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When the National Academy of Sciences established the Artificial limb Program in 1945, the options for amputees were few: crude, wooden prostheses. And for those who chose none: life confined to a wheelchair. Fast-forward 65 years and the United States faces an influx of amputees from the conflict in Iraq, but the opportunities for soldiers returning home from war with an amputation are far more advanced. Listed are some of the most important advancements in robotic prosthetics in the last 20 years that give artificial limbs more function than ever before.
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1. Prosthetic Foot Materials
For years, wood was the dominant material for a prosthesis. But over the last 20 years, materials have emerged to give greater comfort and confidence for amputees. Susan Kapp, an associate professor of orthotics and prosthetics at the University of Texas Southwestern School of Health Professions, says if a prosthetic foot is cut open, most likely the material found inside is carbon fiber. Carbon fiber, according to Kapp, is a much more life-like material, giving amputees a sense of life in their foot. Thermoplastic sockets give prosthesis recipients extended comfort at the site the prosthesis is fitted, and titanium gives a prosthesis longer life and durability.
U.S. Army/ Roger J. Mommaerts Jr.
Bluetooth technology made the jump from the cell phone industry to prosthetics in 2007 when Marine Lance Cpl. Joshua Bleill received two artificial legs after seeing combat in Iraq. Each leg was fitted with a Bluetooth device. Bluetooth is more often recognized for its ability to connect pieces of technology together without the use of wires. In Bleill’s case, the Bluetooth devices communicate with each other to regulate stride, pressure and speed in the prosthetic legs. The benefit of Bluetooth technology, according to Ryan Blanck, a prosthetist at the Center for Prosthetics and Orthotics at Brooke Army Medical Center in Ft. Sam Houston, Texas, is the programmability of the software. “We can take that technology an further develop it to adjust to a patients need,” Blanck said.
3. Microprocessor Knees
With an onboard computer within the prosthesis, people with above-knee amputations have greater control over walking, stopping and moving on inclines. These “robotic” knees, termed microprocessor knees, analyze the pressure an amputee puts on the missing limb. Also contained within the knee is a fluid control unit, which the microprocessor monitors to appropriate joint resistance when walking on inclines. Available since the early 1990s, microprocessor knees have revolutionized the arenas of safety and stability for people without knees. Kapp says people that receive the prosthesis don’t have to worry about the knee buckling under them.
Touch Bionics Inc. and Touch EMAS Ltd.
4. Myoelectric Technology
When the i-LIMB hand debuted in the United Kingdom in July 2007, people caught a glimpse of the future of robotic prosthetics. The i-LIMB applies myoelectric technology, where the prefix myo- denotes a relationship to muscle. Myoelectric prostheses are controlled by placing muscle sensors against the skin at the site of amputation. The electric signals generated by the muscle at an amputee’s stump controls a processor aboard the prosthetic. This myoelectric technology allows for greater control and precision in the five fully functional digits, enabling recipients to perform everyday tasks such as picking up coins and opening tabbed aluminum cans.
5. Targeted Muscle Reinnervation
Amputees are in the infant stages of controlling prostheses directly with their minds. Through targeted muscle reinnervation, the nerves from the amputated limb are reenergized in a different part of the body, for example, the chest. When an amputee wants to use their arm in a particular fashion, he or she thinks the action, prompting the nerves in the chest to react. That reaction sends a message to a microprocessor in the robotic limb, which performs the action. Currently, there are only 35 people in the world with TMR limbs, and Blanck has fit 14 of them. He says the ever-changing prosthetic field aims to allow an amputee think about their prosthesis in a way that is normal. Jesse Sullivan (left) was the first man to receive this treatment technique from the Rehabilitation Institute of Chicago, and Claudia Mitchel (right) was the first woman to receive it.
Although prosthetic hands give amputees a way to grasp objects, they do not offer a sense of touch. That means the person has to watch his or her robotic hand as it reaches to push or pick up an item.
Now researchers at the University of Chicago might have found a way to add touch to prosthetic limbs. The research, which appears in the Proceedings of the National Academy of Sciences, is funded in part by the Defense Advanced Research Projects Agency, and it’s not hard to see why the military would be interested. Beyond dreams of cyborg warriors, there’s the more prosaic matter of helping injured veterans.
The study, led by Sliman Bensmaia, assistant professor in biology and anatomy, identified patterns of neural activity that occur when monkeys manipulate objects and then induced these patterns artificially.
First he and his team connected electrodes to areas of a monkey’s brain that corresponded to each of its finger. The idea was to find out what kind of brain activity occurred when monkeys pick up or touch something.
Next, the researchers touched the animals’ fingers, using a device that applied a specific amount of pressure. The monkeys were rewarded if they correctly identified which finger was touched — the monkey just had to look in the right direction. Next, the researchers repeated the same action, but in reverse, sending an artificial signal through the electrode to the monkey’s brain, which caused the monkey to act the same way it would had it’s fingers been touched by the device — identifying fingers as touched even when they weren’t.
The next step was the sense of pressure. They trained the monkeys to identify whether the pressure on their fingers was smaller or larger. In this case, Bensmaia’s group wrote a computer program to generate the same kind of electrical current that gave rise to pressure sensations. Once again, the animals reacted the same way as if they had actually touched something.
Finally, the scientists examined the brain signals that occurred when there was a “contact event.” When the monkey’s hand was initially touched or pressure released, their brains showed a spike in activity. This spike is in addition to the signals for pressure and the individual fingers — it’s what tells the brain that there’s something in the hand to begin with before the signal settles down. The scientists duplicated that brain activity spike with artificial signals as well.
That implies that by programming those signals into an artificial limb, it’s possible to duplicate the sensation of touch. Just as natural limbs send signals to the brain, the artificial one would do so, too, except it wold be through electrodes linked to the relevant parts of the brain rather than nerve cells. An amputee would actually feel the object they are touching with such a prosthetic.
The setup hasn’t been tested in humans yet. But the monkey results are promising, and it could solve not only the problem of touch sense, but that of sensing limb position and possibly even help a person balance on his or her artificial legs.