Tannic Acid-Complexed Cellulose Nanofiber-Enabled Dynamically Cross-Linked Conductive Hydrogels for Reliable Strain Sensing in Extreme Cold Environments

Abstract

Biomass-reinforced conductive hydrogels featuring tissue-matching compliance and high ionic conductivity retention in extreme cold are needed to address the performance limitations and environmental concerns of conventional wearable devices. Herein, we report tannic acid-complexed cellulose nanofiber (TA@CNF)-enabled dynamically cross-linked conductive hydrogels fabricated by one-step photopolymerization of acrylamide. The TA@CNF functions as a nanofibrillar interfacial regulator that reinforces the polymer network through physical entanglement and hydrogen bonding while providing abundant carboxylate sites. The Li+ ions reversibly bridge carboxylate groups and amide groups, thereby constructing a dynamically cross-linked ion-polymer network. This lithium bond-mediated network affords a tissue-matching Young’s modulus of 34.2 kPa and a high ionic conductivity retention of 89.5% at –40 °C. Molecular dynamics simulations and electrostatic potential analysis confirm Li+ hydration and lithium-bond formation. Ethylene glycol/LiCl synergistically disrupt water hydrogen bonds to inhibit crystallization and preserve low-temperature conductivity. The assembled hydrogel sensor delivers sensitive, steady strain signals for real-time human motion monitoring at low temperatures. An optimized deep-learning algorithm provides a proof-of-concept for rehabilitation-oriented sensing. Therefore, the TA@CNF-reinforced hydrogels fabricated via a facile preparation approach hold great potential for sustainable wearable electronics capable of operating in extreme environments.