Making Robots Microscopic but Mighty

Michael J. Marsella is dreaming small these days.

The assistant professor of chemistry at UC Riverside is trying to create artificial “muscles” no bigger than a single molecule.

Marsella’s muscles might someday maneuver everything from tiny biomedical devices to robotic insects that could keep tabs on a hostile army’s maneuvers.

But first he has to prove his idea will work.

Marsella and his graduate assistant, Rodney Reid, are plowing new territory in the race to build smaller and smaller devices. They think organic is the way to go, mimicking muscles in the animal world.

The goal is to develop a single polymer molecule resembling plastic that will expand and contract as an electric current is applied. That motion could allow a tiny object to move or even a fan to wave back and forth.

That’s very different from the more traditional approach taken by other researchers, including Michael Goldfarb of Vanderbilt University in Nashville. Goldfarb’s research, funded by the Defense Department, has already resulted in small, insect-like devices that can crawl across rugged terrain. Flying “insects” are in the works.

But instead of using organic muscles, Vanderbilt’s critters are maneuvered by electromechanical devices made of ceramic-coated metal plates. The plates flex when a current is applied, thus causing the robots to “vibrate” across the landscape, Goldfarb said.

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This research is a long way from producing anything as ambitious as an artificial limb, but there’s nothing artificial about the Defense Department’s interest in tiny devices that could move undetected across the landscape.

Small robots could carry sensors to detect the presence of chemicals or biological agents, for example. And tiny cameras might be used to transmit images back from a hostile region.

One limiting factor is the amount of battery power that must be carried aboard the robot. The Vanderbilt research shows that tiny robots can be a real drain, and the battery has to be so small that only the most efficient system will suffice.

Marsella said his muscles would be “softer, lighter and more flexible” than the inorganic actuators favored at Vanderbilt. That could make them more suitable for a number of applications, including robotic flying insects, he added. However, the Vanderbilt research shows that building a tiny device that can flap its wings and fly through the air is tough.

The National Science Foundation saw merit in Marsella’s idea and recently funded the research for three years. Additional funding is being provided by the American Chemical Society.

Although their work is just getting started, the researchers have already hit their first milestone. Using polythiophene, a sulfur-containing polymer known to conduct electricity, they demonstrated that a bulk sample does indeed expand and contract when a current is applied.

That’s not surprising, because the bulk sample “behaves kind of like a sponge, sucking up all the ions” as the current flows through it, Marsella said.

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The next step will be harder--getting each individual molecule to do the same thing.

“It’s sort of like a football game,” Marsella said. “If you’ve got all your players out on the field, you can have a game. But if you go down to only one player, you can’t play the game anymore.”

To work, the molecule must be able to carry current, and it must change its dimensions when the current is applied. So the researchers are grafting two polymers together to achieve both goals.

Polythiophene will be used to carry the current, in much the same way current flows through household wiring. The researchers plan to intersperse cyclooctatetraene, a ring of eight carbon atoms, along the polymer chain. Cyclooctatetraene normally is folded like a half-open book, and it flattens out when a current is applied.

So if it works the way Marsella hopes, current flowing through the polythiophene will cause the cyclooctatetraene to flip back and forth like so many hinges.

Proving all this, however, is “going to be tricky,” he said. But if it works, “you can take this all the way down to a single molecule and still have a material that functions as a molecular muscle.” As devices grow smaller and smaller, the need for tiny muscles, or actuators, will also grow.

“We’re mostly interested in anything that requires motions at a small level,” he said, “like small functional hinges or small fans. If you apply an electric field to this material, it can bend. So if you apply the field fast enough, it can bend very rapidly, and it can have a fan-type action to cool off electronics or to move tiny components of a small device.”

But if the research succeeds, one of these days you may want to look twice before swatting that mosquito.

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Lee Dye can be reached by e-mail at leedye@ptialaska.net.