A man who had his lower arm amputated has regained a realistic sense of texture using a bionic finger surgically connected to his nerves
“I could tell the difference between rough and smooth – it was amazing,” says Dennis Sørensen.
People who have had their hand or arm amputated can use a prosthetic body part to help them lift or grip objects. A device that could also recreate their sense of touch would make it easier for them to identify and manipulate objects.
To replicate this sense,and his team at the École Polytechnique Fédérale de Lausanne in Switzerland developed a bionic finger containing electromechanical sensors that deform when touched.
The sensors send an electrical signal to a computer. This converts the signal into a sequence of on-off commands, stimulating nerves via electrodes surgically inserted into the upper arm. The patterns of stimulation closely emulate those that naturally occur when you run your finger across different textures.
To test the sensors, Micera’s team hooked the bionic finger up to a machine that moved it over different pieces of plastic engraved with smooth or rough textures. The finger was also connected to electrodes surgically implanted in Sørensen’s upper arm.
When the finger moved, he experienced the sensation of texture where the index finger of his amputated arm had been. He could distinguish between surfaces 96 per cent of the time.
“It was very close to the feeling in my real arm – you can feel coarseness and the different gaps and ridges,” says Sørensen, who lost his lower arm in a firework accident in 2003 after a rocket blew up in his hand.
The idea is to eventually combine the fingertip sensors within a full prosthesis, allowing people to grip and feel objects.
No surgery required
Micera’s team also tested the bionic finger on four non-amputees using a single electrode inserted into the upper arm like an acupuncture needle. These volunteers were able to distinguish textures 77 per cent of the time.
The minimally invasive procedure should help accelerate the development of realistic-touch prostheses because it means they can be tested without the need for surgery.
By comparing the non-amputees’ brainwaves when they felt texture using their real finger and the bionic version, Micera’s team demonstrated that the sensations picked up by the bionic finger did indeed resemble those felt naturally.
“The brainwaves were similar in both experiments,” says team memberat the Biorobotics Institute in Pisa, Italy.
Rough and ready
A previous study byat the Louis Stokes Veterans Affairs Medical Center in Cleveland, Ohio, and his colleagues in 2014 gave amputees back a sense of touch and pressure, allowing them to without crushing the fruit.
Very important characteristics of sensations were shown in Tyler’s experiments, such as force and pressure, but not fine textures, says Oddo. “Now we are working towards allowing amputees to experience more natural stimuli like the texture of jeans – the things you would touch in the real world.”
Journal reference: eLife, DOI:
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