Biodegradable Polyurethane Fiber-Based Strain Sensor with a Broad Sensing Range and High Sensitivity for Human Motion Monitoring

To date, a majority of polymer-based wearable flexible strain sensors are non-biodegradable, which inevitably causes environmental pollution at the end of their service life. In this work, biodegradable polyurethane (BPU) was synthesized and then processed with carbon nanotubes (CNTs) via wet spinning into BPU/CNT composite fibers used as strain sensors. The synthesized BPU showed excellent biodegradability with a 19.45% weight loss in 42 days in a phosphate buffered saline (PBS) solution. Compared with previously reported strain sensors made from silk, cellulose, and polylactic acid, the BPU/12%CNT fibers achieved a much wider strain-sensing range (0–250%) and a high sensitivity (gauge factors of 15 at 100% strain and of 2468 at 250% strain respectively) while exhibiting reliable stability. These properties allow strain sensors based on BPU/CNT fibers and knitted fabric to be successfully used for monitoring various human motions. Moreover, biodegradability of the BPU/CNT strain sensor in a PBS solution was verified. In consequence, this work provides insights into the development of biodegradable wearable electronic devices.