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Researchers making strides toward neural control of prostheses, tissue regeneration
Soldier amputees to one day be able to control upper extremity prostheses with their minds.
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WASHINGTON – U.S. soldiers are returning from Iraq and Afghanistan with amputated or severely wounded limbs. Thoughts of these soldiers receiving prosthetic arms controlled simply with the power of the mind or regeneration of lost limbs were once only fantastic dreams, however recent investigations by a Department of Defense agency may, someday, make those fantasies come true.
The Defense Sciences Office (DSO) of the Defense Advanced Research Projects Agency (DARPA) is conducting multi-center projects to generate full restoration of tissue function after traumatic injury and to create fully functional prosthetic limbs that respond to neural control.
Eventually the two projects will unite to study osseointegration of prosthetic arms within weeks, rather than months, according to Jon Mogford, PhD, DSO program manager.
“We’re going from thinking of materials as biocompatible to really being truly integrated, biointegrated and fully functional,” Mogford said at the American Society for Surgery of the Hand annual meeting. “This would have enormous impact on the prosthesis program where it can extend the capabilities of an upper extremity prosthesis [considering] the type of distraction forces that those devices are going to undergo.”
Revolutionizing prosthetics
Mogford and Col. Geoffrey Ling, MD, PhD, are DARPA program managers overseeing three programs on revolutionizing prosthetics and restorative injury repair. As a funding agency, DARPA awarded funding to investigators at various academic institutions and set milestones for completion in each program.
Ling oversees the DARPA programs on revolutionizing prosthetics and creating Human-Assisted Neural Devices (HAND), which began 5 years ago. “The idea at DARPA was not so much how can we build a better platform, but how can we actually make this platform better functionally?” he said.
Current prosthetics such as the Utah arm use myoelectric control, but Ling said this limits residual trunk or shoulder muscles to control the hand. “Our idea was to not use a myoelectric approach, but rather use the brain signals themselves to go directly to the nervous system,” Ling said.
Images: Ling G, Mogford J |
Enabling brain activity also provides closed loop capabilities, sending out motor commands and receiving sensory feedback – another feature that is not available with current prosthetics, he said.
HAND project underway
The projects include a 2-year program to deliver a prosthetic arm with a movable hand, separately articulating fingers and full range of motion in the elbow, wrist and shoulder, Ling said.
A 4-year program will deliver capabilities for controlling the new prosthesis with the brain only. There are multiple phases in this program: passing into the nervous system, passing into the peripheral nerves at 2 years, and passing directly into the brain to create sensory capabilities and tactile receptors in the hand at 4 years.
Primate research
Researchers at Duke University, under the DARPA project, already conducted a study using monkeys. They taught the monkeys to use a joystick to position a cursor over a computer screen and move the cursor onto a moving target, while the researchers conducted tests and measured microelectrodes in the monkeys’ brains. Eventually they found the monkeys could move the robotic arm and position the cursor with their thoughts alone, Ling said.
“We really are very much committed to this project, which has a 4-year deliverability goal,” he said. “In 4 years’ time, DARPA’s goal is to deliver this arm ready for FDA approval and by the 2-year mark. Our goal is to actually have delivery of the device.”
Tissue regeneration
With advances in body armor and the speed at which soldiers are transported back to the United States, soldiers are surviving wounds that would previously have been fatal, Mogford said. Previous wound healing programs were not designed to address these types of wounds. “These are complex wounds that are outside the realm of what a typical [research] approach would be, as a single-tissue type of approach,” he said.
DARPA established a program focused on full recovery of the soldiers’ lost structures and lost function – regardless of the tissues involved or the type of wounding action. Researchers will shift the standard wound-healing paradigm of inflammatory cells and restoring fibroblasts to the idea of full recovery, Mogford said. To do this, scientists are evaluating living organisms that regenerate lost structures.
The scientists set out to determine how to create a blastema – a mass of undifferentiated cells that redevelops lost structures – in an animal that does not physically form one and does not regenerate tissue.
“The upside here is that over the last decade or so, enormous work has been done with these lower organisms and a number of gene markers have been identified,” Mogford said. “A number of these markers are also expressed in human and mammalian-wound types, so this lends credence [that it] is something we can achieve.”
Project design
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Mogford’s restorative injury program is also designed in two phases. Phase one is the generation of a blastema in a non-regenerating mammal, based on genetic markers. Mammals that are successful at that phase will move on to demonstrating a controlled morphogenesis of the lost structure, he said.
At the University of Pittsburgh, a DARPA project site, scientists are focusing on the Murphy Roths Large mice (MRL) model, which is a strain of mouse that regenerate for various types of wounds – most typically the ear. In the MRL mouse, only certain wounds and tissues regenerate, which provides scientists with an internal control for comparing cell involvement.
“[These researchers] believe that they can in essence drive a regenerative response by control of the local environment and by the cell population,” Mogford said.
The researchers are evaluating the involvement of infiltrating cells, bone marrow cells, vascular progenitor cells, immune cells and locally produced cells. “The researchers are not actually inventing anything new here,” Mogford said. “They have everything they need in the present technological toolbox, as far as wound healing studies and biology studies to do these experiments.”
In another DARPA project site at the University of Tulane in New Orleans, researchers believe the actual orchestrators of regeneration are local fibroblasts, based on 100 years of their own amphibian regeneration research.
“Their milestones are really focused on picking apart the role of the fibroblast and how it does this and how to translate that into systems that don’t achieve the type of regeneration that these animals do,” Mogford said.
There is also interest in pursuing new areas of reseach to identify new approaches for achieving osseointegration and skin grafting in a matter of weeks, Mogford said.
“What we would like to do is again induce a paradigm shift and to really push this field into achieving very rapid interfacing of the materials, particularly in a construct with human tissue. The key point there is the speed at which this can occur.”
For more information:
- Ling G. Revolutionizing upper extremity prosthesis by 2009 and a prediction for the future.
- Mogford J. Wound healing and tissue regeneration and biotic-abiotic interfaces. Symposium #2. Both presented at the American Society for Surgery of the Hand 61st Annual Meeting. Sept. 7-9, 2006. Washington.
- Col. Geoffrey Ling, MD, PhD, is with the Defense Advanced Research Project Agency, 3701 North Fairfax Drive, Arlington, VA 2203-1714 and can be reached at 571-218-4674, fax 571-218-453, or geoffrey.ling@darpa.mil.
- Jon Mogford, PhD, is with the Defense Advanced Research Project Agency, 3701 North Fairfax Drive, Arlington, VA 2203-1714 and can be reached at 571-218-4928, fax 703-741-7845, or jon.mogford@darpa.mil.