H. Specht, F. Krueger, W. C. Heraeus GmbH, Hanau, Germany; M. Frericks, O. Keitel, W. C. Heraeus GmbH & Co. KG, Hanau, Germany
Coatings have to be optimized in order to enhance the electrode tissue interface properties for cardiac pacing and neuromodulation devices. Various metallic and ceramic coatings, which can be used in these applications, were deposited and the influence of material, thickness and surface morphology on impedance characteristics and application stability was investigated by electrochemical impedance spectroscopy and cyclic voltametry. While the application relevant electrochemical performance is best achieved by morphological changes resulting from process parameters or thickness, the stability of the coating depends on the coating material itself. Knowing the kinetics of the exchange reactions at the electrode tissue interface and the chemical stability of coating materials permits these coatings to be applied with optimized characteristics for electrotherapy.
Summary: Coatings have to be optimized in order to enhance the electrode tissue interface properties for cardiac pacing and neuromodulation devices. Various metallic and ceramic coatings, among them titanium nitride, iridium and platinum, which can be used in these applications, were deposited by magnetron sputtering. The influence of material, thickness and surface morphology on impedance characteristics and application stability was investigated by electrochemical impedance spectroscopy and cyclic voltametry.
The application relevant electrochemical performance is best achieved by morphological changes resulting from process parameters or thickness. With increasing thickness and porosity of the coating these electrochemical properties can be improved. However, it can be concluded that, due to the limited speed at which the charging and de-charging processes at the electrode tissue interface take place, this improvement is limited by a frequency and material dependent saturation.
The stability of coatings, however, was found to be dependent on the coating material itself. Previously reported potential degradation of titanium nitride, when operated in anodic mode can be reduced by depositing a thin layer of platinum on top of the titanium nitride, while maintaining the large physical surface area and thus the application relevant electrochemical performance.
An oxidation that can occur if thin layers of iridium are exposed to stimulation pulses in cardiac and neuro stimulation devices can be prevented by doping the iridium layer with a minimum content of 10 weight percent of Platinum.
Knowing the kinetics of the exchange reactions at the electrode tissue interface and the chemical stability of coating materials permits these coatings to be applied with optimized characteristics for electrotherapy.
