Strategies for minimizing glial response to chronically-implanted microelectrode arrays for neural interface

For several decades, the intracortical penetrating microelectrode arrays have been widely employed for the purpose of neural recording and stimulation in nervous system. However, the long-term application is limited due to the tissue reaction to the implanted electrode array. The tissue response includes the degeneration of nerve cells as well as the formation of dense glial sheath adjacent the implanted electrode called gliosis. The glial encapsulation deteriorates the capacity of electrodes to communicate with neurons by electrically isolating the devices from the neighboring brain regions. To examine and overcome these critical obstacles of microelectrode array for chronic applications, a number of studies have been performed to date including the reduction of electrode geometry, the use of flexible materials for electrode substrates, the pharmacological suppression of the cellular reaction, and the optimized surgical techniques. In this review, the studies to clarify the mechanism of the glial response in central nerve system (CNS) will be described and a variety of strategies for minimizing the glial responses in CNS will be examined.