Will the wonders of carbon nanotubes never cease? Engineers have now used everyone's favorite cylindrical übermolecules to create artificial muscles that can contract and twist, in a manner not unlike like the muscles found in elephant trunks and squid tentacles. The upshot? Researchers say these tiny little motors could soon be used to propel microscopic nanobots throughout your bloodstream.


In nanoscale engineering, the term "artificial muscle" is used to refer to materials that can change their shape in response to stimuli. The mechanical movements created by these muscles have potential applications in everything from cancer therapies to portable electronics.

But scaling down motors into tiny little machines isn't easy; as motors decrease in size, their power output relative to their mass often shrinks as well. Now, an international team of scientists led by UT Dallas engineer Ray Baughman appears to have found a way to circumvent this problem.

By twisting together "untold billions" of microscopic, straw-like carbon nanotubes into filamentous strands of "yarn," Baughman's team was able to create a nanoscale motor capable of spinning at nearly 600 rpms, and turning a weight 2,000 times heavier than the yarn itself. Pictured here is one such carbon nanotube yarn (the angle α indicates the deviation between individual nanotube orientation and yarn direction).


Here's how it works: the coiled structure of each length of yarn measures just one-tenth the diameter of a human hair, but when the researchers immerse one of these threads in an electrolyte (in this case an electrically conductive solution of ions) and attach one end of it to a voltage supply, its constituent fibers "absorb" ions from the surrounding solution, causing them to expand. As the yarn swells, its untethered end is free to rotate at the speed and power described previously. Reversing the voltage causes the thread to coil back in the other direction.

"The torque that we can generate per mass of the yarn is comparable to that of very large electric motors," explains Baughman. "But as you down-size electric motors you dramatically decrease...the torque capabilities per weight."

"Our new type of artificial muscle produces a rotating action 1,000 times larger than previously known [artificial muscle] systems," explains University of Wollongong researcher Geoff Spinks, co-first author on the research paper describing the team's creation, which is published in the latest issue of Science. He continues:



We believe that, with further improvements in performance, it may be possible to propel a micro or nano-bot with these fascinating materials.

Which means they could be coming to a vein near you some time soon.

[Science (doi: 10.1126/science.1211220) via BBC + ABC Science + The Conversation]
Images of carbon nanotube yarns via Science
Nanobot via ABC Science