Anisotropic nanocomposite double network anti-freezing hydrogels with superior conductivity, high stretchability, and excellent resilience for wearable sensors

Hydrogel-based artificial ionic skin (I-skin) has gained significant attention in the fields of flexible sensor and intelligent sensing due to their skin-like physicochemical properties and sensory capabilities. Nevertheless, the simultaneous design of conductive hydrogels that exhibit high mechanical strength, exceptional ionic conductivity, and anisotropic structures remains a considerable challenge. Herein, attapulgite (ATP) nanorods-containing nanocomposite double-network anisotropic hydrogels are fabricated by using a two-step technique of primary photopolymerization followed by secondary freezing-thawing method. The synergistic effect of the first polyelectrolyte chemical network of highly charged poly(AMPS-Na) and the second physical network of polyvinyl alcohol (PVA) and ATP embedding endow the hydrogel with high tensile/compressive strength (0.73/2.85 MPa), excellent stretchability (1200 %), good toughness (2.6 MJ/m³), remarkable resilience, and unique optical anisotropy. Additionally, ZnCl₂ as an effective anti-freezing and conducting agent enhances the freezing tolerance to −102 °C and significantly improves the conductivity to 43 mS/cm. The as-prepared hydrogel-based flexible sensors show fast responsibility, widely sensing range, good durability, and excellent tensile strain/compressive deformation/temperature sensitivity. Furthermore, these flexible sensors are capable of detecting various body movements and working effectively at extremely low temperatures. Consequently, this research provides novel insights into the design of anisotropic hydrogel materials for high-performance wearable flexible devices.