title: Laser patterning of platinum electrodes for safe neurostimulation.
abstract: OBJECTIVE
  Laser surface modification of platinum (Pt) electrodes was investigated for use in neuroprosthetics. Surface modification was applied to increase the surface area of the electrode and improve its ability to transfer charge within safe electrochemical stimulation limits.
  
  
  METHODS
  Electrode arrays were laser micromachined to produce Pt electrodes with smooth surfaces, which were then modified with four laser patterning techniques to produce surface structures which were nanosecond patterned, square profile, triangular profile and roughened on the micron scale through structured laser interference patterning (SLIP). Improvements in charge transfer were shown through electrochemical impedance spectroscopy (EIS), cyclic voltammetry (CV) and biphasic stimulation at clinically relevant levels. A new method was investigated and validated which enabled the assessment of in vivo electrochemically safe charge injection limits.
  
  
  RESULTS
  All of the modified surfaces provided electrical advantage over the smooth Pt. The SLIP surface provided the greatest benefit both in vitro and in vivo, and this surface was the only type which had injection limits above the threshold for neural stimulation, at a level shown to produce a response in the feline visual cortex when using an electrode array implanted in the suprachoroidal space of the eye. This surface was found to be stable when stimulated with more than 150 million clinically relevant pulses in physiological saline.
  
  
  CONCLUSIONS
  Critical to the assessment of implant devices is accurate determination of safe usage limits in an in vivo environment. Laser patterning, in particular SLIP, is a superior technique for improving the performance of implant electrodes without altering the interfacial electrode chemistry through coating. Future work will require chronic in vivo assessment of these electrode patterns.
authors.affiliation: Graduate School of Biomedical Engineering, University of New South Wales, Sydney 2052, Australia.
authors.forename: R A
authors.initials: RA
authors.lastname: Green
authors.forename: P B
authors.initials: PB
authors.lastname: Matteucci
authors.forename: C W D
authors.initials: CW
authors.lastname: Dodds
authors.forename: J
authors.initials: J
authors.lastname: Palmer
authors.forename: W F
authors.initials: WF
authors.lastname: Dueck
authors.forename: R T
authors.initials: RT
authors.lastname: Hassarati
authors.forename: P J
authors.initials: PJ
authors.lastname: Byrnes-Preston
authors.forename: N H
authors.initials: NH
authors.lastname: Lovell
authors.forename: G J
authors.initials: GJ
authors.lastname: Suaning
mesh_terms: D000818:Animals; D002415:Cats; D004558:Electric Stimulation / Q000295:instrumentation*; D004567:Electrodes, Implanted; D019544:Equipment Failure Analysis; D007834:Lasers; D008839:Microelectrodes; D010984:Platinum / Q000737:chemistry* / Q000528:radiation effects*; D011474:Prosthesis Design; D013499:Surface Properties; D014793:Visual Cortex / Q000502:physiology*
chemical_list: D010984:Platinum