Strain-driven negative resistance switching of conductive fibers with adjustable sensitivity for wearable healthcare monitoring systems with near-zero standby power.

Recently, one of the primary concerns in e-textile-based healthcare monitoring systems for chronic illness patients is reducing wasted power consumption as the system should be always-on to capture diverse biochemical and physiological characteristics. However, the general conductive fibers, a major component of the existing wearable monitoring systems, have a positive gauge-factor (GF) that increases electrical resistance when stretched, so that the systems have no choice but to consume power continuously. Herein, we develop a twisted conductive fiber-based negatively responsive switch-type (NRS) strain-sensor with an extremely high negative GF (resistance change ratio ≈ 3.9 × 10 8 ) that can significantly increase its conductivity from insulating to conducting properties. To this end, a precision cracking technology is devised, which could induce a difference in the Young's modulus of the encapsulated layer on the fiber through selective ultraviolet (UV)-irradiation treatment. Owing to this technology, the NRS strain-sensors could allow for effective regulation of the mutual contact resistance under tensile strain while maintaining superior durability for over 5000 stretching cycles. For further practical demonstrations, three healthcare monitoring systems (E-fitness pants, smart-masks, and posture correction T-shirts) with near-zero standby power are also developed, which open up advancements in electronic textiles by expanding the utilization range of fiber strain-sensors. This article is protected by copyright. All rights reserved.