how many hours patients put on them. The company also sells consumables such as the foot sensors and a throwaway perspiration barrier. Rehab clinics can bill Medicare for these expenses at the same rates fetched by other therapies aimed at restoring ambulation.
Some 15 clinics have rented the bionic legs, and when I visited Tibion in October, Remsberg told me he expected that number to hit 20 by the end of the year. (FDA regulations allow companies to sell certain types of medical devices even as efficacy trials are still underway.)
“We are thinking of it as a useful competitive advantage” for rehab clinics, says Ted Driscoll, a technology partner at Claremont Creek and a member of the investing group Life Science Angels. “We sell it to one clinic in Boston, and the next day the clinic across the street wants one.”
With help from Remsberg and Tibion founder Robert Horst, I took a Tibion leg for a test drive—see the video at the end of this article. While it obviously wasn’t possible for me, as an unimpaired adult, to experience the device’s alleged neuroplasticity-inducing effects, I certainly got a sense of the power that the device’s electric motors pack. I weigh about 175 pounds, and as soon as I leaned forward out of my chair, the device was able to lift my body to standing position, with very little assistance from me.
Horst says that coming up with an actuator capable of this feat was the central technological problem he faced back in 2003, when he left his previous employer, NetApp, to work full time on the idea of a bionic leg. He’d recently had knee surgery, and had realized that the state of the art in assistive devices for the movement-impaired was the venerable crutch or cane. “There hasn’t been any technology improvement since the stone age, basically,” Horst says. “Also, my family has a history of stroke and polio and other mobility problems.” In other words, it was the kind of challenge that the veteran tinkerer, who’d put in nearly 25 years at Hewlett-Packard and Tandem Computers and has 70 patents to his name, felt compelled to take on.
The problem with designing a wearable bionic leg is that it has to do two contradictory things: apply a force great enough to lift a person out of a chair, but then swing freely at the right moment. A leg that can’t do both would merely be taking over a patient’s leg, not really helping them relearn how to walk on their own. Horst says he thought electrostatic actuators might provide the necessary flexibility, but it turned out that they couldn’t produce the amount of force needed.
“Then I came up with the idea of using a continuously variable transmission,” he says. Invented by Leonardo da Vinci more than 500 years ago, CVTs are capable of stepping through a range of gear ratios seamlessly; they’re found today inside some automobile drivetrains. Horst developed a compact, electronic CVT that uses separate high-gear and low-gear motors, which are coupled and
