Robust and Adhesive Poly(vinyl alcohol) Hydrogel with High Transparency and Antifreeze Properties for Strain Sensors

Although the use of conductive hydrogels in wearable and flexible strain sensors has received a lot of attention, their usefulness has been hindered by issues such as low strength, inadequate adhesion, and sensitivity to freezing. In this study, carboxyl-modified methacrylated PVA (PGC) was first synthesized using a two-step process involving the grafting of a -C═C- double bond and carboxyl group onto PVA chains. Then, poly(vinyl alcohol) hydrogel with robust mechanical properties, strong adhesion, and freeze resistance was obtained by using dimethyl sulfoxide (DMSO) and water (H₂O) as the binary solvents via photopolymerization of PGC solution. The hydrogel exhibited good compressive strength (590.38 ± 63.28 kPa, 33.79 ± 4.45 kJ/m³ at 90% strain) and tensile strength (24.55 ± 4.35 kPa). Most notably, the hydrogel demonstrated excellent adhesion properties (302.02 ± 50.52 J/m²), enabling stable adhesion to simulated biological surfaces. Furthermore, the hydrogel was highly transparent (>95%) with a minimal amount of DMSO (volume ratio of DMSO/H₂O was 2:8). Additionally, the hydrogel displayed excellent antifreeze characteristics, which were facilitated by interactions between DMSO and water. Based on these characteristics, the hydrogel presented excellent sensitivity to detect microexpression signals, which made it potentially suitable for use in multifunctional wearable sensors.