Biomedical Engineering Reference
In-Depth Information
2.2
Stimulation- and Counter-Electrodes
For impedance measurements, we designed unipolar platinum-iridium (Pt/Ir) micro-
electrodes which were covered with polyesterimide insulation and custom-made by
Polyfil (Zug, Switzerland; Fig. 1). In a first step, dental wires made of biocompatible,
nickel-free steel alloy (18% Cr, 18% Mn, 2% Mo, 1% N, remander iron) of 1 mm
diameter and 10 mm length were used as counter-electrodes (see: Fig. 4a) in combina-
tion with the unipolar DBS electrodes. In a second step, an array of counter-electrodes
was pierced into the necks of a number of rats, to evaluate the influence of the coun-
ter-electrode on the impedance measurement. For this, suture clips (see: Fig. 4b) were
used. Electrochemical electrode effects were negligible at the counter-electrode due to
the low current density at its large surface.
We also designed and implanted bipolar Pt/Ir electrodes (Fig. 2) with two stacked
tips to test the effects of nonaxial symmetric field distributions. Further, this electrode
type does not require the implantation of counter-electrodes.
Fig. 1. Photograph (a) and scheme (b) of the unipolar Pt/Ir electrode (Polyfil, Zug, Switzer-
land). The electrode pole was a round wire made from Pt90Ir10 with a diameter of 200 µm. The
length of the non-insulated tip of the electrode pole was 100 µm. The insulation consists of
polyesterimide 180 with a thickness of 25 µm [15].
Fig. 2. Photograph (a) and scheme of the bipolar Pt/Ir electrode (FHC, Bowdoin, ME, USA). The
two electrode poles were round wires made from Pt90Ir10 with a diameter of 125 µm. The lengths of
the non-insulated tips were 100 µm. The thickness of the epoxylite insulation was 25 µm.
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