3D printable resin/carbon nanotube composites for wearable strain sensors: Enhancing mechanical and electrical properties

Electrically conductive composite materials are widely used for several applications, particularly flexible strain sensors for wearable electronic devices to detect human motions or apply to soft robotic technologies. Among the carbon nanotube (CNT) composites for strain sensors, the CNT composites with polypyrrole (PPy) have been scarcely found for electromechanical property improvement via digital light processing (DLP) 3D printing. Thus, this research presents a 3D printing fabrication of flexible polyurethane/CNT/PPy (FPU/CNT/PPy) composites for high complexity and model specifications, particularly strain sensing. The FPU/CNT/PPy composites were prepared as photopolymer resin with various proportions of the three components. The composites successfully achieved a gauge factor of 91.9 at 20 percent strain with high durability in 100 stretching-releasing cycles. More than 85% of printing accuracy was also found under the DLP 3D printing method. The small deformation of the composites could be detected during the stretching-releasing process during time-dependent testing. Examples of simple human activity and complex spring motion could be successfully detected due to the high responsibility and reproducibility of the finger motion. The composites mentioned in this study could reach the field of strain sensing and can further be applied to other fields such as healthcare and soft robotics.