Influence of materials and geometry on fields produced by cochlear electrode arrays

Area of Science:

• Biomedical Engineering
• Materials Science
• Neuroscience

Background:

• Cochlear prostheses utilize multichannel electrode arrays in the scala tympani for auditory nerve stimulation.
• Variations in electrode materials and geometry impact stimulus strength and neural activity distribution.

Purpose of the Study:

• To characterize activated iridium (AIR) for cochlear electrode applications.
• To investigate the electrical field distributions of AIR electrodes.
• To propose a novel electrode array design based on AIR properties.

Main Methods:

• Fabrication of planar equivalent models of bipolar cochlear electrode geometries using iridium.
• Characterization of impedance magnitude and phase versus frequency for various AIR activation degrees.
• Measurement of electrical fields produced by bipolar contacts in saline.

Main Results:

• Activated iridium exhibits significantly lower metal-electrolyte interfacial impedance compared to platinum and unactivated iridium.
• Close proximity of AIR contacts leads to field distributions dominated by edge effects and high current densities.
• A novel bipolar array design using N+1 contacts for N channels of radially distributed, non-overlapping fields is proposed.

Conclusions:

• Activated iridium is a promising material for cochlear electrode development due to its tunable interfacial properties and low impedance.
• Electrode edge effects in AIR enable efficient and spatially focused neural stimulation.
• The proposed N+1 contact design offers a simplified and effective approach for multichannel cochlear implants.