Functional nanocomposites for 3D printing of stretchable and wearable sensors

This paper presents highly flexible strain sensors fabricated by extrusion-based 3D printing of electrically conductive nanocomposites consisting of multi-walled carbon nanotube (MWNT)/polydimethylsiloxane (PDMS). The effects of printing parameters and nanocomposite formulation on the piezoresistive behavior of the 3D-printed sensors are investigated. Experimental results demonstrate that the 3D printing-induced alignment of MWNTs results in the enhancement of piezoresistive sensing function of the nanocomposites. Detailed analyses are performed using the optimized sensors to characterize their sensing performance, including load rate dependency, repeatability under long-term cyclic loads, and relaxation behavior. The 3D-printed strain sensors demonstrate high flexibility, stretching to 146% strain before fracture, and exhibit a linear piezoresistive response up to 70% strain with a gauge factor of 12.15. The distribution of nanotubes in the polymer and the piezoresistive mechanism of the material are explored by in situ micro-mechanical testing under a scanning electron microscope (SEM). The developed sensors are attached on gloves to monitor the motion of a human hand, demonstrating their application wearable electronics.