A Blank Canvas to Create Smart Limbs Growing up in rural Pennsylvania, Hugh Herr dreamed of becoming a mountaineer. By the time he was 8, he had already scaled Mount Temple, over 11,500 feet, in the Canadian Rockies. But in January 1982, climbing Mount Washington, in New Hampshire, he and a friend were caught off guard by a storm and spent four days wandering through the frozen wilderness. They were finally rescued, but frostbite and hypothermia had set in and both of Hugh Herr's legs were amputated below the knee. He was 17. Today, at 48, Dr. Herr, a biophysicist, designs computerized prostheses and artificial body parts as director of the biomechatronics research group at the M.I.T. Media Lab. He is also the founder of iWalk, which manufactures bionic limbs and joints. We spoke at the annual meeting of the American Association for the Advancement of Science in Boston (before the attack on the marathon that resulted in at least 16 amputations), and then later by telephone. Here is an edited and condensed version of the conversations. What were your feelings after you were rescued from Mount Washington in 1982? You know, it's an interesting experience to believe, wholeheartedly, that you're going to die. And then, not die. There was elation. But also distress. Once we were found, we learned that a volunteer, Albert Dow, had died searching for us. The juxtaposition was profoundly confusing. I felt a lot of anger at myself. At the same time, I had this great passion to climb again. I had a belief that I shouldn't give climbing up because that would disgrace all the people who'd helped us. After the surgery, I was sent to a rehabilitation center. There, patients typically went home on weekends. The first week after I was fitted for my prostheses, they wouldn't let me take them home because they knew I'd go climbing. The staff was terrified I'd further damage what remained of my biologic limbs. When I finally did take them home, my brother and I immediately went climbing along the Susquehanna River. I could barely walk. Like an octogenarian, I hobbled with my back flexed, leaning over two canes. It took me some time to get to the base of the rock wall. But once I got on all fours, climbing, I felt I'd really come home. What were your first artificial legs like? Fragile. They were plaster. One problem was they'd been designed for the horizontal world - standing and very slow walking. They weren't meant for the vertical world of rock climbing. So I took it upon myself to design ones that were. Fortunately, I knew how to build things of wood and metal. I went into the shop and I started cutting, grinding, exploring different limb structures. Climbing became doing experiments, testing my latest contraption. The prosthesis that I'm wearing today, the Biom, which my team designed, is made of carbon, silicone, titanium, aluminum. It has three microprocessors and about 12 sensors. It's motorized. It has its own power supply. It adapts as I walk. If I want to walk faster, it gives you more power and possibilities. When I go up a steep hill, it gives me even more energy. When I go down, it decelerates. My first adventures in design involved designing better limbs so that I could climb again. But soon, I started to make myself different types of prostheses at different heights, for different purposes. I'd go to school, either very tall or short, depending on the day. What was the point of that? I wanted to show my classmates that being a bilateral amputee could be fun. With my designs, I came to think of the artificial part of a person's body as a blank canvas for which to create. I didn't have to live with nature, as long as the design obeyed physical law. I own about eight different prostheses, including a special prosthesis for running, three different types for climbing, one for ice, one for standing on small rock fissures or edges the width of a coin. I also have bionic legs for swimming, which can make me into a merman, with giant fins. What makes your M.I.T.-designed prosthetic devices different from what amputees have been traditionally using? Till recently, the teams that designed and built prostheses were skilled in either engineering or biology. My group understands how the biological body works, and we also have sophistication in engineering and design. The output is a bionic prosthesis that more closely emulates biological motion. For example, we've modeled how the foot, ankle, knee work in the biological body. What are the muscles, what are the tendons, how are the muscles being controlled, how much energy is the muscle using? That information is encoded in the bionic limb we build.