Nanotubes makes super-twisty 'muscle'
Fantastic voyage A nanotube fibre that twists like muscles in an elephant trunk has been discovered, which could one day propel nanobots.
"We stumbled upon a type of material that produces a rotating action when we apply voltage to it," say Spinks.
"Through our investigations we've noted there are quite a few similarities in nature like elephants' trunks and lizards' tongues and even the flagella of bacteria."
About four years ago, team-members at the Nanotechnology Institute at the University of Texas, Dallas, started spinning a fine thread made entirely of carbon nanotubes (CNTs), tiny hollow cylinders of carbon, to make electrically-conductive smart textiles.
"They are looking at multifunctional textiles that could be a battery, an antenna or they might have antiballistic properties," says Spinks.
A team member Javad Foroughi was experimenting with small lengths of the CNT fibre and discovered the material rotates when a voltage is applied to it while it is immersed in an electrolyte.
"If we reverse the voltage it starts to rotate back in the other direction," says Spinks.
Naturally ocurring twisting muscles like octopus limbs involve helically wound fibres that rotate by contracting against an incompressible, bone-less core.
By contrast, the rotation in the helically wound carbon nanotubes is caused by the material soaking up more electrolyte as the voltage is applied.
While there are other rotating materials, Spinks says this material is by far the most twisty material yet. The yarn rotates up to 600 revolutions per minute and 1000 times more per centimetre of thread than other materials.
"The longer the piece of thread the more the end will rotate," says Spinks.
In their paper, Spinks and colleagues, demonstrate the material can be used to make a tiny millimetre-scale paddle mixer to mix fluids.
Beyond this the researchers hope to use the material in micro machines.
"In general it will be useful wherever you want mechanical movement when space is limited," he says,
"It's very difficult to make a very tiny conventional type motor."
He says the material could be used in consumer products, such as zoom lenses in mobile phones.
But it could also help in the development of nanobots that deliver drugs, remove parasites and fight cancer, say the researchers.
Currently one challenge in the use of nanobots has been the how to propel them along in the bloodstream.
Spinks says the new artificial muscle could help do the job by mimicking the flagella of bacteria on the back of these tiny swimming robots.
The researchers are currently working on using a related material to help in the tricky insertion of the cochlear implant. This device must be inserted around corners into a small space with lots of delicate membranes.
Spinks says the team's long-term aim is to develop worn devices that assist human movement.
The researchers are also developing a wearable sleeve that can help with arm movements or massage.
In regards to the safety concerns that surround carbon nanotubes, Spinks, says the "jury is still out".
"There's certainly still a lot more work to be done to decide whether they're safe or under what circumstances they're safe - like most chemicals."