Construction of dual conductive networks based on material jetting for high-performance flexible strain sensors

Flexible strain sensors convert external mechanical stimuli into corresponding electrical signals, offering broad application prospects in electronic devices. However, achieving both a wide operating range and high sensitivity remains a key challenge. Material jetting (MJ) holds significant potential for sensor fabrication due to its con- tactless, maskless, and high-resolution printing process. Herein, we developed a flexible strain sensor with dual conductive networks, consisting of a polyvinyl alcohol/multi-walled carbon nanotubes (PVA/MWCNT) substrate layer and an overlying poly(3,4-ethylenedioxythiophene) polystyrene sulfonate/MWCNT (PEDOT:PSS/MWCNT) layer patterned and deposited layer by layer using a typical MJ technology, aerosol jet printing (AJP). Owing to the synergistic effect between the printed circuit and the flexible substrate, the meander-shaped sensor, fabricated under optimized 16-layer printing, achieved a wide strain response range of 0.6-80 % and high sensitivity with a gauge factor (GF) of 31.2. Additionally, the strain sensor stabilized its current signal under 2000 cyclic loading conditions, demonstrating good stability. We further investigated the effect of patterned grid density on sensor sensitivity, finding that sensitivity increased with grid density initially and then decreased, reaching an impressive GF of 47.52 at a grid density of 2 x 6. Furthermore, the sensor demonstrated remarkable versatility in applications such as full-range human body motion detection, Morse code communication, and UAV flight monitoring, including real-time strain detection during takeoff and landing processes. This study highlights the potential of AJP technology for precise patterning and the fabrication of next-generation flexible strain sensors.