Electrochemical Processes Governing Neural Stimulation Electrodes
Event details
| Date | 15.11.2012 |
| Hour | 16:00 › 17:00 |
| Speaker | Dr. Stuart F. Cogan, EIC Laboratories, Inc. (http://www.eiclabs.com/), USA. |
| Location | |
| Category | Conferences - Seminars |
Electrical stimulation of neural tissue requires electrodes that mediate electronic to ionic conduction across the electrode-tissue interface. An understanding of the mechanisms underlying these charge transfer processes is important for developing electrodes and electrode coatings for neural prostheses requiring higher charge-injection capacities than are available with conventional noble metal electrodes. The electrochemical and transport processes controlling charge-injection with stimulation electrodes and the limitations on these processes imposed by the in vivo environment are discussed.
Charge-injection with a stimulation electrode involves a combination of double-layer charging and reduction-oxidation reactions at the electrode-tissue interface. The current densities and charge-injection levels that can be supported by these reactions depend on the availability and the transport rate of counterions to and from the electrode to preserve charge neutrality. Various electrode reactions require different counterions, such as H3O+, OH-, or Cl-, that are available at different concentrations. These counterions move to or from the electrode by a combination of diffusion and migration. When transport through the tissue limits counterion availability, charge injection capacity decreases or, as in the case of constant current stimulation, other potentially harmful reactions are recruited. An important consequence of counterion transport limitations is the marked increase in charge-injection capacity of electrodes as their size is decreased. Clearly tissue encapsulation and absorption of biomolecules will reduce counterion transport and result in vivo charge-injection capacities that are lower than those determined
in physiological saline. Voltage transient measurements used to determine charge-injection limits of electrodes are described and differences between saline and in vivo transients discussed. Issues of electrode stability and difficulties in differentiating electrode changes from physiological changes are also discussed using examples from chronic animal studies.
Charge-injection with neural stimulation electrodes is governed by a variety of kinetic factors including counterion transport through encapsulating tissue. The limitations imposed by ion transport are significant with in vivo charge-injection limits being considerably lower than those determined in physiological saline.
Charge-injection with a stimulation electrode involves a combination of double-layer charging and reduction-oxidation reactions at the electrode-tissue interface. The current densities and charge-injection levels that can be supported by these reactions depend on the availability and the transport rate of counterions to and from the electrode to preserve charge neutrality. Various electrode reactions require different counterions, such as H3O+, OH-, or Cl-, that are available at different concentrations. These counterions move to or from the electrode by a combination of diffusion and migration. When transport through the tissue limits counterion availability, charge injection capacity decreases or, as in the case of constant current stimulation, other potentially harmful reactions are recruited. An important consequence of counterion transport limitations is the marked increase in charge-injection capacity of electrodes as their size is decreased. Clearly tissue encapsulation and absorption of biomolecules will reduce counterion transport and result in vivo charge-injection capacities that are lower than those determined
in physiological saline. Voltage transient measurements used to determine charge-injection limits of electrodes are described and differences between saline and in vivo transients discussed. Issues of electrode stability and difficulties in differentiating electrode changes from physiological changes are also discussed using examples from chronic animal studies.
Charge-injection with neural stimulation electrodes is governed by a variety of kinetic factors including counterion transport through encapsulating tissue. The limitations imposed by ion transport are significant with in vivo charge-injection limits being considerably lower than those determined in physiological saline.
Practical information
- General public
- Free
Organizer
- André Mercanzini, PhD
Aleva Neurotherapeutics SA