Artificial muscles

It’s not often that a three-year-old makes a significant scientific contribution, but one did recently–inadvertantly.

Ron Pelrine, a senior research engineer with Stanford Research Institute International, wanted to keep his toddler out of the refrigerator, so he and his wife purchased a latch which attached to the side of the refrigerator with a special adhesive.

Pelrine got interested in the properties of that adhesive, and last week the results of his interest were released: that refrigerator-latch glue may be the ideal material from which to make artificial muscles.

Our own muscles are made up of long, stringy cells that, when stimulated by our nervous system, contract. When millions of cells contract at the same time, they’re able to generate a significant amount of force, enough to move the bones to which they are attached and any external object we happen to want to push, pull, lift, kick, etc.

Until recently, robots have had to simulate muscles with complicated systems of cables and pullies. Artificial muscles could change that–and benefit us in many other ways, as well.

Yoseph Bar-Cohen of the Jet Propulsion Laboratory is a leading artificial-muscle researcher. He has created muscles that consists of a lightweight strip of flexible plastic, constructed from chains of carbon, fluorine and oxygen molecules. When an electrical current is applied, charged particles get pushed or pulled to one side or other. More particles on one side of the ribbon than the other effectively makes that side longer, causing the ribbon to bend in the opposite direction. Changing the polarity of the electrical charge changes the direction the ribbon bends.

This simple artificial muscle will be used by the tiny rover that the MUSES-C spacecraft will drop onto the surface of a near-Earth asteroid in 2003 as a tiny windshield wiper to keep dust from blocking the cameras’ lenses.

Bar-Cohen and his team have also developed a different type of artificial muscle that consists of thin sheets wrapped into cigar-shaped cylinders. When an electrical charge is applied, the sheets stretch, causing the cylinder to contract and lengthen. When the power supply is turned off, the cylinder relaxes.

At the Artificial Muscle Research Institute at the University of New Mexico, engineers and medical researchers have created a third type of artificial muscle, made from synthetic silk. Baked to make it stronger, then boiled in a chemical solution that makes it elastic and gives it an electrical charge, it, too, can expand and contract like living tissue. As proof, the institute has re-muscled a skeleto, Myster Bony, which rides a stationary bike.

Last spring, an artificial muscle made of carbon nanotubes was demonstrated by an international team of researchers. Carbon nanotubes are a special form of carbon with unusual strength and an unusual electrical property: an electrical charge makes them expand.

The researchers applied thin sheets of tangled nanotubes to both sides of a length of double-sided adhesive tape. They hooked up electrical leads to each sheet and placed the tape in a saline solution. When current was applied, both sheets of nanotubes expanded–but the side with the negative charge expanded more, and so the piece of tape bent. The big advantage of nanotubes? They’re among the strongest materials known, similar to diamond.

The newest candidate for artificial muscle, Pelrine’s refrigerator-latch glue, (VHB 4910 acrylic, produced by 3M Corp.) is exciting because it can handle even more strain than human muscle can without tearing.

So what will artificial muscles be used for? Smaller, lighter robots, for starters, for all sorts of purposes, from space exploration to (based on the success of Sony’s robot dog Aibo), pets. Those robots could also use different forms of locomotion than they do now. They could hop like grasshoppers, or fly like insects. Artificial muscles could also lead to better artificial hearts. Someday, you might even be able to implant them in people whose own muscles have atrophied, where they would be activated by nerve impulses.

Who knows? Artificial muscles could someday even make the ancient dream of flying like a bird a reality for individual humans. Flapping wings don’t work for human flight because we don’t have strong enough muscles to flap large enough wings to get our overly heavy bodies airborne. Superhumanly strong artificial muscles could lead to artificial muscle suits with wings!

Such things may be years away…or they may be closer than you think. Perhaps all that’s needed to make them a reality is one more scientific breakthrough.

Keep an eye on your three-year-old.

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