Wearable strain sensor based on double network PVA/SA/CNT hydrogel for reliable electrocardiography and motion monitoring

Hydrogel-based wearable devices have attracted tremendous interest in health monitoring, the development of more compatible, effective, and stable sensing material is one of the most daunting challenges. In this work, the poly (vinyl alcohol)/sodium alginate/carbon nanotubes (PVA/SA/CNT) composite hydrogel was prepared, with the formation of PVA/SA double crosslinking network and hydrogen bonds between CNT and PVA. The synergistic enhancement effect of SA and CNT on the PVA hydrogel has been investigated systematically, and the hydrogel with PVA:SA ratio of 9:1 and CNT concentration of 5 mg/mL exhibit optimal comprehensive performance, characterized with high stretchability (∼346 %), good elastic recovery, and anti-fatigue stability over 1000 cycles at 30 % strain. The optimal PVA/SA/CNT hydrogel was applied as the strain sensor for human motion demonstrating sensitive response not only to tiny deformations (such as facial muscle contractions and throat swallowing motions), but to large-range joint flexions (such as finger, wrist and knee), with a low detection limit even under a very slight strain of 0.4 %. Besides, compared to the commercial dry electrodes, the hydrogel skin-like electrodes achieved a significantly elevated signal-to-noise ratio (SNR) from 7.5 dB to 18.2 dB for the electrocardiography monitoring. The study provides new insights into structural design strategies for flexible sensing materials and wearable device.