Variation in Performance of Platinum Electrodes with Size and Surface Roughness

Abstract

Platinum (Pt) has been extensively used in medical electrodes and is proposed as a candidate for stimulation sites in retinal neuroprostheses due to its relative inertness and stability in biological environments. However, as implantable therapeutic devices are created with increasingly smaller dimensions, it is necessary to ensure that electrode properties are optimised. In this study, we present the variation in Pt electrode performance, which occurs as a result of reducing the electrode size. Additionally, the feasibility of laser roughening these electrodes is considered with respect to stability under chronic stimulation. It is shown that as the electrode diameter is decreased, the charge storage capacity (CSC) per unit area is increased twofold. Additionally, the frequency-dependent impedance per unit area decreases, resulting in an increase in the charge injection limit of up to 3.4 times in the biological environment. Finally, the stability of laser-roughened electrodes is demonstrated by continuous biphasic stimulation for more than 1 billion pulses at levels consistent with the activation of the neural retina.

NanoPt—A Nanostructured Electrode Coating for Neural Recording and Microstimulation

“…The new nanoPt coating hence remained stable over a total injected charge density (calculated form the number of applied pulses multiplied by the charge density per pulse) of more than 2.25 MC cm –2 . Previous studies evaluating the stability of rough Pt coatings in contrast only tested up to 0.12 MC cm –2 , 0.10 MC cm –2 , 24 kC cm –2 , or 127 C cm –2 for their coatings. ,,, Thus, nanoPt is not only a suitable material for neural recordings but also presents an interesting material for neural stimulation applications. This could be verified in a chronic animal experiment, where stimulation with nanoPt-coated wires in the medial septal nucleus reliably entrained hippocampal theta oscillations over at least 5 weeks, demonstrating both biocompatibility and excellent stimulation performance.…”

“…One way to circumvent this problem is the use of rough electrode materials that provide a large electrochemically active surface area on minimal geometrical dimensions. ,− Thereby, it is possible to reduce the geometrical size of an electrode contact while retaining the preferential electrochemical properties of a large electrode. Various versions for such materials have been suggested in the literature, expanding from micro- and nanostructured metals − over carbon-based materials to conducting polymers. − Most roughening methods, however, require rather complex processes (e.g., sputter deposition for IrOx or laser roughening for Pt), suffer from limited mechanical stability or toxicity (e.g., for Pt-Black − ), or are prone to delaminate (e.g., for conducting polymers), restricting their use in long-term applications. Thanks to their ease of fabrication, electrolyte-based (electro)­chemically deposited platinum coatings have gained special attention as rough electrode materials for neural implants. ,− While impedance reduction is well documented for these coatings, other important electrode parameters such as biocompatibility, longevity, mechanical stability, and stimulation performance remain to be explored.…”

“…Various versions for such materials have been suggested in the literature, expanding from micro-and nanostructured metals 28−37 over carbon-based materials 38 to conducting polymers. 39−44 Most roughening methods, however, require rather complex processes (e.g., sputter deposition for IrOx 45 or laser roughening for Pt 46 ), suffer from limited mechanical stability or toxicity (e.g., for Pt-Black 47−49 ), or are prone to delaminate (e.g., for conducting polymers 50 ), restricting their use in long-term applications. Thanks to their ease of fabrication, electrolyte-based (electro)chemically deposited platinum coatings have gained special attention as rough electrode materials for neural implants.…”

Advanced electrochemical potential monitoring for improved understanding of electrical neurostimulation protocols

“…High charge densities are needed to polarize the electrodes sufficiently negative to enable the oxygen reduction reaction. It should be noted that these charge densities are not common at the moment but might be for future technologies in therapeutic applications [28,29], and furthermore the potential traces may shift for the application of the same charge densities if the electrode size changes [30]. In addition, these measurements show that even at high charge densities, the surface state of the electrodes has a large impact on the potential development.…”

A flexible retinal device with CMOS smart electrodes fabricated on parylene C thin-film and bioceramic substrate

“…Cyclic voltammetry (CV) measurements and frequencydependent impedance measurements were performed to evaluate the performance of the Pt electrode on the ceramic substrate. 39) CV measurements were performed using a potentiostat (PGSTAT 204, Metrohm Japan Ltd., Japan) SC1022-3…”