Hydrogel Strain Sensors Based on Ordered Iron Nanowires for Human-Machine Interaction

High-flexibility strain sensors are critical components in devices, such as smart wearable devices, human-machine interfaces, and electronic skin. Hydrogel-based sensors are particularly favored due to their modulus close to that of biological tissues, high strain capacity, and biocompatibility. Iron nanowires (Fe NWs) are a typical example of metal nanowires (NWs); compared to other metal NWs, they offer high conductivity, relatively low cost, and high saturation magnetization. The ferromagnetic nature of Fe NWs allows for the manipulation of their orientation using magnetic fields during sensor fabrication, thereby simultaneously affecting the sensor's mechanical and sensing properties. In this article, Fe NWs were incorporated into acrylamide (AM) and polyvinyl alcohol (PVA) to enhance the sensor's conductivity and extend its strain capacity, achieving a maximum strain at break of up to 1038.7%. The resulting sensors exhibit a low detection limit of 0.3% and a fast response time of 87 ms, demonstrating stable reactivity to signals generated by human movements, such as finger, wrist, elbow, and knee bending. Finally, a demonstration involving wireless control of a smart vehicle showcased the potential of these sensors in human-machine interaction applications.