Brain implants coated with nanotubes

U. MICHIGAN (US)—Newly developed brain implants that can more clearly record signals from surrounding neurons in rats may lead to more effective treatment of disorders such as Parkinson’s disease and paralysis.

The new brain implants developed at the University of Michigan are coated with nanotubes made of a biocompatible and electrically conductive polymer that has been shown to record neural signals better than conventional metal electrodes.

“Microelectrodes implanted in the brain are increasingly being used to treat neurological disorders,” says Mohammad Reza Abidian, a postdoctoral researcher in Michigan’s Neural Engineering Laboratory.

“Moreover, these electrodes enable neuroprosthetic devices, which hold the promise to return functionality to individuals with spinal cord injuries and neurodegenerative diseases. However, robust and reliable chronic application of neural electrodes remains a challenge.”

Neural electrodes must work for time periods ranging from hours to years. When the electrodes are implanted, the brain first reacts to the acute injury with an inflammatory response. Then the brain settles into a wound-healing, or chronic, response.

It’s during this secondary response that brain tissue starts to encapsulate the electrode, cutting it off from communication with surrounding neurons.

The researchers found that the nanotubes coated with the polymer known as PEDOT—poly(3,4-ethylenedioxythiophene)—enhanced high-quality unit activity (signal-to-noise ratio >4) about 30 percent more than the uncoated sites.

They also found—based on in vivo impedance data—PEDOT nanotubes might be used as a novel method for biosensing to indicate the transition between acute and chronic responses in brain tissue.

In the experiment, the researchers implanted two neural microelectrodes in the brains of three rats. PEDOT nanotubes were fabricated on the surface of every other recording site by using a nanofiber templating method. Over the course of seven weeks, researchers monitored the electrical impedance of the recording sites and measured the quality of recording signals.

PEDOT nanotubes in the coating enable the electrodes to operate with less electrical resistance than current metal electrode sites, which means they can communicate more clearly with individual neurons.

“Conducting polymers are biocompatible and have both electronic and ionic conductivity,” Abidian says. “Therefore, these materials are good candidates for biomedical applications such as neural interfaces, biosensors and drug delivery systems.”

In previous experiments, Abidian and his colleagues have shown that PEDOT nanotubes could carry with them drugs to prevent encapsulation.

“This study paves the way for smart recording electrodes that can deliver drugs to alleviate the immune response of encapsulation,” Abidian adds.

The results are featured in the cover article of the Oct. 5 issue of the journal Advanced Materials. The work is funded by the Army Research Office, Center for Neural Communication Technology, and National Institutes of Health.

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