(I-339) Conductive Coatings to Improve Neural Stimulation Devices

Introduction:: Utilizing a 3 electrode setup, the electrochemical cell for testing consisted of: a Ag|AgCl reference electrode, Pt wire counter electrode, and the fabricated device (either Au or Pt) working electrodes. The working electrodes had a geometric surface area of 2000µm^2. In preparation for testing electrodeposition, baseline measurements were recorded on each individual electrode. First, a CV (cyclic voltammetry) curve was recorded with a voltage range of -0.6 to 0.8V vs. Ag|AgCl, at a scan rate of 50mV/s. Then, EIS (electrochemical impedance spectroscopy) was conducted to determine the initial impedance of the electrodes. We then performed electrodeposition of conductive coatings. IrOx was deposited after electrochemical cleaning of the electrode surface in PBS (phosphate buffered saline), by running repeating chronoamperometry with a a voltage of 275mV at a frequency of 1 Hz for 2600 cycles using a 3 electrode setup in PBS, and then running CV at 50 mV/s for 50 cycles. PEDOT was deposited by conducting a repeating chronoamperometry run at 0.9 V for 500s in a 3 electrode setup in PBS. Impedance and CSC (charge storage capacity) were the two parameters measured to compare the electrodes before and after coating. CVs were utilized to measure CSC from a window of -0.6 to 0.8V for 5 cycles with a scan rate of 50mV/s. EIS was used to measure the impedance, and this was measured from 100kHz to 1Hz, applying a 10mVrms sinusoid around 0V vs Ag|AgCl.

Materials and Methods:: Utilizing a 3 electrode setup, the electrochemical cell for testing consisted of: a Ag|AgCl reference electrode, Pt wire counter electrode, and the fabricated device (either Au or Pt) working electrodes. The working electrodes had a geometric surface area of 2000µm^2. In preparation for testing electrodeposition, baseline measurements were recorded on each individual electrode. First, a CV (cyclic voltammetry) curve was recorded with a voltage range of -0.6 to 0.8V vs. Ag|AgCl, at a scan rate of 50mV/s. Then, EIS (electrochemical impedance spectroscopy) was conducted to determine the initial impedance of the electrodes. We then performed electrodeposition of conductive coatings. IrOx was deposited after electrochemical cleaning of the electrode surface in PBS (phosphate buffered saline), by running repeating chronoamperometry with a a voltage of 275mV at a frequency of 1 Hz for 2600 cycles using a 3 electrode setup in PBS, and then running CV at 50 mV/s for 50 cycles. PEDOT was deposited by conducting a repeating chronoamperometry run at 0.9 V for 500s in a 3 electrode setup in PBS. Impedance and CSC (charge storage capacity) were the two parameters measured to compare the electrodes before and after coating. CVs were utilized to measure CSC from a window of -0.6 to 0.8V for 5 cycles with a scan rate of 50mV/s. EIS was used to measure the impedance, and this was measured from 100kHz to 1Hz, applying a 10mVrms sinusoid around 0V vs Ag|AgCl.


Results, Conclusions, and Discussions:: Upon comparing the properties of the electrodes, it was discovered that the gold electrode with PEDOT deposited after IrOx had the highest CSCc (cathodal charge storage capacity, and CSCa (anodal charge storage capacity). However, both devices had approximately the same impedance after both coatings had been applied. Based on this data, we can infer that the gold electrode with PEDOT deposited on IrOx would be the most stable for chronic implantation due to its ability to handle higher currents. A particularly important data point is the electrode impedance magnitude at 1kHz as this is a similar frequency to neuronal firing rates and high impedance values are prohibitive to recording low-voltage neural signals. All coated electrodes had impedance values below 1MΩ, making them suitable for most neural recording applications. So, the decision of which coating option is best will be based on how stable impedance values remain over time. Originally, it was known that utilizing either gold or platinum base metal will affect electrodeposition of both PEDOT and IrOx coatings, but this experiment demonstrated in detail the effects of both coatings on the properties of each type of metal electrode. Furthermore, now that the coatings have been actualized, and their abilities to change the electrochemical properties of the electrodes has been realized. We are continuing to study the potential benefits and challenges of combined PEDOT and IrOx coatings. Combining PEDOT and IrOx was shown to improve long term stability of the PEDOT coating, but continued work is needed to fully characterise the effects of varying electrodeposition conditions on performance and long-term stability of these multi-layer coatings. In conclusion, by bolstering electrochemical properties of these devices, we can improve in vivo studies by increasing the time a device remains functional, whilst also being able to withstand increased stimulation and a decreased likelihood of degradation over time. By strengthening these characteristics, a patient in need of a neural implant would have access to devices that would provide effective therapy for the respective condition for a longer period of time.

Acknowledgements (Optional): :

References (Optional): :