Silk Materials for Intelligent Fibers and Textiles: Potential, Progress and Future Perspective

Abstract

Fibers and textiles with good flexibility, air permeability, and mechanical properties are indispensable materials in our daily lives. With the rapid development of flexible electronics, fabricating fibers and textiles that exhibit intelligent characteristics has become an attractive research topic. On the basis of the characteristics of common fibers or textiles, intelligent fibers and textiles may exhibit unique functions such as sensing, feedback, response, self-diagnosis, self-repair, and self-regulation. The development of intelligent fibers and textiles is closely related with the development of material science. Many materials, including metals, artificial polymers and natural biopolymers can be used for fabricating intelligent fibers and textiles. Compared with metals and artificial polymers, natural biopolymers have advantages of green source, biosafety, biodegradability and lightweight. Among natural biopolymers, natural silks, especially that from Bombyx mori, can be obtained in large amounts and have been used for clothes for thousands of years. Silkworm silk has exceptional mechanical properties, attractive luster, good biocompatibility and biodegradability. Therefore, silk materials are considered to be one of most promising candidates for intelligent fibers and textiles. In this review, we firstly introduce the hierarchical structures and basic properties of natural silk fibers. The exceptional mechanical properties of silk fibers can be ascribed to their unique hierarchical structures (from polypeptide chains, secondary structures to macroscopic fibers). The approaches to fabricate regenerated silk materials are briefly reviewed. The basic properties of silk materials, including the mechanical properties, biocompatibility, biodegradability, optical properties, piezoelectric properties, and thermal stability are presented. Then, the application of silk materials in various intelligent fibers and textiles, including fiber-based sensors, actuators, optical devices, energy harvesting and storage devices, are reviewed. Silk fibers can be functionalized and made into strain sensors, pressure sensors, and humidity sensors for applications in health monitoring. They can also transform into electrically conductive materials through high-temperature carbonization and then be fabricated into high-performance sensors or other functional devices. Silk-based actuators have been fabricated based on the response of silk to water or other molecules. Besides, silk-based fluorescence fibers and optical fibers were developed. Silk fibers have also been used in wearable energy devices by designing and fabricating piezoelectric nanogenerators, triboelectric nanogenerators, super-capacitors and batteries. The preparation methods, performance, and working mechanisms of those silk-based intelligent fibers and textiles are discussed in details. Finally, the persisting challenges and future opportunities of silk-based intelligent fibers and textiles are discussed. We believe that silk-based materials have great potential for intelligent fibers and textiles. The further development of this field will be accelerated by the continued development of material science and related techniques.