Kriti Panchal¹, Steven J. May¹, Ekaterina Pomerantseva¹, Shahram Amini^2,31
1Drexel University, Philadelphia, PA
²Pulse Technologies Inc. (An Integer Company), Quakertown, PA
³University of Connecticut, Storrs, CT
Miniaturization and electrochemical performance enhancement of electrodes in emerging neural interfacing devices improves specificity, functionality, and performance. However, surgical site and post-implantation infections are amongst the most devastating complications after surgical procedures and implantations. Additionally, with the increased use of antibiotics, the threat of antibiotic resistance is significant and is increasingly becoming a global problem. Therefore, the need for alternative strategies to eliminate post-implantation infections and reduce antibiotic use has led to development of medical devices with antibacterial properties. In this work, we report on the long-term cycling effects on electrochemical and microstructural evolution of femto-second laser hierarchically restructured (HSR) Pt-10%Ir neural stimulation electrodes coated with ZnO thin films via physical vapor deposition. These electrodes exhibit a hierarchical topography with features that span across multiple length scales. This study explores ZnO coatings as a potential solution, leveraging their well-established antibacterial characteristics. ZnO films were deposited on HSR Pt-10%Ir electrodes using DC sputtering with a pure Zn target and an Ar/O₂ gas mixture. XRD and XPS analyses confirmed the formation of ZnO with n-type conductivity, attributed to oxygen defects. Two deposition durations (5 minutes and 60 minutes) were investigated to assess the impact of film thickness on electrochemical properties. Cyclic voltammetry (CV) revealed that ZnO coatings not only preserved but also enhanced electrochemical performance with increased deposition time. FIB-SEM and EDS analysis showed that the sputtered ZnO coating was non-conformal, primarily covering the pillar tops and increasing their height. This selective coverage increased the active electrochemical surface area (ESA) within the same footprint area, leading to the increased specific capacitance from 462 μF/mm² for uncoated HSR Pt-10%Ir to 539 μF/mm² and 575 μF/mm² for HSR Pt-10%Ir coated with ZnO for 5 minutes and 60 minutes, respectively. XPS further confirmed Ir oxidation in uncoated regions, forming IrO_x, which also contributed to the increase in specific capacitance. After ~1500 CV cycles, specific capacitance declined to 461 μF/mm² and 498 μF/mm² for ZnO coated HSR Pt-10%Ir with 5 minutes and 60 minutes depositions, respectively. The decline in capacitance was attributed to gradual ZnO dissolution into the electrolyte, as revealed by post-cycling EDS mapping. It was also observed that after 1500 CV cycles, ZnO recrystallized as well-formed, highly faceted crystals at localized sites on the electrode surface, likely due to saturation in the confined electrolyte environment. However, in practical applications, when the device is implanted, the dissolved ZnO is expected to interact with bacterial cell walls, release Zn²⁺ ions into their cytoplasm, and effectively eliminate bacteria, thereby preventing ZnO redeposition on the electrode surface. These findings highlight the dual functionality of ZnO coated Pt-10%Ir Ir electrodes, making them promising candidates for neurostimulating implants.