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Structural changes of the surface of platinum wires during acoustic stimulation of a cochlear implant – an in vitro study
18 April 2018 (online)
In literature, platinum dissolution of the electrode contacts have been already described on explanted arrays. The etiology is to a large extent unknown. Therefore, an in vitro model was established in order to investigate changes on the surface of a platinum wire during acoustic stimulation with a cochlear implant under standardized conditions. The objective was to gain a better understanding of processes on the electrode surface during electrical stimulation.
Material and Methods:
A total of 12 platinum wires were embedded in epoxide. The specimen was connected to a cochlear implant (Nucleus) and dipped in a 0.9% sodium chloride solution. The solution was kept at a constant temperature and was stirred with a shakerwith 50 revolutions per minute. The cochlear implant was stimulated with an acoustic signal. Additionally, continuous measurements of pH value and conductibility of the electrolyte were performed. The surface of the platinum wire was evaluated after 500, 600 and1100 hours by laser scanning microscopy.
There was an increase of conductibility of the electrolyte and the impedances of the electrodes up to 2 kΩ during the experiments. In addition, a correlation between the fluctuation of the pH value and temperature was observed. The roughness of the electrode surfaces increased within 500 hours irregularly and reached twice the initial value after 1000 hours. Deposits could be detected on the surface as well.
The developed in vitro model allows a detailed examination of the surface of the stimulated platinum wires under standardized conditions. Significant changes could be measured in the quality of the wire surfaces and electrolytes.