In a development that promises to usher in shape-changing aircraft wings, better sensors and more attractive robots, researchers have created artificial muscles considerably stronger than our own, they reported. The new muscles are made from carbon nanotubes and infused with wax (Science, doi: 10.1126/science.1226762).
‘This artificial muscle can lift a weight about 200 times larger than could be lifted by natural muscle,’ says Ray Baughman of the University of Texas, US, adding that the fibres within the yarn are about 1/10,000 the width of human hair.
The yarn could be made to contract and twist by exposing it to electric heating or a flash of light or even chemicals that cause the wax to expand. ‘Our initial experiments just used paraffin wax we got in a convenience store,’ Baughman adds. ‘As the wax melts it increases the volume of the yarn but the yarn also gets shorter.’
Baughman says the yarn can currently lift a weight of 50g and should be ready for commercialisation in less than two years.
One possible application is more natural facial expressions in robots; Baughman recalls meeting an attractive robot in Korea called Eve. ‘She didn’t have enough muscles in her face to give her a natural expression,’ says Baughman. ‘But for this kind of application you don’t have to generate a lot of stress.’
He also envisages a textile that opens when the body heats up, allowing ventilation, or a textile that becomes more insulating when exposed to extreme heat, useful for emergency services. In the longer term the technology could offer exoskeletons for robotic soldiers or operate the major muscles of humanoid robots.
‘I see this artificial muscle as a new smart material,’ says Mark Schulz of the University of Cincinnati, author of an accompanying perspective article (Science, doi: 10.1126/science.1230428). Biomedical applications are a little further off, as there are biocompatibility and toxicity issues, but these yarns could be integrated into smart composites for aerospace applications, he says. ‘These muscles might be integrated into composites to morph the structure or for shape control. Instead of having an aileron in a wing that has a mechanical linkage, you could just bend the wing itself.’
The challenge now is to scale up the properties of nanotechnology to bulk yarn material, Schulz explains. Growing the nanotubes longer and reducing the yarn diameter are two approaches. ‘There are no physical barriers. It is more of an engineering challenge,’ he says.