| Summary: | 碩士 === 國立陽明大學 === 醫學工程研究所 === 98 === Objective：It is difficulty to observe the damage occurred in a material for a short term mild electrochemical reaction, however, it can be observed through a prolong test. In order to observe the aging phenomenon in a material in a relative short time, we try to speed up the aging process in chosen materials.
Method：Four kinds of metal, gold, platinum, titanium, and tantalum employed for electrode materials were chosen in this study. PSB solution was used as a medium for simulating the environment in retina. For each material, the conduction currents with magnitude and conducting time through the materials are designed as ± 100μA ,31μs; ± 75μA, 62μs; ± 50μA, 125μs; ± 25μA, 250μs, with frequency of 1kHz that under environmental temperatures of 37, 58 and 80℃ respectively. Surface roughness and metal concentration in PBS solution were measured by surface contour instrument(KLA-Tencor αstep-500), and inductively coupled plasma optical emission spectrometer(ICP-OES Varian 700ES) at 24th day, and 7th and 63th day respectively after starting the simulation. Estimation for material aging extent will be calculated according to Arrhenius equation which is an equation of temperature dependent chemical reaction.
Result：Results of the remaining metal ion in PBS solution are undetectable or below the detecting limitation of ICP, indicating that biphasic current stimulation is applicable while used for exciting neurons. For surface roughness measurements, it is estimated that the aging acceleration rate can be up to 43, 16, 26, and 29 folds for Au, Pt, Ti, and Ta respectively at 80℃ while compared to at 37℃ in 24 days.
Conclusion：Increasing temperature can speed up chemical reaction rate. It can be used to build electrode aging process model in this study. Although it may not be able to build a complete aging process model for an electrode in this study due to finite experimental time, materials being used, temperature settings and measuring methods, however, the results still can give references for further selecting electrode material according to the relative aging process rates under the same environment of the tests.
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