Carbon nanotubes have already been demonstrated to be a useful material in the development of artificial muscles. But an international team of researchers led by the University of Texas at Dallas has discovered that if you twist carbon nanotubes into a yarn and infuse them with paraffin wax their capabilities as artificial muscles become staggering.
The researchers claim that the wax-infused muscles can lift 100 000 times their own weight and produce 85 times more mechanical power than natural muscle of equivalent size.
“The artificial muscles that we’ve developed can provide large, ultrafast contractions to lift weights that are 200 times heavier than possible for a natural muscle of the same size,” says Dr. Ray Baughman, team leader, Robert A. Welch Professor of Chemistry and director of the Alan G. MacDiarmid NanoTech Institute at UT Dallas in a press release. “While we are excited about near-term applications possibilities, these artificial muscles are presently unsuitable for directly replacing muscles in the human body.”
You can see Baughman further describe the carbon nanotube-based muscles in the video below:
While Baughman concedes that replacing artificial muscles in humans is out of the application list for this material at the moment, he does believe that it could be used in “robots, catheters for minimally invasive surgery, micromotors, mixers for microfluidic circuits, tunable optical systems, microvalves, positioners, and even toys.”
Baughman further believes that the material can make its way into marketable uses fairly quickly. He notes in the release: “The remarkable performance of our yarn muscle and our present ability to fabricate kilometer-length yarns suggest the feasibility of early commercialization as small actuators comprising centimeter-scale yarn length. The more difficult challenge is in upscaling our single-yarn actuators to large actuators in which hundreds or thousands of individual yarn muscles operate in parallel.”
Whether Baughman can tackle that next challenge remains to be seen, but the research, which was published in the journal Science (“Electrically, Chemically, and Photonically Powered Torsional and Tensile Actuation of Hybrid Carbon Nanotube Yarn Muscles"), is impressive in its elegant simplicity.
The combination of twisting carbon nanotubes into a yarn and infusing them with wax made it possible to simply add a bit of electrical charge to the material to get the wax to expand and then the yarn volume to increase, causing the yarn to shorten. This volume increasing and length decreasing is directly related to the twisting of the carbon nanotube yarn.
In operation, when the wax-filled yarn is heated electrically it untwists, but when the heating is stopped the yarn winds back up. What is remarkable is how fast this twisting and untwisting occurs. The researchers claim that yarn can rotate a paddle that is attached to the yarn at 11 500 revolutions per minute. Perhaps more importantly, it can repeat this cycle more than 2 million times.
Another attractive feature of the material is that fact that it can be treated like a textile. So it could be sewn or woven into clothing to react to outside environmental factors such as heat (a fireman’s coat is given an as an example in the video) and actuate (like a muscle) a change to the textile’s porosity. This change in porosity could provide thermal protection, or chemical protection in the presence of poisonous substances.
Dexter Johnson is a contributing editor at IEEE Spectrum, with a focus on nanotechnology.