Powerful strings

Muscles of polythene, nylon strings open new possibilities

By Vibha Varshney
Published: Monday 31 March 2014

Muscles made of threads can lift hundred times more weight than a human muscle of same length and weightSCIENTISTS have succeeded in making artificial muscles from strings made of polyethylene and nylon. These cost as little as $5 a kilogram and could be used in robotics, prosthetics and climate compatible clothes.

Muscles contract and expand to bring about movement of the body. Scientists around the world are looking for materials that can simulate the action of the muscle tissue. Artificial muscles have been made successfully from materials like metal wires and carbon nanotubes in the past, but these are expensiveÔÇêand difficult to control.ÔÇêThis is the first time artificial muscles have been made from materials used for making fishing lines and sewing threads.

A team led by Ray Baughman from Alan G MacDiarmid NanoTech Institute in the University of Texas, Dallas, US, took the fibres and twisted them till they coiled up like a spring. When these “springs” were exposed to a temperature change, they contracted and expanded, just like a muscle. The temperature changes can be produced electrically, by absorption of light or by chemical reaction of fuels. The artificial muscle dramatically contracts along its length when heated and returns to its initial length when cooled, the researchers say in the paper published on February 21 in Science. These muscles match or exceed the performance of the mammalian skeletal muscle which contracts by only about 20 per cent. The new material can contract by about 50 per cent of its length and liftÔÇêhundred times more weight than a human muscle of same length and weight.

“The application opportunities for these polymer muscles are vast,” says Baughman. “Today’s most advanced humanoid robots, prosthetic limbs and wearable exoskeletons are limited by motors and hydraulic systems, whose size and weight restrict dexterity, force generation and work capability,” he says. These artificial muscles can be used to bring life-like facial expressions to humanoid companion robots. They can also be used to develop textiles in which pores open and close with changes in temperature.

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