Researchers from Southern Methodist University (SMU) Neurophotonics
Research Center are in the process of developing a two-way fiber optic
communication between peripheral nerves and prosthetic limbs. The connection
between peripheral nerves and the prosthesis is crucial to a patient not only
moving their arms or legs but feeling pressurized sensations.
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| Volkan Otugen |
“The mission of this neurophotonic sensor is to create an
all-optical interface between the brain and the limbs,” Volkan Otugen,
PhD, chair of the Lyle School of Mechanical Engineering at SMU, told
O&P Business News. “That is both sensing optically what
the brain is signaling and transferring that information to the muscle to the
nerve system and around the limb where the connection was severed.”
According to Otugen, delivering that information optically will
stimulate the nerve so a motion can be made at the limb level.
“Taking stimulation from the outside and using the same type of
sensing to deliver to the brain and then stimulating back again closes the loop
and makes it a perfect two-way interface,” Otugen said.
Sensation and stimulation groups
Funded by the Department of Defense, the 2-year, $5.6-million
Defense Advanced Research Projects Agency (DARPA) Project is
divided into two groups. The sensation group is led by Otugen and Marc
Christensen, PhD, chair of electrical engineering at SMU, as well as
researchers from the University of Texas, Dallas, and the University of North
Texas. This group will apply technology such as fiber optics and evanescent
waves.
“The current project is focused on ‘sensing and
stimulation,’” Otugen said. “That is, the optical sensors we are
developing will be used to sense the brain and nerve activity, called action
potential.”
Small laser pules
The stimulation group, led by E. Duco Jansen, PhD, his Vanderbilt team
and research teams from Case Western Reserve University, will use fiber optics
to send small laser pulses to be picked up by the neurons still remaining in
the nervous system. Dustin Tyler, PhD, is leading the research team at Case
Western Reserve University.
“What we do is sensing; Duco and his team do stimulation,”
Christensen said. “They are intimately tied together. The stimulation
technology was proven before, so that technology is a little bit more mature.
Ours was unproven technology when we started the program.”
The two technologies would combine and enable a patient to think about
moving their robotic arm and grab something like a loved one’s hands.
Sensors on the robotic arm would give sensory feedback to the person so he or
she can actually feel the warmth and softness of the hand that they grabbed,
according to Christensen.
Construction of the fiber optic link
According to Otugen, the fiber optic link is a small, plastic,
rubber-like implant with a connector to snap it around a nerve embedded in a
polymer silicone cuff. There would be a number of fibers containing optical
signals to direct stimulation. Small fiber ends would protrude into the nerve
bundle and would work their way between the actual fibers in the nerve. Small
spheres attach and bond to the fiber.
“This technology opens up a new range of possibilities — from
a breakdown in the central nervous system to an amputation or spinal cord
damage,” Otugen said. “It has all of the potential and none of the
track record. If it works as well as we hope, it will make a dramatic
difference. But we are in the earliest stages.”
Otugen and Christensen are confident the technology works; it is just a
matter of going through the necessary steps. According to Otugen, the
technology is still too premature for a human trial. Electrical interfaces have
been shown to last up to 6 months. But a soldier coming home with one or more
missing limbs will live 30 to 40 years. Otugen and Christensen’s goal is
to achieve a 10-year life span for the technology.
In the early stages
“The environment around [the implant] is a biological
environment,” Christensen said. “This is not between two pieces of
metal. The implant is in a living, breathing being. The unknown for me is
always scary. There is a laundry list of simple challenges, but none of them
are showstoppers. It is just that we are in the early stages in scientific
development. This is a new methodology for us. I am incredibly hopeful that
this will come together the way it should.”
What makes this project remarkable, according to Otugen, is that
ultimately, this is a biological project, but it is being conducted by a
diverse group of engineers.
“This is the first time I have worked in this area,”
Christensen admitted. “This is a change for me and it is something that
has a socially redeeming value which adds a level of urgency and level of
excitement. It gets me out of bed early thinking about the problems. And it
keeps me up late at night thinking how we are going to create the
solutions.” — by Anthony Calabro
For more information example
For more information:
- Calabro, A. DARPA Project will develop a system that naturally
controls prostheses. O&P Business News. 2011;20(2):22.- Laser Focus World. Fiber optics to improve prosthetics through
DARPA-funded, SMU-led Neurophotonics Research Center. Available at:
www.optoiq.com. Accessed: Nov. 4,
2010.
Disclosure: Christensen and Otugen
have no relevant financial disclosures.
