Essay On Electrode Tissue Junction

The chemistry of electrode-tissue junction is the most important part for successful functionality of neural interfaces. Tissues are full of electrolytes. An inter face is formed between an immerged metal electrodes in electrolyte, extracellular fluid (ECF) of brain [42]. The current flows in the electrode due to electron flow. On the other hand ions, such as chloride, sodium and potassium in the brain fluid, flow causes current flow in tissue or electrolytes. The transition from electronic to ionic flow needs some reaction to be happened [21][42]. When potential applied to the electrodes, ions in the electrolyte start flowing. After some time, an equilibrium is reached and the number of electrons come from and goes to the electrode becomes equal [21]. Charges are concentrated on the electrode surface and

The electrical model is similar to Figure 2.7. As an effect of hydration, the dissolved ion creates a cluster together with the surrounded water molecules. The cluster then accumulated at the surface of the electrodes. When the charges inside the cluster aligned, it works like one plate of the capacitor. Water dipole act as dielectric material and a double layer capacitance form in the electrode-electrolyte interface [12][21]. Galvanic potential is formed between electrode and electrolyte that is the combination of the potential of electrode side walls and potential of electrode-electrolyte interface. It is shown in Figure 2.8 c), Em and Ee is denoting electrode potential and potential of accumulated charge layer near electrode surface respectively and ddl is the width of the capacitor. The mechanism of the double layer capacitance can be approximated by parallel plate capacitor formula, therefore the galvanic potential between electrode and accumulated charge plane is given by equation 2.21