Artificial Muscles In The Offing

A scientist at the Rensselaer Polytechnic Institute in Troy, New York, is attempting to build artificial muscles using carbon nanofibres.

Artificial muscles change length in response to a stimulus, thereby creating a smoother, more human-like motion than jerky electric motors or pneumatic devices. As such, they could be used to power robots, prosthetic limbs and artificial tissue for implantation, say scientists.

Today's most promising artificial muscles are based on electroactive polymers (EAPs) — plastics that change shape when activated electrically or with chemicals. But they lack mechanical robustness and as a result soon succumb to fatigue and fail.

To test the nanotubes ability to resist fatigue, the team led by Dr Victor Pushparaj took a two-millimetre-square block in which many millions of nanotubes were aligned vertically, and repeatedly compressed it between two steel plates once every 0.75 seconds for over 100 hours.

The team found that even after 500,000 compressions, in which the tubes were repeatedly squashed to 75% of their original length, the block kept pinging back almost to its original shape.

"The nanotubes buckled in a zig-zag shape but regained their original shapes when the load was released," said Dr Pushparaj.

The ability of carbon nanotubes to withstand repeated stress yet retain their structural and mechanical integrity is similar to the behaviour of soft tissue, according to the new study.

The report, 'Fatigue resistance of aligned carbon nanotube arrays under cyclic compression,' appears in the July issue of Nature Nanotechnology.

Despite extensive research over the past decade into the mechanical properties of carbon nanotube structures, this study is the first to explore and document their fatigue behavior, said Pushparaj, a senior research specialist in Rensselaer's department of materials science and engineering.

"The idea was to show how fatigue affects nanotube structures over the lifetime of a device that incorporates carbon nanotubes," Pushparaj said.

"Even when exposed to high levels of stress, the nanotubes held up extremely well. The behaviour is reminiscent of the mechanics of soft tissues, such as a shoulder muscle or stomach wall, which expand and contract millions of times over a human lifetime."

***** The far reaching benefits from this research is evident and will be a boon to many millions around the world.
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