Cellulose nanofiber-reinforced dual-network multifunctional ion-conductive hydrogel with highly sensitive temperature and stress sensing properties for wearable flexible sensors

Abstract

Flexible multifunctional hydrogels show tremendous potential for advanced wearable electronics and biosensing applications. This study develops an eco-friendly strategy utilizing cellulose nanofibers (CNF) - renewable, high-aspect-ratio nanomaterials with superior mechanical strength - as multiscale reinforcements in polyacrylamide (PAM) hydrogels. The hierarchical design achieves synergistic performance enhancements through three-scale interactions: molecular-scale hydrogen bonding between CNF hydroxyls and PAM amide groups restricts chain slippage, enabling efficient stress transfer while guiding ordered ion distribution for enhanced strain sensitivity. Nanoscale CNF networks collaborate with dimethyl sulfoxide (DMSO) to optimize microstructure, yielding exceptional thermal stability (<20 % mass loss at 50 °C) through vapor pressure suppression and solvent retention. Macroscopically, CNF acts as physical crosslinkers in the dual-network hydrogel, delivering remarkable mechanical properties including high toughness (0.32 MJ/m³), ultra-stretchability (305 % strain), and autonomous self-healing (>60 % efficiency). The hydrogel demonstrates dual-mode temperature sensitivity with distinct thermal response coefficients (1.703 %/°C at 0–50 °C; 0.394 %/°C at 50–90 °C) and precise motion detection capabilities, enabling real-time monitoring of human activities. This multiscale engineering approach establishes a universal paradigm for designing sustainable, high-performance hydrogels that integrate mechanical resilience, environmental stability, and multi-signal sensing functions.