Long-Term Stable Adhesion for Conducting Polymers in Biomedical Applications: IrOx and Nanostructured Platinum Solve the Chronic Challenge

Abstract

Conducting polymers (CPs) have frequently been described as outstanding coating materials for neural microelectrodes, providing significantly reduced impedance or higher charge injection compared to pure metals. Usability has until now, however, been limited by poor adhesion of polymers like poly(3,4-ethylenedioxythiophene) (PEDOT) to metallic substrates, ultimately precluding long-term applications. The aim of this study was to overcome this weakness of CPs by introducing two novel adhesion improvement strategies that can easily be integrated with standard microelectrode fabrication processes. Iridium Oxide (IrOx) demonstrated exceptional stability for PEDOT coatings, resulting in polymer survival over 10 000 redox cycles and 110 days under accelerated aging conditions at 60 °C. Nanostructured Pt was furthermore introduced as a purely mechanical adhesion promoter providing 10-fold adhesion improvement compared to smooth Pt substrates by simply altering the morphology of Pt. This layer can be realized in a very simple process that is compatible with any electrode design, turning nanostructured Pt into a universal adhesion layer for CP coatings. By the introduction of these adhesion-promoting strategies, the weakness of CP-based neural probes can ultimately be eliminated and true long-term stable use of PEDOT on neural probes will be possible in future electrode generations.

Stability of PEDOT:PSS‐Coated Gold Electrodes in Cell Culture Conditions

“…Delamination of PEDOT:PSS electrodes has been reported before . Delamination is especially believed to be a consequence of poor material binding between the conducting polymer and underlying substrate, and therefore, physical and chemical means of adhesion are recommended. In our case, we have used GOPS as a cross‐linker of the PEDOT:PSS and to help with substrate adhesion; although, it is not expected that there is chemical bonding between this polymer and metal.…”

“…Delamination of PEDOT:PSS electrodes has been reported before. [18] Delamination is especially believed to be a consequence of poor material binding between the conducting polymer and underlying substrate, [32] and therefore, physical [19,33] and chemical [34] means of adhesion are Adv. Mater.…”

Artifact-free and high-temporal-resolution in vivo opto-electrophysiology with microLED optoelectrodes

“…10b). Unfortunately, similar to many other site-level electrode surface modification techniques utilizing electrodeposition of conductive nanoparticles (e.g., Pt nanoparticle 39,40 and PEDOT:PSS [41][42][43] ), long-term in vivo stability of the technique has not yet been validated. Moreover, the low throughput of the siteby-site surface modification technique prevents the mass fabrication of the optoelectrode with low-impedance electrodes.…”

Artifact-free, high-temporal-resolution in vivo opto-electrophysiology with microLED optoelectrodes

“…In future versions of miniSTAR optoelectrodes, electrode surface modification techniques such as site-level electrodeposition of conductive nanoparticles (e.g. Pt nanoparticle 36,37 and PEDOT:PSS [38][39][40] ) might be utilized to reduce the electrode impedance. The relationship between the electrode impedance and the stimulation artifact magnitude can then be studied in depth with groups of different miniSTAR optoelectrodes with significantly different electrode impedance ranges.…”