Mechanically and Functionally Resilient Piezoelectric Fiber Coils and Knots for Reliable Self-Powered Sensing

Electrospun poly(vinylidene fluoride-<i>co</i>-trifluoroethylene) (P(VDF-TrFE)) piezoelectric nanofibers are attractive for self-powered sensing owing to their flexibility and ability to convert mechanical deformation into electrical signals. However, achieving a fully electrode-integrated piezoelectric fiber coil sensor that combines high stretchability with long-term reliability remains a major challenge. Here, we present a mechanically and functionally resilient piezoelectric coil sensor enabled by a hierarchical design that unites a styrene-ethylene-butylene-styrene (SEBS)-assisted interlocked fiber-particle network with a multicomponent-doped poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS)/P(VDF-TrFE) electrode that forms a gradient interfacial layer. The fully integrated coil sensor exhibits stretchability up to 668% and maintains stable electromechanical performance under large strains and repetitive loading. The optimized sensor exhibits linear and stable piezoelectric responses to stretching, bending, and compression stimuli, enabling quantitative multimodal mechanical sensing, which is further validated by supervised machine learning classification. In addition, its adaptive knot configurations, such as reef and grief knots, maintain consistent self-powered output under high loads, demonstrating structural adaptability for various stress-monitoring applications. This work establishes a fiber-based self-powered sensing platform that achieves simultaneous mechanical recoverability and electrical robustness through a hierarchical resilient design, offering a versatile route toward wearable healthcare, soft robotics, and surgical assistance.