Textile-Enabled Highly Reproducible Flexible Pressure Sensors for Cardiovascular Monitoring

Flexible piezoresistive sensors (FPS) with high reproducibility and hysteresis-free pressure response are highly desirable for various emerging biomedical applications. In this work, the potential of using regularly interlaced textile materials to achieve high-repeatability and low-hysteresis FPS is explored. It is found that the structural flexibility and surface regularity of knitted fabric structures can in general provide reproducible pressure response; however, response fluctuations and hysteresis are still present due to the inevitable inelastic deformation of the textiles. To address this limitation, carbon black particles and polyvinylidene fluoride are introduced in the knitted fabric as the electrical and mechanical interconnects, respectively, between the fibers. Through composition optimization, the pressure response variation is reduced to below 2% and the hysteresis loop deviation is decreased to below 10% for single sensors. The performance variation among multiple sensors is as low as 5%, much smaller than the 33% variation of the sensors made with nonwoven fabrics. Utilizing the high sensor repeatability, sensor arrays and multisite sensor network are successfully realized for monitoring superficial temporal artery pulse pressure and pulse wave velocity, which demonstrate the potential of using wearable sensing systems for multifunctional cardiovascular monitoring.