Hydroxypropyl methyl cellulose reinforced conducting polymer hydrogels with ultra-stretchability and low hysteresis as highly sensitive strain sensors for wearable health monitoring

Conducting polymer hydrogels have emerged as promising materials to fabricate highly sensitive strain sensors. However, due to weak bindings between conducting polymer and gel network, they usually suffer from limited stretchability and large hysteresis, failing to achieve wide-range strain sensing. Herein, we combine hydrox-ypropyl methyl cellulose (HPMC), poly (3,4-ethylenedioxythiophene):poly (styrene sulfonic acid) (PEDOT: PSS) with chemically cross-linked polyacrylamide (PAM) to prepare a conducting polymer hydrogel for strain sensors. Owing to abundant hydrogen bonds between HPMC, PEDOT:PSS and PAM chains, this conducting polymer hydrogel exhibits high tensile strength (166 kPa), ultra-stretchability (>1600 %) and low hysteresis (<10 % at 1000 % cyclic tensile strain). The resultant hydrogel strain sensor shows ultra-high sensitivity, wide strain sensing ranges of 2-1600 %, and excellent durability and reproducibility. Finally, this strain sensor can be used as wearable sensor to monitor vigorous human movement and fine physiological activity, and services as bio-electrodes for electrocardiograph and electromyography monitoring. This work provides new horizons to design conducting polymer hydrogels for advanced sensing devices.