Histopathologic evaluation of prolonged intracortical electrical stimulation

Area of Science:

• Neuroscience
• Biomaterials Science
• Neural Engineering

Background:

• Chronic neural stimulation is crucial for advanced neuroprosthetics and brain-computer interfaces.
• Microelectrode material stability is a key challenge for long-term in-vivo applications.
• Platinum-iridium (Pt-30%Ir) and activated iridium are common materials for neural stimulation electrodes.

Purpose of the Study:

• To compare the chronic stimulation performance and tissue compatibility of Pt-30%Ir and activated iridium microelectrodes.
• To evaluate electrode tip stability and neural damage thresholds at various current and charge densities.

Main Methods:

• Implanted Pt-30%Ir and activated iridium microelectrodes in the cat sensorimotor cortex.
• Applied continuous electrical stimulation at varying current densities (10-320 microA) for 24 hours or 7 days.
• Monitored neuronal activation via pyramidal tract recordings and assessed tissue response using light and electron microscopy.

Main Results:

• Both electrode types activated neurons at similar thresholds (5-15 microA).
• No neural damage observed with currents up to 80 microA for both materials.
• Pt-30%Ir electrodes showed dissolution at 320 microA, while activated iridium remained stable at this intensity.
• Electrode dissolution correlated with charge and current density; activated iridium eroded only at the highest tested densities.

Conclusions:

• Activated iridium microelectrodes demonstrate superior tip stability over Pt-30%Ir for chronic neural stimulation.
• Activated iridium is a more robust material for long-term neural implants, showing minimal erosion at effective stimulation levels.
• Material choice significantly impacts the longevity and safety of chronic neural stimulation devices.