A highly resilient and ultra-sensitive hydrogel for wearable sensors

Conductive hydrogels have drawn increasing attention, but their applications are severely hindered due to insufficient sensitivities at tiny strains and poor recovery ratio upon external loads. Herein, a poly(vinyl alcohol)/aluminum sulfate composite hydrogel (T-PVA-Al) was designed to address this issue by introducing aluminum sulfate into poly(vinyl alcohol) aqueous solution, followed with three freezing–thawing cycles. The triply dynamic knots (hydrogen bonds, crystalline regions, and coordination interactions) worked in tandem to achieve high resilience (94% recovery ratio after 100 cycles) and fatigue resistance. Remarkably, the introduction of the immobile Al 3+ cation and free sulfate (SO 4 2− ) anion endowed the T-PVA-Al hydrogel with outstanding sensitivity (a gauge factor=13.9, at 0.2% strain). It could precisely and quickly monitor external stress as low as 0.5 kPa, superior to most conductive hydrogels. Notably, the hydrogel sensor possessed the capacity to precisely and reliably detect subtle variations, for example, gentle finger touching, making it an ideal candidate for human-motion detections, artificial skins, and wearable devices.