Highly sensitive LIG/MWCNTs flexible strain sensor enabled by fingerprint-inspired microcrack engineering

Flexible strain sensors are essential components of wearable electronic devices. However, simultaneously achieving high sensitivity, stable electrical conductivity, a wide working strain range, and controllable structural fabrication remains a major challenge. In this study, a laser-induced graphene/multi-walled carbon nanotube (LIG/MWCNTs) composite conductive network regulated by fingerprint-inspired microcracks was fabricated through laser direct writing. MWCNTs were incorporated into a poly (amic acid) precursor to improve the continuity and stability of the conductive network, while regularly arranged fingerprint-inspired microcracks were predesigned within the sensing region to amplify strain-induced changes in the electrical contact state. The resulting sensor exhibited a distinct piecewise strain-response behavior, with gauge factors of 30.86, 116.59, and 864.66 over the strain ranges of 0-10%, 10-30%, and 30-40%, respectively. The response and recovery times were approximately 37 and 35 ms, respectively. Moreover, the sensor maintained good repeatability after 1,500 consecutive loading-unloading cycles. Human-joint motion tests demonstrated that the sensor generated clear and reproducible resistance responses to the bending motions of the elbow, wrist, and fingers. This study presents a controllable microcrack-engineering strategy for improving the sensing performance of LIG-based flexible strain sensors and provides a new design approach for wearable human-motion monitoring.