Highly stretchable and sensitive liquid-type strain sensor based on a porous elastic rope/elastomer matrix composite structure

In this study, we present a new liquid-type strain sensor based on porous elastic rope/elastomer matrix (PER/EM) composite structure. The liquid-impregnated porous elastic rope (LIPER) was immersed into a flexible silicone matrix to fabricate the sensor, making the manufacture process easy. The effect of liquid viscosity on the hysteresis of the sensor has been understood through selecting water, ethylene glycol and hydrogel as the sensing liquids. The most attractive performance of the PER/EM strain sensor is its ability to detect both stretching and compression deformations as well as to realize temperature sensing. Simultaneously, high stretch strain over 100% and pressure up to 612 kPa can be subjected. A minimum tensile strain of 0.5% and a minimum applied pressure of 5 kPa can be detected, indicating the good sensitivity of the as-fabricated strain sensor to the subtle deformation. In particular, our devices exhibited the excellent long-term durability after completing >6000 stretching-releasing cycles (100% strain) and >10000 compression-expansion cycles (50 kPa). On this basis, the PER/EM strain sensor was successfully employed to detect the full-scale human motion ranging from swallowing to joint bending. We further made a smart insole and achieved the real-time monitoring of walking, running and jumping. Our results show that the as-fabricated PER/EM strain sensor has the great potential for the applications in healthcare, human motion monitoring and electronic skin.