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'Metal Muscles' Flex a New Bionic Hand

  • George Putic

Artificial limbs, including the most complex of them – the human hand – are getting more life-like and useful due to constant advances in tiny hydraulic, pneumatic and electric motors called actuators. But now scientists in Germany say the future of the prosthetic hand may be not in motors, but in wires that can ‘remember’ their shape.

The human hand is one of the most mechanically complex systems in nature, so making an artificial replica is a daunting task. An ideal prosthesis should be light and flexible, with a reasonably powerful grip and controlled by the owner’s mind.

Presently, prosthetics rely on relatively heavy hydraulic, electric or pneumatic actuators to flex artificial fingers, but scientists at Germany's Saarland University are experimenting with much lighter fibers made of a nickel-titanium alloy that change shape when connected to a source of electricity.

“The movement of the hand is done by the wire. This wire, when activated, they contract. And we are able to exploit this contraction to make the finger move. And we can move each phalanx independently,” said Filomena Simone, a PhD engineering student.

Artificial muscles, tendons

Bundles of memory wires could form more powerful yet lightweight artificial muscles and tendons. Their flexing can be controlled independently by measuring the electrical resistance of the wires.

“We can monitor the position of the finger without adding any other sensor; only exploiting this embedded feature of the wire,” said Simone.

Scientists believe that with further advances of so-called shape memory alloys, it will be possible to build more natural-looking prosthetic hands.

“If you look down the road to future prostheses generations, you'd like to see this integrated with the human body in a way that you can actually sense the nerve stimuli and then can feed that into a micro-controller which there will be translated to a corresponding signal to activate the muscle," said Stefan Seelecke at Saarland University.

Saarland University scientists are now looking into how natural patterns of hand movements could be applied to memory alloy muscles.