Highly Conductive and Freeze-Resistant Hydrogel Reinforced by Poly(vinyl alcohol) and Tannic Acid Skeleton via Calcium Chloride Treatment for Multifunctional Sensors

Conductive hydrogel-based strain sensors have garnered considerable research interest across diverse application fields. Nevertheless, most conventional conductive hydrogels exhibit relatively high rigidity owing to the polymerization of conductive polymers, which not only compromises the wearing comfort but also raises environmental concerns due to their nonbiodegradable nature. To address these limitations, the incorporation of natural polymeric compounds into hydrogel matrices has attracted increasing research attention. In this work, we developed a low-cost, multifunctional, eco-friendly and highly applicable PVA-based conductive hydrogel (denoted as PBTC) via a facile aqueous synthesis route, using poly(vinyl alcohol) (PVA,1.20 g) and tannic acid (TA,0.06 g) as the skeletal framework, calcium chloride (CaCl 2, 2 mL, concentration 0.4 g/mL) as the conductive ionic source, and boric acid (B(OH) 3, 2.57 g) as the crosslinking agent. The as-prepared PBTC hydrogel demonstrates outstanding comprehensive properties, including exceptional stretchability (400%), high tensile strength (714 kPa), favorable toughness (1300 kJ/m –3 ), excellent ionic conductivity (9.47 S/m), as well as remarkable antifreeze performance and long-term stability. Leveraging these merits, a wearable strain and sweat sensor with high sensitivity (gauge factor, GF = 2.56) and superior cyclic stability was fabricated, which enables convenient real-time monitoring of physiological signals, such as human motions and sweat biomarkers, over a wide strain range.