Nanotechnology researchers at the University of Texas at Dallas (UTD) have made chemically powered artificial muscles that are up to 100 times stronger than natural muscles. Fueled by alcohol or hydrogen, the muscles are also able to do 100 times more work per cycle than natural muscles.
Dr. Ray H. Baughman, who headed up the project, said that although batteries can be used for autonomous robots, they store too little energy and deliver it at too slow a rate for prolonged or intense activity. The more than 30 times higher energy density obtainable from fuels like alcohol, compared to that for the most advanced batteries, can translate into much longer operational lifetimes without refueling.
Baughman explained that one of the new types of artificial muscle his team created functions simultaneously as a fuel cell and a muscle. Writing in Science, he described one of the new muscles as having a catalyst-containing carbon nanotube electrode that functioned as both a fuel cell to convert chemical energy to electrical energy and as a supercapacitor to store the electrical energy, which it then converts into mechanical energy. "Fuel-powered charge injection in a carbon nanotube electrode produces the dimensional changes needed for actuation due to a combination of quantum mechanical and electrostatic effects present on the nanoscale," said Baughman.
In the other type of artificial muscle, the chemical energy in the fuel is converted to heat by a catalytic reaction with air. The resulting temperature increase in this "shorted fuel-cell muscle" causes the contraction of a shape memory metal muscle wire. Subsequent cooling completes the work cycle by causing expansion of the muscle. Baughman said that this type of muscle was the more powerful of the two and could have widespread application. "The shorted fuel cell muscles are especially easy to deploy in robotic devices, since they comprise commercially available shape memory wires that are coated with a nanoparticle catalyst. The major challenges have been in attaching the catalyst to the shape memory wire to provide long muscle lifetimes, and in controlling muscle actuation rate and stroke," he explained.
Perhaps unsurprisingly, the research leading to these new artificial muscles was funded by DARPA, an agency of the U.S. Department of Defense. It's likely that successful development of the muscles could see them employed in autonomous robots having very long mission capabilities and powerful exoskeletons for military personnel.
Intriguingly, the fuel-powered muscles can be easily downsized to the micro- and nano-scales, and arrays of such micro-muscles could be used in "smart skins" that improve the performance of marine and aerospace vehicles. And by replacing the metal catalyst with tethered enzymes, it might even be possible to use artificial muscles powered by food-derived fuels for use in the human body.
Source: University of Texas at Dallas
