A bionic hand that restores the sense of touch to amputees could soon be developed thanks to new research that has enabled two patients to feel sensations, new research shows.
Claudia Mitchell, 27, a former U.S. Marine who lost her left arm at the shoulder in a motorcycle accident three years ago, and Jesse Sullivan, 60, who lost both arms to electrical burns, were both fitted with prosthesis by Dr. Todd Kuiken of the Rehabilitation Institute of Chicago.
In fitting their prosthetic arms, Kuiken used a new surgical technique that rerouted the nerves from their injured arms to the skin on the chest.
Thanks to the surgery, the two now can sense pressure, temperature and pain as if their missing hands were still present, according to a study published in the Proceedings of the National Academy of Sciences.
The two report that when they touch things or are touched they can feel detailed sensations as if they had come from their phantom limbs, the researchers said in their study. The researchers say the 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,” 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 Kuiken, whose targeted reinnervation 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, Mitchell, 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 range of movement were published in the medical journal, The Lancet. At the time, Mitchell said, “I just think about moving my hand and elbow, and they move. I think, ‘I want my hand open’ and it happens. My original prosthesis wasn’t worth wearing – this one is.”
In the new study, the patients report that signals from the hand nerves occasionally overlap with those of the nerves that naturally serve the chest skin, but they can clearly distinguish which is which. Pressure and hot and cold temperatures can be felt, as can pain.
“We have provided evidence that amputated-hand nerves can establish a cutaneous expression of sensation, referred to the missing limb, in foreign skin,” Kuiken said.
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,” Kuiken said.