On the stability of morphology and performance of neural interfacing electrodes fabricated via CO2-snow-assisted hierarchical surface restructuring
Abstract
Long-term implantable neural interfacing devices play a critical role in treating various neurological disorders, with their functionality largely dependent on the performance of electrodes and microelectrode arrays. Femtosecond laser Hierarchical Surface Restructuring (HSRTM) is an advanced surface treatment technology that significantly enhances a platinum-10% iridium (Pt-10Ir) electrode’s electrochemical performance, improving energy efficiency, specificity, and signal-to-noise ratio. Additionally, HSRTM facilitates electrode miniaturization, allowing them to be manufactured smaller, for a less invasive profile. Electrode surfaces produced via HSRTM technology contain multiscale structures, including nanoscale features that, while contributing to superior performance, are sometimes weakly bonded and may detach due to mechanical agitation during testing or implantation. This detachment could lead to a high initial performance, which may gradually decline during prolonged use. Preemptively removing these nanostructures stabilizes the electrode surface, enhancing the stability of its morphology and potentially electrochemical performance. This study introduces a novel, in-operando, CO₂-snow-assisted HSRTM process and benchmarks it against other prevalent surface cleaning methods post-fabrication, such as ultrasonic cleaning, on improving electrode stability and performance. Both qualitative and quantitative analyses indicate that all cleaning methods enhance electrode stability. However, ultrasonic cleaning was found to be more destructive compared to CO₂-snow-assisted HSRTM processing, resulting in reduced electrochemical performance. In contrast, in-operando CO₂-snow-assisted processing provided similar or superior improvements in surface stability, while preserving higher electrochemical performance in vitro and enabling a faster processing time. This study is the gateway to further assess the stability in vivo, which is the intended next step of the research.
Dataset DOI: 10.5061/dryad.ht76hdrwv
Description of the data and file structure
This data is collected as part of a study to evaluate the morphological stability and electrochemical performance of femtosecond laser–fabricated HSR™ Pt-10Ir electrodes subjected to CO2-snow surface cleaning, and other methods.
Specifically, this data includes cyclic voltammetry, electrode impedance spectroscopy, and stereoscopic SEM surface quantification results for electrodes produced at 3 different laser fluences:
- 1.8 J/cm²
- 3.6 J/cm²
- 9.7 J/cm²
The surface processing/cleaning conditions included:
- Control: HSR™ electrode with no post-fabrication cleaning.
- Lag CO2: CO2-snow-assisted cleaning applied after laser restructuring
- Tandem CO2: CO2-snow-assisted processing applied simultaneously with femtosecond laser restructuring
- Ultrasonic: HSR™ electrodes submerged in ethanol and cleaned in an ultrasonic bath for one minute.
The study was designed to determine whether removing weakly bonded surface nanostructures improves the morphological stability of HSR™ electrodes while preserving electrochemical performance. Morphological stability was assessed by comparing SEM-derived surface parameters before and after electrochemical agitation. In this study, cyclic voltammetry cycling served both as an electrochemical characterization method and as a surface agitation process.
Files and variables
File: Data.xlsx
Description: Spreadsheet containing data for cyclic voltammetry, electrode impedance spectroscopy, and surface quantification
Sheet: CV
This sheet contains cyclic voltammetry data for HSR™ Pt-10Ir electrodes fabricated at different laser fluences and subjected to different cleaning/processing methods. CV testing was performed to evaluate electrochemical performance, especially charge storage behavior. The manuscript describes CV testing over a potential window of approximately -0.6 V to 0.8 V vs. Ag/AgCl at a voltage sweep rate of 50 mV/s. Repeated CV cycling was also used as the primary electrochemical agitation method for evaluating surface stability. Results are grouped by 3 repeats (R1-R3), cleaning process, and laser fluence.
- XY: Applied potential during the CV sweep, reported in volts versus Ag/AgCl.
- R1, R2, R3: Current-density values for three electrodes fabricated under the same fluence and cleaning/processing condition.
- AVERAGE: Mean of the three replicate measurements at the corresponding potential point.
- Std Dv: Standard deviation of the three replicate measurements at the corresponding potential point.
Sheet: EIS
This sheet contains electrochemical impedance spectroscopy data for the same electrode processing conditions and laser fluence levels. EIS was used to evaluate electrode impedance behavior and to support extraction of specific capacitance by fitting the results to a equivalent Randles circuit model. The manuscript describes EIS as a key method for assessing electrochemical performance after different cleaning treatments. Impedance at 1 kHz is particularly relevant for neural interfacing applications and is discussed in the associated manuscript. Results are grouped by repeat, fluence, and cleaning method.
- XY: Frequency, in Hz.
- Fit 1 [RANDLES]: Impedance magnitude, in ohms, after fitting to Randles equivalent circuit fitting.
Sheet: Surface Parameters
This sheet contains quantitative surface morphology measurements derived from stereoscopic 3D SEM reconstructions. Surfaces were analyzed with ISO 25178 area roughness parameters, and the change in these surface parameters as a result of surface agitation were used to characterize the relative stability of electrodes treated with the different cleaning methods. Surfaces were analyzed at each fluence except 9.7 J/cm², which excluded from quantitative stereoscopic SEM surface-parameter analysis because the large surface height variations at that fluence greatly reduced the accuracy of the measurement technique. Due to the intensity and time required to perform this analysis, only two electrodes were characterized for each condition. The left hand table is the first repeat, and the right hand is the second, with averages and standard deviations calculated for each parameter.
- Sa: Arithmetic mean height of the reconstructed surface, in microns.
- Sq: Root-mean-square height of the reconstructed surface, in microns.
- Sdr: Developed interfacial area ratio, reported as a percentage.
- Pre EC Test: Surface parameter measured before electrochemical testing/agitation.
- Post EC Test: Surface parameter measured after electrochemical testing/agitation.
- Sa Change (um): Change in Sa after electrochemical agitation.
- Sq Change (um): Change in Sq after electrochemical agitation.
- Sdr Change (%): Change in Sdr after electrochemical agitation.
- Averages: Mean change values calculated across measurement sets.
- SD: Standard deviation of the corresponding change values.
For data included in each sheet, findings are analyzed and synthesized in greater detail, in the associated publication.