3D printed highly elastic strain sensors of multiwalled carbon nanotube/thermoplastic polyurethane nanocomposites

3D-printable, flexible, and conductive thermoplastic-based material was successfully developed for strain sensing applications. Thermoplastic polyurethane/multiwalled carbon nanotube (TPU/MWCNT) were compounded, their filaments were extruded, and the sensors 3D printed using fused deposition modeling. Mechanical, electrical, and piezoresistivity behaviors were investigated under monotonous and cyclic loadings. MWNCTs enhanced the printing capability of TPU by increasing its stiffness. Very modest decreases were observed in the elasticity modulus of printed nanocomposites (similar to 14%, compared to that of bulk counterparts), indicating excellent interlayer adhesion and superior performance to those reported in literature. Consequently, the conductivity was largely preserved after printing, in both through-layer and cross-layer directions. The piezoresistivity gauge factors of as high as 176 were achieved under applied strains as large as 100%. A highly repeatable resistance-strain response was also obtained under cyclic loadings. The results demonstrate TPU/MWCNT as an excellent piezoresistive feedstock for 3D printing with potential applications in wearable electronics, soft robotics, and prosthetics, where complex design, multi-directionality, and customizability are demanded. (C) 2017 Elsevier Ltd. All rights reserved.