High-performance carbon nanotube/polyaniline artificial yarn muscles working in biocompatible environments

Implantable artificial muscles are of great importance for muscle function restoration and physical augmentation but are still challenging. Herein, we report an artificial muscle by soaking-polymerization of polyaniline (PANI) inside a carbon nanotube (CNT) yarn. Working in aqueous biocompatible solutions, the yarn muscle generates a large contractile stroke of 17% and high isometric stress of 8 MPa at voltages lower than 2 V. The excellent performance can be ascribed to the large actuation volume that is enabled by the fast electrochemical redox of PANI confined in a coiled yarn structure. The actuation performance outperforms that of previously reported aqueous artificial yarn muscles. Moreover, the yarn muscle can work well and maintain excellent actuating performance in other biocompatible solutions such as normal saline and Na₂SO₄ aqueous solution, which makes the CNT/PANI yarn muscles suitable for implantable bionic applications. Finally, a biomimetic arm was fabricated to demonstrate the applications of the CNT/PANI yarn artificial muscle in implantable muscle, underwater robots, and soft exoskeletons.