A highly stable auxetic braided smart yarn for seamless motion-sensing textiles

Fiber- and yarn-based strain sensors are promising for wearable biomonitoring, human-computer interaction, and robotic perception due to their simple sensing mechanisms, material flexibility, and structural adaptability. The unique deformation mechanism of auxetic structures enhances the sensitivity and comfort of one-dimensional sensors, garnering substantial research interest. In this study, we design and fabricate a structurally stable auxetic braided strain yarn sensor (ABSYS) optimized for industrial-scale automated production. The ABSYS is constructed by wrapping rigid conductive multifilament and highly elastic nylon-spandex covered yarn around an elastic core yarn in a mesh pattern using circular braiding technology. It demonstrates a pronounced auxetic effect and exceptional sensing performance. When seamlessly embedded into fabric, the ABSYS exhibits a broad working range of 2–60 %, a rapid response time of 0.018 s, and reliable stability, effectively capturing a broad spectrum of human motion. Moreover, the sensor works while maintaining wearer comfort and fabric aesthetics, offering a practical and scalable solution for next-generation strain-sensing wearables.