Flexible, Lightweight, and Hydrophobic TPU/CNT Nanocomposite Foam With Different Surface Microstructures for High-Performance Wearable Piezoresistive Sensors

Abstract

Flexible piezoresistive pressure sensors, due to their lightweight, bendable, and highly sensitive characteristics, have been widely used in fields such as wearable devices, electronic skin, and intelligent robotics. Besides the development of various high-performance materials, the performance of these sensors is closely related to the design of their surface microstructures. Different surface microstructures can significantly enhance the sensitivity, stability, and durability of piezoresistive sensors. In this paper, three types of flexible thermoplastic polyurethane (TPU)/carbon nanotube (CNT) nanocomposite foam piezoresistive sensors with different surface microstructures and internal porous structures were prepared using supercritical carbon dioxide (sc-CO₂) foaming process. The effects of the three surface microstructures on the piezoresistive sensing performance of TPU/CNT nanocomposite foams were studied in detail. The results show that the foam sensor with a double-ridge surface microstructure exhibits significantly enhanced sensing performance, including high sensitivity (0.309 kPa⁻¹), fast response time (~40 ms), wide working range (0–80 kPa), and stability over more than 600 cycles. Additionally, the prepared flexible piezoresistive sensors can be integrated into smartwatches, fitness bands, and smart clothing, enabling real-time monitoring of heart rate, blood pressure, respiratory rate, and physical activity. This provides precise data support, demonstrating the promising application prospects of these flexible surface microstructure foam piezoresistive sensors in the future.