A large-stroke nylon-spandex compound twisted and coiled polymer artificial muscle with greatly adjustable actuation performances

Twisted and coiled polymer (TCP) artificial muscles have attracted considerable interest for soft robotics and lightweight bionic actuation, owing to their large stroke, high work capacity, and power density. In practical applications, the actuation performance of TCP muscles, such as stiffness, optimal load range, and contractile stroke, must be tailored to meet the specific requirements of diverse scenarios. Although the studies on performance modulation of traditional nylon-based artificial muscles have been conducted, the systematical experimental researches and corresponding experimental data are still scarce. Additionally, the performance-regulating approaches for multi-fiber based compound muscles remain underdeveloped. Herein, through blend spinning approach, we developed a nylon-spandex compound TCP muscle with core-shell structure, which show large stroke (37.60%) and strong contraction force (6.07 MPa), and we systematically studied how multiple factors affect the muscle performances. More importantly, by adjusting the key preparation parameters, the performances of the compound muscles can be regulated in a wide range: their stiffness and optimal working load can be modulated by more than 15 times and 7 times, respectively. In addition, intertwining elastic spandex fibers with nylon improves the uniformity of the muscle coils, the core-shell structure makes the muscle waterproof, and the strain self-sensing capability enables the muscle to perform controllable actuation. These advanced performances make the nylon-spandex compound TCP muscles very suitable for wide applications in diverse scenarios.