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Video: Tiny Artificial Muscles Dance Like Mexican Jumping Beans

MIT scientists have created thin polymer sheets that expand and contract when in contact with water, lifting several times their weight

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Another one of the products of science that seem too amazing to be true: Researchers at MIT have invented the technological equivalent of Mexican jumping beans. As seen in the video above, they’ve created polymer films that act like artificial fast-twitch muscles, spontaneously curling up and dancing around in an eerily life-like way.

The polymer sheets are specially designed to rapidly expand when they come into contact with water, and contract when they expel it. Thus, by placing the sheets on a slightly moist surface, Mingming Ma and colleagues were able to make them dance around completely on their own. They published the details of their invention today in a paper in Science.

Although the polymers are simply pretty cool to watch, the researchers had a practical application in mind when they developed them: producing electricity. When they covered the sheets with a piezoelectric polymer that generates electricity from pressure and stress (30 seconds into the video), and wired it to a capacitor, they were able to store minute amounts of energy expelled by all that folding and flipping.

They say the sheets produced bursts of electricity peaking at about 1 volt. Since the polymer can also be stimulated by the mere presence of water vapor in the air—and not just water on a table—they speculate that these types of thin water-powered sheets could someday be harnessed to provide electricity for small ubiquitous objects, like environmental sensors.

“With a sensor powered by a battery, you have to replace it periodically,” lead author Ma said in a statement. “If you have this device, you can harvest energy from the environment so you don’t have to replace it very often.”

It’s even possible, they suggest, that this type of material could be sewn into clothing, in order to harvest electricity from the sweat that evaporates off your body. ”You could be running or exercising and generating power,” said Liang Guo, a co-author.

The sheets are made from a pair of polymers: one called polypyrrole, which serves as a rigid supporting matrix, and another called polyol-borate, a flexible gel substance woven throughout that does the expanding and contracting when in contact with water. The researchers were inspired by the configuration of animal muscles (including our own), which are made from a rigid network of collagen fibers woven with elastic microfibrils.

In the video above, when the superthin film comes in contact with minute amounts of moisture, the bottom layer absorbs water and quickly curls upward. Then, once the bottom is lifted off the table and comes into contact with the air, the moisture evaporates off of it, and it flattens back out.

The team even tested the strength of this fascinating polymer construction, using clamps and heavy objects, to see just how much weight the polymer sheets could lift when stimulated. They found that a 25-milligram piece of film could lift a stack of glass slides 380 times heavier than itself and produce up to 27 megapascals of pressure—80 times more than the amount of pressure generated by typical mammalian muscle. Pretty amazing for a paper-thin sheet of film.

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