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SPIE Professional January 2011: Photonics for a Better World

Neurophotonic sensors for bionic limbs

Researchers at the Neurophotonics Research Center at SMU are working on improved prosthetic devices

Photonics research into improving prosthetic limbs for injured soldiers and other amputees got a boost from the U.S. Department of Defense last year with the establishment of the $5.6 million Neurophotonics Research Center at Southern Methodist University in Dallas, Texas.

Two-way fiber-optic communication between prosthetic limbs and peripheral nerves will be key to operating realistic robotic arms, legs, and hands that move like the real thing, and “feel” sensations like pressure and heat, researchers say.

Successful completion of this fiber optic link will allow for sending signals seamlessly back and forth between the brain and artificial limbs, giving amputees revolutionary freedom of movement and agility.

Marc Christensen, director of the Neurophotonics Research Center, says he and his colleagues also envision man-to-machine applications that extend far beyond prosthetics, leading to medical breakthroughs like brain implants for the control of tremors, neuro-modulators for chronic pain management, and implants for patients with spinal cord injuries.

“This technology has the potential to patch the spinal cord above and below a spinal injury,” Christensen says. “Someday, we will get there.”

Biocompatible connection

Currently available prosthetic devices commonly rely on cables to connect them to other parts of the body for operation — for example, requiring an amputee to clench a healthy muscle in the chest to manipulate a prosthetic hand. The movement is usually deliberate, cumbersome, and far from lifelike.

Replacing experimental electronic nerve interfaces made of metal with optical fibers and polymers may also lessen the likelihood of an immune response.

The research goal is to develop a link compatible with living tissue that will connect powerful computer technologies to the human nervous system through hundreds or even thousands of sensors embedded in a single fiber.

“Enhancing human performance with modern digital technologies is one of the great frontiers in engineering,” Christensen says. “Providing this kind of port to the nervous system will enable not only realistic prosthetic limbs, but also can be applied to treat spinal cord injuries and an array of neurological disorders.”

Military incentive

The Defense Advanced Research Projects Agency (DARPA) is funding the $5.6 million center with industry partners as part of its Centers in Integrated Photonics Engineering Research (CIPhER) project, which aims to dramatically improve the lives of the large numbers of military amputees returning from war in Iraq and Afghanistan.

The center brings together researchers from SMU, Vanderbilt University, Case Western Reserve University, the University of Texas at Dallas, and the University of North Texas, and industry partners Lockheed Martin, Aculight, Plexon, Texas Instruments, National Instruments, and MRRA.

The center formed around a challenge from the industrial partners to build a sophisticated fiber-optic sensor scaled for individual nerve signals. “Team members have been developing the individual pieces of the solution over the past few years, but with this new federal funding we are able to push the technology forward into an integrated system that works at the cellular level,” Christensen says.

illustration from SMU

The research builds on partner universities’ recent advances in light stimulation of individual nerve cells and new, extraordinarily sensitive optical sensors developed by SPIE member Volkan Otugen, chair of mechanical engineering at SMU and director of its Micro-Sensor Laboratory.

Otugen is site director for the new center and has pioneered research on tiny spherical devices that sense the smallest of signals utilizing a concept known as “whispering gallery modes.” A whispering gallery is an enclosed circular or elliptical area, like that found beneath an architectural dome, in which whispers can be heard clearly on the other side of the space.

The ultimate combination of advanced optical nerve stimulation and nerve-sensing technologies will create a complete, two-way interface that does not currently exist. “It will revolutionize the field of brain interfaces,” Christensen says.

Tell us your story

Articles in our Photonics for a Better World series highlight optics and photonics technologies that bring tangible gains to humanity.

Do you have a story to tell about the work that you or colleagues do to make the world a better place? Write to us at spieprofessional@spie.org

Have a question or comment about this article? Write to us at spieprofessional@spie.org.

DOI: 10.1117/2.4201101.04

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