Prosthetics meet robotics

Prosthetics meet robotics

Today's advanced artificial limbs are taking advantage of the latest robotic technologies to enable warfighters injured in battle to lead normal lives-sometimes with capabilities better than the original limb.

BY J.R. Wilson

Robotics research is merging with the latest medical technology to create a new generation of prosthetic feet, legs, hands, and arms to give users a more natural feel and capability. Developments began with comparatively simple microchip-controlled actions, then processors that translate muscle movements into prosthetic responses and clinical trials on controlling prosthetic movements through computer-interpreted brain waves.

As these developments push the human-mechanical interface further along, the ultimate result-one seen as achievable, at least in part, during this decade-is a form of symbiosis.

"In some discussions with the international standard-setting body for prosthetics, there is talk of no longer speaking of prosthetic arms but of wearable robotic devices because today's prosthetics are increasingly more robotic," says Dr. Robert Jaeger, director of deployment health research in the Veterans Health Administration (VHA) Office of Research & Development.

The fully articulated robotic hand RAPHaEL
The fully articulated robotic hand RAPHaEL (Robotic Air Powered Hand with Elastic Ligaments) can hold objects firmly as heavy as a can of food or as delicate as a raw egg. It also is dexterous enough to gesture for sign language. (Photo courtesy of Virginia Tech Robotics & Mechanisms Lab.)

"The biggest breakthrough for arms is the brain-computer interface. The dream of upper extremity prosthetic researchers is acquiring signals directly from that part of the brain that controls the arm and processing those with a computer, so the person using the arm doesn't have to do a lot of conscious movements. Instead, the prosthetic reacts to them simply thinking about a movement. It's still a long way off, but there could be a breakthrough at any time and certainly is an area the VA, the U.S. Department of Defense (DOD) and NIH are looking at for potential breakthroughs."

While the greatest public attention in recent years has been on significant advances in prosthetic feet and legs-including robotic elements such as the power ankle and power knee-the broad definition of prothetic includes everything from artificial teeth and eyes to hearing aids, wheelchairs, and crutches.

All of which have seen advances that would have seemed like science fiction only a few years ago. And all of which are the subject of new R&D that could make today's most advanced prosthetics seem as archaic as a wooden peg before today's youngest veterans reach middle age.

"In my definition-and the VA's-a wheelchair is a prosthetic device because it augments or replaces a functional loss. We've also been involved in the development of a smart walker or blind cane and I would say the definition applies to them, as well," says Rory A. Cooper, founder and director of the joint VA/University of Pittsburgh Human Engineering Research Lab (HERL). "The fitting of a wheelchair is just as complicated as any other prosthetic-the seat has to match the person sitting on it, the wheels have to be properly aligned, you have to do functional training and so on.

NASA astronaut Chris Cassidy wears tele-operation gear consisting of a vest, gloves, and visor to test Robonaut 2's maneuvers telerobotically
In the International Space Station's Destiny laboratory, NASA astronaut Chris Cassidy wears tele-operation gear consisting of a vest, gloves, and visor to test Robonaut 2's maneuvers telerobotically. Cassidy was able to manipulate R2's head, neck, arms, and fingers telerobotically through his own movements as well as through verbal commands.

"We also have a research kitchen that uses cuing to help veterans with TBI [traumatic brain injury], which might be considered a prosthetic, as well, because it augments a cognitive loss. It gives instructions on cooking, cleaning, and other typical kitchen activities and does so intelligently, based on where you are in the process, using multidimensional cues-visual, auditory, etc. That includes being able to recognize items. It's easy for a robot if it can read a barcode on the package, but an apple is more difficult. It also allows you to tailor which appliances are safe for a given individual to use."

This prosthetic arm, controlled by brain waves, enables a quadriplegic woman to feed herself
This prosthetic arm, controlled by brain waves, enables a quadriplegic woman to feed herself. (Photo courtesy University of Pittsburgh School of Medicine.)

History of prosthetics

Artificial limbs and other prosthetic devices have existed for thousands of years, although not nearly at today's level of sophistication. Mythology, ancient historians, and archaeology have outlined the history of prosthetics-the art of designing replacements for damaged or severed arms, legs, and feet-for the past 6500 years. Greek, Celtic, Inca, and Aztec gods aside, the oldest known fictional (presumably) and factual prosthetics were made for women.

The first recorded reference is from the Indian poem Rig-Vega, written around 3500 BC. It tells of the warrior Queen Vishpla, who lost a leg in battle and was fitted with an iron prosthesis so she could return to the fight.

In 2000, archaeologists discovered a wood-and-leather, triple-jointed artificial big toe on the mummy of a 50-to-60 year-old noble woman entombed near the ancient city of Thebes around 1000 BC. Because the amputation site was well-healed and the toe showed signs of wear, researchers believe it was a functional prosthesis the woman had used for some time rather than something attached to her body during mummification, which was a common practice to ensure full mobility in the afterlife.

XOS 2 Test Engineer Rex Jameson does push-ups
XOS 2 Test Engineer Rex Jameson does push-ups during a demo at the Raytheon Sarcos research lab in Salt Lake City.

While not part of the historical record, the first prosthesis no doubt was a tree limb used to help a wounded hunter remain mobile, perhaps as long as 100,000 years ago. When the first wooden pegleg went into actual use remains unknown, but the researchers say the Egyptian toe pushes the known use of artificial limbs more than a millennium earlier than previously thought.

References to prosthetic legs, hands, and arms slowly became more common with the advent of historians and playwrights. In both cases, the earliest references come from ancient Athens. Greek historian Herodotus wrote of a prisoner, sentenced to death around 500 BC, who escaped by cutting off his chained foot, later replacing it with a wooden substitute. In his 5th Century BC play, "Birds," Aristophanes incorporated a character with a prosthetic leg.

One of the earliest documented cases was Pliny the Elder's history of the Punic Wars (some 250 years before his birth). He wrote of Roman General Marcus Sergius, who lost his right arm in battle against Carthage in the Second Punic War (218-210 B.C.) and was fitted with an iron hand so he could hold his shield and continue to fight for the rest of the war.

The historical record indicates the first several thousand years of prosthetics involved the replacement of limbs lost in battle, although some-such as the Egyptian toe-may have been related to amputations resulting from diabetes or some other ailment. It was not until 1529, however, that modern medicine caught up with the ancient Egyptians when French surgeon Ambroise Pare began using the procedure to save lives. Pare also is credited with the first scientific approach to developing prosthetic limbs, which earned him credit as the father of modern prosthetics.

Artificial limbs became far more common and better known by the general public as a result of the American Civil War, during which more than 60,000 amputations were reported, roughly equally divided between Union and Confederate soldiers. While the most common prosthetics were still made of wood and leather, with little, if any, flexibility, they were widely advertised in newspapers, magazines, and promotional brochures and posters in the years that followed.

It was not until World War II that prosthetics became a major research and development effort by the major militaries in that conflict, especially the U.S. Slow but significant improvements were made in the last half of the 20th Century, but it was not until the ongoing decade-plus of combat in Southwest Asia and the high level of amputations resulting from improvised explosive device (IED) blasts that prosthetics truly began to integrate cutting-edge technologies and materials.

Brazilian Athlete Marinalva de Almeida
Brazilian Athlete Marinalva de Almeida holds the new walking leg provided by Loma Linda University Medical Center, and wears the running leg she hopes will enable her to compete in the 2016 Paralympics. She was able to walk, for the first time in 15 years, three days after receiving the prosthetic legs in June 2013.

State of the art

Some results of these cutting-edge prosthetic technologies today are entering clinical trials. Here are some examples:

  • Powered Ankle, combining a small motor, springs, pneumatics, and microprocessors to simulate the "push-off" muscles, nerves and tendons give a biological foot and ankle, enabling a more natural gait with less stress on the user.
  • Powered Knee, a similar enhancement of knee/lower leg movement, weight distribution and balance.
  • Powered Ankle/Knee System, incorporating advanced powered ankle and knee into a single prosthetic to achieve a more natural walk with reduced user effort; test subjects have increased walking speed significantly compared to those using only a powered ankle.
  • Modular Prosthetic Limb, that incorporates sensors for touch, temperature, vibration, and proprioception (sensing prosthetic arm/hand position relative to other parts of the body), giving an upper-extremity amputee the ability to feel and manipulate objects as would someone with a biological hand.
  • Powered smart wheelchairs that include various developments include sensors for navigation, anti-collision, object identification, grade detection and speed control; user control using eye or head movements, voice or brain waves; evolving levels of artificial intelligence.
  • Remote Controlled Retractable Training Cane, which helps the visually impaired learn to deal with "drop-offs"-curbs, stairs, and other changes in the walking surface.
  • ReWalk P, a bionic exoskeletal leg support, utilizing powered leg attachments to enable paraplegics to stand upright, walk, and climb stairs.
  • DEKA iBot, a self-balancing wheelchair that allows the user to go up and down staircases, navigate difficult terrain, and "stand" at eye level with the ambulatory people around them.
  • Touch Bionics' i-LIMB Hand, which has five independently powered digits, the first commercially available multi-articulating bionic hand.
  • Murr-ma, a prototype amphibious prosthetic limb, developed by four UK graduate students and inspired by the dorsal fin of the fast-swimming sailfish; they claim it enables the user to run quickly across uneven beach terrain, then transition to swim mode with more thrust and faster speeds than able-bodied people.

"It's exciting what is happening with robotics, which has seen a big step forward in the last 15 years," notes former VA Director of Prosthetics Fred Downs, now a consultant with Paralyzed Veterans of America. "The difference between a robot and a robotic arm is the latter has a melding of the robotic with the human body. From a practical sense, they already are working with linking nerves to robotics. Right now, though, manual control is the best approach-the chip in the brain is a ways down the road yet."

Leaded Implantable Myoelectric Sensors
Artist's concept of Leaded Implantable Myoelectric Sensors (LIMES) to be used as a novel peripheral interface technology with targeted muscle reinnervation (TMR).

Sherman Gillums Jr., PVA's associate executive director for veterans benefits, added that some of the current prototypes may meet engineering goals, but fail in the real world. "There are some researchers who develop a great idea, but it isn't really practical and so it fails. The exoskeleton holds a lot of promise, but there has to be a level of practicality. I spoke to the developers about how someone like me, in a wheelchair, actually would be able to use it," he says. "The iBot is another example-it's too large, currently, to fit my lifestyle.

"It's important the research doesn't go too far before determining its practical use," Gillums continues. "We can make all the advances we want, but there must be feedback from those who will have these things wired into their nerves and muscles. You have to test them in a real setting, in the user's home." At the same time, he adds there is a growing synergy between technology advances that help veterans and the needs of the wider community.

"Once this tech is out there and found to be useful, providing it to our veterans also will be a benefit to society as a whole," Gillums says. "For example, some of the research advances made after more than a decade of war benefitted the victims of the Boston bombing, especially children. Some veterans visited some of the Boston victims and related their injuries to what had happened to them."

A major goal of robotic prosthetics is not only to make it easier for the user to return to previous activities, but do so with as little pain and unnatural exertion as possible. That has been the prime driver behind the powered ankle and knee.

"When you start to walk, your natural ankle is forced down by contractions in the leg muscles, which creates push-off and lets you move forward. When you get a powered ankle that can do that, it improves the symmetry of walking and makes it easier for the user because power is being put into a phase of the walking cycle to assists the veteran," Jaeger explains. "One of the things that will have to be researched more in the future is how the powered ankle and knee will work together.

"Attachment of the prosthetic is important, as is the weight, but control is the key, particularly for the upper extremities. Human standing and walking are kind of rhythmic activities that are easier to program and control. But with an arm, you have a whole host of things you may want to manipulate that cannot possibly be programmed into the device. So you have to build into it a type of natural control where the person feels like the arm is part of their body and they can control it without a lot of intensive thought."

Cooper's HERL-one of a growing number of academic and joint research labs working on next-generation prosthetics-was created in 1994, partly stemming from his own service-related disability, as a center for advanced engineering technologies designed for veterans with disabilities.

"We do a wide array of things, which is our strength. We do new technology and development, from high to low tech-building robots, chairs, prototypes, technology transfer, running user trials-all the way up to multi-site clinical trials. We then work with commercial partners to develop products for manufacturing," Cooper says.

"One of our large volume low-tech products is the natural fit hand rim used to push a wheelchair forward. A mid-tech item would be our Smartwheel, a clinical tool that basically is a sensor that measures the forces applied to the push rim, wirelessly sends those to an on-board computer and analyzes some of the problems experienced by wheelchair users. On the high-tech end is our Strongarm, a robotic arm that mounts to a wheelchair and helps facilitate transferring an individual in and out of a wheelchair."

A key effort pushing the development and application of new technologies for future robotic prostheses is the Revolutionizing Prosthetics program of the U.S. Defense Advanced Research Projects Agency (DARPA) in Arlington, Va. Begun in 2005, the program has a primary focus on the most difficult goal: A fully functioning artificial hand and arm. The DOD agency is working with industry and academic partners, including HERL and DEKA Integrated Solutions Corp., whose founder, Dean Kamen, is best known for the Segway, a two-wheeled, self-balancing electric vehicle.

ancient Egyptian prosthetic device
Even the ancient Egyptians used prosthetic devices, although much less sophisticated than today. (Photo by the Egyptian Museum, Cairo.)

The DARPA program's first three-year clinical study (2009 to 2012) involved the Generation 2 DEKA Arm.

"DARPA funded DEKA for Gen-2 arms that were tested by veterans in VA centers under very controlled conditions. We were looking for any tweaks that might be needed. The results seemed favorable-veterans were able to stack blocks and do other tasks, such as picking up a grape without crushing it," Cooper says. "Last year we began a take-home study, where veterans will use the arm for about a month outside the VA center, without all the technical and clinical people there to fix anything that goes wrong."

Meanwhile, DEKA has developed a Gen-3 Arm, controlled by sensors attached to the feet, so it can only be used when the veteran is sitting or standing, but not walking. Specific movements can be tailored to the user's wishes, but, basically, foot movements are sensed by the Arm's computer, which then translates them into related arm movements.

Converting to a fully robotic arm, such as that developed by NASA and General Motors for the Robo- naut-a C3PO-like humanoid robot that has been part of the International Space Station crew for about two years-will require further advances in weight reduction and smaller, lighter power systems.

"Both are extremely important and are the major factors we're working toward refining. And we expect a lot of future advances in those areas," Jaeger says. However, he added, another major key to successful robotic prosthetics is not, itself, robotic nor even electronic.

"One of the major problems in prosthetics, both lower and upper extremity, is how they attach to the body. For the lower extremity, that involves some kind of socket that the stump sits in. But the stump tends to swell, shrink, sweat, etc., so even the greatest robotic in the world can't be used if it causes the veteran pain or other problems," Jaeger explains.

"One of the most exciting things in the VA now is a clinical trial for osseointegration at the VA Center in Salt Lake City. The principle is if you have a stump above the knee, the remaining bone would have a bio-compatible metal bolt screwed into it and a threaded pin outside the skin covering the stump that the prosthetic leg would screw onto, eliminating the need for a socket."

Between DEKA Arm-type sensors on the feet and electrodes implanted in the brain, there are many places on the body where potential control signals can be picked up, such as targeted muscle reinnervation, which can use surface electrodes or tiny implanted electrodes in muscles around the shoulder.

When the brain thinks about moving those muscles, the electrical activity can be picked up and translated into commands for a prosthetic arm, similar to direct brain recording, although fewer signals can be acquired that way compared to the brain.

Current brain wave control technology requires some degree of invasive implants, from electrodes attached to the outer lining of the brain (the dura) and protruding through the scalp and attaching or wirelessly connecting to a computer to electrode/miniaturized transmitter packages beneath the skull and communicating wirelessly with a computer controller.

Leaded Implantable Myoelectric Sensors
Artist's concept of Leaded Implantable Myoelectric Sensors (LIMES) to be used as a novel peripheral interface technology with targeted muscle re innervation (TMR)

DARPA's Reliable Neural-Interface Technology (RE-NET) program, looking into the long-term viability of brain interfaces, is researching development of high-performance, reliable peripheral interfaces using nerve or muscle signals to both control prosthetics and provide direct sensory feedback.

"Although the current generation of brain, or cortical, interfaces have been used to control many degrees of freedom in an advanced prosthesis, researchers are still working on improving their long-term viability and performance," RE-NET Program Manager Jack Judy says. "The novel peripheral interfaces developed under RE-NET are approaching the level of control demonstrated by cortical interfaces and have better biotic and abiotic performance and reliability.

"Because implanting them is a lower risk and less invasive procedure, peripheral interfaces offer greater potential than penetrating cortical electrodes for near-term treatment of amputees. RE-NET program advances are already being made available to injured warfighters in clinical settings."

HERL, meanwhile, is continuing research on direct brain interfaces.

"External signals-EEGs-are not very neural activity-specific and tend to be too slow for complex tasks. I think a more likely future will be less invasive electrodes," Cooper says. "A neurosurgeon will go through the skull and place electrodes on the dura, then close the hole and it will interface wirelessly with a headset, in some ways similar to how a cochlear [ear] implant works.

"I would say that is probably 10 to 15 years away. It's not only a technical challenge, but also has policy barriers. Somebody has to be willing to manufacture it and somebody has to be willing to pay for it. By the FDA's definition, these really are orphan products."

But Cooper sees the evolution of robotic prosthetics-including brain waves controllers-benefitting from future generations of humanoid robots, such as Robonaut, which GM hopes to put on the factory floor, working alongside humans, as well as medical and household robots.

"I think this technology will have a lot of synergy with a class of robots designed with great dexterity. The work on humanoid robots will influence prosthetic leg and arm design-and vice versa-as well as robots that will be used in the home or in manufacturing, working with humans to perform factory tasks rather than away from them," Cooper predicts. "That kind of human-robot interaction-actually, symbiosis-also can be taken into the home, to help clean or cook, to assist people with disabilities. And, eventually, become part of a person."

The ReWalk from Argo Medical Technologie
The ReWalk from Argo Medical Technologies in Haifa, Israel, is an upright that enables people with lower limb disabilities to stand, walk, and even take stairs independently.

As advances in microprocessing speed, memory, size and weight, sensors, and lightweight and stronger materials continue with the increasing speed of recent years, thought control is expected to evolve at an equally accelerated pace. But as those technologies are incorporated into future "wearable robotic devices," even with veterans involved at every stage of design and testing, just how far the man/machine interface ultimately goes is not a question of technology, according to Jaeger.

"The choice of which methods to use will be up to the veterans. Some may say they don't want brain surgery for arm control," Jaeger says. "We have had both active duty military at the Center for the Intrepid in San Antonio and veterans involved in our research studies. And a key part of those studies is what the user wants and needs. So veterans are a very integral part of trying to refine the way these prosthetics are fit to them, what they like or don't like, how it's made to work and so on."

While those choices ultimately will be made by individuals, both veterans and civilians, Cooper believes there will be sufficient acceptance of-even demand for-robotic prosthetics to carry current developments to the symbiotic future he foresees, despite a high cost the VA has vowed to accept, but civilian insurance may not.

"The future of prosthetics, to a large extent, is robotics, merging those technologies. You already can see that happening with lower extremity prosthetics, with power knees and ankles, which really are just single purpose robotics," Cooper concludes. "The private sector typically is slower to adopt new technologies than the DOD and VA, but I think this effort does tend to benefit both. Eventually, the tech trickles down to the civilian sector-and after enough units are sold, costs come down.

"In the long run, I think robotics, intelligent systems, are going to play a larger and larger role in the lives of people with disabilities, but also with the general public, giving people more autonomy. We're already starting to see more of that in our homes, even if they may not be seen as such, from more advanced appliances."


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