Highly Flexible, Freezing-Resistant, Anisotropically Conductive Sandwich-Shaped Composite Hydrogels for Strain Sensors

Anisotropically conductive hydrogels have promising applications in artificial intelligence and wearable flexible electronics. However, for conductive hydrogels, the integration of comprehensive properties, such as high electrical conductivity, strong moisture retention, and high mechanical properties, is very important. In this article, sandwich-shaped anisotropically conductive hydrogels were constructed with a conductivity of up to 1.5 S/m. The difference in conductivity along the different directions is about a factor of 6. The formation of dynamic coordination bonding enhances the cross-linked network between poly(acrylic acid) and Nd3+, which causes the hydrogels to have excellent self-healing properties and fatigue resistance, with a self-healing efficiency of up to 90%. The middle layer of the hydrogels is compounded with nanographene, which cuases the hydrogels to have good mechanical properties, such as ultrastretchability (∼1930%) and high strength (∼0.7 MPa). The binary solvent consisting of glycerin and water gives the hydrogels an excellent moisturizing and antifreezing function. It maintains good flexibility and conductivity even at −18 °C. Based on the rapid response and high sensitivity, the sandwich-shaped hydrogel strain sensors can detect human motion (such as knuckle motion, wrist movement, etc.), showing great application potential in flexible sensors.