In vitro versus in vivo impedance modeling for electrochemically deposited iridium oxide electrodes

We present here an electric circuit model that fits the behavior of iridium oxide coated electrodes when tested in vitro and in vivo. Our objective is to understand the interface between the active iridium oxide and the biological tissue. In order to do that we have first measured the impedance and the cyclic voltammetry in five electrodes which we later implanted in the hippocampi of rodents. While implanted, we have again measured the charge delivery through cyclic voltammetry and the impedance through spectroscopy. We later explanted the electrodes and performed the exact same tests, demonstrating that the electrodes had not been damaged either by our tests or by the implant. Here we will present the impedance values and the fit of the models we suggest, which include a solution resistand and a constant phase element. A charge transfer resistance is only present in our in vitro model, and this phenomenon is discussed in the current paper.