Description
Glassy Carbon (GC) has become a material of choice for multiple biological applications such as brain computer interface (BCI) devices like neural probes due to its high biostability, biocompatibility, and ability to retain its principal electrical and electrochemical properties after hundreds of thousands of cycles of use. Recent progress in first-principle Molecular Dynamics simulation of the core pyrolysis process where SU8 polymer breaks down and carbon rings form has shed some fundamental insight on the time-temperature dependent events and different stages of the pyrolysis process. Among these are the formation of more 5-, 6-, and 7-membered carbon rings that create the composition of glassy carbon. These nanostructures of 3D cagey shape have significant effect on the electrical and electrochemical properties of the resulting glassy carbon. Based on insights of the pyrolysis process obtained from MD modeling, microelectrode array (MEA) neural probe test beds were microfabricated using negative tone resist SU8-10 electrodes that were pyrolyzed into glassy carbon at different time-temperature profiles in a controlled nitrogen environment. Flexible polyimide was used as an insulator and platinum/titanium were used for conductive metal traces. The probes were tested for electrochemical impedance spectroscopy (EIS) and cyclic voltammetry (CV) in a phosphate buffer saline (PBS) solution using a potentiostat at varying frequencies and voltages. Here, opportunities available for optimization are presented in regard to the electrical and electrochemical properties of GC probes, particularly their impedance, phase angles, and charge storage capacity, by revisiting and engineering the pyrolysis protocols that are used during their manufacturing. The data mainly shows that as pyrolysis ramp-up, ramp-down, and holding time are extended, impedance increases in particular ways while charge storage capacity (CSC) greatly decreases.
