Organic microelectrode arrays for bioelectronic applications

Microelectrode arrays (MEAs) are devices that gather multiple microscopic electrodes in a small area and are used to electrically record and/or stimulate the biological activity of cells. Recently, MEAs that use organic mixed ionic and electronic conductors (OMIECs) as active materials, have gained significant attention due to the profound advantages over traditional metal-based MEAs. OMIECs, usually polymer-based, can be processed from solution and offer high-charge capacitance and mechanical properties that match those of cells. These advantages offer organic microelectrode arrays with a high signal-to-noise ratio and low electrochemical impedance. Organic MEAs (OMEAs) have been applied for in vivo applications, showing outstanding biocompatibility and lowering the “foreign body responses”. They have also been applied for the study of in vitro systems with various scales, such as tissues (macroscopic), cells (microscopic), membranes (nanoscale thickness), and biomolecules (nanoscopic). Here we present an overview of OMEA technology. First, we discuss the properties of OMIECs and the benefits over traditional MEA technology. Then, we introduce OMEAs device physics based on typical electrochemical techniques and discuss exemplar OMIECs for OMEAs. We then present an overview of microfabrication methods for functional OMEAs. Finally, we collect together recent breakthroughs in device design and novel bioelectronic applications of OMEAs, spanning from in vivo long-term implants for electroactive recordings to in vitro systems for drug discovery, among others. The possibility of using light-sensitive and optically transparent OMEAs to optically stimulate biological activity is also discussed in this section. Overall, we put together all aspects necessary for further advancement of OMEAs technology, i.e. fundamental materials and device principles, fabrication and bioelectronic applications to foster further advances of OMEA technologies.