Prosthetic hand helps amputees control the intensity of their touch

October 27, 2016

With other prosthetics, users have to judge the intensity of touch by eye
The artificial hand lets amputees differentiate between soft or firm touch
Implanted electrodes let them feel pressure as they would with a hand

Associated Press

and
Shivali Best For Mailonline

Published:
19:42 EST, 26 October 2016

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Updated:
05:15 EST, 27 October 2016

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A next-generation artificial hand is letting two amputees tell the difference between a soft or firm touch – like holding a child without squeezing too tightly.

Implanted electrodes allow the men to feel the same intensity of pressure in the artificial hand as they could in their other hand.

The groundbreaking device is another step toward developing prosthetics that can feel.

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A next-generation artificial hand is letting two amputees tell the difference between a soft or firm touch – like holding a child without squeezing too tightly. Pictured is Keith Vonderhuevel, testing the experimental device

HOW DOES IT WORK?

For amputees, key nerves that once control the hand still remain in the stump of the missing limb.

Two years ago, Case Western researchers wired those nerves to a prosthetic outfitted with sensors that let the two volunteers sense different textures.

When the prosthetic sensors were touched, they activated a portable stimulator that sent electrical signals to the nerves, which detected textures like a cotton ball or sandpaper.

But this new study goes further by looking at how to stimulate the intensity of touch.

In a series of experiments, the team from Case Western learned how the number and frequency of nerve fibre stimulations adjust with different amounts of pressure.

The two volunteers can now use the experimental hand at home, not just the laboratory, to start learning if it makes a difference in everyday life.

To Keith Vonderhuevel, testing the experimental device meant finally cradling his granddaughter without first taking off his artificial hand for fear of hurting her.

‘Just to be able to touch and feel, it’s an amazing thing,’ said Mr Vonderhuevel who lost his right arm below the elbow 11 years ago in a work accident.

‘It feels like a light pressure.

‘The harder I squeeze, the stronger that pressure gets.’

The prosthetic limb has been developed by researchers from Case Western Reserve University in Ohio.

The two volunteers can now use the experimental hand at home, not just the laboratory, to start learning if it makes a difference in everyday life.

Dustin Tyler, who leads the project, said that getting to the point where users respond as they would to a normal limb is key ‘to moving toward truly creating a replacement for the hand.’

Normally when people reach for something, the hand automatically grasps with just enough force to hang on.

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Nerves in the skin fire rapid messages to the brain so the muscles immediately squeeze tighter or loosen up.

But users of prosthetic hands don’t have that intuitive control. Instead they have to judge every motion by eye so they don’t crush or drop something, difficult even with practice.

That’s why many hesitate over shaking hands or holding something delicate.

Normally when people reach for something, the hand automatically grasps with just enough force to hang on (stock image). But users of prosthetic hands don’t have that intuitive control. Instead they have to judge every motion by eye so they don’t crush or drop something

Earlier this month, researchers at the University of Pittsburgh reported harnessing brain waves to help a paralyzed man not only move a robotic arm with his thoughts but, in a first, to feel pressure in his own motionless fingers when the artificial ones were touched.

Electrodes implanted in the part of his brain that controls hand sensation made this possible.

For amputees, key nerves that once control the hand still remain in the stump of the missing limb.

Two years ago, Case Western researchers wired those nerves to a prosthetic outfitted with sensors that let the two volunteers sense different textures.

When the prosthetic sensors were touched, they activated a portable stimulator that sent electrical signals to the nerves, which detected textures like a cotton ball or sandpaper.

But this new study goes further by looking at how to stimulate the intensity of touch.

In a series of experiments, the team from Case Western learned how the number and frequency of nerve fibre stimulations adjust with different amounts of pressure.

Mr Tyler said: ‘Our stimulation is as sensitive as your real hand.

‘He’s been gratified to feel Vonderhuevel change from ‘the wet-fish handshake to the solid I’m-interacting-with-you handshake.

‘There is so much information in the subtleties of touch.’