Researchers from Qingdao University, Northeast Normal University, and Heze University have developed a novel dual-structure silver (Ag)/polyurethane (PU) fiber-based strain sensor that offers tunable sensitivity and strain insensitivity, addressing a critical challenge in the field of flexible electronics. The study, published in Engineering, presents a mechanical pre-stretching strategy that enables precise regulation of strain sensitivity and sensing range through controlled substrate deformation.

The development of fiber-based strain sensors has gained significant attention due to their intrinsic compliance and textile compatibility, making them suitable for a wide range of applications from health diagnostics to motion tracking. However, achieving both ultra-high sensitivity and stable signal transmission in a single sensor has been a persistent challenge. The research team overcame this limitation by integrating wet spinning and interfacial metal ion deposition (IMID) techniques to fabricate Ag@PU_x fibers. These fibers exhibit distinct sensing performances based on whether they have undergone pre-stretching treatment.
For fibers without pre-stretching, the Ag layer forms a microcrack-dominated architecture, resulting in high sensitivity with a gauge factor (GF) of 7.7 within a strain range of 40%–46%. This sensitivity is attributed to the strain-induced crack propagation, which disrupts conductive paths and increases resistance. In contrast, pre-stretched fibers develop a microscale conductive network, characterized by exceptional electrical stability and strain insensitivity. These fibers maintain a high quality factor (Q) of 10.1 at 50% strain, with minimal resistance change (ΔR/R₀ < 0.03) even under 360° torsional deformation.

The mechanical pre-stretching strategy induces a pre-compressive state in the Ag layer during deposition. Upon releasing the pre-stress, the Ag layer undergoes brittle fracture, forming fragmented Ag islands that stack to create a microscale structure. This structure ensures the integrity of conductive paths through hierarchical structural sliding and crack-bridging mechanisms, enabling stable electrical signal transmission even under complex strain conditions.

The Ag@PU_x fibers demonstrate remarkable potential for various applications, including human motion monitoring, voice recognition, and gesture detection. The strain-sensitive fibers can accurately capture subtle movements and physiological signals, making them ideal for wearable health monitoring devices. Meanwhile, the strain-insensitive fibers can serve as stable conductors for signal transmission in smart garments and thermal therapy belts.

Furthermore, the Ag@PU_x fibers exhibit additional functionalities such as electrical heating, antibacterial properties, and electromagnetic shielding. These multifunctional characteristics make the fibers highly suitable for developing next-generation wearable devices that integrate health management, thermal therapy, and electromagnetic protection.

The study highlights the versatility and adaptability of Ag@PU_x fibers, offering a promising approach for the development of flexible, multifunctional electronics tailored to specific application requirements.

The paper “Microcrack/Microscale Decorated Fiber-Based Electronics for Waist Rehabilitation,” is authored by Feiyu Tong, Jingmin Shi, Qi Jiang, Ming Li, Ruidong Xu, Ganghua Li, Yuanyuan Liu, Xinyu Zhang, Jinfeng Yang, Mingwei Tian, Yutian Li. Full text of the open access paper: https://doi.org/10.1016/j.eng.2025.07.004. For more information about Engineering, visit the website at https://www.sciencedirect.com/journal/engineering.