Integrated electrode and high density feedthrough system for chip-scale implantable devices.

High density feedthroughs have been developed which allow for the integration of chip-scale features and electrode arrays with up to 1141 stimulating sites to be located on a single implantable package. This layered technology displays hermetic properties and can be produced from as little as two laminated 200 µm thick alumina sheets. It can also be expanded to a greater number of layers to allow flexible routing to integrated electronics. The microelectrodes, which are produced from sintered platinum (Pt) particulate, have high charge injection capacity as a result of a porous surface morphology. Despite their inherent porosity the electrodes are electrically stable following more than 1.8 billion stimulation pulses delivered at clinically relevant levels. The ceramic-Pt constructs are also shown to have acceptable biological properties, causing no cell growth inhibition using standard leachant assays and support neural cell survival and differentiation under both passive conditions and active electrical stimulation.

Substrate dependent stability of conducting polymer coatings on medical electrodes.

Conducting polymer (CP) coatings on medical electrodes have the potential to provide superior performance when compared to conventional metallic electrodes, but their stability is strongly dependant on the substrate properties. The aim of this study was to examine the effect of laser roughening of underlying platinum (Pt) electrode surfaces on the mechanical, electrical and biological performance of CP coatings. In addition, the impact of dopant type on electrical performance and stability was assessed. The CP poly(ethylene dioxythiophene) (PEDOT) was coated on Pt microelectrode arrays, with three conventional dopant ions. The in vitro electrical characteristics were assessed by cyclic voltammetry and biphasic stimulation. Results showed that laser roughening of the underlying substrate did not affect the charge injection limit of the coated material, but significantly improved the passive stability and chronic stimulation lifetime without failure of the coating. Accelerated material ageing and long-term biphasic stimulus studies determined that some PEDOT variants experienced delamination within as little as 10 days when the underlying Pt was smooth, but laser roughening to produce a surface index of 2.5 improved stability, such that more than 1.3 billion stimulation cycles could be applied without evidence of failure. PEDOT doped with paratoluene sulfonate (PEDOT/pTS) was found to be the most stable CP on roughened Pt, and presented a surface topography which encouraged neural cell attachment.