title: Electron transfer processes occurring on platinum neural stimulating electrodes: calculated charge-storage capacities are inaccessible during applied stimulation.
abstract: Neural prostheses employing platinum electrodes are often constrained by a charge/charge-density parameter known as the Shannon limit. In examining the relationship between charge injection and observed tissue damage, the electrochemistry at the electrode-tissue interface should be considered. The charge-storage capacity (CSC) is often used as a predictor of how much charge an electrode can inject during stimulation, but calculating charge from a steady-state i-E curve (cyclic voltammogram) over the water window misrepresents how electrodes operate during stimulation. We aim to gain insight into why CSC predictions from classic i-E curves overestimate the amount of charge that can be injected during neural stimulation pulsing.
  
  
  
  In this study, we use a standard electrochemical technique to investigate how platinum electrochemistry depends on the potentials accessed by the electrode and on the electrolyte composition.
  
  
  
  The experiments indicate: (1) platinum electrodes must be subjected to a 'cleaning' procedure in order to expose the maximum number of surface platinum sites for hydrogen adsorption; (2) the 'cleaned' platinum surface will likely revert to an obstructed condition under typical neural stimulation conditions; (3) irreversible oxygen reduction may occur under neural stimulation conditions, so the consequences of this reaction should be considered; and (4) the presence of the chloride ion (Cl-) or proteins (bovine serum albumin) inhibits oxide formation and alters H adsorption.
  
  
  
  These observations help explain why traditional CSC calculations overestimate the charge that can be injected during neural stimulation. The results underscore how careful electrochemical examination of the electrode-electrolyte interface can result in more accurate expectations of electrode performance during applied stimulation.
authors.affiliation: Department of Chemical and Biomolecular Engineering, Case Western Reserve University, AW Smith Building, Cleveland, OH, United States of America.
authors.forename: Eric M
authors.initials: EM
authors.lastname: Hudak
authors.forename: Doe W
authors.initials: DW
authors.lastname: Kumsa
authors.forename: Heidi B
authors.initials: HB
authors.lastname: Martin
authors.forename: J Thomas
authors.initials: JT
authors.lastname: Mortimer
mesh_terms: D004558:Electric Stimulation / Q000295:instrumentation / Q000379:methods; D055664:Electrochemical Techniques / Q000295:instrumentation* / Q000379:methods; D004563:Electrochemistry; D004566:Electrodes; D004583:Electrons; D010984:Platinum / Q000008:administration & dosage / Q000737:chemistry*
chemical_list: D010984:Platinum