Stretching was another matter. Silicon, no matter how thin, won’t oblige. One day, a student who was building flexible devices told Rogers about a problem he was having. Sometimes, as the circuits pulled free from their anchors, the silicon buckled, making it difficult to get it to adhere to its new base. Nobody had previously discovered that property of silicon; Rogers realized that it could be his way around the material’s inelasticity. He would fabricate silicon in accordion-like shapes that could unfold and fold without breaking: stretchability without stretching.

At first, Rogers thought that he would deploy his technologies outdoors. The military was interested in funding giant dish-shaped antennas that could fold up into a backpack, or X-ray machines that could wrap around the hull of a tanker. Then, in 2007, a doctoral candidate in bioengineering heard Rogers give a lecture at the University of Pennsylvania and asked him if he’d ever considered putting devices on the brain. He had not. “That just seemed like a compelling direction,” Rogers told me. “It was utterly obvious that we should be doing that.”

Rogers is friendly, organized, and supportive, seemingly as much substrate as circuit. When I visited his lab, he handed me a typed, two-day itinerary, labelled in half-hour blocks, that mirrored his own. “Maybe before we go too far through the process I’ll step you through the schedule to make sure you accomplish what you need to accomplish,” he said. I watched fourteen PowerPoint presentations given by students on devices-in-progress, listened to three conference calls with collaborating scientists, and talked with Rogers for several hours. I kept asking what inspired him and how he managed to find solutions to problems that no one else realized existed. “I think a lot of it has to do with persistence,” he said finally. “It’s not the case that I go on a bike ride and come up with a good idea. It’s more that I’m thinking about it all the time. It’s always kind of rattling around.”

Rogers grew up in Sugar Land, Texas, a humid suburb of Houston. His father, John, Sr., worked for Texaco as a geophysicist. His mother, Pattiann, is a poet. As a child, Rogers played in bayous near his home, catching fish, frogs, and snakes. He was also fascinated with the sophisticated computers that his father used in his job. He finished high school early and spent the next year working in his father’s office, using state-of-the-art processors to probe underground with sound waves, looking for oil. His father had been an Eagle Scout, and Rogers still wears a gold ring with a blue stone that he got when he earned his Eagle Scout badge, by building an elaborate locker facility for the community pool.

Rogers majored in chemistry and physics at the University of Texas and then went to graduate school at M.I.T., where, among other things, he used lasers to measure materials that, for various reasons, it is best not to touch. He built exponentially smaller, more precise laser systems. “He would just show up in my office when a project was finished,” his M.I.T. adviser, Keith Nelson, a chemist, told me. “I wouldn’t even know about it until it had already been done.” In Nelson’s lab, Rogers met Lisa Dhar, a fellow materials scientist, and the two eventually married. After finishing his Ph.D., he decided to devote part of his final year to what he refers to as “the Super Bowl for M.I.T. geeks,” a startup-business competition hosted by the university. He learned how to draft a business plan, and though his project, conceived around the new laser setups, didn’t win, it did become a company, Active Impulse Systems. Three years later, in 1998, Philips bought the company, for an eight-figure sum that Rogers prefers not to name.

Professor-entrepreneurs aren’t unusual at the University of Illinois, and Champaign itself harbors a surprising number of moguls, including a sandwich czar and the owner of the Jacksonville Jaguars; by these standards, Rogers insists that he’s not wealthy at all. He drives a thirteen-year-old BMW and spends part of his minor fortune investing in his six companies. One, Semprius, uses the same stamping technique as his flexible devices do to print the world’s smallest solar cells onto flat panels; the cells, made with gallium arsenide, a high-performance semiconductor, and coated with lenses the size of pinheads, are too small to handle with traditional tools. Recently, a prototype Semprius solar module set a record for efficiency, converting thirty-seven per cent of light into electricity. In principle, the cells could be printed on any surface: curved helmets, fabric tents.

Another company, MC10, focusses on fitness and medical applications. It recently launched its first commercial product, the Reebok CheckLight, a mesh skullcap designed to be worn while playing contact sports. Inside, it has a collection of accelerometers and a gyroscope to detect the force of blows to the head and L.E.D.s to indicate their severity, in red and yellow. The company, co-founded with Marvin Slepian, is also helping to develop the balloon catheter that Slepian showed me. Rogers says he saves the rest of his income to finance his research group in case of an emergency. “I have responsibility for these postdocs,” he said. “A lot of them have families. I have to be able to pay their salary no matter what. So I’ve always felt the need to have a sort of nest egg that I could draw upon, to support the group.”

Rogers doesn’t work in the lab anymore. He supervises eighty undergraduate, graduate, and postdoctoral students, who carry out experiments he helps to design and report back to him. Often, as we listened to students and colleagues, his leg bounced and his fingers worried a nearby object—his keys, his pen. I asked him if he ever found it frustrating not to do experiments himself anymore. “It’s great if you can do things with your own two hands,” he said. “But then you’re limited by your own two hands, right?”

Still, sometimes he can’t resist testing devices on himself. For a while, he travelled around wearing a dummy version of the epidermal electronic system, to see what it felt like and to show it off. As a demonstration vehicle, he said, “it tended to be really effective, because people would come up after talks and rub their finger across the device on my skin and get a more intuitive feeling for the kinds of technologies we’re working on.” The device would stay on for a week and a half, even with a daily shower; it helped if he added a new coat of Walgreens spray-on bandage each morning. “But my students were going crazy, because they have to build them by hand,” he said. “So I had to stop doing that. But you can get through a metal detector, no problem.”

Rogers was trained in the so-called hard sciences, but the more time he has spent with the spongy materials of biology the more he has wanted to get his devices deep inside tissue. A couple of years ago, researchers at the Litt Lab, at the University of Pennsylvania, tested a device, designed with Rogers, on an epileptic cat. Studying epilepsy typically involves temporarily removing a portion of a subject’s skull and placing metal electrodes, each embedded in plastic and hooked up to individual wires, on the brain’s surface. But the approach can accommodate no more than a hundred and fifty electrodes. Rogers designed an array of three hundred and sixty flexible electrodes, collectively smaller than a postage stamp, that melds into the brain’s folds, achieving better contact and resolution. In testing the array on the cat, the researchers discovered that electrical activity arose in advance of seizures from much smaller areas and in more complicated electrical patterns than they had previously thought. Coming versions of the device will slide in through a small hole in the skull, unroll over the brain, detect unusual activity, and potentially treat it with precise electrical pulses.

“We keep it simple. That’s our god of fertility.” Facebook

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But most of what goes on in the brain happens below the surface. Lately, Rogers has been following the emergence of a new research field called optogenetics, which entails threading light-emitting devices into the brain to trigger neurons with photons. It is the most precise method yet for exploring how exact constellations of neurons affect behavior—which unique pattern of synaptic firings permits one’s fingers to close around a friend’s hand, sense her touch, and generate a sense of comfort—and how to manipulate them. The first step, using a virus to gain entry, is to infect a specific group of brain cells with a protein that makes them sensitive to light. Then a fibre-optic cable is implanted next to the cells, to beam in photons. Turning on the light activates the cells, while neighboring cells are unaffected—a feat of spatial and temporal precision impossible to achieve with drugs or electrical stimulation. Delivering light to the brain means tethering subjects—just mice, for now—to a cumbersome fibre-optic cable that is fastened to a light source. This has limited a mouse’s mobility, sabotaging its social life and making it difficult to parse the behavioral effects of turning certain neurons on and off.