Stepwise Artificial Yarn Muscles with Energy- Free Catch States Driven by Aluminum-Ion Insertion

Present artificial muscles have been suffering from poor actuation step precision and the need of energy input to maintain actuated states due to weak interactions between guest and host materials or the unstable structural changes. Herein, these challenges are addressed by deploying a mechanism of reversible faradaic insertion and extraction reactions between tetrachloroaluminate ions and collapsed carbon nanotubes. This mechanism allows tetrachloroaluminate ions as a strong but dynamic locker to achieve an energy-free high-tension catch state and programmable stepwise actuation in the yarn muscle. When powered off, the muscle nearly 100% maintained any achieved contractile strokes even under loads up to 96,000 times the muscle weight. The actuation mechanism allowed the programmable control of stroke steps down to 1% during reversible actuation. The isometric stress generated by the yarn muscle (14.6 MPa in maximum, 40 times that of skeletal muscles) was also energy freely lockable and step controllable with high precision. Importantly, when fully charged, the muscle stored energy with a high capacity of 102 mAh g(-1), allowing the muscle as a battery to power secondary muscles or other devices.

Automated summary

This study addresses the challenges of poor actuation step precision and energy input to maintain actuated states in artificial muscles. The deployment of a reversible faradaic insertion and extraction reaction mechanism on collapsed carbon nanotubes enables high-tension catch state and programmable stepwise actuation. The muscle can maintain achieved contractile strokes even under heavy loads, and the actuation mechanism allows programmable control of stroke steps with high precision. Furthermore, the muscle can store energy and be used as a battery for other devices.