Modeling in vitro neural electrode interface in neural cell culture medium

A stable neural interface between neural electrodes and surrounding tissues is a critical point to achieve long-term signal recording stability, and flexible polymer-based neural microelectrodes are attracting growing interests due to their mechanical properties compatible to surrounding tissues and potential to minimize post-implantation injury. As a fundamental study to have an insight into the flexible polymer-based microelectrode–tissue interface in vivo, the neural microelectrode interface was investigated in vitro in neural cell culture medium. Flexible polyimide-based gold electrodes used for recording neural signals were micro fabricated and packaged to model the in vitro neural microelectrode–cell medium interface. The surface of gold recording sites of the neural microelectrode was observed using scanning electron microscopy (SEM), and island-like structure with the size of 537.4 ± 357.2 nm was visualized. To better understand biological processes that affect neural signal recording, the microelectrodes were immersed in neural cell culture medium for 9 days, and electrochemical impedance spectroscopy (EIS) measurement was carried out at each time point. Nyquist and Bode plots resulting from the EIS measurement were analyzed by fitting the experimental data with equivalent circuit models. On the basis of equivalent circuit models, physical processes occurring at the interface were described. Moreover, the mechanism for the impedance variation of recording sites in cell culture medium was discussed.