Electrodeposition of platinum-iridium coatings and nanowires for neurostimulating applications: Fabrication, characterization and in-vivo retinal stimulation/recording. EIS studies of hexavalent and trivalent chromium based military coating systems

The studies presented in this thesis are composed of two different projects demonstrated in two different parts. The first part of this thesis represents an electrochemical approach to possible improvements of the interface between an implantable device and biological tissue. The second part of this thesis represents electrochemical impedance spectroscopy (EIS) studies on the corrosion resistance behavior of different types of polymer coated Al2024 alloys.;In the first part of this thesis, a broad range of investigations on the development of an efficient and reproducible electrochemical deposition method for fabrication of thin-film platinum-iridium alloys were performed. The developed method for production of dense films was then modified to produce very high surface area coatings with ultra-low electrochemical impedance characteristics. The high-surface area platinum-iridium coating was applied on microelectrode arrays for chronic in-vitro stimulation.;Using the same method of producing dense films, platinum-iridium nanowires were fabricated using Anodized Aluminum Oxide (AAO) templates for hermetic packaging applications to be used in implantable microelectronics. The implantable microelectronics will be used to perform data reception and transmission management, power recovery, digital processing and analog output of stimulus current.;Finally, in-vivo electrical stimulation tests were performed on an animal retina using high surface-area platinum-iridium coated single microelectrodes to verify the charge transfer characteristics of the coatings.;In the second part of this thesis, three different sets of samples with different combinations of pretreatments, primers with the same type of topcoat were tested in 0.5 N NaCl for period of 30 days. The surface changes measured by EIS as a function of time were then analyzed. The analysis of the fit parameters of the impedance spectra showed that the different primers had the most effect on the corrosion protection properties of the coatings in which the primers with hexavalent chromium ions (Cr6+) provided better corrosion protection compared to primers with trivalent chromium ions (Cr3+).;After 30 days of the exposure of the samples in 0.5 N NaCl, one sample from each set of samples was scribed and exposed to 0.5 N NaCl for 3 days. Analysis of the impedance spectra revealed that the samples with chromium conversion coating pretreatment and hexavalent chromium primer showed "self healing" characteristics and provided better corrosion protection on the scribed areas compared to the scribed samples with trivalent chromium pretreatment and non-hexavalent chromium primer.