Electrochemically Roughened Platinum Electrodes for Neural Stimulation

Abstract

The use of platinum as stimulating microelectrodes for high-resolution and site-specific neural prostheses is challenging due to its limited interfacial properties, which are not adequate to elicit the appropriate neural response. In order to improve the performance of platinum for neural stimulation applications, the surface has to be modified to enhance its electrochemical and biological properties. In this research, the interfacial properties of electrochemically roughened platinum electrodes as well as the adsorption behaviour of perilymph proteins are investigated. The oxidation-reduction technique of roughening a platinum surface was systematically optimised using a central composite experimental design. The interfacial properties and performance of roughened platinum surfaces as stimulating electrode were investigated by electrochemical impedance spectroscopy, cyclic voltammetry, voltage transient and inductively coupled plasma mass spectrometry (ICP-MS) techniques. Complementary surface topography analysis was performed with atomic force microscopy. Fibroblast proliferation was used to examine fibrous tissue encapsulation on the electrochemically roughened platinum surface. It was revealed that the oxidation potential and duration of oxidation-reduction cycle had significant influence in controlling surface roughness. There was also a significant negative interaction between oxidation and reduction potentials on surface roughness. The electrochemically roughened platinum electrode had superior interfacial properties which increased with increase in surface roughness. The surface roughness can also be optimised for different neural stimulation applications based on the available charge density at a particular pulse width of stimulation. The roughened surface further displayed excellent mechanical, electrochemical and biological stability, indicating the potential of this biological interface to be safe and stable. The adsorption and interaction of perilymph proteins on electrochemically roughened platinum surface were also investigated using a combination of QCM-D and ELISA. The results demonstrated that the roughened platinum surface did not influence the mass of proteins adsorbed but affected the viscoelasticity of the adlayer. Furthermore, none of the proteins adsorbed were displaced by subsequent adsorbed protein, but rather layered on top of the previously adsorbed protein. The results from simultaneous adsorption however showed competition between proteins.