Sheath-run artificial muscles

Although guest-filled carbon nanotube yarns provide record performance as torsional and

tensile artificialmuscles, they are expensive, and only part of themuscle effectively contributes

to actuation.We describe a muscle type that provides higher performance, in which the

guest that drives actuation is a sheath on a twisted or coiled core that can be an inexpensive

yarn. This change from guest-filled to sheath-run artificial muscles increases the maximum

work capacity by factors of 1.70 to 2.15 for tensile muscles driven electrothermally or by

vapor absorption. A sheath-run electrochemical muscle generates 1.98 watts per gram of

average contractile power—40 times that for human muscle and 9.0 times that of the

highest power alternative electrochemical muscle.Theory predicts the observed performance

advantages of sheath-run muscles.