Bionic arms restore touch

A bionic hand that restores the sense of touch to amputees could soon be developed thanks to US research that has enabled two patients to feel sensations.

The man and the woman can sense pressure, temperature and pain as if their missing hands were still present, after surgery rerouted the nerves from their injured arms to the skin on the chest.

Claudia Mitchell, 27, who lost her left arm at the shoulder in a motorcycle accident three years ago, was fitted with the world’s most advanced prosthetic arm after the operation pioneered by Todd Kuiken, of the Rehabilitation Institute of Chicago. Jesse Sullivan, who is 60, lost both arms in an electrical burns accident in 2001, and has also been fitted with prostheses by Dr Kuiken’s team.

Thanks to the procedure, when they touch things or are touched they can now feel quite detailed sensations as if they had come from their phantom limbs, the researchers reported yesterday. The remarkable results suggest that the technique could soon be used to make artificial arms that can reproduce feeling, possibly within as little as two years.

As well as giving amputees back their sense of touch, the breakthrough opens up the possibility that bionic limbs could be controlled more precisely through the power of thought.

“Our results illustrate a method for creating a portal to the sensory pathways of a lost limb,” Dr Kuiken said. “This work offers the possibility that an amputee may one day be able to feel with an artificial limb as though it was his own. Sensors could be placed in a prosthetic hand to measure contact forces and temperature, while a device could press or thermally stimulate the reinnervated skin to provide sensory feedback that appropriately correlates to hand perception.”

The advance is the latest of several recent developments by Dr Kuiken, whose targeted reinnervation (TR) technique is pushing back the boundaries of artificial limb technology.

The nerves that would normally serve the missing hand are moved so that they extend to the upper part of the chest, from where they grow to reach the skin. As their electrical signals can be picked up here, these can be used, with training, to guide an artificial limb. Last year Ms Mitchell, a former US Marine, spoke of her delight at being able to use her bionic arm to cut a steak and peel a banana. It is effectively controlled by her thoughts, as sensors attached to her chest pick up electrical cues from her rerouted arm nerves.

In February, details of the TR arm’s unprecedented range of movement were published in the medical journal The Lancet. “I just think about moving my hand and elbow, and they move,” Ms Mitchell said. “I think, ‘I want my hand open’ and it happens. My original prosthesis wasn’t worth wearing – this one is.”

While there were hints then that the surgery had also restored some feeling, a fuller investigation has now been published in the journal Proceedings of the National Academy of Sciences.

Signals from the hand nerves occasionally overlap with those of the nerves that naturally serve the chest skin, but the patients can clearly distinguish which is which. Pressure and hot and cold temperatures can be felt, as can pain.

Dr Kuiken said the work examined “the intriguing sense of touch, temperature and pain from the hand that developed in the chest skin” of the two patients. “We have provided evidence that amputated-hand nerves can establish a cutaneous expression of sensation, referred to the missing limb, in foreign skin,” he added.

The team’s ultimate goal is to attach pressure and temperature-sensitive sensors to the fingers and palm of a bionic hand. These will then send back electrical signals to the chest, where they will stimulate the arm nerves and send sensations to the brain. Such feeling could greatly improve the range of movement available to patients using prosthetic limbs. “It will also be interesting to learn how the patients’ perceptions may change with time and consistent use of a prosthesis providing cutaneous feedback,” Dr Kuiken said.

Source - The Times

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