Open Master's Thesis Project

Implantable neural interfaces rely on electrical stimulation to communicate with the nervous system. To ensure safe operation, stimulation parameters are commonly selected based on electrochemical metrics such as impedance, charge injection capacity, and electrode polarization. However, the onset of irreversible electrochemical reactions, including gas evolution, remains insufficiently understood, particularly under short-pulse stimulation conditions relevant to neurotechnology.

The aim of this project is to investigate the formation of gas bubbles at microelectrodes during electrical stimulation using high-speed microscopy. Microelectrodes fabricated from materials such as gold/platinum, laser-induced graphene (LIG), and PEDOT:PSS will be integrated into test platforms. Electrical stimulation will be applied using both monophasic and charge-balanced biphasic pulse waveforms while systematically varying pulse amplitude, pulse width, repetition rate, and total injected charge.

A high-speed camera (available in the group) will be coupled to a microscope setup and used to directly visualize gas nucleation, growth, coalescence, and detachment events with temporal resolutions ranging from microseconds to milliseconds. Simultaneously, electrochemical measurements will be performed to correlate bubble formation with electrode polarization and stimulation parameters.

The project will address questions including:

• Under which stimulation conditions does gas evolution occur?
• How do different electrode materials influence gas nucleation thresholds?
• Does charge-balanced biphasic stimulation suppress gas formation compared to monophasic stimulation?
• How do experimentally observed gas-evolution limits compare to commonly used electrochemical safety metrics?

The work combines building the high-speed imaging setup with optimal speed/lightning conditions, microfabrication, and integration of test electrodes, electrochemistry, and quantitative image analysis. The results are expected to provide new insights into the electrochemical limits of neural stimulation electrodes and contribute to the development of safer bioelectronic interfaces.

Methods and Techniques

• Microfabrication of microelectrode devices
• High-speed microscopy and image analysis
• Electrochemical characterization of electrodes
• Data analysis and modeling

Prerequisites

• Background in electrical engineering, physics, or a related subject
• General lab experience
• Interest in bioelectronics, microfabrication, electrochemistry, and building/testing a high-speed imaging setup. Prior experience in one of these areas is beneficial but not required.

If interested, please contact: Bernhard Wolfrum

Bernhard.wolfrum@tum.de