As a teenager, MIT professor Hugh Herr was caught in a blizzard while climbing Mount Washington. He lost both legs below the knee to frostbite. His Cambridge start-up, iWalk, has spent the last five years developing the worlds most advanced prosthetic foot. iWalks PowerFoot BiOM device requires less effort to walk on than a traditional prosthetic, by storing energy as you walk and releasing it at the right point in your stride. The first devices were shipped to Walter Reed Army Medical Center earlier this year, and a wide release is planned for 2012.