Nanostructured Copper−Nickel Alloy Coated Conductive Threads for Negative-Resistance Wearable Strain Sensing in Human Motion Monitoring

Wearable textile-based strain sensors are highly desirable for human motion tracking, physiological monitoring, and rehabilitation applications. However, their practical deployment requires the development of textiles that possess a synergistic combination of high electrical conductivity, mechanical durability, and stable electromechanical performance. Herein, nanostructured Cu−Ni alloy-plated cotton threads were fabricated via a scalable four-step electroless plating process and evaluated as wearable textile strain sensors. The deposited Cu−Ni alloy nanoparticles form an interconnected nanoscale conductive network, facilitating efficient charge transport and improved environmental stability. The resulting conductive thread exhibits an electrical conductivity of ∼3.034 × 104 S/m and a distinct reversible negative resistance response under tensile strain. This unique sensing behavior originates from a strain-induced densification mechanism, where tensile deformation enhances interparticle and interfiber contacts to improve overall electrical conductivity. Unlike conventional metal-coated textile strain sensors governed by crack propagation, this contact-dominated mechanism ensures stable electromechanical performance with negligible baseline drift over 4500 continuous cycles. Furthermore, the sensor achieves a gauge factor of −3.28 (0−4% strain range) and −4.60 (4−9% strain range). A comparative analysis with commercial silver conductive threads highlights the distinct strain-responsive characteristics of the nanostructured Cu−Ni alloy network. Finally, the fabricated sensors successfully capture localized body motions, including finger and wrist flexion, demonstrating their potential for wearable healthcare, rehabilitation monitoring, and smart textile applications. These findings establish nanostructured Cu−Ni alloy conductive networks as a cost-effective, scalable, and mechanically resilient platform for next-generation textile electronics.