Cost to Develop: $100,000
Time: 8 years
Prototype | | | | | Product
Gordon Link, a diabetic and foot amputee, is not looking to climb Mount Everest, run a marathon, or snowboard off a cliff. “I just want to walk without stumbling like I’m a drunk,” he says. It may not sound like a tall order, but until he was fitted with a prototype prosthetic foot that simulates the body’s natural movements, walking on uneven ground was like navigating an obstacle course. “Hitting a low spot of even one inch with my old foot was like a non-amputee stepping into a four-inch hole,” he adds. “Not good.”
With 26 bones, 35 joints, and the awesome responsibilities of weight-bearing and propulsion, the foot is one of the trickiest body parts to mimic. Today, amputees must choose between mechanical models, which rely on flat carbon-fiber platforms that bend slightly with each step, or a computer-controlled motorized foot that better reproduces a natural gait but can cost up to $18,000 and often isn’t covered by insurance.
Working by night in a Boulder, Colorado, cabin, Rifkin built something that combined the natural step of a bionic foot with the simplicity and low cost of a mechanical prosthetic. His jointed foot has a heel, a forefoot, a big toe—and no joint at the ankle. Instead, a novel midfoot joint, which connects the heel and forefoot, does the job of both the ankle and the arch. Like an ankle joint, it flexes up and down to give the wearer a more natural step. And, like a real midfoot joint, it creates a flexible arch in the middle of the foot. A spring and cable connect it to a second joint at the toe, to create extra push-off at the end of each step. Other tensioned steel cables serve as the tendons and ligaments that govern its range of motion—the user doesn’t control it, it simply responds to the pressure of walking. Because the front and back of the foot can move independently, it can react to uneven terrain.
Rifkin’s main concern now is with durability; a spring keeps popping, mostly because he nicks and weakens its cables during the amputee fittings. “If he can work out the durability issues,” says Stanford University prosthetist Gary Berke, “then it could be excellent for the active adult who wants to walk through the city or hike in the park.” As for Link, he’s moving on to tougher terrain. “It’s so natural, I can walk on a golf course.”
Five amazing, clean technologies that will set us free, in this month's energy-focused issue. Also: how to build a better bomb detector, the robotic toys that are raising your children, a human catapult, the world's smallest arcade, and much more.