Electrical performance of penetrating microelectrodes chronically implanted in cat cortex.

Area of Science:

• Neuroscience
• Biomaterials Science
• Electrophysiology

Background:

• Chronic implantation of neural electrodes is crucial for brain-computer interfaces.
• Sputtered iridium oxide (SIROF) electrodes offer potential for neural recording and stimulation.
• Understanding long-term electrochemical performance in vivo is essential for device reliability.

Purpose of the Study:

• To evaluate the long-term electrochemical performance of SIROF microelectrode arrays implanted in cat cerebral cortex.
• To investigate changes in electrode properties over time using various electrochemical techniques.
• To assess charge injection capacity in vivo and compare it with in vitro measurements.

Main Methods:

• Implantation of SIROF microelectrode arrays in cat cerebral cortex.
• Electrochemical characterization using cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS), and current pulsing.
• Scanning electron microscopy (SEM) of explanted arrays to examine insulation integrity.
• In vivo and in vitro measurements of electrode performance.

Main Results:

• Charge storage capacity increased linearly with time for some arrays, suggesting increased apparent surface area.
• A modest decrease in 1 kHz impedance was observed over the implantation period.
• In vivo charge injection capacity was lower than in vitro and increased with interpulse bias and pulse width.
• SEM revealed cracking of Parylene insulation, likely causing electrical leakage pathways.

Conclusions:

• Long-term in vivo performance of SIROF electrodes is influenced by insulation degradation and leakage pathways.
• In vivo electrochemical measurements are critical for accurate assessment of chronic neural electrode performance.
• Findings emphasize the need for robust insulation materials and in vivo validation for neural implantable devices.