Three-Dimensional Braided Wearable Flexible Strain Sensors: Fabrication and Performance

Flexible and stretchable strain sensors are highly desired in wearable electronics, with textile-based sensors standing out for their superior flexibility, comfort, and seamless integration into clothing. However, simultaneously achieving high sensitivity and wide operable strain ranges remains a critical challenge. This study presents a simple, scalable approach to fabricate three-dimensional (3-D) braided strain sensors with both high sensitivity and exceptional stretchability, with a representative performance of a 340 gauge factor at 280% strain and a peak sensitivity of 1152 at 180% strain. The sensors utilize polyurethane filaments (PUF) as an elastic matrix with carbon nanotubes (CNTs) and graphene nanoplatelets (GNPs) as conductive fillers. Fabrication involves a four-step 3-D braiding process, subsequently followed by hybrid dip-coating and spray deposition. Characterization results reveal that CNTs form long-range conductive pathways for electrical continuity and strain tolerance, while GNPs enhance sensitivity through rapid resistance changes caused by the interlayer sliding under strain. The asymmetric bilayer conductive network─comprising an inner GNP layer for fast resistance response and an outermost CNT layer for stable conduction─synergistically improves both properties. Additionally, the interlaced spatial architecture of 3-D braided fabrics significantly extends the detectable strain range. By adjustment of structural parameters such as braiding angle and yarn arrays, sensors with customizable geometries can be engineered. This work achieves a synergistic balance between stretchability and sensitivity through innovative structural design and process optimization, providing a promising solution for high-performance flexible strain sensors and the advancement of wearable health monitoring systems.