title: Improved Poly(3,4-Ethylenedioxythiophene) (PEDOT) for Neural Stimulation.
abstract: OBJECTIVE
  This study compares the stability of three variations of the conductive polymer poly(3,4-ethylenedioxythiophene) or PEDOT for neural micro-stimulation under both in vitro and in vivo conditions. We examined PEDOT films deposited with counter-ions tetrafluoroborate (TFB) and poly(styrenesulfonate) (PSS), and
  PSS combined with carbon nanotubes (CNTs).
  
  
  METHODS
  For the in vitro stability evaluation, implantable micro-wires were coated with the polymers, placed in a vial containing phosphate buffered saline (PBS) under accelerated aging conditions (60°C), and current pulses were applied. The resulting voltage profile was monitored over time. Following the same polymer deposition protocol, chronic neural micro-probes were modified and implanted in the motor cortex of two rats for the in vivo stability comparison. Similar stimulating current pulses were applied and the output voltage was examined. The electrochemical impedance spectroscopic (EIS) data were also recorded and fit to an equivalent circuit model that incorporates and quantifies the time-dependent polymer degradation and impedance associated with tissue surrounding each micro-electrode site.
  
  
  RESULTS
  Both in vitro and in vivo voltage output profiles show relatively stable behavior for the
  TFB modified micro-electrodes compared to the
  PSS and CNT:
  PSS modified ones. EIS modeling demonstrates that the time-dependent increase in the polymeric resistance is roughly similar to the rise in the respective voltage output in vivo and indicates that the polymeric stability and conductivity, rather than the impedance due to the tissue response, is the primary factor determining the output voltage profile. It was also noted that the number of electrodes showing unit activity post-surgery did not decay for
  TFB as was the case for
  PSS and CNT:
  PSS.
  
  
  CONCLUSIONS
  
  TFB may be an enabling material for achieving long lasting micro-stimulation and recording.
authors: Department of Bioengineering, George Mason University, Fairfax, VA, USA.
authors: Himadri Shekhar
authors: HS
authors: Mandal
authors: Department of Bioengineering, George Mason University, Fairfax, VA, USA.
authors: Jemika Shrestha
authors: JS
authors: Kastee
authors: Department of Molecular Neuroscience, The Krasnow Institute for Advanced Study, George Mason University, Fairfax, VA, USA.
authors: Daniel Glenn
authors: DG
authors: McHail
authors: Department of Chemistry, Georgetown University, Washington, DC, USA.
authors: Judith Faye
authors: JF
authors: Rubinson
authors: Department of Bioengineering, George Mason University, Fairfax, VA, USA.
authors: Joseph Jewell
authors: JJ
authors: Pancrazio
authors: Department of Molecular Neuroscience, The Krasnow Institute for Advanced Study, George Mason University, Fairfax, VA, USA.
authors: Theodore Constantine
authors: TC
authors: Dumas
mesh_terms: D000818:Animals; D001881:Borates; D001888:Boric Acids / Q000494:pharmacology; D019086:Bridged Bicyclo Compounds, Heterocyclic / Q000737:chemistry / Q000494:pharmacology*; D004338:Drug Combinations; D004567:Electrodes, Implanted; D005260:Female; D037742:Nanotubes, Carbon; D009474:Neurons / Q000187:drug effects* / Q000502:physiology; D011108:Polymers / Q000737:chemistry / Q000494:pharmacology*; D011137:Polystyrenes / Q000494:pharmacology; D051381:Rats; D020318:Rats, Long-Evans; D013997:Time Factors
chemical_list: D001881:Borates; D001888:Boric Acids; D019086:Bridged Bicyclo Compounds, Heterocyclic; D004338:Drug Combinations; D037742:Nanotubes, Carbon; D011108:Polymers; D011137:Polystyrenes; C121383:poly(3,4-ethylene dioxythiophene); C003321:polystyrene sulfonic acid; C098759:fluoroboric acid
keywords: Conductive polymer; PEDOT; neural stimulation