Electroactive Polymers
Artificial muscles made of electroactive polymers impart lifelike movements to biomedical and robotic devices.
In the Artificial Muscle Research Institute at the University of New Mexico, electricity is in the air. When lab director Mohsen Shahinpoor applies a voltage to an artificial “hand” made of a polymer-metal composite, its fingers curl into a fist. Poke around the lab and you’ll see robotic fish swimming, wings flapping, and arms lifting-all gaining their muscle from electrically activated polymers. You’ve seen robots before, but there is something different about these. They look alive.
Since the early 1990s, materials scientists and engineers have been developing electroactive polymers for use as sensors, actuators, and artificial muscles. An applied voltage changes the polymer’s composition or molecular structure so that it expands, contracts, or bends. The motion is smoother and more lifelike than movement generated by mechanical devices: like muscles, polymers are flexible, unhampered by the clunky rigidity of gears and bearings. Scientists believe that with this similarity to natural motion, electroactive polymers could revolutionize robotics and biomedical devices. Such materials could make it possible to design robots that maneuver with the grace of a human, prosthetic legs that move and feel real, and implantable microdelivery systems that smoothly and quietly pump drugs to where they’re needed.
Until recently, however, electroactive polymers have presented practical problems. They consumed too much energy. They couldn’t generate enough force. And they didn’t last long enough. But researchers in academia and industry have found ways to make the polymers stronger, more robust, and more efficient. These improvements, says Yoseph Bar-Cohen, a senior research scientist at NASA’s Jet Propulsion Laboratory and one of the field’s pioneers, “will enable faster implementation of science fiction ideas into engineering reality.”
Last September, in a breakthrough that could lead to lower-power medical devices, Qiming Zhang and his colleagues at Pennsylvania State University reported that they had created an electroactive actuator that requires one-tenth the voltage previously needed. Zhang’s key advance: a polymer-semiconductor composite that gets more electric bang for the buck and remains very flexible. The advantages of this class of device are its high efficiency and fast response. But “this is just the start,” says Zhang. He predicts that pharmaceutical products based on the technology-for example, small wearable insulin pumps powered by low-voltage batteries-could be available within five years.
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