Durable, Breathable, and Sweat-Resistant Nanocrack-Based Fiber Strain Sensors for Joint Monitoring in Elderly Stroke Rehabilitation

Flexible fiber-based strain sensors show great promise for joint motion monitoring in stroke rehabilitation and elderly care. However, the rational design of low-cost sensors that simultaneously offer high sensitivity, excellent stability, and practical applicability is still a great challenge. In this study, multiwalled carbon nanotubes were incorporated into thermoplastic polyurethane to fabricate a coaxial fiber structure with crack effects via wet spinning. By adjusting the extrusion speed ratio between the core and sheath layers, the thickness of the fiber shell was optimized and a fine crack network was formed, enhancing both sensitivity and mechanical properties. Experimental results show that the fabricated fiber sensor exhibits a high sensitivity (strain range: 70–175%, gauge factor = 3.154), with a wide detection range (250% strain), an ultralow detection limit (<0.1%), and excellent cyclic durability (>2000 cycles). The sensor can be effectively applied to monitor human joint movements. Meanwhile, the nanocrack-based fiber sensor (NFS) exhibits excellent photothermal characteristics, strong resistance to sweat and washing, and good breathability (981.9 mm/s). Notably, the NFS enables real-time monitoring of physiological movements with Bluetooth data transmission. Furthermore, its localized photothermal effect can promote blood circulation, providing additional therapeutic value in stroke rehabilitation. These features highlight the great potential of NFS sensors in smart healthcare and wearable health technologies.