A Bifunctional Organic Hydrogel-Based Standalone Self-Powered Hybrid Strain Sensor Band for Rehabilitation Monitoring and Human-Machine Interfacing

Triboelectric nanogenerators (TENG) are widely adopted as self-powered strain sensors in wearable applications. However, the reported designs are limited to achieving fully standalone and stretchable all-directional strain sensors capable of generating voltage signals during stretching-releasing operations. Herein, the bifunctional (conductive and tribopositive) property of highly stretchable and shape-adaptable organic hydrogel (BOH) is investigated to develop standalone self-powered strain sensors (SPSS) having directional and omnidirectional features. The tribopositive property of BOH is verified through surface potential analyzer (0.25 kV) and Fourier-transform Infrared Spectroscopy (FTIR). While pairing with Ecoflex, BOH demonstrates comparable performance (peak power 0.522 mW at 18 M Omega) with commercially available positive materials. Therefore, BOH is strategically patterned and encapsulated within the Ecoflex to realize standalone directional and omnidirectional SPSSs. This strategy allows multiple instances of internal contact separation between pairs while stretching, owing to their elastic modulus differences. The developed SPSSs are attached to various body parts for monitoring high-range linear-rotatory joint movements to low-range verbal exercises and several rehabilitation activities without skin-induced triboelectrification. Finally, a hybridized SPSS-integrated smart band is developed and demonstrated for multipurpose real-time applications such as interactive rehabilitation, grip strength monitoring, and human-machine interfacing (HMI), highlighting its potential in next-generation wearable electronics.