New artificial muscles can lift 12,600 times their weight

Scientists have designed new carbon fibre-based artificial muscles capable of lifting up to 12,600 times their own weight.

The strong muscles are made from carbon fibre-reinforced siloxane rubber and have a coiled geometry.

When electrically actuated, the artificial muscles show excellent performance without requiring a high input voltage, according to the study published in the journal Smart Materials and Structures.

The researchers showed how a 0.4 milimetre (mm) diameter muscle bundle is able to lift half a gallon of water by 1.4 inches with only 0.172 volt/centimetre (V/cm) applied voltage.

"The range of applications of these low cost and light weight artificial muscles is really wide and involves different fields such as robotics, prosthetics, orthotics, and human assistive devices," said Caterina Lamuta, a postdoctoral fellow at University of Illinois at Urbana-Champaign in the US.

"The mathematical model we proposed is a useful design tool to tailor the performance of coiled artificial muscles according to the different applications," said Lamuta.

The artificial muscles themselves are coils comprised of commercial carbon fibres and polydimethylsiloxane (PDMS).

A carbon fibres tow is initially dipped into uncured PDMS diluted with hexane and then twisted with a simple drill to create a yarn with a homogeneous shape and a constant radius.

After the curing of the PDMS, the straight composite yarn is highly twisted until it is fully coiled.

The team set a target of transforming carbon fibres, a very strong lightweight material which is readily commercially available, into artificial muscles.

"We simply filled carbon fibre tows with the suitable type of silicone rubber, and their performance was impressive, precisely what we had aimed for," said Sameh Tawfick, an assistant professor at University of Illinois.

The study demonstrates that muscle contraction is caused by an increase in the radius of the muscle yarn due to thermal expansion or solvent absorption of the silicone filing.

"The muscles flex when the silicone rubber locally pushes the fibres apart within the tow, by applying a voltage, heat or swelling by a solvent," said Tawfick.