News in Science

Spun fishing line turned into muscle

Spring-like coils Using household tools such as an electric drill and hair dryer, researchers have turned nylon fibres into artificial muscles that can lift 100 times more weight than human muscles.

The work, published today in Science, shows that extensive twisting of common fishing line and sewing thread leads to a spring-like coil with super-strength qualities.

Collaborator Professor Geoff Spinks says it is a much-sought breakthrough that could open the door to the use of artificial muscles in clothing and prosthetic manufacture, robotics, and as a green energy source.

Spinks, from the Australian Research Centre of Excellence for Electromaterials Science at the University of Wollongong, says the discovery is "almost embarrassing".

"It is ironic that we spent all these years looking at exotic materials — and of course the lessons we learned from those years led us to this dramatic discovery — but it is remarkable that such ordinary materials can do such amazing things," he says.

The breakthrough is the result of a 15-year international collaboration led by scientists at the University of Texas.

"We knew from our previous work with carbon nanotube artificial muscles that having a particular geometry was critical, and that was a helically twisted fibrous structure," says Spinks.

"We knew in nylon fibres the molecules are aligned within that solid fibrous structure, so we just wondered whether the individual polymer molecules would act in the same way that was happening with the carbon nanotube system."

"So it was just a matter of getting these commercially available polymer fibres from the fishing store and twisting them and seeing what happened."

Twist and heat

Spinks says they attached the fishing line to an electric drill and applied tension to the thread.

As it twists, the fibre forms tight coils in a spring-like arrangement. Once heat is applied to the coils it permanently fixes that spring-like shape.

Spinks says to use these springs as artificial muscles heat is again applied, causing the whole coil to contract.

Critically, with the ordinary fibres, the amount of contraction is as much as 50 per cent of the starting length of the coil, he says.

"The comparison we like to make is how do we match up against human muscle," says Spinks.

"Essentially we get similar levels of contraction in similar speeds of a second or less, but our [artificial] muscles can lift 100 times more weight."

Practical applications

The researchers were able to demonstrate practical applications of the artificial muscles by weaving them into fabrics that can respond to heat.

This allows the material to change, by either allowing air to circulate to cool the wearer, or closing up to protective in situations such as fighting a bushfire.

The researchers also used the artificial muscles to automatically open and close building windows using heat generated by the building.

"We have automatic opening window shutter systems that use a motor and consume energy," says Spinks.

"We built a simple device that uses the heat generated in the building to cause our muscles to contract and open the windows without using any power."

Spinks says the discovery is a game changer in the materials science field.

Previously, cost has been a major barrier to any commercial development, he says.

Shape memory alloys that have similar heat-controlled capabilities can cost as much as $3000 per kilogram whereas the fishing line and sewing thread system is just $5 per kilogram.

"Straight away you have a huge cost advantage," says Spinks

He says the movement and load these artificial muscles can carry is also more commercially viable.

"We are now working at the kind of scale that is useful; it is not microscopic any more. We are producing muscle-like forces and movements."