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Stimulus induced pH changes in retinal implants.

Amy P Chu1, Kjersti Morris, Robert J Greenberg

  • 1Second Sight Med. Products Inc., Sylmar, CA, USA.

Conference Proceedings : ... Annual International Conference of the IEEE Engineering in Medicine and Biology Society. IEEE Engineering in Medicine and Biology Society. Annual Conference
|February 3, 2007
PubMed
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Electrical stimulation can alter pH near retinal implants. Monophasic pulses significantly shift pH in unbuffered solutions, unlike biphasic pulses, highlighting risks for neural tissue. This impacts implant safety and design.

Area of Science:

  • Biomedical Engineering
  • Neuroscience
  • Electrochemistry

Background:

  • Neural electrical stimulation involves charge injection via Faradaic and non-Faradaic reactions.
  • Certain Faradaic reactions can cause significant pH changes, potentially damaging biological tissues.

Purpose of the Study:

  • To investigate stimulus-induced pH changes at the electrode/tissue interface during retinal implant stimulation.
  • To evaluate the impact of different stimulation parameters on pH shifts.

Main Methods:

  • Electrodes were stimulated with monophasic and biphasic pulses in various solutions (buffered saline, balanced salt solution, unbuffered saline).
  • Stimulation intensity was varied, while frequency and pulse width remained constant.
  • pH changes were measured using a microelectrode and confirmed with a color indicator (phenol red).

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Main Results:

  • No significant pH changes were observed in buffered solutions.
  • Monophasic stimulation in unbuffered saline caused notable pH shifts, directly related to stimulation duration.
  • Biphasic, charge-balanced pulses resulted in minimal pH alterations.

Conclusions:

  • Monophasic electrical stimulation poses a higher risk of pH-induced tissue damage compared to biphasic stimulation in retinal implants.
  • Understanding these electrochemical mechanisms is crucial for designing safer neural stimulation devices.
  • Stimulation parameters, particularly pulse type and duration, critically influence local pH environments.