Multichannel Systems MEA Manual - Manual (Page 55)

Stimulation
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8.3 Aspects of Electrode Size and Material
Titanium nitrite (TiN) electrodes are generally more robust than electrodes from other materials, for
example platinum (Pt). In the Appendix, you find safe charge injection limit curves that document maximum
current and stimulus durations for standard TiN electrodes. Please note that these curves document the
limits. Stimulus pulses should be kept safely below these limits. The safe charge injection limit of platinum
(0.4 mC/cm
2 ) is much smaller than for TiN (23 mC/cm 2 ). This fact results in a considerably lower charge that
you can inject into the electrode before faradic reactions occur that will lead to electrolysis of the electrode.
Please note that, when using voltage driven stimulation, the current flow to the electrode depends on the
electrode impedance. The lower the impedance, the higher is the current. Please make sure to obey the
safe charge injection limits always. Generally, TiN electrodes have lower impedances than Pt electrodes, and
larger electrodes also have lower impedances than smaller.
When using TiN electrodes, it is extremely important to not charge the electrodes positively, as this will
lead to electrolysis. (This is not an issue for Pt electrodes.) Therefore, when using voltage driven stimulation,
it is important to apply negative voltages only. Positive voltages will shortly charge the electrodes positively,
even though the electrode is discharged at the end of the pulse. As a consequence, biphasic voltage driven
stimulation is not recommended. When using current stimulation, it is required to use biphasic stimulation,
and to apply the negative phase first, to avoid a positive net charge on the electrode.