19 April 2010

Fly-by-Wire Brains: Melt in Place Brain Machine Interfaces

The stretchable, ultrathin design would make for better brain-computer interfaces (BCIs), which record brain activity in paralyzed patients and translate thoughts into movements of computer cursors or robotic arms. Because it’s so thin and flexible, a silk-based device could reach regions of the brain that were previously inaccessible. _Wired

Brain scientists are making progress in the design of better brain-machine interfaces. The newest version -- pictured above -- is a surface mount electrode array that conforms to the curvature of the underlying brain, "melting" in place for better connection.
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. _MITTechReview

More on this new approach from Wired:
The research team printed electrode arrays onto silk films that disintegrate after they are placed on the brain’s surface and flushed with saline. They’re just 2.5 microns thick, so thin that they need to rest on a platform so they don’t fall apart during fabrication or implantation. After the silk film dissolves, the array wraps around the curves on the brain.

...The scientists would like to extend their findings by making fully dissolvable implantable electronics for monitoring and stimulating tissue growth. They have also developed rolled-up devices, which they could deliver to the brain without making large holes in the skull during surgery. Eventually, they hope to adapt the technology for retinal and cochlear implants and to treat patients with a wide range of psychiatric and neurological diseases. _Wired

This approach is certainly better than the scar-inducing metallic electrodes that penetrate -- and inadvertently destroy -- deep brain tissue. But it is a far cry from the elegant targeted self-assembly process by which the brain originally develops, and constantly re-forms itself throughout its lifetime.

A surface-mount conformable biocompatible electrode array is only the starting point. Such a surface mounted array would naturally constitute a "base station" for sending targeted and self-assembling probes safely into the brain to connect with specific brain pathways and grey matter nuclei.

The U Penn researchers have developed a fascinating early incarnation of a system that will grow far more sophisticated and complex as the tools from biotech, nanotech, materials science, and information technology become available.

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