I ISSUED A CHALLENGE a few years ago to my fellow researchers: build a robot using muscles of electrically activated polymers that could arm-wrestle a human. I was trying to jump-start research in the field of electroactive polymers, or artificial muscles, and given the state of the art at the time, I didn't really expect to see the challenge fulfilled for a couple of decades.
I was wrong. A little over a year ago, researchers from SRI International, a research institute in Menlo Park, Calif., told me that their technology could be capable of meeting the challenge. Since then, Environmental Robots Inc. and the Swiss Federal Laboratories for Materials Testing and Research informed me that they would be ready to compete less than a year from now! I couldn't be more delighted--even if it means that my obligations as an impresario are a lot closer than I'd envisioned.
The arm-wrestling match, when it does come off, will be a watershed on more than one count. Today's machines--from assembly-line robots to electric toothbrushes--move thanks to rotary power, often cleverly translated by gears, pulleys, hydraulic tubes, and other intervening parts. Yet such watchmaker's cleverness has its limits, and over the centuries, engineers have imagined countless wonderful machines that sadly could not see the light of day. Now, at last, a streamlined solution is at hand: artificial muscles.
Artificial muscles are plastics that change shape and size under electrical stimulation. Because they are plastics--that is, polymers--they are light and can be cheap, pliable, quiet, and shatterproof. Also, they can be designed for particular properties, filled with sensors and other components, shaped for specific actuators, and manufactured on scales both macro and micro. Unlike most active materials, such as semiconductors and shape-memory alloys, however, these electroactive polymers work according to a variety of principles, offering different tradeoffs of power, extensibility, reaction time, and other qualities.
The list of hoped-for applications of electroactive polymers reads like an excerpt from a sci-fi writer's notepad: artificial limbs and organs, steerable endoscopic catheters, strength-amplifying exoskeletons for astronauts and disabled people, and muscles to make truly lifelike humanoid robots. It includes small robots that fly like insects or burrow like worms, robotic hands that transmit the sense of touch directly to the hand of an operator through virtual-reality gloves, and wall coverings that sense sound waves and generate antinoise waves to cancel them out. In fact, the first commercial applications of these polymers have already appeared, if only as toys--in December 2002, a Japanese company, Eamex Corp., in Osaka, produced robot fish that swim in an arrestingly natural way. Pulses of power from a coil in the fish tank are received by a corresponding coil in the fish. These power the toy's polymer actuators, propelling it through the water.
I entered this field, inadvertently, a decade ago. I had won a three-year contract from NASA to develop an artificial muscle based on polymer actuators described in a 1982 paper, for, among other things, amplifying the strength of an astronaut in a spacesuit. The authors claimed their actuators generated an enormous amount of force and had a whopping contractility, or strain, of almost 15 percent--meaning they could contract 15 percent of their length. After about a month working on the project, my team and I discovered that they had erred on the high side to the tune of four orders of magnitude. The hope of making a muscular spacesuit deflated before my mind's eye, and so I began a feverish search for alternatives.