## 1 Introduction  
In recent years, flexible strain sensors have gained significant attention due to their extensive applications in health monitoring [1], soft robotics [2], human-machine interaction, and biomedical engineering [3, 4]. These sensors are categorized into various types based on their working mechanisms, including resistive, piezoelectric, triboelectric, and capacitive sensors [5, 6, 7, 8]. Among them, flexible resistive strain sensors, which convert mechanical deformation into resistance signals, stand out for their high sensitivity, wide working range, and ease of signal acquisition. However, achieving a balance between high sensitivity, wide strain range, and long-term stability remains a major challenge in their development, making the design of sensors that integrate these properties a critical focus in the field. Flexible resistive strain sensors typically consist of a flexible substrate and conductive materials [9]. The substrate primarily determines the application scenarios, while the conductive materials directly influence the sensors' electrical performance. Comparedwith traditional polymer substrates, electrospun fiber membranes have garnered increased attention due to their high specific surface area, excellent mechanical flexibility, and high porosity [10]. Among these, thermoplastic polyurethane (TPU) has emerged as an ideal candidate for flexible substrates owing to its superior tensile properties, excellent elastic strain recovery, abrasion resistance, temperature tolerance, and ease of fiber formation [11]. For instance, [PERSON] et al. fabricated a flexible sensor by modifying TPU fiber membranes with polydopamine (PDA) and incorporating silver nanoparticles (AgNPs) through hot embossing technology, achieving a wide detection range and excellent stability [12]. Despite the promising performance of single conductive networks, achieving both high sensitivity and a wide strain range remains challenging. Recently, constructing synergistic conductive networks by integrating two or more conductive materials into the flexible substrate has proven to be an effective strategy to address this limitation. Studies have demonstrated that the synergistic interaction between different conductive materials can deliver superior performance that single conductive networks cannot achieve [13; 14]. For example, [PERSON] et al. used Monte Carlo simulations and percolation models to reveal the significant influence of synergy between carbon nanotubes (CNTs) and carbon black (CB) on strain sensor performance [15]. [PERSON] et al. fabricated a three-dimensional synergistic conductive network using electrospun TPU fiber membranes, multi-walled carbon nanotubes (C-MWCNTs), and PEDOT, achieving high sensitivity, a wide strain range, and exceptional durability [16]. Additionally, [PERSON] et al. developed a flexible strain sensor combining MXene, CNTs, and TPU, which exhibited a wide detection range (0-450%), ultra-low detection limit (0.05%), and high sensitivity. These studies emphasize the critical role of synergistic conductive network designs in enhancing the performance of flexible strain sensors [17]. However, the trade-off between high sensitivity and a wide strain range remains a significant challenge in sensor design. For instance, PDMS-based flexible strain sensors with Au/Ti microcracks exhibit high sensitivity (~5000) within a narrow strain range (<1%), but their strain range is limited [18]. Similarly, sensors based on CB and wrinkled Ecoflex composites achieve a strain range of up to 500%, but their sensitivity is only 67.7 [19]. Additionally, layered composites composed of reduced graphene oxide (rGO), silk fibroin (SF), and cellulose nanocrystals (CNC) demonstrate high sensitivity in small strain ranges and are suitable for arterial pulse detection, but their performance under large strain conditions is restricted [20].