Network cracks-based wearable strain sensors for subtle and large strain detection of human motions

As an imitation of human skin's tactile sensing ability, flexible and stretchable strain sensors are highly desirable because of their various applications in health monitoring, robotics, and human-machine interfaces. However, it is still a big challenge to fabricate strain sensors with both high sensitivity and broad sensing range. Herein, we report a simple, low cost and scalable fabrication strategy to construct high performance strain sensors based on network cracks formed in multilayer carbon nanotubes (CNTs) films/polydimethylsiloxane (PDMS) composites. The microscopic thickness of multilayer CNTs can be precisely controlled to tune the formation of network cracks in CNTs films/PDMS composite, which is critical for simultaneously amplifying the sensitivity signal and sensing range of strain sensors. The optimized CNTs films/PDMS composite under appropriate stretching would fracture into gaps, islands, and bridges connecting separated islands. The formed network cracks easily, resulting in both high gauge factor (maximum value of 87) and a wide sensing range (up to 100%) of the strain sensor, which allows the detection of strain as low as 0.007% with excellent stability (1500 cycles), making it suitable for both subtle and large strain detection, including subtle signals of artery pulses, music vibration and large scale motions of joint bending.