Bio-impedance characterization technique with implantable neural stimulator using biphasic current stimulus.

Area of Science:

• Biomedical Engineering
• Neural Engineering
• Electrochemistry

Background:

• Accurate bio-impedance characterization is vital for functional electrical stimulation (FES) applications.
• Electrode-tissue interface impedance influences electrode proximity assessment and stimulus parameter safety.
• Understanding equivalent circuit parameters is key to preventing electrode damage, such as exceeding the water window.

Purpose of the Study:

• To develop and validate a novel impedance characterization technique for electrode-electrolyte/tissue interfaces.
• To implement a proof-of-concept system using an implantable neural stimulator and microcontroller.
• To accurately derive equivalent circuit parameters, including double-layer capacitance and Faradaic resistance.

Main Methods:

• Utilized large signal analysis with low-intensity biphasic current stimulus and inter-pulse delay.
• Acquired transient electrode voltage at three specific timings.
• Validated the technique using emulated Randles cells and custom platinum electrode arrays in vitro.

Main Results:

• Successfully estimated equivalent circuit parameters for both emulated circuits and custom electrodes.
• Demonstrated accurate impedance measurements comparable to an impedance analyzer.
• Validated the derivation of double-layer capacitance and Faradaic resistance.

Conclusions:

• The proposed technique provides accurate bio-impedance characterization at the electrode-electrolyte/tissue interface.
• The method is suitable for integration into implantable or commercial neural stimulators with minimal overhead.
• Offers low power consumption, low hardware cost, and light computational requirements.