New module could give prosthetic arms delicate sense of touch

New York : Losing an arm need not mean losing all sense of touch as researchers have developed a new sensory control module that may enable users of prosthetic arms to to be able to reliably feel and hold things as delicate as a child's hand.

"We're giving sensation back to someone who's lost their hand. The idea is that we no longer want the prosthetic hand to feel like a tool, we want it to feel like an extension of the body," said Aadeel Akhtar of University of Illinois at Urbana-Champaign in the US.
"Commercial prosthetics don't have good sensory feedback. This is a step toward getting reliable sensory feedback to users of prosthetics," said Akhtar who is the lead author of a paper describing the sensory control module.

In the study published in the journal Science Robotics, the researchers described a control algorithm that regulates the current so a prosthetics user feels steady sensation, even when the electrodes begin to peel off or when sweat builds up.

Prosthetic arms that offer nerve stimulation have sensors in the fingertips, so that when the user comes in contact with something, an electrical signal on the skin corresponds to the amount of pressure the arm exerts.

For example, a light touch would generate a light sensation, but a hard push would have a stronger signal.However, there have been many problems with giving users reliable feedback, said principal investigator of the study Timothy Bretl, Professor at University of Illinois at Urbana-Champaign.

During ordinary wear over time, the electrodes connected to the skin can begin to peel off, causing a build-up of electrical current on the area that remains attached, which can give the user painful shocks.

Alternately, sweat can impede the connection between the electrode and the skin, so that the user feels less or even no feedback at all."A steady, reliable sensory experience could significantly improve a prosthetic user's quality of life," Bretl said.
The new controller monitors the feedback the patient is experiencing and automatically adjusts the current level so that the user feels steady feedback, even when sweating or when the electrodes are 75 per cent peeled off, the study said.

In a test where the electrodes were progressively peeled back, the researchers found that that the control module reduced the electrical current so that the users reported steady feedback without shocks.

The researchers believe that adding the controlled stimulation module would cost much less than the prosthetic itself.The group is working on miniaturising the module that provides the electrical feedback, so that it fits inside a prosthetic arm rather than attaching to the outside.