Scaling of Electrode-Electrolyte Interface Model Parameters In Phosphate Buffered Saline

Area of Science:

• Biomedical Engineering
• Electrophysiology
• Materials Science

Background:

• Spinal cord stimulator (SCS) implants utilize platinum electrodes.
• Understanding electrode-electrolyte interface behavior is crucial for device safety and efficacy.
• Phosphate-buffered saline (PBS) is often used as a surrogate for in-vivo biological fluids.

Purpose of the Study:

• To quantify the relationship between platinum electrode impedance and phosphate-buffered saline (PBS) concentration.
• To investigate how electrode-electrolyte interface model parameters vary with PBS concentration.
• To determine the effect of PBS concentration on the safe electrical limits for platinum electrodes.

Main Methods:

• Impedance measurements were performed on a platinum electrode array across various PBS dilutions.
• A non-linear electrode-electrolyte interface model was fitted to the impedance data.
• A novel DC measurement technique was employed to assess Faradaic conduction onset.

Main Results:

• The constant phase element of the electrode model scaled logarithmically with PBS concentration.
• Resistivity was found to be inversely proportional to PBS concentration.
• The onset of Faradaic conduction, indicating safe exposure limits, was independent of PBS concentration.

Conclusions:

• Electrode impedance parameters are sensitive to PBS concentration, but safe electrical limits are not.
• The use of PBS as a sole substitute for in-vivo measurements in spinal cavities may be limited.
• Further investigation is needed to fully understand electrode behavior in physiological environments.