Development of ultrastretchable and skin attachable nanocomposites for human motion monitoring via embedded 3D printing

Accurate monitoring of human motion holds enormous promise for broad applications, such as athlete training, rehabilitation, health monitoring, and gaming. Wearable sensors are required to have intimate contact with the skin, wide sensing range, high sensitivity, and outstanding durability. In this paper, we report ultrastretchable and wearable strain sensors that are fabricated using embedded 3D printing technology. Piezoresistive sensitivity of the 3D printed sensors is optimized by tailoring the loading of carbon nanotubes, curing temperature, and 3D printing parameters to impart beneficial alignment of nanoparticles in the strain sensing direction. The optimized sensors demonstrate an average gauge factor in a wide strain range as high as 3.4, a low elastic modulus of 83.4 kPa, and a 535% maximum tensile strain before fracture, allowing long-lasting, comfortable, and reliable contact with the human skin. The 3D printed sensors are used to detect skin elongation during limb movement, showing excellent dynamic and step sensing functionalities with negligible strain rate dependence and superb durability.