Asymmetric Carbon Nanotube Yarns for Electrochemical and Mechanical Balance in Artificial Muscle Fascicle

Abstract

Artificial muscle fascicles that mimic the hierarchical structure of biological muscles are essential for translating the high performance of individual artificial muscles into scalable soft robotics applications. However, in electrochemical artificial muscles, the muscle fascicles that consist of anodic and cathodic muscles have asymmetric actuation due to electrochemical imbalance between the anodic and cathodic sides, including voltage, capacitance, and ion volume. This imbalance reduces the overall actuation of muscle fascicles and poses a challenge for soft robot design. We here demonstrate an asymmetric configuration for carbon nanotube (CNT) artificial muscles to resolve both the electrochemical imbalances and the subsequent mechanical imbalance. The ratio of cathodic-to-anodic muscles in the fascicles was tuned to achieve electrochemical balance, and the spring index of the coiled structure was adjusted to match the mechanical modulus between the muscles. This asymmetric strategy was further extended to multiplied structures, forming the basis of artificial muscle fascicles with improved performance. These results provide a scalable strategy for translating high-performance individual CNT artificial muscles into efficient and powerful artificial muscle fascicles for future soft robotic systems.