How a Team of SFU Researchers Aims to Change the Future of Prostheses
A group of biomedical engineering and kinesiology students has developed a more intuitive and natural technology called "force myography."
January 4, 2017
Danny Letain’s left forearm is a glistening black shell of carbon-fibre weave and fibreglass laid over a thermoplastic inner socket. There is a raised compartment packed with custom electronics, and, at the wrist, the arm connects to a black hand with long, spidery fingers and titanium joints.
As amazing as the prosthesis looks, the technology behind it is even more impressive. Letain just has to think about closing his fingers—which flexes the muscles in his stump—and his bionic hand responds by curling into a fist. The device is powered by a new type of technology, called “force myography,” that a crew of Simon Fraser University biomedical engineering and kinesiology students has developed. Originally used for rehabilitating stroke victims, the technology comprises an arm band packed with micro-sensors that are fitted inside the prosthetic socket. These sensors monitor the movements of the muscles in Letain’s stump as he carries out tasks. This data is then converted into a sensor map by computer algorithms that decode Letain’s intentions and send an electrical message to the hand, telling it how to move.
“I’ve always had the sensation of having fingers at the end of my stump. I’ve just never been able to use it—until now,” says Letain, a former locomotive engineer, who lost his left arm just below the elbow in a rail yard accident in 1980. Ever since, he has used a traditional pincer-and-hook prosthesis that can be opened or closed by pulling cables attached to the opposite shoulder. The hook is durable and quick to respond, but controlling it with straps isn’t natural and it’s physically taxing.
But with this new high-tech prosthesis, Letain feels like he’s actually opening and closing his hand. “The most exciting moment for me was feeling my left index finger and the little finger for the first time since my accident. With the hook you don’t use those muscles at all. This system puts my mind to work in a whole new way.”
It is early fall and the 59-year-old Maple Ridge resident has been practising with the bionic technology for a year, preparing for an international competition that pits disabled athletes wearing prostheses and exoskeletons against one another in timed races. In Letain’s event, competitors must perform a series of tasks, such as carrying objects, opening a jar, slicing bread and hanging laundry, within an eight-minute span. “It may all sound really mundane, but it’s extremely challenging when you’re powering new technology,” he explains.
Taking place in Zurich, Switzerland, the inaugural event is known as the Cybathlon—nicknamed the Bionic Olympics. Organizers hope the showcase will spur innovations that will allow people with disabilities to regain independence. In total, the Cybathlon will feature 66 teams competing from 25 countries, but SFU’s team is the only Canadian entry.
The project is a collaborative effort with two other parties. The arm was provided by Barber Prosthetics of Vancouver, while the high-tech robotic hand, the Bebionic3, was donated by its British manufacturer, Steeper Prosthetics. The SFU team launched a crowdfunding campaign and signed up several sponsors to pay for the trip to Switzerland.
“The more data you give it, the more it will learn.” —Lukas-Karim Merhi
Letain, who was recruited in May 2015, was the perfect candidate. Recently retired, he had the time to devote to the project, and he was also physically fit, giving him a potential advantage when navigating the Cybathlon course. A former professional skier, he had worked as a coach and ski instructor before and after his injury—he currently teaches adaptive skiing at Kamloops’ Sun Peaks Resort—and in 1992, he raced for Canada at the Winter Paralympics in France.
Letain notes that there is a real need for improved technology for arm amputees because of design shortcomings in prostheses. According to Brittany Pousett, head of research and development at Barber Prosthetics, about 30 percent of upper limb amputees don’t use a prosthesis. The technology has been slow to evolve both because it’s hard to mimic the complexity of a human hand and because there are far fewer arm amputees than those with missing legs.
The main alternative to cable-operated limbs are myoelectric arms that use sensors to detect electrical signals from the muscles. However, the drawback with this myoelectric method is its complexity. Because it measures only two electrical signals in the limb, the user must learn to isolate specific muscles in the biceps or triceps and then flex them repeatedly to make robotic fingers open or close. Normally, we unconsciously use multiple muscles at the same time to complete a movement.
The advantage of SFU’s force myography system is that it is much more intuitive and natural, according to SFU alumnus Lukas-Karim Merhi, who leads the interdisciplinary team, which calls itself M.A.S.S. Impact (Mass Activity Sensor Strip). “Our sensors recognize the pressure map for a specific grip pattern and then tell the hand to move that way,” he says. Merhi notes that this technology also collects computer models to use for future activities: “The more data you give it, the more it will learn.”
Pousett says the SFU innovation “is a completely new approach to picking up signals and controlling an electric prosthesis from someone’s body.” She believes it has the potential to increase the motion currently available to prosthesis users.
Merhi admits that the SFU technology still needs refining before it can be commercially applied, which is the ultimate goal. The prototype was tested at a Cybathlon trial in the summer of 2015 and placed second, but the team has made several refinements since then. “At the trials, one of the team members was literally running alongside me with his Bluetooth and laptop as I moved from station to station,” says Letain. Today, that computer has been reduced to a Chiclets-sized packet that fits inside the prosthetic arm. “We feel good about our chances,” Letain says, shortly before leaving for the Cybathlon.
Unfortunately, things don’t go as planned. It’s October, the day before the SFU team is set to fly to Switzerland, and the Bebionic3 hand has stopped working, knocked out of commission by a faulty main electronic board. By sheer luck, the team manages to borrow a replacement from Barber Prosthetics, but there is a problem—this prosthetic hand is a medium and Letain has done all of his training with the large model.
“This had a huge impact on my performance since we didn’t have sufficient time to practise with the new hand and could only train the software (provide it with data) once before leaving,” he says.
Letain completes the course, but his precision has been disrupted and he doesn’t make the finals. In an ironic twist, a Dutch team using a conventional hook-and-pincer prosthesis wins the event, defeating eight teams that are all using myoelectric technology.
Despite the disappointing result, Merhi is proud of what his team has accomplished. “We’ve only been working on this for a year and a half and it’s all been volunteer,” he says. To affirm his point, he describes how some of the technologies they were competing against have benefited from years of research and billions of dollars in funding.
Looking ahead, Merhi hopes to continue to improve the functioning of the prosthetic arm and perhaps compete in the next Cybathlon in 2020 in Tokyo, when it will be held in conjunction with the Paralympics. Exactly how the team will proceed from here is still being discussed. Merhi estimates that advancing the sensing technology to a commercial state will take several years.
“Additional tests would have to be conducted with multiple amputees, and running these sorts of feasibility studies requires at least a year and considerable funding,” he says.
In the meantime, the SFU team leader is focusing on the positive aspects of the Cybathlon experience. “I feel privileged to have attended the event. Watching paralyzed people stand and walk in their exoskeletons was incredibly inspiring. It’s made us even more determined to make a difference.”