Prosthetic arms can provide controlled sensory feedback
Losing an arm doesn’t have to mean losing all
sense of touch, thanks to prosthetic arms that stimulate nerves with mild
electrical feedback.
Researchers have
developed a control algorithm that regulates the current so a prosthetic user
feels steady sensation, even when the electrodes begin to peel off or when
sweat builds up.
“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 a researcher.
Commercial prosthetics
don’t have good sensory feedback. This is a step toward getting reliable
sensory feedback to users of prosthetics,” he said.
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 aerospace
engineering professor, the principal investigator of the study. During ordinary
wear over time, the electrodes connected to the skin can begin to peel off,
causing a buildup 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,” the Prof. said.
The 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 percent peeled off.
The researchers tested
the controller on two patient volunteers. They performed a test where the
electrodes were progressively peeled back and found that the control module
reduced the electrical current so that the users reported steady feedback
without shocks. They also had the patients perform a series of everyday tasks
that could cause loss of sensation due to sweat: climbing stairs, hammering a
nail into a board and running on an elliptical machine.
“What we found is that
when we didn’t use our controller, the users couldn’t feel the sensation
anymore by the end of the activity. However, when we had the control algorithm
on, after the activity they said they could still feel the sensation just
fine,” the researcher said.
Adding the controlled
stimulation module would cost much less than the prosthetic itself, he said.
“Although we don’t know yet the exact breakdown of costs, our goal is to have
it be completely covered by insurance at no out-of-pocket costs to users.”
The group is working
on miniaturizing the module that provides the electrical feedback, so that it
fits inside a prosthetic arm rather than attaching to the outside. They also
plan to do more extensive patient testing with a larger group of participants.
“Once we get a
miniaturized simulator, we plan on doing more patient testing where they can
take it home for an extended period of time and we can evaluate how it feels as
they perform activities of daily living. We want our users to be able to
reliably feel and hold things as delicate as a child’s hand,” he said. “This is
a step toward making a prosthetic hand that becomes an extension of the body
rather than just being another tool.”