Recyclable Organic Ionic Conductive Hydrogels for Flexible Wearable Sensors with Excellent Environmental Resistance

Hydrogel sensors encounter limitations in practical applications due to factors such as a narrow operating temperature range, suboptimal mechanical properties, and limited recyclability. The development of hydrogel-based wearable sensors that can effectively operate in hot-wet or cold-dry environments remains a significant challenge. In this study, the PVA@CNF-FeCl3-CNT (PCFC) hydrogel, based on poly(vinyl alcohol) (PVA) and cellulose nanofibers (CNFs), was prepared using a one-pot cyclic freeze–thaw process and a binary solvent system instead of pure water. The PCFC strain/pressure sensor exhibited remarkable characteristics including high sensitivity (S = 4.013% kPa–1 over a pressure range of 0–398 kPa), wide response range (7615 kPa), and exceptional durability (over 10,000 cycles), as well as short response time (83 ms) and recovery time (83 ms). It accurately detected various limb movements (e.g., finger flexion) and physiological signals (e.g., pulse) in real-time at both low (−25 °C) and high temperatures (50 °C). Furthermore, the PCFC organic hydrogels are fully reusable, owing to their construction based on noncovalent interactions and their remarkable thermoplasticity. This work presents a promising approach for utilizing hydrogel sensors as long-term wearable devices in extreme environments, while also addressing the recycling of waste hydrogel materials.