Highly stretchable and ionically conductive PVA/PAM-based piezoelectric hydrogel for wearable bioelectrodes and fully flexible integrated sensor

The CLZPP hydrogel with zwitterionic surfactant has high conductivity (16.19 S/m) and large tensile strain of 1083.76%. • CLZPP hydrogel electrodes show higher signal-to-noise ratios than commercial ones in EMG, ECG, and EOG monitoring. • The integrated device fabricated via layered pouring and stepwise cross-linking shows stable output over 1000 cycles. Flexible self-powered devices can operate without external power supplies and are therefore attractive for wearable health monitoring. Here, cocamidopropyl betaine (CAPB), LiCl, and ZnO nanoparticles were incorporated into a poly(vinyl alcohol)/polyacrylamide (PVA/PAM) double-network matrix to form a highly conductive and stretchable hydrogel. The optimized CAPB/LiCl/ZnO/PVA/PAM (CLZPP) hydrogel achieved a tensile stress of 116.41 kPa and a tensile strain of 1083.76%. Its toughness and ionic conductivity reached 0.66 MJ/m 3 and 16.19 S/m, respectively. It also exhibited sensitive strain responses and reliable cycling stability. As a wearable sensor, the hydrogel detected motions of the finger, wrist, knee, and neck, together with weak physiological signals associated with speech. As a bioelectrode, it recorded electromyographic (EMG), electrocardiographic (ECG), and electrooculographic (EOG) signals with performance comparable to commercial electrodes and higher signal-to-noise ratios. An all-hydrogel, fully flexible integrated piezoelectric sensor was then fabricated by sequential casting and stepwise crosslinking. The integrated piezoelectric sensor generated stable voltage through the piezoelectric response of ZnO, converting deformation-induced mechanical energy into electrical energy for self-powered sensing. Piezoelectric signatures produced by contact with different materials were further combined with machine learning to enable rapid material classification. This work provides a strategy for jointly optimizing the mechanical, electrical, and piezoelectric properties of hydrogels and supports their use in self-powered wearable health monitoring and intelligent human-machine interfaces. Download: Download high-res image (208KB) Download: Download full-size image