Electrode Size Scaling and Electrochemical Performance in MRI‐Compatible Neural Interfacing

ABSTRACT Geometry and size of electrode contacts are fundamental characteristics of neural electrodes, significantly influencing their performance in both neural recording and stimulation applications. While small contacts facilitate highly focused electric fields, which are essential for single‐unit recording and precise neural modulation, they inevitably lead to signal attenuation and susceptibility to thermal noise and interference. Despite rapid advances in high‐density microelectrode arrays, systematic scaling effects on electrochemical properties remain underexplored. In this study, the influence of scales on the electrochemical performance of metallic MRI‐compatible alloy and Ir/IrO _x ‐coated electrodes is systematically investigated both in vitro and in vivo. Through comprehensive electrochemical characterization the electrodes with diameters ranging from the scale of cortical columns down to that of individual neurons, transition of the relationships between electrode radius and the characteristics occurred as the size continually decreasing. Furthermore, the electrochemical scaling effects for larger electrodes in vivo show similarity to that in vitro, but differences are observed for smaller electrodes. As a first step toward establishing in vivo scaling laws, these findings provide preliminary insights into the electrochemical behavior of differently scaled electrodes under acute physiological conditions.