Multi-interaction lignosulfonate ester-integrated poly(acrylic acid-co-N-isopropylacrylamide) hydrogels with thermo-responsive electrical behavior for wearable motion and temperature detection.

Thermo-responsive hydrogels based on poly(N-isopropylacrylamide) (PNIPAM) combine temperature responsiveness with biocompatibility, making them promising for wearable sensing and temperature monitoring. However, their intrinsic brittleness and limited mechanical robustness restrict their broader practical applications. Introducing multiple supramolecular interactions, including hydrogen bonding, van der Waals forces, and π-π stacking, provides an effective strategy for reinforcing hydrogel networks while improving their functionality. Herein, esterified lignosulfonate was integrated into a poly(acrylic acid-co-NIPAM), P(AA-co-NIPAM), copolymer network to introduce hydrogen-bonding and π-π interactions, while the introduced unsaturated double bonds participated in copolymerization with AA and NIPAM, providing additional covalent crosslinks. The synergistic combination of supramolecular and covalent interactions reinforces the network architecture and enhances the mechanical and thermo-responsive properties of the hydrogels. The optimized hydrogel exhibits a distinct thermo-responsive transition accompanied by thermally induced dehydration and network reorganization near physiological temperature, resulting in pronounced temperature-dependent changes in both volume and electrical conductivity. It also exhibits sensitive responses to both large-scale and subtle human motions, with repeatable electrical signals during cyclic sensing tests. After 24 h of unencapsulated ambient storage, the hydrogel retained repeatable tensile and compressive sensing responses despite measurable water loss, demonstrating short-term operational stability under the tested conditions. This dual-responsive sensing behavior enables the detection of strain, compression, and temperature variations. Overall, this work presents a sustainable strategy for constructing lignin-derived multifunctional hydrogels and provides a promising material platform for wearable electronics and intelligent health-monitoring systems.