A Flexible, Conductive Hydrogel for Strain Sensor and Triboelectric Nanogenerator toward Human Motion Monitoring

A flexible and conductive PVA/sodium alginate hydrogel was made using the freeze/thaw method for gelation and immersing in NaCl aqueous solution for better mechanical and electrical properties. The effects of the different concentrations of NaCl aqueous solutions were systematically investigated. After optimization, the PVA/SA-3 hydrogel shared a high conductivity of 4.1 S/m and excellent mechanical properties. Additionally, the hydrogel's ability to work as a strain sensor to distinguish different human activities was also explored. Triboelectric nanogenerators (TENGs) which are used during exercise need to be flexible because the devices are frequently in a dynamic state. However, traditional electrode materials for TENGs are not flexible enough, limiting their potential applications. To address this issue, we designed a flexible TENG using the PVA/SA-3 hydrogel to work as the electrode material. Furthermore, we designed a human motion monitoring system consisting of a hydrogel-based TENG (H-TENG), a microcontroller unit, and a smartphone. The motion monitoring system can display the total steps and the cadence during exercise on the smartphone simultaneously, demonstrating its great potential in sport sensing fields.