Flexible Strain Sensors Based on Ag/CNT/TPU Multi-Level Conductive Network With High Sensitivity and Wide Sensing Range

Flexible strain sensors, owing to their stretchability, tunable mechanical properties, and biocompatibility, hold great promise for electronic skin and human-machine interaction devices. However, material and structural limitations often preclude the simultaneous achievement of high sensitivity and a wide detection range, thereby constraining their practical application. In this study, we first used high-frequency ultrasound to develop a Carbon Nanotube/Thermoplastic Polyurethane (CNT/TPU) composite fiber membrane on electrospun TPU, and then printed a conductive silver paste pattern onto its surface to fabricate an Ag/CNT/TPU strain sensor. This sensor features a hierarchical conductive network, comprising a densely packed silver paste layer overlying a CNT-modified TPU fiber network. Benefiting from the synergistic interaction between these two levels, the sensor exhibits a maximum gauge factor of 2711.3, a broad working range of 0%–400%, ultrafast response and recovery times, and excellent long-term stability. Finally, we demonstrated its utility in monitoring human motion, from small-amplitude finger bending to large-range knee flexion, and successfully employed it to drive a complex bionic hand, thereby advancing the use of flexible strain sensors in human-machine interaction applications.