Physical Poly(vinyl alcohol)–Tannic Acid/Liquid Metal Composite Hydrogels for Degradable Strain Sensors

Liquid metal (LM) hydrogels have emerged as promising materials for next-generation flexible electronic devices. The inherent dynamic recyclability of LM makes it particularly attractive for the development of degradable electronic devices. However, existing LM hydrogels predominantly rely on chemically cross-linked polymer networks, where nondegradable networks significantly hinder the release of LM droplets from the hydrogel matrix and subsequent recycling. Herein, we propose a facile and versatile strategy to prepare a physically cross-linked poly(vinyl alcohol)–tannic acid/LM composite hydrogel (PVA-TA/LM) using an ethanol evaporation-induced gelation process. In this approach, ethanol temporarily disrupts PVA-TA cross-linking to form a homogeneous solution, enabling uniform mixing with the LM dispersion. Subsequent evaporation of ethanol allows the reestablishment of hydrogen bonds between PVA and TA, resulting in a dynamic PVA-TA/LM composite hydrogel. This composite hydrogel exhibits excellent mechanical properties, good conductivity, and self-healing capabilities. As a wearable strain sensor, it can monitor human physiological signals in real time from both minor and significant deformations. Notably, the composite hydrogel fully dissolves in dimethyl sulfoxide (DMSO) upon disrupting intermolecular hydrogen bonds, facilitating hydrogel degradation and LM recycling. This PVA-TA/LM hydrogel provides a promising platform for designing degradable devices, with potential applications in flexible electronics, health monitoring, medical diagnostics, and beyond.