Fabrication and Performance of Nano-Silver Conductive Ink-Based Flexible Wearable Sensors

To address the challenges in morphology control, sintering efficiency, and the underdevelopment of flexible sensors in the scalable application of nanosilver conductive materials, this study proposes a method for preparing strain sensors based on silver nanoparticles (AgNPs). Specifically, AgNPs were synthesized by a chemical reduction method, and they were compounded with polyimide (PI) films to prepare conductive films and then sintered. We compared high-temperature and chemical sintering, finding that chemical sintering achieved a low resistivity of 1.356 × 10–5 Ω·m with significantly reduced energy consumption. An optimized conductive ink (AgNI) formulation (20% AgNPs, 48% H2O, 16% EG, 16% glycerol) exhibited a resistivity of 1.05 × 10–5 Ω·m. The single-layer (SLSS) and double-layer (DLSS) strain sensors were fabricated through multilayer printing and chemical sintering. The sensors exhibit a fast response time (0.17 s), high strain sensitivity (R > 0.97, GF = 5.2–10), good stability, and a broad strain range (0–15% tensile, 30°–150° bending, 5–30 N pressure). The sintering process synergistically enhanced the microstructure by promoting AgNPs fusion. The sandwich-structured single- and double-layer sensors effectively improved the bending/tensile/pressure response performance, demonstrating application potential in human activity monitoring (such as finger and elbow bending/stretching, plantar pressure, and other major joint movements). This study provides a valuable reference for the development of flexible sensors.