Multifunctional Double-Network Self-Healable Hydrogel and Its Application to Highly Reliable Strain Sensors

Self-healable hydrogels present an emerging capability in energy harvesting, drug-release agents, artificial skin, and tissue engineering. Despite the various advantages of hydrogels, their low thermal stability, dehydration resistance, and mechanical properties hinder their practical applications. Herein, we introduced glycerol, 1,2,3,4-butanetetracarboxylic acid (BTCA), and sodium polyacrylate (SPA) into a hydrogel composed of poly(vinyl alcohol) (PVA)/agarose/borax. This resulted in the fabrication of a dual network hydrogel (DNH) that integrates attractive properties such as self-healing properties induced without physicochemical stimuli, stretchability, dehydration resistance, anti-drying capability, or anti-freezing capability. The DNH developed in this study maintains flexibility after storage for 1 h at -20 °C and 77.3% of its original weight after storage at 50 °C for 168 h, indicating its superior anti-freezing capability and water retentivity along with excellent self-healing properties. In addition, by blending carbon nanotubes (CNTs) to impart electrical conductivity, we have demonstrated that the CNT-embedded DNH can be successfully applied as an adhesive conductive medium for a stimulus-sensitive sensing channel of strain sensors, one of the key prospects of wearable electronic skins. In particular, the CNT-embedded DNH-based strain sensor can monitor human motion efficiently when attached to human skin without any skin trouble, even after being attached to the skin for several days. Our study can open an avenue for exploring core conductive adhesive hydrogel materials for next-generation wearable electronic devices.