyacrylamide, is first constructed, incorporating sodium ions and polyaniline nanoparticles to establish a robust and stretchable conductive network. Subsequently, a hydrophobic layer is seamlessly integrated onto the hydrogel surface through modification with stearic acid. This bilayer architecture endows the hydrogel with exceptional liquid resistance, outstanding anti-drying and anti-swelling properties, remarkable stretchability (up to 830%), and stable adhesion to diverse substrates. Consequently, the hydrogel strain sensor maintains stable and sensitive electrical responses under varying temperatures and humidity, exhibits a tunable gauge factor, and demonstrates excellent durability over 700 stretching-releasing cycles, enabling precise monitoring of both subtle and large human motions. The hydrogel efficiently converts mechanical stimuli into electrical signals, functioning as a reliable strain sensor and a smart pressure-responsive switch. This work provides a viable design strategy for environmentally stable cellulose-based hydrogels, paving the way for their reliable application in complex scenarios such as outdoor wearables and underwater soft robotics.