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posted by Fnord666 on Saturday February 25 2017, @01:53AM   Printer-friendly
from the it's-empty dept.

For the first time ever, a single flexible fiber no bigger than a human hair has successfully delivered a combination of optical, electrical, and chemical signals back and forth into the brain, putting into practice an idea first proposed two years ago. With some tweaking to further improve its biocompatibility, the new approach could provide a dramatically improved way to learn about the functions and interconnections of different brain regions.

[...] The fibers are designed to mimic the softness and flexibility of brain tissue. This could make it possible to leave implants in place and have them retain their functions over much longer periods than is currently possible with typical stiff, metallic fibers, thus enabling much more extensive data collection. For example, in tests with lab mice, the researchers were able to inject viral vectors that carried genes called opsins, which sensitize neurons to light, through one of two fluid channels in the fiber. They waited for the opsins to take effect, then sent a pulse of light through the optical waveguide in the center, and recorded the resulting neuronal activity, using six electrodes to pinpoint specific reactions. All [of] this was done through a single flexible fiber just 200 micrometers across -- comparable to the width of a human hair.

[...] The key ingredient that made this multifunctional fiber possible was the development of conductive "wires" that maintained the needed flexibility while also carrying electrical signals well. After much work, the team was able to engineer a composite of conductive polyethylene doped with graphite flakes. The polyethylene was initially formed into layers, sprinkled with graphite flakes, then compressed; then another pair of layers was added and compressed, and then another, and so on. A member of the team, Benjamin Grena, a recent graduate in materials science and engineering, referred to it as making "mille feuille," (literally, "a thousand leaves," the French name for a Napoleon pastry). That method increased the conductivity of the polymer by a factor of four or five, Park says. "That allowed us to reduce the size of the electrodes by the same amount."

Seongjun Park, Yuanyuan Guo, et al. One-step optogenetics with multifunctional flexible polymer fibers. Nature Neuroscience, 2017; DOI: 10.1038/nn.4510


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