Interfacing Conducting Polymer Nanotubes with the Central Nervous System: Chronic Neural Recording using Poly(3,4‐ethylenedioxythiophene) Nanotubes

Development of advanced chronic, high-fidelity neural interfaces is accelerating research into brain function[1] and more effective treatments for neurological conditions.[2–5] The primary functional requirements of these interfaces include recording and/or stimulating from a number of discretely sampled volumes of the brain at requisite spatial resolutions for specific time periods that may extend from hours to years.[6–9] This translates to a push towards smaller electrodes that are more biologically transparent and biocompatible[10–12] with a high density of electrode sites that remain functional for long period of time.[13–15] As electrode size goes to the microscale (higher spatial selectivity), the impedance of electrode site increases, and consequently, the quality of signal recordings decreases (lower sensitivity). Thus, there is a trade off between the size (spatial selectivity) and quality of signal recordings (sensitivity) in neural microelectrodes.[16–18] Studies have also shown that the response of brain tissue to implanted microelectrodes includes an acute injury and a chronic reactive tissue response. The chronic response is characterized by the presence of both activated microglia and reactive astrocytes, which eventually encapsulate the electrode to some degree.[10,12,19–21] Consequently, in addition to the initial high impedance of microelectrodes, these reactive tissue responses have been associated with a progressive increase in the impedance of the electrode/tissue interface.[10,12] Therefore, achieving a very low impedance electrode/tissue interface is important for maintaining and improving signal quality.