Synergistic Reinforcement of Poly( N -isopropylacrylamide- co -acrylamide) Hydrogels via Ionic Liquid-Induced Noncovalent Interactions for Dual-Responsive Wearable Sensors

Achieving a synergy between mechanical robustness and multimodal sensing is pivotal for advanced wearable electronics. Herein, a dual-responsive ionic liquid hydrogel (ILH) is engineered via photoinitiated copolymerization of N-isopropylacrylamide (NIPAM) and acrylamide (AM) in the presence of 1-butyl-3-methylimidazolium tetrafluoroborate (BMIMBF₄). The strategic incorporation of the IL induces extensive noncovalent interactions, including hierarchical hydrogen bonding and electrostatic coupling, which refine the network into a stable, amorphous three-dimensional (3D) architecture. This IL-mediated structural reinforcement endows the ILH with exceptional stretchability (1153 ± 2%) and rapid elastic recovery. Benefiting from superior ionic conductivity, the ILH functions as a high-performance dual-modal sensor with a gauge factor of 2.68 and a temperature coefficient of resistance of -1.12%/°C. The ILH wearable sensor demonstrates high-fidelity tracking of complex knee rehabilitation movements (e.g., flexion and squats) while simultaneously monitoring localized thermal fluctuations relevant to postsurgical inflammation. This molecular engineering strategy provides a facile route to high-performance, multifunctional hydrogel interfaces for personalized healthcare and clinical monitoring.