PVA-Based Hydrogels With Engineered Surface Roughness for Triboelectric Wearable Sensors

The rapid growth of wearable devices for healthcare monitoring and portable consumer electronics has driven the demand for new sensors that are lightweight, flexible, and capable of real-time, continuous monitoring. Wearable sensors must conform to the human body and enable personalized, accessible health diagnostics beyond traditional point-of-care testing. The wearable sensor market is expected to grow significantly, from U.S. $1.6 billion in 2023 to U.S. $4.2 billion by 2028. Hydrogel-based wearable sensors, particularly those using polyvinyl alcohol (PVA), are promising candidates due to their flexibility, biocompatibility, hydrophilicity, and tunable electrochemical and mechanical properties. Triboelectric nanogenerators (TENGs) convert low-frequency mechanical energy into electrical energy by contact electrification between materials with different electronegativities. Hydrogel-based TENGs combine hydrogels’ mechanical and ionic properties with triboelectric effects to create self-powered, wearable sensors for monitoring human motion, pressure, and physiological signals. Surface roughness of PVA hydrogels significantly affects triboelectric sensor performance by increasing the contact area and enhancing charge generation, thus improving sensitivity and output. Optimizing surface roughness, hydrogel composition, and mechanical properties is crucial for developing high-performance wearable triboelectric sensors. In this study, PVA hydrogels with optimized surface roughness were fabricated using silicone rubber templates with varying porosity. The resulting single-electrode TENGs (S-TENGs) were tested as pressure sensors, with the best sensor achieving a sensitivity of 12.78 × 10^−3 nC/Pa in the 20160 Pa range. For wearable applications, safer hydrogels were developed by replacing sulfuric acid (H2SO4) with potassium chloride (KCl), making the devices more suitable for biomedical uses. A wearable sensor prototype based on this optimized PVA hydrogel demonstrated effective human motion detection, showcasing its potential for healthcare monitoring.