High strength, anti‐freezing, and conductive poly(vinyl alcohol)/urea ionic hydrogels as soft sensor

Abstract Hydrogel‐based sensors with excellent flexibility and stretchability have received extensive attention. However, fabricating anti‐freezing, high‐strength, and conductive hydrogel‐based sensors remains a significant challenge. A stretchable sensor with high strength and anti‐freezing herein is constructed using poly(vinyl alcohol)/urea (PVA/urea) ionic hydrogels. The PVA/urea ionic hydrogels were prepared by a simple strategy of soaking the freeze–thawed PVA hydrogels in sodium citrate (Na 3 Cit) water/urea aqueous solutions. The presence of Na 3 Cit in the hydrogel produces hydrophobic aggregation, endowing the PVA/urea ionic hydrogel with high mechanical properties (~1.51 MPa) and makes the hydrogel have high strain gauge factors (GF = 1.94). The synergistic effect of Na 3 Cit and urea endows the PVA/urea ionic hydrogel with anti‐freezing properties (~−20°C). The obtained sensors have excellent stability (100 cycles at ε = 85%) and could detect various human activities even at −20°C. More importantly, joint motion can be monitored wirelessly via Bluetooth at −20°C. This work provides a feasible method to construct anti‐freezing, high‐strength, and conductive hydrogel. It paves the way for versatile applications in human‐motion detection, intelligence device, and biomimetic skin.