WASHINGTON, July 11 (Xinhua) -- An international team including engineers in the United States and China developed a kind of powerful artificial muscles using a polymer sheath around inexpensive yarns, which can generate a power 40 times that of human muscles.
The study published online Thursday in the journal Science described the sheath-run artificial muscles in which the outside sheath absorbs energy and drives the actuation of the yarns inside.
Previous artificial muscles were made by twisting yarns, such as carbon nanotubes (CNT), fishing line and nylon thread, to the point that they coil. Those twisted yarns can drastically contract when heated and return to initial conditions when cooled, according to the study.
"In our previous twisted and coiled muscles, we applied thermal energy to the entire muscle, but only the outer, twisted part of the fiber was doing any mechanical work. The central part was doing little," said the paper's lead author Mu Jiuke at the University of Texas at Dallas.
"Also, it takes a relatively long time to transmit the energy into the inner part of yarns, thus slowing down the muscle's response speed," Mu told Xinhua.
With the sheath, however, the input energy can be converted into the mechanical energy of the muscle more quickly and efficiently, said Mu.
In the experiment, the researchers twisted the yarns while the sheath was still wet since the sheath will crack after it has dried.
When activated electrochemically, a muscle consisting of a CNT sheath and a nylon core generates an average contractile power that is 40 times that of human muscle and nine times that of the highest power alternative electrochemical muscle, according to the study.
The researchers from Donghua University in Shanghai also demonstrated a consumer application of sheath-run artificial muscles. They knitted them into a textile that increases porosity when exposed to moisture in order to bring more comfort to cloth wearers.
