Uncomfortable shoes. Awkward crutches. Painful artificial limbs. When technology meets biology, the interface is rarely flawless—and the devices often hinder the bodies they are supposed to help. Hugh Herr, SM ’93, believes that technologists can do better. An associate professor of media arts and sciences and leader of the Biomechatronics Group in MIT’s Media Lab, Herr is building sophisticated devices that aid human movement by mimicking nature.
In March, Herr gave a headline-grabbing TED talk about work in his lab to create a special prosthesis that allowed Adrianne Haslet-Davis, a dancer whose leg was partially amputated after the 2013 Boston Marathon bombings, to execute a rumba for the audience. But more than highlighting a single project, Herr’s talk invited the public into his larger vision: a world in which technology erases disability, and in which the synthetic and biological worlds meld seamlessly.
It’s unusual to find a researcher whose work and personal history are so entwined, and not just because Herr, himself a double amputee, now walks on bionic legs that his lab designed. As both a rock climber and a user of prostheses, Herr has direct experience with frustratingly poor prosthetic designs—and an athlete’s determination to overcome them. His lab is working to understand the tricks the human body uses for moving efficiently, and then translating that knowledge into robotic devices that can not only restore function to those who have lost it but enhance normal human capabilities.
“Imagine 50 years from now, with truly advanced bionic technologies, [if] you want a third arm, you can have a third arm,” he says. “That’s cool.”
A Redirected Passion
Herr, 50, describes himself as a focused person, and he speaks with a solemnity that makes it easy for people to miss his dry humor. When he was young, that intense focus was directed at one thing: climbing. “My singular objective was to be the best climber in the world,” he says. His academic interests were, he readily admits, nonexistent. In 1982, when he was 17, Herr and a friend were caught in a blizzard while climbing Mount Washington in New Hampshire. They were stranded for three nights before being rescued; one man who was trying to rescue them died. Herr’s frostbitten legs were amputated below the knees.
“It’s alarming to every person who first receives an artificial limb how low-tech and archaic the technology is—certainly back then,” he says. His first prostheses were temporary ones with plaster sockets, and he was instructed not to walk without crutches or another support: the plaster would shatter under his full weight. Later he got permanent prostheses made of wood, rubber, and plastic, but they were stiff and painful.
Yet Herr found that he could still excel in the vertical world of rock climbing. In high school, he had trained in tool and die machining at a vocational school; shortly after returning home from the hospital, he set up a workshop in the garage and put those skills to work designing and building his own prosthetic limbs for rock and ice climbing. Climbing is a sport in which the typical human body can feel awkward, as anyone who has tried to balance on a small foothold or wedge a foot into a crack can attest. So Herr’s designs didn’t look like feet at all. “I quickly abandoned this notion that the prosthesis has to look like a human limb, and I started to think: what’s optimal, what’s best for function?” he says. He created tiny feet that could balance on a whisper-thin ledge, and hatchetlike blades that could fit into a crack.
Soon enough, Herr began climbing harder routes than he’d mastered before his accident. “That was deeply inspiring,” he says. “I had never appreciated the capacity of technology to change an individual’s life so precipitously.” The obvious career path he might have taken, working in his father’s house-building business, was no longer an option for him, and he now had a vested interest in making artificial limbs better. So although Herr had never intended to go to college, a few years after his accident he decided to give it a try, earning a bachelor’s degree in physics at Millersville University in Pennsylvania at age 25. “It replaced my passion for climbing,” he says. “In two years I went from not being able to take 10 percent of a hundred to studying graduate-level quantum mechanics.” While at Millersville he also got his first patent, for a prosthetic socket designed with fluid bladders for better comfort.
After graduating, Herr came to MIT, where he completed a master’s degree in mechanical engineering in 1993. His thesis project involved the unusual idea of developing an elastic suit to make vertical climbing easier: the motion of reaching up to grab a handhold stretches the elastic, and its stored energy is then used to aid the more tiring motion of pulling the body upward. His lab is still working on the idea today. For his PhD in biophysics at Harvard, he developed a numerical model to describe how a horse runs and established principles for mimicking it robotically. He also worked in MIT’s Leg Lab, which made advances in building legged robots that could walk and run. The lab was then led by Gill Pratt ’83, SM ’87, PhD ’90 (its founder, Marc Raibert, had already left to work full time at the company he founded, Boston Dynamics). When Herr graduated, Pratt hired him as a postdoc.
Herr worked with Pratt to develop a computer-controlled knee joint that uses a magnetorheological fluid—a fluid whose viscosity changes when a magnetic field is applied—to vary the stiffness of the joint as a person walks.
Pratt was so impressed with Herr’s work on the knee, which was eventually commercialized as the Rheo Knee, that he made him co-director of the lab, though Herr was just a postdoc. “Hugh had tremendous practical knowledge about prosthetics, he had tremendously good intuition about control, and he was also very strong in terms of physics,” says Pratt, now a program manager at DARPA. When Pratt left MIT in 2000, Herr took over the lab, which eventually became the Biomechatronics Group within the Media Lab.
The Science of Walking
Visitors to the Biomechatronics Group, which fills half of a large open room on the Media Lab’s second floor, may come to see the future of bionics, but they often comment on the clutter. The lab, which is typically packed with students and postdocs working on projects, is strewn with computer parts, coffee cups, wires, rolls of tape, random tools, and plastic molds of human feet. At the center of the space is a raised platform with a treadmill and a set of hip-high parallel bars. Ten cameras trained on the platform capture the motions of subjects as they run and walk on the treadmill. That’s because an important part of the lab’s work is describing how the human body moves. Walking, though a seemingly simple act, is still largely mysterious, using energy in a very economical manner that is difficult to re-create in robotics. “We do not entirely understand how the muscles are being controlled, which surprises a lot of people,” Herr says. Though researchers have been able to simulate human walking well enough to create walking robots like those used in DARPA’s robotics challenge, these robots require huge amounts of power to do what humans accomplish with incredible efficiency and grace. It will take a few more years, Herr says, to understand walking well enough to program robots and develop prosthetic devices that efficiently replicate human function.
This science, he says, is critical for designing the hardware and software control systems of bionic devices. Daniel Ferris, director of the Human Neuromechanics Laboratory at the University of Michigan, says that Herr’s strength is “knowing the biological mechanisms and physiology and function in a way that most engineers don’t.” While many engineers have built robotic devices for movement, “none have really matched Hugh’s ability to fuse biology with engineering.”
His lab’s work to model the human ankle joint ultimately led to the development of the prosthesis Herr uses today, sold as the BiOM T2 by his startup company BiOM (formerly called iWalk). It is the first foot and ankle prosthesis that behaves, as he puts it, more like a motorcycle than a bicycle, meaning that it puts energy into the system rather than relying solely on human power.
In human walking, the calf muscle and the ankle joint contribute the most power. The BiOM T2 uses a battery to power a system of microprocessors, sensors, springs, and actuators; the joint provides stiffness during a heel strike to absorb shock, then power to help propel the lower leg up and forward during a step. “When you’re missing that power, it’s substantial,” he says. “When you get it back, it’s life-changing.”
To help Adrianne Haslet-Davis perform, Herr and his team studied and modeled human dancing and reprogrammed the prosthesis with algorithms that would allow it to execute the necessary rotations. They also designed it to minimize the battery at the calf, to keep it from getting in the way of dance steps.
The goal of such devices is to make prostheses more natural and, by lowering the energy costs of walking, reduce joint stress and fatigue. But bringing bionic devices into the clinic is not easy. Bob Emerson, a prosthetist at A Step Ahead Prosthetics who helps connect patients to research projects in Herr’s group, says it’s challenging to persuade insurers to pay for devices like BiOM. “It’s a far-reaching technological platform; people don’t understand it really well,” he says. He says it takes vision and persistence to drive major technological innovations in such a small and specialized market.
There are still drawbacks to current bionic designs—ankle prostheses like Herr’s go through one or two battery charges a day, for instance—so Herr and his colleagues are working to make prosthetic devices smaller, lighter, quieter, and more efficient. They’re also involved in efforts to design more comfortable sockets to attach prosthetic limbs to the body. Humans “are soft and malleable,” says Herr, “and we’re not static; we change in time, we swell, we shrink. So how you attach the machine world to that is a really hard problem.”
Herr has already tackled the problem of giving humans better, more seamless control over artificial limbs; his BiOM ankle prostheses adjust their torque and power in response to muscle contraction. Now he is going a step further, collaborating with surgeons and other researchers on ways to allow bionic limbs to be controlled directly by the nervous system, which he hopes to demonstrate in a human in the next few years. Whereas brain-machine interfaces would require invasive surgery for brain implants, he wants to connect electronic devices to the peripheral nerves at the site of the injury, allowing people to control bionic limbs with their existing nerves and potentially even perceive sensations in the limb. Amputation, which is currently a fairly crude surgery, might become a sophisticated procedure of setting up the body to interface with a bionic limb.
Extending Human Capability
Along one wall of the Biomechatronics Group lab, wheeled shelves known as the “dessert cart” hold an array of prototypes of current and past projects: ankle joints, 3-D-printed leg sockets, wooden feet, and ski boots that interface with motors and metal parts. While the collection of prosthetic devices his lab has already produced is impressive, Herr isn’t content merely to restore lost capability. His lab is also working on technologies that could enhance normal human function, allowing us to walk or run faster, carry more weight, or climb more easily. The dessert cart holds early designs for wearable exoskeletons that would allow people to commute to work on foot as quickly as they might on a bicycle, or carry heavy loads without getting tired.
Building an exoskeleton that makes movement easier is challenging—the device must provide a benefit to the user that exceeds the burden of wearing it. Luke Mooney, a graduate student in the Biomechatronics Group, says that many people think “exoskeleton” and imagine an Iron Man–style suit. But he recently worked with Herr on a far more minimalistic approach, focusing solely on providing mechanical power to the ankle to reduce the energy it needs for walking. Their prototype, a hiking boot attached to a brace on the lower leg and powered by a wearable battery pack, is the first exoskeleton that can actually lower the metabolic costs of walking, as demonstrated in a study published this May in the Journal of NeuroEngineering and Rehabilitation. “When you unplug it, suddenly you feel like your feet are blocks of concrete,” says Mooney.
Even with these successes, technologists are still a long way from replicating the natural abilities of the body or building wearable devices that can dramatically boost its abilities. “I admire Hugh’s creativity and unique approach and his drive,” says Woodie Flowers, SM ’68, ME ’70, PhD ’72, an emeritus professor of mechanical engineering who helped supervise Herr’s graduate research work. But Herr is “working in a very complex research area that involves a very intimate relationship between a complex human and a complex machine,” he points out. “I respect how hard that is.”
Redefining the Good Body
In spite of the practical challenges, Herr has a far-reaching vision for melding technology with biology. While some researchers and engineers gloss over the social implications of their work, he has become an outspoken champion for the ways that technology can improve the body.
“A lot of folks who have been injured look up to him for motivation,” says Pratt. Part of that inspiration comes from Herr’s attitude toward prostheses. Once he realized he could climb with prosthetic legs, he began celebrating them rather than hiding them, painting them bright colors. Today, he sometimes wears trousers cut off at the knees, making his prostheses visible.
Herr has never been concerned with appearing to have “normal” legs; in addition to climbing feet, he built himself artificial limbs that allow him to be short or very tall. Many people want to camouflage their prostheses, he says, because they associate looking normal with being attractive. “I didn’t make the connection,” he says with a laugh. His sense of attractiveness was shaped by climbing; as an athlete, he always felt that sexiness was determined by ability more than looks. “I don’t care what you look like,” he says. “If you’re not weak—if you’re the opposite—you’re very sexy.”
Indeed, as artificial limbs become more powerful and functional, they can sometimes be perceived as the opposite of a disability. In 1986, Herr became the second person to do a free climb of a 120-foot crack in Washington state called City Park, at the time considered the hardest such climb in the country. When another climber ascended it in 2006, Herr’s achievement was discounted by a major climbing magazine because his prosthetic legs were seen as giving him an advantage. He sees parallels with how the world responded to Olympic runner Oscar Pistorius, a double amputee who was accused of cheating when he used his prosthetic legs to compete with able-bodied athletes.
“Our culture is trained to think about a person with an unusual body or mind as weak,” Herr says. “When there’s not weakness, when there’s an athlete who’s actually winning against the normal body, there’s a confusion that occurs.”
He believes that ideas about prosthetics will change. “We’re all so cell- and tissue-centric,” he says. “We somehow think our cells are holy, and that as soon as a part of our bodies is made of titanium atoms or something, it’s less human—that you can’t embed humanity into synthetics.” But he predicts that this bias will persist only as long as the objects we attach to the body are crude, uncomfortable, and ill-performing. An artificial limb that makes no attempt to look like a human limb might appear ugly, he says, but “when you take that same aesthetic and you make it highly functional and powerful, then [it] will become intriguing and beautiful.”
In time, he believes, people will care less about what we’re made of. “It just matters what we are and what we do—the quality of our lives,” he says.
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