A 2.7-μm-thick robust, permeable, and antifreezing hydrogel electrode for long-term ambulatory health monitoring

Adaptable hydrogel bioelectronics that sustain long-term, uninterrupted operation are critical for early disease diagnosis and personalized health care. However, conventional hydrogel electrodes suffer from mechanical fragility, rapid dehydration, freezing, and poor comfort because of thickness-induced interfacial gaps. We report a 2.7-micrometer-thick robust, permeable, and antifreezing hydrogel electrode for high-quality 8-day electrophysiological monitoring under everyday scenarios. The ultrathin electrode is fabricated using gelatin hydrogels with temperature-controlled phase change properties reinforced by nanomesh while incorporating lithium chloride, and a binary solvent achieves antifreezing and antidehydration characteristics. The design minimizes flexural rigidity, resulting in high interfacial adhesion energy with human skin, and enhances gas (air, oxygen, and carbon dioxide) permeance and water vapor transmission rate. Consequently, the ultrathin hydrogel electrode exhibits high biocompatibility, superior wear comfort, and minimized motion and sweat artifacts, enabling reliable, uninterrupted, wireless health monitoring over eight consecutive days across various real-life activities and adaptation to cold environments.