Ultra-stretchable, tough, and crack-resistant polyoxometalates-composited hydrogels for wearable sensors

Hydrogels with good ionic conductivity and high stretchability hold great promise for flexible sensors, but are challenged by the low toughness and poor crack resistance, which severely limit their performance under complex mechanical conditions. Herein, we report an ionically conductive polyoxometalates (POMs)-composited hydrogel fabricated by incorporating chitosan oligosaccharide-modified silicotungstic acid (COS@SIW) nanocomplexes into a polyacrylamide (PAM) network. The incorporation of COS effectively enhances the interfacial bonding between COS@SIW and the PAM matrix through abundant electrostatic and hydrogen-bonding interactions among COS, SIW, and PAM chains, facilitating efficient stress transfer and energy dissipation. As a result, the obtained POM-composited hydrogel exhibits integrated mechanical properties, including ultrahigh stretchability (2,423%), high toughness (3.77 MJ·m^-3), and excellent crack resistance (fracture energy of 8.3 kJ·m^-2). Moreover, the hydrogel demonstrates a high ionic conductivity of 0.17 S·m^-1, attributed to the intrinsic proton mobility of SIW. The resulting hydrogels exhibit superior strain sensitivity with a wide working range, rapid response, and excellent reliability, enabling their application as wearable sensors for monitoring diverse human motions. Furthermore, the hydrogel can function as a bioelectrode for accurate and reliable detection of electrocardiogram (ECG) signals. This work provides a new strategy for designing ionically conductive hydrogels with high stretchability, toughness, and superior crack resistance, offering promising opportunities for advanced wearable sensing platforms.