Kai Xia

Composite process to fabricate low impedance and long electrical stability platinum gray microelectrodes using iridium oxide

The performances and stability of implantable microelectrodes for chronic neural stimulation heavily depends on the electrode surface materials. In this paper, we proposed that platinum (Pt) gray/iridium oxide (IrOx) and IrOx/Pt gray composite could be electroplated on the surface of Pt electrode. The surface morphologies of microelectrodes with four different electroplating methods were characterized by scanning electron microscopy (SEM). Consequently, the Pt microelectrode coated with IrOx showed dendritic morphology while the one with Pt gray coating appeared granular. The electrochemical performances of these electrodes were measured by electrochemical impedance spectroscopy (EIS) and cyclic voltammetry (CV) tests, showing that Pt microelectrode decorated with IrOx/Pt gray had the best electrochemical characteristics and long-term stability.

Iridium oxide/platinum gray composite coatings on microelectrodes for neural stimulation

The shrinking size of microelectrodes leads to high electrode/tissue interfacial impedance and low charge injection ability. In order to achieve safe, efficient and durable electrode performances, we proposed a layer-by-layer electrodeposition method to modify the bare platinum microelectrodes with nanostructures. Combining the advantages of platinum gray (Pt gray) with iridium oxide (IrOx), herein a low impedance, high cathodic charge storage capacity (CSCc) and high charge injection IrOx/Pt gray microelectrode was fabricated with nanoscale roughness, which was much higher than each simple coating. Furthermore, it demonstrated superior mechanical and electrochemical stability. Morphological tests showed that nanocone-shaped Pt gray provided large area and hence good adhesion for dense IrOx deposition, which was beneficial for long-term mechanical stability of the composite coating.

Design and fabrication of a high-density flexible microelectrode array

Retinal prosthesis can be utilized for restoring vision to blind patients caused by retinitis pigmentosa or age-related macular degeneration. We proposed a 1025-channel high-density flexible microelectrode array (fMEA) for retinal prosthesis based on two kinds of substrate materials: polyimide (PI) and parylene-C (PA). We designed the fMEA with 25×41 pixels, and the diameter of each stimulating microelectrode was 60 µm with a center-to-center spacing of 160 µm. The fMEA was microfabricated with dual-metal-layer structure based on a simplified fabrication process. Meanwhile, the as-fabricated samples were electroplated with platinum gray, which significantly reduced the electrochemical impedance from 110 kΩ to 16 kΩ at 1 kHz, and also provided much larger charge storage capacity. We expect these results will promote the engineering of high-density fMEA for neural stimulation and recording.

Surface modification of neural stimulating/recording microelectrodes with high-performance platinum-pillar coatings

High-fracture platinum (Pt)-pillars were electrodeposited on Pt microelectrodes using a potential sweep technique. Detailed investigations of the structure, morphology and electrochemical properties of the electrodeposited Pt-pillar coatings were performed. Cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) measurements revealed that Pt-pillar coated microelectrodes exhibited significantly increased charge storage capacity and real surface area compared with uncoated Pt electrodes. Stability tests of Pt pillars revealed good mechanical stability as well as electrochemical stability, which is highly preferred for effective neural stimulation and recording in various applications.

Surface modification of neural stimulating/recording electrodes with high-performance platinum nano-leaf coatings

This paper reports a novel surface modification method using platinum (Pt) nano-leaf coatings which can significantly improve electrochemical performances of microelectrodes arrays (MEAs) for neural stimulating or recording. Three dimensional nano-leaves have been deposited on Pt electrodes using a constant potential electrodeposition. After deposition, the typical electrochemical impedance of an Pt electrode (150 μm in diameter) declined significantly from 45.7 kΩ to 1.44 kΩ at 1 kHz, while the cathodic charge storage capacity (CSCc) vital for effective stimulation increased by more than 35 times. This modification also showed excellent long term stability.

Electrodeposition layer by layer process to fabricate composite platinum gray/iridium oxide for neural stimulus electrode

Multi-electrodeposition process to fabricate low impedance and electrical stability platinum (Pt) gray microelectrodes using iridium oxide (LrOx) were investigated in this paper. The Surface morphologies of different modified electrodes were characterized by scanning electron microscopy (SEM). IrOx had dendritic morphology while Pt gray had granular morphology. Through the accelerated aging test, IrOx/Pt gray electrodes perform optimally for the lowest impedance and the longest stability, which is preferred for practical applications for neural stimulation.