No abstract

Twisted yarn artificial muscles have attracted great interests for diverse applications, such as soft robotics, miniaturization controllers and smart textiles. A challenging issue in fabricating the twisted yarn artificial muscles is to retain the inserted twist. Different from the exiting strategies of forming double-helical structures or harnessing complex chemical technologies, we herein propose a simple combination of plasma and UV-light treatments to train natural wools into twist-stable single-helical yarn artificial muscles without external torsional tethering, which realizes easy fabrication of twisted actuators, and achieves better moisture-actuating performance (nearly 5 times higher in maximum rotation) compared to equivalent double-helical actuators. The stable morphology of woolen yarn muscles affected by the opening and closing of disulfide bonds is explained from microstructure characterization and theoretical analysis. The charming properties of single-helical yarn muscles will provide new inspiration for the development of fiber-based actuators in industrial routines, which is expected to promote the practical application of yarn muscles in smart textiles and wider fields.

Yarn-based muscle actuators are highly desired for applications in soft robotics, flexible sensors, and other related applications due to their actuation properties. Although the tethering avoiding release of inserted twist, the complex preparation process and harsh experimental conditions make tether-free structures yarn actuator with reliable cycle recovery effectiveness is needed. Herein, a tether-free, multi-hierarchical hybrid construction of a moisture-sensitive responsive yarn-based actuator with the viscose/PET ratio (VPR) = 0.9 exhibited a contraction stroke of 83.15%, a work capacity of 52.98 J·kg–1, and an exerting force of 0.15 MPa. Additionally, the maximum cycle recovery rate of 99% is comparable to that of human skeletal muscles, confirming the advantages of a two-component hybrid structure. The underlying mechanism is discussed based on geometric characterization and energy conversion analysis between the actuation source and the spring frame. The mechanical manufacturing process makes it simple to expand the structurally stable yarn muscles into fabric muscles, opening up new opportunities to advance the usage of yarn-based actuators in smart textiles, medical materials, intelligent plants, and other versatile fields.

The self-adaptive nature of smart textiles to the ambient environment has made them an indispensable part of emerging wearable technologies. However, current advances generally suffer from complex material preparation, uncomfortable fitting feeling, possible toxicity, and high cost in fabrication, which hinder the real-world application of smart materials in textiles. Herein, humidity-response torsional and tensile yarn actuators from twisted and coiled structures are developed using commercially available, cost-effective, and biodegradable viscose fibers based on yarn-spinning and weaving technologies. The twisted yarn shows a reversible torsional stroke of 1400° cm−1 in 5 s when stimulated by water fog with a spraying speed of 0.05 g s−1; the coiled yarn exhibits a peak tensile stroke of 900% upon enhancing the relative humidity. Further, textile manufacturing allows for the scalable fabrication to create fabric artificial muscles with high-dimensional actuation deformations and human-touch comfort, which can boost the potential applications of the humidly adaptive yarns in smart textile and advanced textile materials.