Multichannel Systems MEA Manual - Manual (Page 56)

MEA Manual
56
8.4 Recommended Stimulus Amplitudes and Durations
The higher the amplitude and the longer the stimulus, the higher is the impact on the electrode
performance. Therefore, the amplitude and duration should be as low as possible. It is advisable to start
with a low amplitude and duration, and then increase it slowly until responses are evoked.
The allowed product of amplitude and duration is directly proportional to the electrode surface. The higher
the amplitude, the shorter is the maximum duration of the pulse, and vice versa. Do not apply pulses with
a higher amplitude or for a longer time than is recommended for the electrode type. TiN electrodes have
a rough surface structure and therefore have a larger surface than electrodes of the same size but made of
a different material. The safe-charge injection limits in the appendix describe the relationship between
maximum pulse amplitude and time for TiN electrodes.
As a consequence of the points discussed above, Multi Channel Systems recommends using negative
monophasic voltage pulses to make sure that the voltage level of the stimulating electrode is zero,
and thus the electrode is discharged, at the end of the pulse.
According to the experience of MEA users, voltage pulses should be < 1 V (–100 mV to –900 mV) for
neuronal applications to avoid damage to electrode and cells. Generally, pulse durations between 100 to
500 μs are used. (See also Potter, S. M., Wagenaar, D. A. and DeMarse, T. B. (2005). “Closing the Loop:
Stimulation Feedback Systems for Embodied MEA Cultures.” Advances in Network Electrophysiology Using
Multi-Electrode Arrays. M. Taketani and M. Baudry, Springer; Wagenaar, D. A., Madhavan, R., Pine, J. and
Potter, S. M. (2005). "Controlling bursting in cortical cultures with closed-loop multi-electrode stimulation."
J Neurosci 25(3): 680-8.)
For pacing cardiomyocytes, higher voltages and durations are generally required, for example, –2 V for
2 ms. As these pulses are not supported by standard MEA electrodes, the use of larger stimulating
electrodes is recommended. A special MEA with four pairs of large (250 x 50 μm) stimulating electrodes
(60StimMEA200/30) and a special stimulation adapter is provided for such applications by Multi Channel
Systems.
Warning: When using MEA electrodes of TiN material, use only negative voltages pulses or biphasic current
pulses applying the negative phase first. Always regard the safe-charge injection limits as described in
the appendix of this manual. Otherwise, electrodes can be irreversibly damaged by electrolysis.