Developed by the Defense Advanced Research Projects Agency and the Johns
Hopkins University Applied Physics Lab as part of the agency’s 7-year,
Revolutionizing Prosthetics program, the Modular Prosthetic Limb has nearly as
much dexterity as a natural limb.
Technology
Although not yet commercially available, the brain-controlled Modular
Prosthetic Limb (MPL) consists of 17 high-torque motors, allowing for 26
degrees of actuated control. Mike McLoughlin, program manager of the
Johns Hopkins University Applied Physics Lab (APL), is confident the MPL can
perform the tasks a natural limb is capable of doing. It is designed for upper
extremity amputees, quadriplegics and individuals with neurodegenerative
disease. The MPL is capable of picking up utensils and bottles for feeding. He
called the MPL “the most technologically advanced upper extremity
device” available today.
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| The technology behind the MPL allows the arm to interpret the amputee’s thinking. |
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| Image: DARPA/JHUAPL/HDT Engineering Services |
“Individuals will be capable of taking care of themselves and their
children,” McLoughlin told O&P Business News. “They can
work in an office setting and earn a living. In terms of ability, the user can
move the fingers individually,” McLoughlin said. “The MPL’s
wrist has three degrees of freedom. The arm is designed to have the similar
strength of a man in the 50th percentile.”
The MPL, which weighs 8 pounds to 9 pounds, can curl 50 pounds and its
pinch grip ranges from 15 pounds to 20 pounds.
“In the past 5 years we have been developing the technologies that
have finally allowed us to reach this point,” he said. “The most
exciting part of the project is starting now.”
Neural-controlled integration
McLoughlin and the APL team are currently focusing on the MPL’s
brain-controlled upper extremity movement. For upper extremity amputees, the
nerves on the spinal cord are still intact and connected to some of the nerves
connected to the arm. When they imagine moving their arms, neurons will still
fire in the brain, but the signals have nowhere to go.
“If we capture the signals from the brain or peripheral nerve, we
can interpret what the patient wants to do and convert that to moving the
arm,” he said. “If the patient thinks of bending his or her elbow we
want the elbow to bend.”
It has taken nearly 5 years to create and incorporate enabling
technologies for the MPL, according to McLoughlin. Electrodes can be implanted
in the brain to capture neural activity. The MPL technology can pick up some of
those signals and interpret them. Those signals would then be converted to a
computer signal that would move the MPL. He believes training with the device
would be relatively simple because the technology allows the arm to interpret
the patient’s thinking, rather than the patient learning how to control
the arm.
“We are working with University of Pittsburgh and the California
Institute of Technology for implanting electrodes in spinal cord injury
patients, quadriplegics and patients with neurogenerative conditions,” he
said. “It is all coming together this year. It really is an exciting time
for the program.”
Not one size fits all
McLoughlin said targeted muscle reinnervation (TMR) surgery is an
excellent way to control the MPL, especially for amputees who elect not to have
the brain implant surgery. Spare muscles, normally found in the chest, are
denervated and then reinnervated with residual nerves of the amputated limb.
The reinnervated muscles provide signals that are similar to the original nerve
functions of the missing limb. For a spinal cord injury patient, a cortical
implant would be the only way to interface with the arm, given that the
peripheral nerve system is incapable of functioning.
“Amputees who have endured extensive damage to their peripheral
nerve system may not have enough residual nerve for a TMR surgery,” he
said. “This is not a one-size fits all approach.”
What’s next?
On Jan. 24, Air Force Sgt. Joe Delauriers became the first
patient to use the MPL at the Walter Reed National Military Medical Center in
Bethesda, Md. Four months earlier, Sgt. Delauriers was injured by an improvised
explosive device in Afghanistan, causing him to lose both of his legs and part
of his left arm.
“We are sponsored by the Department of Defense and taking care of
wounded soldiers is our top priority,” he said. “But it does not stop
there. We all recognize that we have the potential to bring aid to a much
broader range of patients in the civilian sector. The wounded soldier was the
motivation, but this is something that can benefit anybody.”
While still in the early stages of human testing, the MPL is heading
down the path to commercialization. McLoughlin and his team are always on the
lookout for a technological game changer, but they must also avoid being in a
constant state of change.
“We always have to think about the next device in the
pipeline,” he said. “There are a series of things that can transition
out of this program and evolve over time. But we do not want to be in a
constant state of flux or we will never commercialize anything. For someone who
is a quadriplegic or who can not use his or her natural arms, there is nothing
available. The MPL offers the promise of something that would change their
lives — an opportunity to be more independent. It is something we are
deeply committed to.” — by Anthony Calabro
For more information:
Fortnoy, Stephanie. WRNMMC Uses New, Brain-Controlled Prosthetic Arm.
Available at: http://www.navy.mil/search/display.asp?story_id=65123. Accessed:
April 10, 2012.
Rehabilitation Institute of Chicago. Targeted muscle reinnervation:
Control your prosthetic arm with thought. Available at:
http://www.ric.org/conditions/pocc/services/bionic.aspx. Accessed: April 10,
2012.
