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ARTIFICIAL muscles can match the speed, size or strength of human muscle, but
not all at the same time. Now researchers at MIT have worked out how to overcome
the limitations of artificial muscles made from conducting polymers鈥攁
breakthrough that might lead to a new generation of artificial hearts.

Conducting polymers look and feel like cassette tape and are bathed in a
fluid or gel electrolyte. Applying a voltage to the electrolyte forces ions to
flow in and out of the tape, causing it to swell or contract. Researchers have
known for several years that the conducting polymer polypyrrole can produce up
to a thousand times more force than human muscle with the same cross section.
But the polymers react very slowly, so any robot powered by them would be hugely
powerful but painfully slow.

鈥淭he limiting factor is the rate at which ions can diffuse in the material,鈥�
says John Madden, a researcher on the team. But boosting ion flow by raising the
voltage destroys the polymer. Now Madden has discovered that a rapidly
alternating voltage dramatically speeds up the flow without that destruction.
The voltage builds up mainly across the electrolyte, sparing the polymer.

Ray Baughman, an artificial muscle researcher at AlliedSignal in Morristown,
New Jersey, says the next step will be to mimic the structure of natural muscle,
comprising billions of submicroscopic fibres.