An Electrochemical Investigation of the Impact of Microfabrication Techniques on Polymer-Based Microelectrode Neural Interfaces

The electrochemical (EC) properties of microelectrodes on flexible polymer substrates can vary as a result of microfabrication and postfabrication processes. These in turn may impact the chronic recording performance of such electrodes. In this paper, electrochemical techniques were utilized for the preparation and nonbiological evaluation of microfabricated flexible neural probes consisting of platinum electrode recording sites supported and insulated by Parylene C. The polymer substrate mitigates the mechanical mismatch between neural tissue and the probe. In addition, the thermoplastic nature of the polymer enables the probe to be shaped postfabrication using a thermoforming technique to impart a unique 3-D structure that further promotes tissue integration and supports the use of bioactive coatings. The EC techniques provided a simple means to clean electrode surfaces (80.2% decrease in 1-kHz impedance), identify functional devices, and evaluate their EC properties prior to implant. Both electrochemical impedance spectroscopy and cyclic voltammetry measurements were performed on electrode sites following fabrication, cleaning, mechanical manipulation for assembly, thermoforming, and sterilization. The results reveal in some cases changes in EC properties. Although changes following thermoforming did not impact the ability to acquire electrophysiological recordings, further investigation with additional tools is required to elucidate the exact nature of the structural and EC changes resulting in the observed increase in impedance and reduction in electrode surface area following thermoforming.