Flexible sensors have attracted great research interest due to their applications in artificial intelligence, wearable electronics, and personal health management. However, due to the inherent brittleness of common hydrogels, preparing a hydrogel-based sensor integrated with excellent flexibility, self-recovery, and antifatigue properties still remains a challenge to date. In this study, a type of physically and chemically dual-cross-linked conductive hydrogels based on 2,2,6,6-tetramethylpiperidine-1-oxyl (TEMPO)-oxidized cellulose nanofiber (TOCN)-carrying carbon nanotubes (CNTs) and polyacrylamide (PAAM) matrix via a facial one-pot free-radical polymerization is developed for multifunctional wearable sensing application. Inside the hierarchical gel network, TOCNs not only serve as the nanoreinforcement with a toughening effect but also efficiently assist the homogeneous distribution of CNTs in the hydrogel matrix. The optimized TOCN-CNT/PAAM hydrogel integrates high compressive (∼2.55 MPa at 60% strain) and tensile (∼0.15 MPa) strength, excellent intrinsic self-recovery property (recovery efficiency >92%), and antifatigue capacity under both cyclic stretching and pressing. The multifunctional sensors assembled by the hydrogel exhibit both high strain sensitivity (gauge factor ≈11.8 at 100-200% strain) and good pressure sensing ability over a large pressure range (0-140 kPa), which can effectively detect the subtle and large-scale human motions through repeatable and stable electrical signals even after 100 loading-unloading cycles. The comprehensive performance of the TOCN-CNT/PAAM hydrogel-based sensor is superior to those of most gel-based sensors previously reported, indicating its potential applications in multifunctional sensing devices for healthcare systems and human motion monitoring.
Keywords: carbon nanotubes; hydrogel; nanocellulose; self-recovery; sensor.