鈥淥NE day you could find yourself sitting in a bar next to a humanoid robot, who is taking a shot of vodka to give himself the energy to go to work.鈥� So says Ray Baughman, a nanotechnologist at the University of Texas at Dallas, who has developed self-powered artificial muscles that could ultimately be used in robotic limbs and prosthetics.
Baughman and his colleagues have designed two types of artificial muscle by adapting fuel cells so that the power source is part of the muscle itself, rather than coming from a separate battery.
The first is made from a nickel-titanium 鈥渟hape-memory鈥� wire coated in a platinum catalyst. A mixture of oxygen and either methanol or hydrogen is passed over the platinum coating, which catalyses a reaction between the gases. This releases heat, which warms the wire and makes it contract. When the flow of fuel stops, the wire expands back to its original length. The wire muscle exerts 100 times the force of a natural muscle of the same size, Baughman says.
Advertisement
Methanol is a particularly useful fuel because it has such a huge store of energy, says Siegmar Roth, an artificial muscle specialist at the Max Planck Institute for Solid State Research in Stuttgart, Germany. Methanol-powered fuel cells have the potential to deliver 30 times the energy of a conventional lithium-ion battery of the same size. This would mean the muscles could generate sufficient power to move a prosthetic muscle without adding unnecessary weight.
The team is now trying to find practical ways to supply the muscle with fuel. One possibility, Baughman says, is to use a valve mechanism controlled by very slight movements that could be used by people with limited finger or arm mobility. Another challenge is to find ways to prevent the muscle from overheating as it contracts, he says.
The researchers鈥� second artificial muscle is made from sheets of carbon nanotubes coated in a catalyst. It is not yet as powerful as the wire muscle, but could potentially overtake it, Baughman says. The nanotube sheet acts as a fuel cell electrode, and as the methanol or hydrogen reacts with oxygen above its surface, charge is transferred to the nanotubes, causing the sheet to expand. Neutralising the charge should make the sheet return to its original size, but the team has not yet succeeded in doing this. They are now investigating how this could be achieved.
The nanotube muscle can also act as a super-capacitor, storing electrical energy for later use, Baughman says.
