How a Robotic Exoskeleton Is Helping a Paralyzed Acrobat Walk Again


Silke Pan walks in the Twiice exoskeleton while the engineers who designed the mobility device look on. Image Credit: EPFL

Silke Pan usually swung 22 feet above the ground on the trapeze, but on that day in September 2007, she was just 13 feet up. Pan, a performer with Switzerland’s Nock Circus, had just finished a seven-month gig at the Fiabilandia Amusement Park in northern Italy, where her troupe performed seven days a week, six shows a day. Now they were on a two-week break. But Pan, a contortionist and acrobat, didn’t take the break. She and her long-time partner, Didier Dvorak—a juggler, unicyclist, and her husband—wanted to fine-tune their act before the next gig began. So back up on the trapeze they went.

Pan remembers that Dvorak was hanging by his feet from his trapeze, his hands outstretched to her, as she swung from her own trapeze, hands reaching toward him. She knows she was meant to catch his hands in hers, as she had countless times during the 15 years she had been performing professionally.

But she doesn’t know what happened next, because she can’t remember. Others have had to fill in the blanks for her (but not her husband; it’s too painful for him to talk about, she says). They say that as she and Dvorak swung toward each other and she let go of the trapeze, they missed each other’s grip.

Pan plummeted to the ground. She landed on her head at the feet of the spotter, whose job it was to catch her if something went wrong. He, too, had missed.

“At first they thought I was dead because I didn’t move or respond,” she says.

She awoke in an Italian hospital to learn she was paralyzed from the waist down due to an injury to her T10 and T11, or 10th and 11th thoracic vertebrae, located in the lower mid-back.

For someone who had devoted her entire life to pushing the boundaries of what her body could do in the service of entertaining people, it was devastating to be unable to move. “I felt as if I was born again,” she recalls. “I lost everything from my identity. People who knew me, knew me as a circus artist and an acrobat. I was like a baby in an adult body. I didn’t know what to do with my life. All the things I had thought before about what I could do were things that weren’t anymore possible.”

Yet last year—nearly a decade after she became paraplegic—Pan began to do something she never thought would be possible again: walk. It became possible thanks to Twiice, a powered lower-limb exoskeleton developed by engineers and scientists at the Laboratoire de Systèmes Robotiques (LSRO) at the Ecole Polytechnique Federale de Lausanne (EPFL) in Lausanne, Switzerland. Pan has taken so thoroughly to the exoskeleton that not only does she walk in it—she competes in it.

The augmentation of the human body with technology isn't new; prosthetics can be found as far back as ancient Egypt. Nor is the idea of enveloping the body in a functional shell revolutionary; armor is essentially an exoskeleton. But taking the concept of the exoskeleton from protection to mobility is more recent. As robotics specialist José Pons and his colleagues from Spain's Instituto de Automatica Industrial recount in Wearable Robots: Biomechatronic Exoskeletons, in 1883 one H. Wangenstein proposed a "Pneumatic Bodyframe" for paraplegic scientists that would be controlled by "Neuro-Impulse Recognition Electrodes" attached to the wearer's temples. He enthused, "Even running and jumping are not beyond its capabilities, all controlled by the power of the user's mind." It's unclear whether Wangenstein ever attempted to build his bodyframe.

Decades later, in the early 1960s, the U.S. military began investigating designs for a powered "suit of armor," Pons writes, as did the Cornell Aeronautical Laboratory and General Electric. This interest has continued to the present day; in 2000, the Defense Advanced Research Projects Agency (DARPA) funded the development of the Bleex exoskeleton, built by a team at the Berkeley Robotics & Human Engineering Laboratory; later iterations were called the ExoHiker and HULC. In 2015, DARPA beta tested an exoskeleton created by Harvard's Wyss Institute on enlisted soldiers; the goal is to lighten the load of their heavy packs and reduce their metabolic cost during long missions.

But while the military has been at the forefront of developing the tech, wearable robotics for industry, prosthetics, and orthotics are catching up. In the past decade or so, the number of teams developing wearable robots has grown tremendously. Today, many companies are making them. They serve a variety of purposes, from load bearing (military and industry) to helping people move (prosthetics and orthotics).

It's with orthotics that LSRO comes into the picture. The Rehabilitation and Assistive Robotics lab, a division of LSRO, is headed by robotics engineer Mohamed Bouri, and it was his idea to build the exoskeleton that restored Pan's ability to walk. Bouri's initial goal was to create one for people less than 5 feet tall—mainly children. While there are several commercially available adult-size exoskeletons, including the Phoenix, ReWalk, REX P, and Ekso, there are none for kids, says Tristan Vouga, a Ph.D. student in microengineering at LSRO. (One child exoskeleton is in preclinical trial.)

Bouri tasked Vouga with creating a design for the exoskeleton. Microengineering is key to the production of Switzerland's most famous export—watches—but it's also highly useful in robotics, Vouga says. In early 2015, he came up with the initial design for an exoskeleton that was lightweight, easy to operate, relatively low cost, modular, and adjustable. The latter was especially important because every spinal injury is different, and kids grow. Ideally, every exoskeleton would be customized for its user.

The LSRO engineers and scientists built the exoskeleton in 18 months, using mostly carbon-fiber parts that Vouga fabricated in the lab with new manufacturing techniques developed specifically for the exoskeleton (details of which Vouga won’t disclose because they’re proprietary). Weighing about 30 pounds, it’s one of the lightest exoskeletons in the world. The lab can manufacture a personalized exoskeleton in a few days.

The engineers named the device Twiice. “The idea is that they’re two people walking—actually, two pairs of legs: the human and the robot, and they have to walk together,” Vouga says. “It’s a collaboration. It’s like a dance: You have coordinate, to be aware of each other, and there’s this real symbiosis between the two actors.”

But there was a snag: a pressing deadline. The team had learned about the first-ever Cybathlon, a competition for disabled athletes to be held in Kloten, Switzerland, on October 8, 2016. The goal was to showcase the latest developments in assistive technology—devices aimed at making daily life easier for people with disabilities.

Bringing a child in to “pilot” or beta test the very first trial of this new technology was going to be problematic. “It’s hard to bring children in for ethical reasons,” Vouga says. It would require a complex approval process involving not only a child but their parents and doctors. By that point, October was just months away. They needed to train someone to use the exoskeleton if they wanted to field an entry in the Cybathlon.

The team decided that what they needed was a very small—but adult—competitor. That meant they also needed a new, slightly larger, exoskeleton. Switching gears, the team constructed another one in just two weeks.

Now they needed the competitor to pilot it. They approached a local wheelchair club looking for the ideal recruit: small and slim, with superior upper body strength.

But that wasn’t all. They aimed not only to enter the Cybathlon, but to win it. “We wanted to find someone who is competitive and who was already an athlete,” Vouga says. “That’s hard to find.”
Shortly after her accident, doctors in the Italian hospital implanted a metal spine stabilizer in Pan’s back. As she recovered, they told her they were impressed with her positive outlook and that her sunny smile was an example to other patients.

“I hadn’t realized I was smiling,” she recalls. It was sheer habit. “As a circus artist, I had learned to keep smiling. When I was on stage, I always had to smile, and the smile had to come from my heart, because if I would smile only with my face, I always thought it wouldn’t look real.”

The truth was, she told her doctors, “‘I‘m really sad. It’s terrible for me.’ But I didn’t show it.”

After leaving Italy, Pan spent nearly seven months recovering in a Swiss hospital. When she left the facility, she tried to return to her old life. She and Dvorak developed a show in which she performed in a wheelchair. It was successful enough that the pair was contracted by Fiabilandia to bring the show to the amusement park.

That’s how, in 2009—two years after the fall that took her mobility—she found herself back at the scene of the accident. “I thought it would be good because I didn’t want to close my eyes to what had happened,” she said. “I thought I needed to see the reality.”

She badly miscalculated how it would affect her. The experience was devastating. “It was a most difficult time, because every day, I heard the music I had heard two years before. I met some of the same artists I had worked with, and every day I couldn’t stop comparing myself to what I had been,” she says. “That was very hard, because I felt really handicapped. I saw myself in the wheelchair. I could only move my arms and speak, and before I was … standing on one hand, and hanging from my trapeze. Compared to what I was before, I felt as though I was nothing.”

She decided she had to leave her old life behind. But after performing with the circus for many years, she and Dvorak were committed to creating “joyful events,” she says. She wanted to do something she could physically create herself, within the constraints of her disability. The two also had to make money: Because she had been injured between job contracts, the circus hadn’t covered the hospital costs, and the couple was in tremendous debt. (Eventually, a lawyer helped get the costs covered.)

They poured all their money into launching Canniballoon Team, a decorating company that stages enormous, elaborate balloon installations—castles, Christmas scenes, winter sports, ocean depths. It was slow going at first: Few in Switzerland, where they live, knew the industry. But after Pan and Dvorak created the largest balloon maze in the world, using 20,000 balloons, their business took off.

Meanwhile, Pan had taken to paracycling with a handbike, an arm-powered machine that puts its driver in a recumbent position nearly parallel to, and just above, the ground. The handbike became another outlet for her intense athleticism and competitiveness. She spent more and more time training, and by 2012, she had begun to race internationally as a member of the German para national team. (She was born in Germany but has lived in Switzerland since she was a child.)

Racing helped her to come to terms with her body. “After the accident, it was difficult to accept that paralyzed body that was looking at me in the mirror. I saw my legs, and it wasn’t me. It wasn’t myself as I had always known me,” she says. “After I began that sport, I felt really better inside my body. I thought that [while] this body was handicapped, it was possible with that body to perform—and to do great performances.”

Pan became one of the world’s top competitors in paracycling. She broke records and earned multiple medals, including at the Union Cycliste Internationale (UCI) Para-cycling Road World Cup competitions. In 2015, she was the top-ranked UCI paracyclist in the world in the H4 category; this group is for paraplegics with spinal injuries at or below T11, the 11th thoracic vertebra. These competitors have limited lower limb mobility but typically have normal trunk stability.

In the video below, she wins the 2015 World Cup (in French).

Despite being on top and having one eye on competing at the Paralympics in Rio, in 2015 Pan decided to give up racing for the German national team. Living in Switzerland, she felt cut off from her teammates, and when she wasn’t selected for the Paralympic team, she resigned. Instead, she decided, she would compete independently.

She was still ranked ninth in the world when, in July 2016, she learned about a unique opportunity: the chance to beta-test an exoskeleton that, she was told, would put her on her feet for the first time in nearly a decade. She had learned about the recruitment call from a fellow former patient at the Swiss hospital where she had recovered. Intrigued, she called the LSRO lab.
The LSRO engineers couldn’t believe their luck. Pan was exactly the kind of pilot they were looking for: strong, small, athletic, competitive. Moreover, Vouga noted, “she is quite famous.”

On July 5, Pan visited the lab for the first time and tried out the Twiice. The lab team positioned her hips and her legs in the exoskeleton, which has flexible joints at the knees and hips controlled by two electric motors per leg. They strapped the entire exoskeleton to her body at her lower chest, around her hips, below her knees, and at her feet. A backpack held the battery, capable of powering the exoskeleton for three hours. They gave her a pair of crutches, which helped to support her weight and provide control, and instructions on how to operate the exoskeleton. It’s controlled by just four buttons, which are located in the crutch hand grips. She could choose to walk fast or slow, sit or stand, climb steps, go up or down a ramp, or change modes.

Bouri says it took Pan just 15 minutes to master the functions. Then she took her first steps.

“For the first time, after nine years in the wheelchair, I saw my legs moving,” Pan says. “It was so emotional for me because I hadn’t seen my legs doing that movement for so many years.”

During the long months she spent in the hospital after her injury, well-intentioned visitors tried to give her hope by telling her about people who had healed after spinal injuries. She believed them—at first. But disillusionment quickly set in. “At the beginning, I dreamt of being healed, of being able to walk again,” she says. “And then I knew it wouldn’t be possible.”

And yet that dream came to life on July 5 when she stood in the exoskeleton. “At that moment, I had the impression that all the dreams of walking again would come true,” she says. “I knew it wasn’t my own legs, but it felt as if it were my own legs.”

She wore the exoskeleton for a few hours, which was exhausting, as she had to use her arm strength to keep herself holding onto the crutches. Despite her weariness, she didn't want to stop.

And yet the exhaustion made her doubt whether she could compete at the Cybathlon. Three months didn't seem like enough time. She told the LSRO team, “It’s not possible. It’s too difficult. I can’t even walk, and you want me to climb stairs?”

Nevertheless, she signed on for a rigorous training program to prepare her for the event: three days a week, four to five hours each day, until October.

“From there we made good progress. The team was amazed. After one month," she says, "I could walk by myself.”

“We were very lucky to find Silke,” Bouri says. “She was just a pilot at the beginning. But as time has passed, she has become part of the project. Silke speaks of all the parts of the group as ‘her engineers.’”

As Pan practiced walking, sitting, standing, and climbing stairs, her feedback helped them to refine the Twiice. For instance, she needed more support in her midsection to keep her upright and maintain her balance, so they added that. This was an adjustment they were excited about, because it fit into their initial goal to make Twiice both adjustable and customizable to the individual user.

She also told them that because she lacked sensation in her feet, it was hard to know when her steps landed unless she looked down the entire time, which was both inconvenient and impractical. Some indication of her footfall would be helpful for maneuvering, she told them. So they put pressure sensors in the feet of the exoskeleton, wired to indicators in the hand grips. When she takes a step, the sensor now registers the pressure and sends a signal to the indicator, which vibrates.

In early October, Pan and the Twiice team traveled to the SWISS Arena Kloten, near Zurich, for the Cybathlon. Sixty-six pilots, including Pan, were to demonstrate the capacity for these technologies to help their users independently handle everyday tasks, from climbing stairs to slicing bread. There were six categories of competition: powered leg prosthesis, powered arm prosthesis, electronic stimulation, powered wheelchairs, brain-computer interfaces, and powered exoskeletons. In the final category, the competing teams came from as near as Zurich and as far as Pensacola, Florida.

Almost immediately, the LSRO team ran into a major problem: Three electronic boards in the exoskeleton had died. “It was probably because of the huge amount of electromagnetic interference on the main floor,” Vouga says. “These are not commercial devices, so they’re not checked for electromagnetic interference. And so you don’t know what they throw out there. That’s probably one of the reasons we had this crash that had never happened before and it’s never happened again since then.”

Vouga and two team members immediately drove more than two hours back to Lausanne, where they worked late into the night to repair the faulty components, and then, sleepless, found a ride back to Kloten. By the morning of October 8, they were ready for Pan to strap on the Twiice.

Four pilots competed in the final. Sitting, standing, walking, climbing up and down a ramp while opening a door, maneuvering around obstacles—Pan managed the race challenges well until she got to the last obstacle: a staircase. The exoskeleton balked at climbing them. Pan was disappointed. Climbing stairs is a difficult action for both an exoskeleton and its user—few exoskeletons have the capability—yet she had mastered the actions in the lab. But Twiice wasn't functioning properly, so she couldn't show how adept she was at climbing.

They wound up coming in fourth, just missing a medal, Vouga says. “But we were really happy with these results, considering we were so near to not being able to complete."

He continues, “It was an amazing experience for all of us. It was extremely stressful because we were coming out of 18 crazy months of development at a very high pace, and the last 10 or 15 days had been almost sleepless for all of us. So we were all completely exhausted. But it was a huge emotion for us to see Silke actually competing.”

They were also proud of their finish because they were up against some stiff competition: commercially available exoskeletons that had been developed and refined by teams for years, including the ReWalk (1st place) and the X1 Mina (2nd place), which has the backing of NASA. (Third place went to SG Mechatronics.) Compare that to Twiice, which was only 18 months old at the time. "It was an honor for us to compete along with these guys,” Vouga says.


In the months since the competition, the team has shifted gears towards the daily functionality of Twiice. Most of it is there, Vouga says. “The things that it can do—like going up the stairs, going up and going down ramps, getting up and sitting down—these are the things [Silke] can already do alone. I think they’re very much representative of the daily life activities that you would need to perform. So we’re really close to something someone can bring home and use on a daily basis.”

What they're still developing is a way for the user to get into the exoskeleton without assistance. "It’s like, you know, in Formula 1—the pilot still needs assistance to get into the car. It’s the same thing with the exoskeleton,” says Vouga.

So the next step is to refine the exoskeleton so it won’t need a pit crew? “Yes,” he says, laughing. “Exactly.”

Pan is still in the lab regularly, strapped into Twiice, helping them make these enhancements. “We have continued to develop the exoskeleton so that it becomes more and more useful in everyday life,” she says. “In particular, we sought to increase walking speed, make the balance easier to manage, and provide additional movements. We would also like the person who uses it to put it on himself and are creating a variant where the disabled person can move very quickly from a wheelchair to a standing position.”

People who walk, Bouri says, don’t think much about the fact that they can stand at will. That’s not true of people who can't. “For people with spinal cord injuries, it’s very important to be in a vertical position,” he says. When it comes to rehabilitation, recovery, or assistive technology, “the first motivation [of people with] spinal cord injury is not necessarily walking—it’s really to be in a vertical position. To be part of the ‘vertical’ society.”

Bouri points to testimonials by people who have used the exoskeleton produced by Rex Bionics as evidence of the desire to view life from one’s natural height and have the ability to stand with other people and simply see them eye to eye. “Socialising in REX has got to be one of the best feelings; it’s almost natural standing and having a chat,” says one user. “At home I just want to use it for daily activities … and in the kitchen I want to cook a proper meal standing up,” says another.

And yet, another opportunity to show off Twiice’s—and Pan’s—competitive edge is coming up this weekend. LSRO was one of 20 finalists chosen to participate in the UAE AI & Robotics Award for Good competition, which takes place in Dubai on February 17 and 18. The event will award $1 million U.S. to “the best uses of AI and robotics in public service and improving people’s lives” in three categories: education, healthcare, and social services. The team is traveling to the UAE for the event. “We are preparing intensively for this,” Pan says.

Vouga estimates that, pending clinical trials, the Twiice exoskeleton may be commercially available within two years. It will be relatively inexpensive for the sophistication of the technology, he says, but that doesn’t mean it will be cheap: It’s still going to cost between $20,000 and $40,000 US. (Similar exoskeletons can cost anywhere from $60,000 to $120,000, though lower-cost versions are being developed.) They’re going to provide customization and modification: For that much money, Vouga says, users should expect some high-end "customer service."

LSRO recently teamed up with the company Sonceboz, which produces actuators like the ones used at Twiice's joints. Sonceboz is funding a 2.5-year project at LSRO to refine the exoskeleton. Bouri believes they can create "amazing and useful devices for the daily living activities of paraplegic people," he says.

And yet despite this enthusiasm, Bouri also wants to make clear that they are a while off from being able to manufacture these exoskeletons on an industrial scale. “If we say that we are capable to make an exoskeleton in two weeks, that probably means we’ll probably receive a lot of requests to do a lot of personalizations,” Bouri says. “We are faced with paraplegics who are suffering, and we really do not want to give them false hope.”

As for Pan, she vowed last fall to give up “big international competitions” in paracycling. But the resolution didn't stick. She was lured back to the sport in December 2016 by an Italian team called Active Sports. She’ll race in May with them at the Giro d'Italia 2017, a 2200-mile, weeks-long event.

And in June, she’ll compete in the ultra-endurance Race Across America (“The World’s Toughest Bicycle Race”) with seven other cyclists. On her team’s 3000-mile journey from Los Angeles to New York, hers will be the only handbike. She’s the only paraplegic on the team.