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Artificial Muscles Gain Strength

New materials pave the way for artificial muscles just as strong as Arnold himself.
February 15, 2002

Flying an F-15 can be hazardous during sharp maneuvering. Blood can instantly pool into the pilot’s abdomen and extremities and cause him or her to pass out. One possible solution is an “anti-gravitational suit”-or a g-suit-that squeezes the lower body, forcing blood to flow back through the torso and up toward the head. Unfortunately, current g-suits designed using hydraulics and pneumatics are slow to respond and often limit a craft’s maneuverability.

A group at MIT thinks they may have a better way. Led by mechanical engineer John Madden, a project leader in Ian Hunter’s BioInstrumentation Laboratory, and working in collaboration with MIT chemist Timothy Swager, the researchers have developed materials with properties closer to human muscles than anything yet seen. They believe that their muscle material will be perfect for an anti-gravitational suit, as well as for therapeutic and commercial devices.

The team has recently launched a company called Molecular Mechanisms in Cambridge, MA to develop the technology. The group expects to produce a variety of working prototypes within the next six months that may even lay the foundation for what Swager calls a “superman suit” for the armed forces. Such a suit could enable soldiers to run, jump and lift to a nearly superhuman degree. “Imagine,” he says, “the psychological damage it would wreak on a foe if we had entire troops able to leap over 20-foot walls?”

Think Accordion

The idea of being able to construct an artificial muscular system has inspired some grand visions-biological robots, to name one. Researchers have had some success in the last decade with electroactive polymers, molecules that absorb a solvent and then expand and contract when an electric charge is applied. The good news is that these materials require a very low voltage in order to respond. The bad news is that these molecules don’t have anywhere near the power or flexibility of natural mammalian muscles. As a result, researchers need to mechanically influence the dimensions of movement in these materials.

But now, Madden and his group have taken a different approach. Working with polypyrrole-the polymer of choice for most artificial muscle research-Madden and Swager have engineered molecules that undergo a fundamental change in their structure when a voltage is applied. The new molecules go through an accordion-like deformation, stretching out and becoming highly elongated, then buckling in. On a larger scale, this movement mimics that way mammalian muscles work, which is why Madden and his colleagues are so excited.

The material created from these molecules looks nothing like human muscle. The thin, black ribbon feels almost like electrical tape. But, “these materials are 100 times stronger than mammalian muscle,” Madden claims, with guarded enthusiasm. Guarded, because these results haven’t yet been published.

However, Madden and his colleague Patrick Anquetil will be presenting these results next month at the International Society for Optical Engineering, and if this evidence holds up under the scrutiny of peer review, this work will mark a significant advance in the field. Says Gordon Wallace, director of the Intelligent Polymer Research Institute in Australia’s Wollongong University, “Madden’s and Swager’s ideas are very novel concepts. When you go back to designing the polymer materials, then you have the potential to make a major breakthrough.”

Before Superman

Applications are countless. According to Yoseph Bar-Cohen, senior research scientist as NASA and author of Electroactive Polymer Actuators as Artificial Muscles, (currently the only published book on the subject), “This is an exciting field. We can start thinking in terms of copying nature. Instead of having motors with gears and bearings, we’ll soon be able to take a blob, attach wires, and it will change shape as desired.”

And while the superman suit might be the long-term goal, more prosaic applications should emerge sooner. Madden’s group has already begun working on a leg sock that will prevent venous thrombosis-abnormal blood clotting that can potentially clog arteries-for people who are at risk due to long periods of immobility. In this device the artificial muscular system enclosed in the sock would massage the legs just enough to prevent the blood from pooling. Two other possible medical applications include a cardio-wraparound for patients with weakened heart muscles and an artificial urinary sphincter.

But because these materials could cost as little as one dollar per kilogram to mass produce, Madden is also looking at consumer applications like toys (moving action figures) and cosmetic and toothpaste dispensers. Anything that requires motion is fair game, and could be on the market in one to two years.

Man vs. Machine

While there’s presently a lot of interest in electroactive polymers, most research is confined to the university lab. Aside from Madden’s Molecular Mechanisms, the only other company devoted exclusively to this technology is Linkoping, Sweden-based Micromuscle, which focuses primarily on technologies for powering microelectromechanical systems.

This field is still in its infancy and has yet to put any of its claims to the test, but that hasn’t curtailed the zeal of its proponents. Bar-Cohen, for one, has so much faith in the potential of electroactive polymers that he has made a public challenge: once his team at NASA has completed their prototype of an artificial arm, he dares anyone to stop by and try to arm wrestle it.

If Madden and his group have their way, the volunteer may show up in a superman suit.

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