In vitro models for measuring charge storage capacity

Abstract

The interaction of the nervous tissue with electrode surfaces impacts the efficacy of the charge transfer capacity of the electrode. A better understanding of the interface between electrodes and tissue will inform the design of electrically conductive interfaces for implantable electrodes. Here we propose two in vitro models that reproduce the in vivo electrochemical characteristics of Iridium oxide (IrOx) electrodes. Cyclic voltammetry (CV) was performed in phosphate buffer saline solution (PBS) with Ag|AgCl as reference electrode. The charge storage capacity (CSC) of each electrode was measured three times, in this order: (1) in PBS; (2) in the in vitro model; (3) in PBS, after cleaning. Our proposed in vitro models are sheep brain and ground meat. We then compared the in vitro results against in vivo data. The CSC of the iridium oxide electrode decreased from 199.4 μC (in PBS) to 83.7 μC in sheep brain. After cleaning, the CSC increases to a value lower than the initial CSC. Our in vitro models replicate the data presented by the previously performed in vivo (rat) experiments in terms of the characteristics of the CV and impedance curves. We suggest that the similarity of the tissue environment, which involves proteins and extra-cellular matrix, is responsible for the observed charge loss. The specific factor responsible for changing the CSC will be determined by doing further studies. Utilization of these models would decrease the use of lab animals characterize the electrical performance of the implantable neural electrodes. © 2010 Springer-Verlag.