Charge transfer and stability of implantable electrodes on flexible substrate

Beyond their biocompatibility, implanted electrodes for neuromuscular stimulation require careful consideration of conductivity, stability, and charge delivery capacity (CDC) to avoid irreversible faradaic reactions. To study these requirements, metal electrodes of platinum (Pt), gold (Au), and titanium (Ti) on flexible liquid crystal polymer are fabricated using electron-beam evaporation, and investigated by electrochemical impedance spectroscopy, cyclic voltammetry and atomic force microscopy. A theoretical model is used to explain the physical functionalities. Frequency dependent electrochemical interfacial impedance is observed. The impedance as well as long-term electrochemical stability is influenced by the surface roughness, reactivity and capacitance of the electrodes. Pt electrode offers lower impedance in the neuromuscular stimulation frequencies and higher CDC than that of Ti and Au, but is not as stable as Au electrode.