The influence of hot-steam sterilization on hydrated sputtered iridium oxide films

Sputtered iridium oxide films (SIROFs) serve often as state of the art material when high charge injection capacities and robust coatings are desired. The main advantage above activated iridium oxide films (AIROFs) is that activation in-vivo is not needed since iridium oxide is already formed during the sputtering process. However, it is commonly accepted that SIROF coatings are in need of a hydration procedure to clean the surface and to transfer the stoichiometry into the favorable Ir³⁺ and Ir⁴⁺ oxidation states. This is usually done via cyclic voltammetry after fabrication of the devices, i.e. in-vitro. In order to implant such devices however, they have to be disinfected and sterilized. We report here on the influence of disinfection and sterilization in hot-steam on the hydration level of SIROF coatings. Therefore, samples were subjected to electrochemical impedance spectroscopy and cyclic voltammetry prior to disinfection and sterilization and afterwards. It could be observed that sterilization in hot-steam has a major impact on the hydration level of iridium oxide films. Subsequently, the different parameters of the sterilization procedure, i.e. vacuum pressure and temperature, were simulated to test whether the one or the other is responsible for the alteration. Finally, it could be shown that elevated temperatures decrease the charge storage capacity and increase the impedance of the coating.