Artificial muscle contracts and expands with changes in humidity

July 24, 2013

( —A small plastic strip can do "weight training" to effortlessly lifts many times its own weight, driven by cyclic changes in the humidity of the surrounding air. This strong "artificial arm" is based on the interaction between microgels and a layer of polycations that shrinks as it dries, according to a report presented by Canadian researchers in the journal Angewandte Chemie.

Polymer materials that perform work in response to a chemical or physical stimulus are often called "". These are very interesting for a number of applications, including controlling the movements of "gentler" robots. All components of such robots need to be soft and flexible so that they don't damage delicate objects and can move in tight spaces.

The arm developed by researchers working with Michael J. Serpe at the University of Alberta is constructed in the following way: A strip of a is coated with chromium and gold, followed by a microgel . Microgels are cross-linked polymers that swell up with a solvent such as water to form gel particles with diameters of up to a few micrometers. The Canadian researchers used negatively charged microgels made from poly(N-isopropylacrylamide) and . A solution containing polycations is deposited onto the gel. These act as positive counterions.

When this system dries out, the between the hydrocarbon regions of the polymer cations increase considerably, which causes the layer containing the polymer cations to shrink. Because the electrostatic attraction between the polycations and the microgel is very strong and the microgel layer is very firmly attached to the coated sheet of plastic, the ends of the strip bend upwards and the system curls up. When the is increased, it stretches back out.

The researchers hung one of their strips up in a chamber with controlled humidity conditions. By changing the humidity, they were able to make their artificial arm "grip" the handle of a small package and to "hold on" as it rose up. In another experiment, they hung a chain of paperclips to the end of one extended mini-arm. Cyclic changes in the humidity caused the arm to raise and lower this weight, which was 14 times as heavy as the arm itself, like a miniature weight-lifting exercise. "Given that a human arm is approximately 6.5 % of the total mass of the human body, this is equivalent to a 75 kg human with a single arm that is capable of lifting 68.3 kg," Serpe says to illustrate the strength of his miniature arm. Even hanging 52.2 g of weight from a curled-up arm was not enough to stretch it out. If a 75 kg human wanted to achieve a similar feat, he would have to keep his arm bent even with 1280 kg pulling on it.

Explore further: Whether grasping Easter eggs or glass bottles -- this robotic hand uses tact

More information: Angewandte Chemie International Edition, DOI: 10.1002/anie.201303475

Related Stories

Microgels' behaviour under scrutiny

April 30, 2013

Being a physicist offers many perks. For one, it allows an understanding of the substances ubiquitous in everyday industrial products such as emulsions, gels, granular pastes or foams. These are known for their intermediate ...

ARM chip makers set to reach 3GHz next year

July 10, 2013

( —ARM chip makers TSMC and GlobalFoundries have revealed that they plan to release ARM processor chips capable of running at 3GHz sometime next year. Such chips will almost certainly be welcomed with open arms ...

Recommended for you

New polymer creates safer fuels

October 1, 2015

Before embarking on a transcontinental journey, jet airplanes fill up with tens of thousands of gallons of fuel. In the event of a crash, such large quantities of fuel increase the severity of an explosion upon impact. Researchers ...

Researchers print inside gels to create unique shapes

September 30, 2015

(—A team of researchers at the University of Florida has taken the technique of printing objects inside of a gel a step further by using a highly shear-rate sensitive gel. In their paper published in the journal ...

How a molecular motor untangles protein

October 1, 2015

A marvelous molecular motor that untangles protein in bacteria may sound interesting, yet perhaps not so important. Until you consider the hallmarks of several neurodegenerative diseases—Huntington's disease has tangled ...

Anti-aging treatment for smart windows

October 1, 2015

Electrochromic windows, so-called 'smart windows', share a well-known problem with rechargeable batteries – their limited lifespan. Researchers at Uppsala University have now worked out an entirely new way to rejuvenate ...


Please sign in to add a comment. Registration is free, and takes less than a minute. Read more

Click here to reset your password.
Sign in to get notified via email when new comments are made.