This article is one in a series of 10 stories we're running this week covering today's most significant emerging technologies. It's part of our annual "10 Emerging Technologies" report, which appears in the March/April print issue of Technology Review.

In late spring 2000, John Guttag came home from surgery. It had been a simple procedure to repair a torn liga­ment in his knee, and he had no plans to revisit the hospital anytime soon. But that same day his son, then a junior in high school, complained of chest pains. Guttag's wife promptly got back in the car and returned to the hospital, where their son was diagnosed with a collapsed lung and immediately admitted. Over the next year, Guttag and his wife spent weeks at a time in and out of the hospital with their son, who underwent multiple surgeries and treatments for a series of recurrences.