Goldfarb's multigrasp prosthesis

Bionics, robotics and lasers: the latest in prosthetics

April 15, 2011
by Olga Deshchenko, DOTmed News Reporter
This report originally appeared in the April 2011 issue of DOTmed Business News

On Jan. 12, 2007, a roadside bomb, the weapon of choice among Iraqi insurgents, blew off the legs of a 24-year-old corporal. After being treated in a military hospital in Landstuhl, Germany, he was flown to the Andrews Air Force Base near Washington, D.C. and then transported to the Walter Reed Army Medical Center.

The following week, Time Magazine deemed the corporal’s arrival home “a grim milestone” of the Iraq war – he was the conflict’s 500th major amputee.

Thanks to improvements to body armor equipment and military transport, the casualty rate of the Iraq and Afghanistan conflicts is relatively low, but the number of soldiers coming back with major and partial amputations is still painfully high. According to a 2010 Congressional Research Service report, 1,621 military personnel lost a limb as a result of serving in Operation Iraqi Freedom, Operation Enduring Freedom and other conflicts between the Septembers of 2001 and 2010. Many of the soldiers return home with life-changing injuries that complicate the process of resuming the lives they led as civilians.

Fortunately, the field of prosthetics is evolving with the needs of returning veterans. Manufacturers are rolling out cutting-edge devices and researchers are working on technology that not only comes close to the look of a biological limb, but also strives to offer the feeling of one.

A bionic foot, now available
Last February, Randall Tipton, a veteran who served in both Iraq and Afghanistan, was fitted with the iWalk PowerFoot BiOM at the Michael E. DeBakey VA Medical Center in Houston, Texas. The prosthesis is the world’s first bionic lower leg system that replaces the action of the foot, Achilles tendon and calf muscle, providing a nearly perfect gait to amputees, according to the U.S. Department of Veteran Affairs.

The BiOM was invented by Hugh Herr, director of biomechatronics with the Massachusetts Institute of Technology. The Telemedicine and Advanced Technology Research Center and the Department of Defense injected initial funding into the multi-million-dollar product development.

Herr knows what it’s like to lose a limb – both of his legs were amputated below the knee when he was 17 due to a climbing accident. Before developing the BiOM through iWalk, his Cambridge, Mass.-based company, Herr invented the Rheo knee. (It’s now a product in Össur’s portfolio, a leading prosthetics company headquartered in Reykjavik, Iceland.)

The BiOM works by simulating the action of the muscles in the foot and gathering information on the position of the foot and the terrain. By sensing the position of the ankle and the type of surface, the foot adjusts the amount of force it has to use with every step, according to iWalk’s website. And preliminary results of a study at the Brooke Army Medical Center at Fort Sam Houston show that the BiOM doesn’t require amputees to expend additional energy to use the prosthesis as compared to a healthy foot.

The first commercial units of BiOM were delivered to military medical centers in February and the demand is likely to grow, given the revolutionary technology behind the product.

“We have seen a significant difference in function in this device over the other 200 plus feet we have used here at the DeBakey VA,” Mark Benveniste, a prosthetist with the center, said in a statement. “It is the most improvement over conventional prosthetics in the last 20 years.”

A smart arm on the way
For veterans who’ve lost an arm, a groundbreaking upper-extremity prosthetic is currently in the works. The device is called the Modular Prosthetic Limb and was developed by researchers at The Johns Hopkins University Applied Physics Laboratory in Laurel, Md. The lab was awarded more than $30 million by the Pentagon’s Defense Advanced Research Projects Agency to develop the device.

The technology behind MPL is pioneering because it involves mind control – amputees will direct the device using their thoughts through an implanted microchip in the brain. The current prototype of the MPL is silver and black, a robotic wonder that looks like it could be a part of Iron Man’s futuristic suit. The prosthesis can move 27 different ways, performing as many rotating and twisting motions as a biological arm.

The military hopes to bring the MPL to veterans soon – it plans to place the microchips on the surface of patient’s brains this year. That’s because the promise of the robotic arm caught the attention of the U.S. Food and Drug Administration. The agency is using MPL as the pilot for its new Innovation Pathway program. The initiative aims to accelerate the process of approval for breakthrough medical devices through a speedier review, encouraging manufacturers to bring innovative medical devices to market.

The microchip that will be implanted on people’s brains will record the neuronal activity and relay the signals to the MPL for control, according to the FDA.

In the works: multi-grasp prosthesis
If the MPL successfully reaches the market through the Innovation Pathway, the FDA is likely to see more applicants from the prosthetics field. Engineers at institutions like Vanderbilt University are continuously working on advancing mobility and functionality for amputees.

Researchers at the Nashville, Tenn.-based university’s Center for Intelligent Mechatronics have been working on a transradial (below the elbow) multi-grasp prosthesis since 2005.

Michael Goldfarb, professor of mechanical engineering with institution, says there are currently two options for upper-limb amputees, a body powered or a myoelectric prosthesis.

The body powered prosthesis is the most common and has been around since World War II. It consists of split hooks connected to a harness an amputee wears around the shoulders. The shrugging motions of the shoulders open and close the hooks, enabling people to pick up and put down objects.
The myoelectric prosthesis came about in the 1970s and works by reading the electrical activity in the muscles from the skin. These devices are molded to look like hands with real fingers, which is an important factor for amputees, says Goldfarb.

But the current offerings have their drawbacks – despite differences in price and fragility, both types of prostheses offer the same, limited functionality to the amputee – opening and closing of the device. A myoelectric user cannot point a finger or hold out a flat hand. And with body powered prosthesis, an amputee cannot reach above the head or shoulders.

There is also a problem of sensory feedback. Unlike healthy people, amputees lack a sense of proprioception, or knowing where their limbs are without looking at them. Force feedback, or knowing how hard something is squeezed, for instance, is also largely absent.

Some of the sensory information is retained with the body powered prosthesis, but the more expensive option fares worse. “The only sensory feedback amputees have from a myoelectric prosthesis is visual,” says Goldfarb. “If you have to stare at your hand the whole time you’re using it, then it’s really not that useful.”

Beyond functional aspects of the prostheses, there are also psychological effects. Amputees may not feel like a prosthetic device is a part of their body but rather “just kind of this artificial appendage,” says Goldfarb.

To overcome the limitations of today’s typical devices, Goldfarb’s team is working on a multi-grasp prosthesis that offers a lot more dexterity. Rather than having a device that just opens and closes, the fingers of Goldfarb’s invention perform nine common grasps that people use in their every day lives. (Examples include pointing, a tip grasp and a tripod grasp, used to hold a writing utensil.)

Unlike Johns Hopkins’ Modular Prosthetic Limb, Goldfarb’s team isn’t relying on implanted microchips. It’s using surface electrodes. “The reason we don’t do implants is because right now, there are many challenges with the implementation of implants and we want people to be able to use the prosthesis in the near term,” says Goldfarb.

“Implants are probably 20 years away,” he says. “We’re working on things that hopefully will be useable within the next decade by amputee populations.”
In Goldfarb’s design, the controller takes over some functions of the brain. “We imbue the hand with a lot of its own low-level intelligence, its own coordination, so that it requires a lot less attention from the user,” he explains.

For example, if a healthy person picks up an apple off a table, there isn’t any conscious thought about what each of the joints is doing because it’s taken care of by low-level coordination centers, located in the medulla oblongata and the cerebellum parts of the brain. Goldfarb’s prosthesis mimics that capability. “We have low-level coordination centers that are run off little micro-controller chips on the hand and then the person just gives [the prosthesis] higher level information,” says Goldfarb.

Goldfarb’s work is being funded by the National Institutes of Health, and this year, his team plans to test the prosthesis on five amputees. The researchers will compare their ability to do activities of daily living using Goldfarb’s invention to a standard myoelectric prosthesis.

The controller of the device, says Goldfarb, is unlike anything else on the market. “But what we believe isn’t really that important, that’s why we want to do these tests,” he says.

“We think what we have will really advance this field and provide more functionality and improve quality of life for upper-extremity amputees,” Goldfarb says.

Ongoing research: sense & control
While some researchers are working on improving the dexterity of current prostheses, others continue to explore ways to make amputees feel like their prostheses are a natural part of their bodies. But for prosthetic limbs to truly feel like biological arms or legs, researchers must overcome a significant challenge: establishing a two-way connection with the peripheral nervous system.

Such a system should be able to not only sense the activity of the nerves and direct the motion to the prosthesis but also stimulate sensory nerves to offer feedback to the amputee’s brain to control the device.

Thanks to a $5.6 million DARPA grant, a number of facilities are currently collaborating on a two-year effort to develop a system that will do just that. The project is split in two parts – nerve stimulation and sensing.

Vanderbilt University is one of the facilities working on the stimulation side of the initiative. E. Duco Jansen, a professor of biomedical engineering and neurosurgery with the university who’s working on the project, says that today’s prosthetics function with the help of an electrode that either sends or picks up signals from the nerves or muscles. Although this technology works fairly well, it has some fundamental limitations. “The main one is really one of spatial accuracy,” he says. “How accurately can you control that prosthetic device?”

For Vanderbilt’s portion of the research, Jansen’s team is using lasers to stimulate the nerves. The researchers are employing infrared lasers, which can effectively focus on even individual neurons. As tissue is exposed to the light, the neural tissue absorbs it, causing the nerves to fire an action potential. “That’s the currency that the nervous system talks in and so that way, we have a way to use light to encode action potentials in the nervous system with high precision and code those back into or pick them up from the nervous system and put them in the robotic arm,” says Jansen. “It’s really the area of building better neural interfaces and in our case, we’re pursuing laser technology to do that.”

Jansen says the idea for using beams of light for neural stimulation was an “accidental discovery.” Several years ago, a neurosurgeon from Vanderbilt’s medical school sought help from the biomedical engineering department. During surgical procedures where clinicians insert electrodes into the brain for say, controlling Parkinson’s disease or epilepsy, surgeons can spend hours probing different parts of the brain for activity in order to determine exactly where the electrodes should be placed. The procedure is extremely tedious, burdensome and expensive. The surgeon wanted to know if there was a way to ease the process by optically “seeing” electrical activity in the brain.

While researching the neurosurgeon’s problem, the team came up with its own question. “If you could see electrical activity in the brain with light, why can’t we turn it around and induce electrical activity in the brain with light?” asks Jansen.

For starters, they exposed a nerve in a frog’s leg to laser pulses, hypothesizing a set of laser parameters they thought might work. When they focused the pulses directly on the leg’s sciatic nerve, it contracted. “With every laser pulse, we saw a little twitch of a muscle in the frog leg,” says Jansen.

Still, it was possible they were stimulating a reflex arc, similar to what a physician does when tapping on a knee with a little rubber hammer. So they cut the connection between the nerve and the spinal cord. “And yet, when we put the laser on the nerve, we still saw the muscle twitches. That was direct evidence that we were inducing action potentials leading to motor responses in the frog leg,” says Jansen.

The researchers then moved on to work on a rat model and laser development. Initially, they used the FreeElectron Laser, funded by the Department of Defense at Vanderbilt for medical applications. Access to the state-of-the-art device enabled researchers to identify the necessary parameters but they needed something smaller. “That laser was basically a whole building. It’s useful for research purposes but not so practical for widespread use,” says Jansen.

The research team enlisted the Washington-based Aculight Corporation to design a customized laser, which shares its technology concepts with missile defense systems.(Aculight has since been acquired by Lockheed Martin.) The current version of company’s nerve stimulation laser is just a little larger than a laptop, but it will have to shrink significantly to be considered as an implant for prosthetics — prototypes as small as an iPod Nano are already in development.

So far, researchers have used one fiber and interfaced it with a nerve to make it twitch. “The first milestone that we’re close to accomplishing is to have a system where we have four different fibers coupled to the same laser but when turning on different fibers, we can activate different muscles groups asynchronously,” Jansen says.

The researchers are also working on aligning the fiber optic next to the nerve, rather than perpendicular to it. This comes with the challenge of figuring out how to get the light to fire sideways from the fiber to go into the nerve, as opposed to firing forward. “That’s the other part we’ve been working on – can we make tiny fiber optics that fire the light out sideways? We’ve demonstrated that concept with one channel so far,” says Jansen.

By the end of the two-year project, the stimulation team (which also includes researchers at Case Western Reserve University in Cleveland, Ohio), hopes to have a multi-channel, side-firing system with side-firing fibers implanted in a cuff that can be wrapped around a nerve and placed into an animal to show its ability to activate individual groups of muscles. The sensory group hopes to build a multi-channel system that can sense the electrical signals in or around the nerves in a significant number of nerve cells simultaneously.

The concept may be easy to demonstrate in a Petri dish but it becomes harder to replicate its efficacy beyond that. “You put this in an animal and ultimately a human and there are all these confounding factors that you now have to start worrying about,” says Jansen.

But for now, the aim of this feasibility pilot project is to show that light is a useful avenue to pursue neural interfaces for sensor and motor control, which could make a huge impact on prosthetics in the future, Jansen says. “So far, so good. No doubt there are significant challenges that we’re going to have to overcome with all these parts but that’s a DARPA project for you. We have ideas on how we’re going to get there,” he says.