Ultrathin and permeable silver nanowires/polyvinyl alcohol epidermal electrode for continuous electrophysiological monitoring

Abstract

The development of ultrathin and highly permeable epidermal electrodes is critical for continuous health monitoring, enabling early diagnosis and effective disease management. However, conventional epidermal electrode materials and designs face significant challenges in achieving the necessary combination of ultrathin geometry, gas permeability, seamless adhesion, and high stretchability for long-term wearability. To address these issues, we report an ultrathin gel electrode consisting of a polyvinyl alcohol gel and silver nanowires with a thickness of only 14.7 μm. The high electrical conductivity and nanomaterial reinforcement of silver nanowires, and the flexibility, biocompatibility, and adhesion of polyvinyl alcohol provide silver nanowires/polyvinyl alcohol with excellent performance. This composite structure synergistically combines the strengths of each component, overcoming the limitations of traditional single-material designs, resulting in excellent mechanical properties, including stretchability up to 662% strain, a tensile strength of 1.5 MPa, and a water mist-induced adhesion energy of 270.5 μJ cm⁻². Additionally, the gas permeability of the gel electrode is 113 times higher than that of a 100 μm-thick polydimethylsiloxane film, with an air permeance value of 0.03 cm_STP³ cm⁻² s⁻¹ cmHg⁻¹, resulting in enhanced humidity regulation and improved thermal comfort. In practical applications, the ultrathin silver nanowires/polyvinyl alcohol gel electrode demonstrates outstanding electrophysiological signal acquisition capabilities. Its signal-to-noise ratios for electromyography and electrocardiography match those of commercial gel electrodes, enabling continuous, high-fidelity wireless health monitoring for up to 3 h during daily activities. Furthermore, in electroencephalography measurements, the sensor reliably captures stable alpha waves with minimal background noise, underscoring its excellent real-time frequency response performance.