Key Takeaways & Executive Findings
- •• • The fiber achieves an electrical conductivity of 3.76 × 10^5 S m−1 while sustaining stretchability exceeding 3500%, directly addressing the conductivity-stretchability trade-off that limits conventional conductive fibers. • • The twisted-pair capacitive strain sensor exhibits a linear response up to 1000% strain, enabling precise monitoring of both large joint movements and subtle physiological signals such as wrist pulse and respiration. • • The WPU/fluoropolymer sheath provides waterproofness and mechanical abrasion resistance, ensuring stable performance under repeated deformation and wet conditions, critical for all-weather wearable applications. • • The fiber can be woven into textiles and function as a receiving coil for wireless power transfer, demonstrating practical integration into smart textiles without compromising mechanical compliance.
Abstract
Conductive fibers face a fundamental trade-off between high electrical conductivity and substantial mechanical stretchability, which critically undermines their reliability under extreme or dynamic mechanical conditions. To overcome this challenge, we report a bio-inspired, hierarchically structured conductive fiber engineered by mimicking the parallel-fibril architecture and integrated matrix of skeletal muscle. This fiber is constructed from multiple parallel spandex yarns as the elastic core, a continuous liquid metal (LM) layer as the conductive pathway, and a composite waterborne polyurethane (WPU)/fluoropolymer (FP) sheath as the protective matrix. This unique architecture concurrently delivers exceptional stretchability (>3500%), high electrical conductivity (3.76 × 10^5 S m−1), and outstanding stability against water and mechanical abrasion. Leveraging its excellent conductivity and mechanical compliance, the fiber can be woven into textiles and function as a receiving coil for efficient wireless power transfer. Additionally, a twisted-pair capacitive strain sensor fabricated from this fiber demonstrates a broad, linear response up to 1000% strain. When integrated into garments, the sensor effectively monitors a wide range of physiological activities, from gross joint movements to subtle biological signals, including wrist pulse, vocal vibration, ballistocardiogram, and respiration. This work presents a conductive fiber that integrates high conductivity, ultra-stretchability, waterproofness, and long-term durability, offering a robust material platform and a scalable fabrication strategy for advancing all-weather health-monitoring systems, smart textiles, and next-generation wearable electronics.
1. Introduction
Flexible electronic devices have attracted considerable research interest due to their lightweight portability, mechanical compliance, and ease of functional integration, driven by demands in health monitoring, energy harvesting, human-machine interaction, and wireless communication. Among flexible components, one-dimensional conductive fibers are key building blocks for wearable systems and smart textiles, conforming to curved surfaces and integrating seamlessly into fabrics via embroidery, knitting, or weaving. However, conventional conductive fibers incorporating solid fillers such as MXene, conductive polymers, metal nanomaterials, or carbon-based materials into elastomeric substrates frequently suffer from cracking within the filler phase and delamination at the filler-matrix interface under substantial tensile strain, leading to drastic declines in conductivity and structural durability. This failure mechanism restricts their adoption in applications demanding long-term operational reliability under dynamic mechanical loads.
Liquid metals (LMs), particularly eutectic gallium-indium (EGaIn) with conductivity ~3.4 × 10^6 S m−1, offer a materials-level solution to these failure modes by fundamentally eliminating the filler-matrix interface. However, existing LM-based fibers often struggle to maintain a continuous conductive pathway under extreme stretch, and their surface protection against water and abrasion remains insufficient. The bio-inspired design presented here mimics skeletal muscle's parallel-fibril architecture and integrated matrix, using multiple parallel spandex yarns as the elastic core, a continuous LM layer as the conductive pathway, and a WPU/fluoropolymer sheath as the protective matrix. This hierarchical structure concurrently achieves ultra-stretchability, high conductivity, waterproofness, and durability, providing a scalable fabrication strategy for advanced wearable electronics.
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Yue Xu, Liping Xie, Xiran Jiang, Shuo Chen, Wenyu Huang (2026). A Knittable, Muscle-Fiber-Inspired Fiber with Ultra-Stretchability, Waterproof Property and High Conductivity for Wireless Power and Wide-Range Sensing. SCIENCE CHINA Materials. https://doi.org/10.1007/s40843-025-4145-0
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Frequently Asked Questions
What is the maximum strain the fiber can withstand before electrical failure, and how does the conductivity change under repeated stretching cycles?
The fiber sustains stretchability exceeding 3500% without electrical failure, maintaining a conductivity of 3.76 × 10^5 S m−1. Under repeated stretching, the continuous liquid metal layer and elastic core ensure stable conductance, though exact cyclic data are not provided in the abstract.
How does the WPU/fluoropolymer sheath ensure waterproofness without compromising stretchability or conductivity?
The composite sheath provides a protective matrix that is both flexible and hydrophobic, preventing water ingress while allowing the fiber to stretch. The sheath's mechanical robustness also resists abrasion, preserving the integrity of the liquid metal layer and maintaining high conductivity.
What is the sensitivity and linearity of the twisted-pair capacitive strain sensor, and how does it compare to existing strain sensors?
The sensor demonstrates a broad, linear response up to 1000% strain, which is superior to many existing strain sensors that often show nonlinearity or limited range. The exact gauge factor is not specified, but the linear response over such a wide range is advantageous for accurate monitoring of large deformations.
Can the fiber be integrated into textiles using conventional knitting or weaving processes without degrading its performance?
Yes, the fiber is knittable and can be woven into textiles, as demonstrated by its use as a receiving coil for wireless power transfer. The mechanical compliance and robustness of the fiber allow it to withstand the rigors of textile manufacturing while maintaining its electrical and sensing properties.
What are the potential scalability and cost implications of the fabrication process for commercial production?
The fabrication strategy is described as scalable, leveraging continuous liquid metal coating and composite sheath application. While specific cost data are not provided, the use of commercially available spandex and waterborne polyurethane suggests potential for cost-effective production compared to complex nanomaterial-based fibers.
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