Improved brain implants possible with Electrically Conductive Polymers

10-Nov-09

New findings could lead to improved treatment of neurological disorders such as Parkinson’s disease and paralysis. Brain implants that can clearly record signals from surrounding neurons in rats have been created at the University of Michigan. 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. During this secondary response, the brain tissue starts to encapsulate the electrode, cutting it off from communication with surrounding neurons. The new brain implants are coated with nanotubes made of poly(3,4-ethylenedioxythiophene), a biocompatible and electrically conductive polymer that has been shown to record neural signals better than conventional metal electrodes. 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 nanofibre 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. The researchers found that PEDOT nanotubes enhanced high-quality unit activity (signal-to-noise ratio >4) about 30% more than the uncoated sites. They also found that 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. 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.