Robotic Exoskeleton Replaces Muscle Work
A robotic exoskeleton controlled by the wearer's own nervous system
could help users regain limb function, which is encouraging news for
people with partial nervous system impairment, say University of
Michigan researchers.
The ankle exoskeleton developed at U-M was worn by healthy subjects to
measure how the device affected ankle function. The U-M team has no
plans to build a commercial exoskeleton, but their results suggest
promising applications for rehabilitation and physical therapy, and a
similar approach could be used by other groups who do build such
technology.
"This could benefit stroke patients or patients with incomplete
injuries of the spinal cord," said Daniel Ferris, associate professor
in movement science at U-M. "For patients that can walk slowly, a brace
like this may help them walk faster and more effectively."
Ferris and former U-M doctoral student Keith Gordon, who is now a
post-doctoral fellow at the Rehabilitation Institute of Chicago, showed
that the wearer of the U-M ankle exoskeleton could learn how to walk
with the exoskeleton in about 30 minutes. Additionally, the wearer's
nervous system retained the ability to control the exoskeleton three
days later.
Electrical signals sent by the brain to our muscles tell them how to
move. In people with spinal injuries or some neurological disorders,
those electrical signals don't arrive full strength and are
uncoordinated. In addition, patients are less able to keep track of
exactly where and how their muscles move, which makes re-learning
movement difficult.
Typically, robotic rehabilitative devices are worn by patients so that
the limb is moved by the brace, which receives its instructions from a
computer. Such devices use repetition to help force a movement pattern.
The U-M robotic exoskeleton works the opposite of these rehabilitation
aids. In the U-M device, electrodes were attached to the wearer's leg
and those electrical signals received from the brain were translated
into movement by the exoskeleton.
"The (artificial) muscles are pneumatic. When the computer gets the
electrical signal from the (wearer's) muscle, it increases the air
pressure into the artificial muscle on the brace," Ferris said.
"Essentially the artificial muscle contracts with the person's muscle."
Initially the wearer's gait was disrupted because the mechanical power
added by the exoskeleton made the muscle stronger. However, in a
relatively short time, the wearers adapted to the new strength and used
their muscles less because the exoskeleton was doing more of the work.
Their gait normalized after about 30 minutes.
The next step is to test the device on patients with impaired muscle function, Ferris said.
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This work was supported by a grant from the National Institute of Neurological Disorders and Stroke.
For more on Ferris, who also has an appointment in biomedical engineering and physical medicine and rehabilitation, see: http://www.kines.umich.edu/faculty/full-time/ferris.html.
Contact: Laura Bailey
University of Michigan
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