Doctors can put arrays of electrodes on the surface of the brain to pinpoint the source of epileptic seizures; patients can use such electrodes to control a computer cursor. But it's still not safe to leave these devices in the brain over the long term, and that's a quality that needs to be developed before researchers can develop better brain-computer interfaces.

Now a group of researchers is building biocompatible electronics on thin, flexible substrates. The group hopes to create neural interfaces that take higher-resolution measurements than what's available today without irritating or scarring brain tissue.

"Biocompatibility is a major challenge for new generations of medical implants," says Brian Litt, professor of neurology and bioengineering at the University of Pennsylvania Medical School. "We wanted to make devices that are ultrathin and can be inserted into the brain through small holes in the skull, and be made out of materials that are biocompatible," he says. Litt is working with researchers at the University of Illinois at Urbana-Champaign who are building high-performance flexible electronics from silicon and other conventional materials on substrates of biodegradable, mechanically strong silk films provided by researchers at Tufts University.

This week in the journal Nature Materials, the team reports using a silk electrode device to measure electrical activity from the surface of the brain in cats. Silk is mechanically strong--that means the films can be rolled up and inserted through a small hole in the skull--yet can dissolve into harmless biomolecules over time. When it's placed on brain tissue and wetted with saline, a silk film will shrink-wrap around the surface of the brain, bringing electrodes with it into the wrinkles of the tissue. Conventional surface electrode arrays can't reach these crevices, which make up a large amount of the brain's surface area.

"A device like this would completely open up new avenues in all of neuroscience and clinical applications," says Gerwin Schalk, a researcher at the Wadsworth Center in Albany, NY, who is not affiliated with the silk electrode group. "What I foresee is placing a silk-based device all around the brain and getting a continuous image of brain function for weeks, months, or years, at high spatial and temporal resolution."