Striving for Impact:
Q & A with John Rogers
Your early work at Bell Labs in the ’90s focused on consumer products, like flexible screens with the look and feel of real paper. Why did you pivot to other areas, such as medical devices?
Many consumer electronic gadgets have limited societal benefit, and most are quickly supplanted by some next-generation thing. We’re hoping some of the things we’re pursuing can have some qualitatively different level of significance. The shift accelerated in 2002 after I gave a talk at the University of Pennsylvania, and a neuroscience student in the audience expressed an interest in putting our electronics on brains. That conversation led to a fruitful, long-lasting collaboration with his adviser and opened up clinical medicine as a focus of our research.
You went from using semiconductor materials that are inherently flexible to using silicon, a more conventional material not known for its flexibility. That feels like a step backward. Why did you do it?
I started looking for new ways to make flexible electronics out of necessity. When I was at Bell Labs, I was surrounded by amazing organic chemists who could cook up all kinds of interesting polymers and organic molecules that we could use to build transistors. When I left for Illinois, I knew I wouldn’t have my chemistry collaborators next door anymore, so I needed to find a different way to make an impact. We started to get interested in ultrathin silicon because thin geometries render any material flexible. A 2-by-4 is rigid, but a sheet of paper is not — similar materials, just different thicknesses. The same goes for silicon. A wafer is rigid and brittle, but sheets of silicon with nanoscale thicknesses are floppy and flexible.
Your devices are not only flexible, but stretchable. Why does that matter?
It makes it possible to wrap them around hemispherical shapes or soft biological tissues, like the brain or heart. For seamless, minimally invasive integration
of an abiotic system, like electronics, with a biological one, the mechanics and shapes must match up precisely. Since we can’t change biological systems to make them look like silicon chips, we’ve focused on the reverse.
How did you realize that stretchability is as important as flexibility?
Sometime in early 2005, a postdoc noticed that during the initial step of the printing process, the rubber stamps we use to print the ultrathin silicon could sometimes be slightly stretched in handling just before contact with the thin silicon. That can cause the silicon to adopt a wavy shape, almost like an accordion bellows. These shapes were formed initially by accident.
So relaxing the rubber then compressed the silicon. What effect did that have?
We were, in a sense, making the silicon do gymnastics — to buckle, stretch and deform. It took us a while to precisely understand the underlying physics of what was going on and to optimize the process, but as we’ve done so, we’ve come up with dozens of applications, including devices that conform precisely to the surfaces of body organs; or that can be attached to surgical instruments for insertion into the body with minimal harm to surrounding tissues; or that mimic nature in ways previously impossible, such as cameras that replicate mammalian-eye or insect-eye capabilities. — Jim Sullivan
[This article originally appeared in print as "Stretchy, Flexy Future."]