Thermosensitive Self-Healing PNIPAM-Based Organohydrogels for Dual-Signal Sensing with a Low Limit of Detection Based on Stress-Induced Phase Transition

Strain and temperature dual-signal sensors are critical for health monitoring and wearable technology due to the complexity of physiological signals. Poly( N -isopropylacrylamide) (PNIPAM)-based hydrogels, known for their thermosensitivity, show significant potential as dual-signal sensors. However, hydrogels are susceptible to freezing and water loss, limiting sensing durability and temperature range. Conversely, organohydrogels that employ organic solvents often compromise thermosensitivity. Furthermore, accurately monitoring micromovements remains a severe challenge. To address these issues, this study develops a conductive PNIPAM-based organohydrogel featuring high stretchability, thermosensitivity, self-healing, water retention and frost resistance, enabling dual-signal sensing capabilities. Specifically, multiple dynamically cross-linked dual-network hydrogels are rapidly formed by incorporating MXene nanosheets into a polymer glycerol–water mixture solution consisting of hydroxypropyl chitosan- graft -β-cyclodextrin, poly( N -isopropylacrylamide- co -adamantyl acrylate), and aldehyde group-modified polyethylene glycols. Experimental results reveal that by precisely controlling the glycerol content in glycerol–water mixture at 7/31 v/v, the PNIPAM-based organohydrogel exhibits exceptional mechanical properties (160 kPa, 681% strain), notable thermosensitivity (volume phase transition temperature of 11.9 °C), satisfactory water retention (over 45% after 24 h), and frost resistance at −20 °C. The organohydrogel can function as temperature and strain dual-signal sensors with a wide sensing range, high sensitivity, and long durability. Especially, based on the innovative design by introducing β-cyclodextrin and admantyl host–guest reversible cross-linking PNIPAM network, the sensing limit of detection is significantly lowered to 0.43% for the hydrogel and 1.48% for the organohydrogel. Comparative experiments and theoretical analysis verify the corresponding mechanism that the PNIPAM chains can be released and accelerate shrink upon the host–guest disassembly with stressing, so as to enhance the change of resistance and amplify the weak signal. This study presents an approach for advancing durability and reducing detection limit for organohydrogel-based temperature and strain dual-signal sensors, presenting important academic significance and application value.