PVA/CS-based multifunctional hydrogel strain/gas flexible sensor for health monitoring

Flexible sensing materials have emerged as pivotal tools for human health monitoring and motion detection. However, single-functional flexible sensors currently suffer from insufficient versatility to address complex detection demands, particularly in multifaceted application scenarios such as real-time physiological signal monitoring and environmental gas sensing. Herein, a strategy of using PVA and CS as matrix materials is reported to fabricate strain/gas multifunctional flexible hydrogels, which are endowed with ionic conductivity and mechanical robustness via immersion in LiCl electrolyte solution. The as-prepared PVA 7 /CS 3 -LiCl 1.5 hydrogel exhibited remarkable strain sensitivity with response values of 6.5 % (tensile) and − 24 % (compressive) at 8 % strain. After 200 cycles of stretching, the relative resistance remained stable, demonstrating superior mechanical stability and cyclic durability. And relative resistance change (ΔR/R₀) showed linear dependence on strain, with gauge factors (GFs) of 0.45 (1–7 % strain), 2.66 (7–10 % strain), and 0.93 (10–90 % strain), respectively. Optimal performance was achieved at 3 wt% CS and 1.5 mol/L LiCl, where the hydrogel exhibited a 2.5 % response to 20 ppm acetone with 5-fold higher selectivity than benzene, ethanol, and ammonia. These multifunctional hydrogels enable versatile room-temperature applications, particularly for human physiological signal monitoring, offering promising strategies for sensing materials in complex environments.