Impedance characterization of microarray recording electrodes in vitro

The mechanisms underlying performance degradation of electrodes chronically implanted in the central nervous system (CNS) remain unclear. Several components of the normal brain wound healing response were evaluated to determine if their presence correlates with increased electrical impedance that may be a factor in loss of device performance. Microelectrode recording arrays were electrically characterized in vitro in the presence of saline, culture media with 10% fetal bovine serum (FBS), and various CNS cell types isolated from Sprague-Dawley rats and cultured in media with 10% FBS. Electrochemical impedance spectroscopy (EIS) and cyclic voltammetry (CV) were performed using a three-electrode system. Potential cycling during CV caused an immediate decrease in electrical impedance, which increased with time toward the pre-cycling value, with the effect of cycling remaining significant for several days. The addition of serum caused a significant but not substantial increase in impedance. The inclusion of various cell types known to participate in the brain wound healing response caused a significant increase in impedance immediately after seeding on the order of 50%, and this value increased or remained constant for up to several weeks. It is unclear whether the magnitude of increased impedance is sufficient to account for loss of device performance.