Semi-Interpenetrating Highly Conductive and Transparent Hydrogels for Wearable Sensors and Gesture-Driven Cryptography

Developing conductive hydrogels that balance high conductivity, stretchability, transparency, and sensitivity for next-generation wearable sensors remains challenging due to inherent trade-offs. This study introduces a straightforward approach to fabricate a semi-interpenetrating double-network hydrogel comprising polyvinyl alcohol (PVA), polyacrylamide (PAM), and lithium chloride (LiCl) to overcome these limitations. Leveraging hydrogen bonding for energy dissipation and chemical cross-linking for structural integrity, the design achieves robust mechanical properties. The incorporation of 1 mol/L LiCl significantly enhances ionic conductivity, while also providing plasticizing and moisture-retention benefits. The optimized hydrogel exhibits impressive ionic conductivity (0.47 S/m, 113% enhancement), excellent mechanical performance (e.g., 0.177 MPa tensile strength, 730% elongation, 0.68 MJ m−3 toughness), high transparency (>85%), and superior strain sensitivity (gauge factors ~1). It also demonstrates rapid response/recovery and robust fatigue resistance. Functioning as a wearable sensor, it reliably monitors diverse human activities and enables novel, secure data handling applications, such as finger-motion-driven Morse code interfaces and gesture-based password systems. This accessible fabrication method yields versatile hydrogels with promising applications in health tracking, interactive devices, and secure communication technologies.