Dr. Ray H. Baughman, a professor of chemistry at the University of Texas at Dallas (UTD), along with Nobel laureate Alan MacDiarmid and their colleagues in Texas and Korea, has built something that will be crucial for future androids: artificial muscles.

However, these artificial muscles break from the shackles of batteries, as they use fuel instead.

The UTD nanotechnologists have made alcohol- and hydrogen-powered artificial muscles that are 100x stronger than natural muscles, are able to do 100x greater work per cycle and can produce, at reduced strengths, larger contractions than natural muscles. Among other possibilities, these muscles could enable fuel-powered artificial limbs, "smart skins" and morphing structures for air and marine vehicles, autonomous robots having very long mission capabilities and smart sensors that detect and self-actuate to change the environment.

While today's crude humanoid robots already use gears, pulleys and pistons to mimic the actions of muscles, they are electrically powered and thus require being plugged in and tethered by an extension cord or powered by batteries, which drain quickly. The energy density obtainable from fuels like alcohol is more than 30 times higher than that for the most advanced batteries and can translate into much longer operational lifetimes without refueling.

As a recent New York Times article put it simply, "Just like real muscles, they power themselves instead of relying on external electrical power. Chemical energy also delivers a greater bang."

The team from UTD's NanoTech Institute developed two different types of artificial muscles that, similar to natural muscles, convert the chemical energy of an energetic fuel to mechanical energy.

According to Baughman, corresponding author of the March 17 journal Science article in which the breakthroughs are described, the new muscles "simultaneously function as fuel cells and muscles."

In one described muscle type, Baughman explains, a catalyst-containing carbon nanotube electrode is used: as a fuel cell electrode to convert chemical energy to electrical energy; as a supercapacitor electrode to store this electrical energy; and as a muscle electrode to transform this electrical energy to mechanical energy. Fuel-powered charge injection in a carbon nanotube electrode produces the dimensional changes necessary for actuation due to a combination of quantum mechanical and electrostatic effects present on the nanoscale.

Of the two new muscles, the more powerful type — and perhaps the one with more widespread application — is a nickel-titanium alloy coated with platinum, which causes the fuel — currently methanol, but hydrogen or alcohol could work, too — to react with oxygen, producing heat. The resulting temperature increase in this "shorted fuel-cell muscle" causes contraction of a shape memory metal muscle wire that supports this catalyst. Subsequent cooling completes the work cycle by causing expansion of the muscle. The metal shrinks; the muscle flexes. And the artificial muscle can apply 100 times as much force as real muscle.

(Super-strong robot Frankenstein, Jr.)

According to Baughman, the shorted fuel cell muscles are "especially easy to deploy in robotic devices," as they comprise commercially available shape memory wires that are coated with a nanoparticle catalyst. The major challenges, he says, have been in attaching the catalyst to the shape memory wire to provide long muscle lifetimes, and in controlling muscle actuation rate and stroke. To put such artificial muscles into robots will require solving other problems, such as how to control the amount of fuel going to the muscles.

"One day you could find yourself sitting in a bar next to a humanoid robot, who is taking a shot of vodka to give himself the energy to go to work," joked Baughman in a recent New Scientist article.

Of note, and particularly intriguing, the fuel-powered muscles can be downsized to the microscale and nanoscale easily, and arrays of such micro-muscles could be used in "smart skins" for improving the performance of marine and aerospace vehicles. (The research leading to these new artificial muscles was funded by the U.S. Department of Defense's DARPA agency.) Further, 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, notes Science a Go Go.

Baughman says the technology is simple enough that it could find commercial applications in as few as three years.

References

For Robots, Fuel Cells That Double as Muscles
by Kenneth Chang
New York Times, March 21, 2006

University of Texas at Dallas press release

Fuel-Powered Artificial Muscles
Report: Von Howard Ebron, Zhiwei Yang, Daniel J. Seyer, Mikhail E. Kozlov, Jiyoung Oh, Hui Xie, Joselito Razal, Lee J. Hall, John P. Ferraris, Alan G. MacDiarmid, Ray H. Baughman
Science, March 17, 2006

Methanol-powered artificial muscles start to flex
by Zeeya Merali
NewScientist, March 16, 2006

Super Strong Artificial Muscles Could Power Next Generation Of Robots
Science a Go Go, March 17, 2006

Additional

Fake Muscles Work Like Real Thing
by Tracy Staedter
Discovery News, March 20, 2006

Methanol fuel cells could power robot limbs
Engadget, March 17, 2006