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SUMMARY:Electrochemical Processes Governing Neural Stimulation Electrodes
DTSTART:20121115T160000
DTEND:20121115T170000
DTSTAMP:20260408T085639Z
UID:54aa40ba1bb9007e8bf69f61baa7cc22691991b5c156d02d816b0a23
CATEGORIES:Conferences - Seminars
DESCRIPTION:Dr. Stuart F. Cogan\, EIC Laboratories\, Inc. (http://www.eic
 labs.com/)\, USA.\nElectrical stimulation of neural tissue requires electr
 odes that mediate electronic to ionic conduction across the electrode-tis
 sue 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 capaciti
 es than are available with conventional noble metal electrodes. The elect
 rochemical and transport processes controlling charge-injection with stimu
 lation electrodes and the limitations on these processes imposed by the i
 n vivo environment are discussed.\n\nCharge-injection with a stimulation e
 lectrode involves a combination of double-layer charging and reduction-ox
 idation reactions at the electrode-tissue interface. The current densities
  and charge-injection levels that can be supported by these reactions dep
 end 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 av
 ailable at different concentrations. These counterions move to or from th
 e electrode by a combination of diffusion and migration. When transport t
 hrough the tissue limits counterion availability\, charge injection capaci
 ty 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-injectio
 n capacity of electrodes as their size is decreased. Clearly tissue encap
 sulation and absorption of biomolecules will reduce counterion transport 
 and result in vivo charge-injection capacities that are lower than those d
 etermined\nin physiological saline. Voltage transient measurements used to
  determine charge-injection limits of electrodes are described and differ
 ences between saline and in vivo transients discussed. Issues of electrod
 e stability and difficulties in differentiating electrode changes from phy
 siological changes are also discussed using examples from chronic animal 
 studies.\n\nCharge-injection with neural stimulation electrodes is governe
 d by a variety of kinetic factors including counterion transport through 
 encapsulating tissue. The limitations imposed by ion transport are signifi
 cant with in vivo charge-injection limits being considerably lower than t
 hose determined in physiological saline.
LOCATION:BM 1.130  http://plan.epfl.ch/?room=BM%201130
STATUS:CONFIRMED
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