Open Access
Andre, Dana Lynn
Graduate Program:
Engineering Science
Master of Science
Document Type:
Master Thesis
Date of Defense:
June 17, 2010
Committee Members:
  • Bruce Gluckman, Thesis Advisor
  • Corina Stefania Drapaca, Thesis Advisor
  • fluorescent imaging
  • brain
  • pH
  • iridium oxide
  • Electrical stimulation
  • electrode
  • electric field
  • diffusion
Electrical stimulation in the brain is commonly used to interact with neural activity. It is used as treatment for the muscle tremors associated with Parkinson’s disease and is being investigated for many other clinical applications, including seizure prevention. Efficacy and safety of stimulation are highly linked to the electrical parameters used and the electrode’s material properties and geometry. Our research investigates the electrochemical behavior of iridium oxide coated electrodes, selected for their efficient charge passing capabilities and biocompatibility. Charge-passing dynamics are mediated by surface reactions in the iridium oxide, chemical diffusion, electric flux, and chemical reactions in the surrounding environment. We use a novel pH-sensitive fluorescent imaging method to observe charge-passage under the hypothesis that hydrogen is a byproduct of the electrochemical surface reactions. We have developed a computational model of the reaction-diffusion dynamics using the Nernst-Planck and Butler-Volmer equations. Using experiments and computational simulations we have proved that electrical stimulation causes two separate hydrogen and hydroxide producing reactions in the iridium oxide coating. We have shown that increasing current amplitude or decreasing frequency of stimulation increases the amplitude and propagation distance of pH waves. Increasing frequency also increases the propagation rate of pH waves. We have also established that the initial phase of a waveform drastically influences the overall pH dynamics that it creates. Furthermore, we have discriminated between electric field and diffusion effects, and have shown the influence of chemical reactions in the bulk. These findings contribute to a greater understanding of neural stimulating electrodes, which ultimately will improve their performance and thus improve clinical treatments.