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Thought-powered bionic arm
May 23, 2013, 1:05 pm


The idea of an amputee tinkling on piano keys with all the flair and grace of an able-handed person may seem like a futuristic fantasy.

But now amputees can effortlessly arch and extend each finger on their bionic arm.

Its makers describe the robotic limb as the most sophisticated of its kind in the world, recreating virtually every movement of a natural arm — and all controlled by brain power.

Featuring 100 sensors, 26 joints, 17 motors and a tiny computer built into the palm of the robotic hand, the revolutionary Modular Prosthetic Limb (MPL) is the work of researchers at Johns Hopkins University in Maryland.

Weighing four kilograms — much like a normal arm — it can mimic almost all the same movements. By order of magnitude the developers have increased the ability to do very highly dexterous kinds of motions. So you can think about things like eventually playing the piano.

The MPL is programmed to respond to electrical impulses in the user’s residual limb — he simply has to think about moving his old arm.

The amputee underwent targeted muscle reinnervation — surgery that involves rewiring electrical signals in the stump. Only 50 people in the world have had the operation, which takes a couple of hours.

All the electrical signals that are going down to the missing limb are taken and rerouted residual muscles that are still there. Thus when the amputee has a natural thought about moving that missing limb, he contracts that muscle and we are able to capture those signals and translate them into messages for the prosthetic limb.

Within two weeks of surgery, one is able to feel the phantom limb for the first time in years.

The ambitious bionic limb, seven years in the making, is incredibly lifelike in its movements, thanks to a complex symphony of muscle triggers. Other robotic arms have relied on direct signals, whereas the MPL picks up a chorus of muscle motions — creating a more fluid movement.

A lot of electrode sites are in play when it comes to the robotic arm. The array of muscle contraction is more like a chord in music, so one is able to get more complexity of motion.

While many prosthetic limbs look lifelike, finding one that also moves naturally has proved more of a challenge.

There are now plans to cover the MPL in a skin-like substance, which could make it the most inconspicuous artificial arm in history.

There is an elegance to it, and that is actually one of the most important things for the users of prosthetics. The natural movement is almost more important than the appearance.

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