A Highly Stretchable and All-Directional Triboelectric Strain Sensor for Chronic Joint Stress Monitoring

In this work, a highly stretchable, all-directional triboelectric strain sensor patch has been newly designed and demonstrated for chronic joint stress and fatigue monitoring. The sensor encapsulates a polar array of serpentine structures of charge-generating and transporting gelatin hydrogel within highly electronegative silicone rubber. The symmetrical polar array configuration of the hydrogel, combined with triboelectrification during internal contact separation between the material pair, enables all-directional, self-powered strain sensing in the proposed patch sensor. The sensor exhibits excellent linearity and sensitivity towards diagonal (0.178 V/%), longitudinal (0.180 V/%), and lateral (0.175 V/%) direction strain, manifesting all direction behavior. This behavior of the sensor allows monitoring of complex joint movements such as clockwise and anticlockwise rotation of the wrist, making it highly applicable for determining fatigue rate and fatigue intensity in case of chronic joint stress conditions including carpal tunnel syndrome.