Researchers at University of Pennsylvania School of Medicine, University of Illinois in Urbana-Champaign, and Tufts University have demonstrated that silk can be used as an excellent brain-computer interface material. Because silk can hug and grasp the surface of the brain, there’s a potential of developing much more precise and sensitive brain reading implants.
From a National Institutes of Health press release:
The implants contain metal electrodes that are 500 microns thick, or about five times the thickness of a human hair. The absence of sharp electrodes and rigid surfaces should improve safety, with less damage to brain tissue. Also, the implants’ ability to mold to the brain’s surface could provide better stability; the brain sometimes shifts in the skull and the implant could move with it. Finally, by spreading across the brain, the implants have the potential to capture the activity of large networks of brain cells, Dr. Litt said [Brian Litt, M.D., an author on the study and an associate professor of neurology at the University of Pennsylvania School of Medicine in Philadelphia].
Besides its flexibility, silk was chosen as the base material because it is durable enough to undergo patterning of thin metal traces for electrodes and other electronics. It can also be engineered to avoid inflammatory reactions, and to dissolve at controlled time points, from almost immediately after implantation to years later. The electrode arrays can be printed onto layers of polyimide (a type of plastic) and silk, which can then be positioned on the brain.
Recently, the team described a flexible silicon device for recording from the heart and detecting an abnormal heartbeat.
In the current study, the researchers approached the design of a brain implant by first optimizing the mechanics of silk films and their ability to hug the brain. They tested electrode arrays of varying thickness on complex objects, brain models and ultimately in the brains of living, anesthetized animals.
The arrays consisted of 30 electrodes in a 5×6 pattern on an ultrathin layer of polyimide – with or without a silk base. These experiments led to the development of an array with a mesh base of polyimide and silk that dissolves once it makes contact with the brain — so that the array ends up tightly hugging the brain.
Next, they tested the ability of these implants to record the animals’ brain activity. By recording signals from the brain’s visual center in response to visual stimulation, they found that the ultrathin polyimide-silk arrays captured more robust signals compared to thicker implants.
NIH press release: A Brain-Recording Device that Melts into Place…
Abstract in Nature Materials: Dissolvable films of silk fibroin for ultrathin conformal bio-integrated electronics