A Review of Flexible Strain Sensors Based on Natural Fiber Materials

Flexible strain sensors with outstanding stretchability and sensitivity can be widely used in medical health, smart robot, intelligent garment, man-machine interaction, and other fields. The use of natural fibers enables a green manufacturing pathway to design strain sensors within the context of increasingly serious environmental pollution. Commercialized natural fibers, including cellulose fibers (cotton and fibrilia), protein fibers (wool and silk), and their regenerated materials (viscose and silk fibroin) exhibit low cost, easy acquisition, and degradability as the basis materials. This paper reviews the preparation methods, performances, and applications of flexible strain sensors based on these natural fibers. Cellulose and protein fibers are carbonized or coated with conductive nanomaterials to form the strain sensing network, and then, elastic polymers are used to improve the sensor strain range. Regenerated natural fiber materials can be uniformly mixed with conductive materials to form conductive composites for sensors. The strain-sensing performances and mechanisms are analyzed and compared. Natural fiber-based strain sensors are studied to pave the way for practical integration in electronic systems.