Abstract:

Objective Smart textiles with thermal and humidity management function have attracted great interest from material researchers. Recently, the development of fiber-based artificial muscles based on fibrous twisting structure has provided new ways and effective methods for new development of the smart textiles. Fiber-based artificial muscles show sensitive and rapid actuating response to external stimuli based on the mechanism of anisotropic volume expansion. The current research aims to show that man-made fibers (e.g., carbon nanotubes, graphene, and shape memory alloys) and natural fibers (such as silk, spider silk, and cotton) can be used to prepare twisted fiber-based glexible actuators. However, the current fiber-based artificial muscles generally suffer from high cost, harsh stimulation conditions, chemical toxicity or complex manufacturing processes, which hinder the wide applications of fiber-based artificial muscles. Therefore, it is necessary to develop fiber-based artificial muscles with mild and moisture-response, high actuating response, stable actuating performance and low cost based on the use of environment-friendly fiber materials to promote the applications of the yarn muscles as a type of smart textiles.
Method A cross-scale processing strategy was harnessed to process viscose fibers into high-performance artificial yarn muscles. With the help of nano-micro structure regulation of fiber and the inherent multi-hierarchical structure designability, scalability, softness and mechanical robustness of textiles, the bottom-up textile configuration technology and stress engineering methods were used to develop a moisture-responsive artificial yarn muscle actuator with rapid response and large actuating strain. Furthermore, through the topological weaving/knitting configuration, the one-dimensional deformation of the yarn actuator was expected to extend to a fabric actuator with sizable dimension and multiple deformations. A large-scale processing method was to be identified for the formation of yarn and fabric actuators, so as to facilitate the design and development of smart textiles with moisture-response.
Results When alternatively exposed to dry and wet conditions, the artificial yarn muscles were found to be able to produce reversible torsional rotation. By applying water fog of 0.05 g/s to actuate the artificial muscles, the muscles demonstrated encouraging actuating performance. The maximum rotation degree of the hot-drawn artificial yarn muscles reached 1 657 (°)/cm, which is 1.7 times higher than that of the artificial yarn muscles prepared from the original viscose fibers without hot-drawn treatments, with an average speed of 331 r/min, exceeding the original viscose artificial yarn muscle (254 r/min). Through the integration of spinning technology and topological textile design, the mechanized production of artificial yarn muscles was achieved, and the fabric artificial muscle actuators were developed and fabricated, extending the simple deformation of the one-dimensional artificial yarn muscles to the high-dimensional diversified deformation in two-dimensional fabric artificial muscles.
Conclusion This paper proposes a cross-scale design strategy from micro structure (fiber aggregated structure) to macro configuration (fiber-yarn-fabric structure) to prepare moisture-responsive fiber-based artificial muscles with high actuating strain. The actuating performance of the artificial muscles is characterized and the application field and deformation dimension of fiber-based artificial muscle actuator are expanded through textile processing technology. The findings from this study provide a new method for improving the performance of fiber-based artificial muscles, and are also conducive to promote the development and application of fiber-based artificial muscles in smart textiles and related fields.

Key words: artificial muscle, actuator, moisture-responsive material, viscose fiber, smart textile, fabric muscle