Objective. Intracortical microelectrode arrays (MEAs) are implantable devices used for neural recording and stimulation. However, their long-term performance is often compromised due, at least in part, to glial scar formation, initiated by microglial migration and astrocyte activation following implantation. To address this issue, ultra-thin MEAs (UMEAs) have been proposed as an alternative due to their reduced cross-sectional area (CSA) and enhanced flexibility that minimizes the mechanical mismatch between brain tissue and the electrode. These properties are expected to mitigate the persistent foreign-body response associated with micromotion. However, unaided implantation of UMEAs can be challenging, as their high flexibility may increase the likelihood of buckling and curtail the precise penetration into the brain. Approach. We investigated flexible amorphous silicon carbide (a-SiC) probe designs with varying CSAs and lengths to identify geometries that enable unsupported implantation into the cerebral cortices of rat, pig, and macaques. The critical buckling force of the a-SiC probes was experimentally determined as a function of geometry and formally described via finite element modeling, which predicted buckling behavior. Additionally, the penetration behavior of a-SiC probes was evaluated by measuring force–displacement responses during insertion into cortical tissues across species. Main results. Our findings demonstrated that the penetration force and cortical dimpling depth were not significantly influenced by the range of probe geometries tested. However, we observed that penetration force and dimpling depth were significantly lower in rat cortices than in larger species. Importantly, probe geometries with a higher ratio (⩾2) of critical buckling force to penetration force exhibited a 100% success rate for unaided insertion. Significance. This study provides a framework for designing and evaluating UMEA geometries to optimize unsupported implantation in both small and large animal brains.

Objective. To investigate sputtered ruthenium oxide (RuO _x ) as a low impedance coating for recording neural activity with intracortical microelectrode arrays (MEAs). Approach. RuO _x was sputtered onto active sites of amorphous silicon carbide (a-SiC) MEAs and evaluated electrochemically and as a recording electrode coating over 6 weeks in rat motor cortex. The RuO _x was 250 nm thick with a 200 μm² geometric electrode surface area. We performed weekly electrochemical impedance spectroscopy and cyclic voltammetry (CV) measurements and single-unit action potential recordings. Main results. From 1 to 6 weeks post-implantation, we observed that median 1 kHz impedance decreased from 1.06 MΩ to 0.68 MΩ, median 1 Hz impedance decreased from 24.5 MΩ to 20.7 MΩ, and median 30 kHz impedance remained constant at 0.19 MΩ. Linear regression fits indicated that the 1 kHz and 1 Hz impedance exhibited small decreases whereas the 30 kHz impedance values had no discernible trend. The CV-based charge storage capacity (CSC_c) also exhibited consistency over time. The median CSC_c at 50 mV s⁻¹ was 24.3 mC cm⁻² on week 1 and 20.1 mC cm⁻² at week 6. At 50 000 mV s⁻¹ sweep rate, the median CSC_c was 2.4 mC cm⁻² at 1 week and 2.8 mC cm⁻² at 6 weeks. Regressions for both sweep rates exhibited no significant slope deviations from zero. Neural recordings spanning 6 weeks demonstrated consistent single unit action potential with a 75% single unit active-electrode-yield over 6 weeks. Median V _pp values on week 1 were 97.6 µV and 105 µV by week 6. The median and quartile signal-to-noise ratio (SNR) was 12 at week 1 and 12 at week 6. There were no deviations from zero on the regressions for both V _pp and SNR. Significance. The findings suggest that RuO _x is stable over subchronic implantation periods. Future research will explore long-term chronic performance and broader applications of RuO _x in neural interface devices.

Ruthenium oxide has emerged as a promising electrode coating material for intracortical microstimulation applications due to its favorable electrochemical properties. However, its long-term in vivo stimulation performance has not been well characterized. Using a go/no-go behavioral paradigm, we show that ruthenium oxide-coated microelectrode arrays support functionally relevant intracortical microstimulation-induced percepts for up to 25 wk postimplantation in rat somatosensory cortex, highlighting stable electrochemical properties and the utility of ruthenium oxide for chronic applications.

Insertion of microelectrode arrays (MEAs) into brain tissue remains a mechanical challenge, especially for long, thin probes designed to access deep structures. This study investigates the mechanical properties of 5 mm long amorphous silicon carbide (a-SiC) probes with different geometries and the effect of vibration-assisted insertion on penetration into rat brain. Methods: Two planar a-SiC probe designs were fabricated with identical lengths and thicknesses but differing width geometries: one with a uniform width (175 µm) and the other with a tapered shape (tapering from 175 to 75 µm). Critical buckling forces (FCs) were estimated by finite element modeling (FEM) and validated experimentally. Insertion mechanics were assessed in a brain mimic of 1.2% agarose gel at varying insertion speeds (20–1000 µm/s) and in vivo by implantation in rat cortex. Insertion metrics included penetration force (F_P), cortical dimpling depth (D_d), maximum insertion force (F_max), and success rate of insertion, all evaluated with and without vibrational assistance. Results: The tapered design exhibited lower penetration force and higher insertion success compared to the uniform-width probe, despite having a lower critical buckling force. An optimal insertion rate of 100 µm/s was identified, balancing insertion time with low F_max and high insertion success across designs. Higher F_P and D_d with a lower success rate were observed for uniform probes compared with tapered probes in rat brain. Vibration-assisted insertion was then investigated with tapered probes. Applying vibration significantly reduced F_P, whereas D_d and F_max remained unchanged. Notably, in 40% of actuated insertions in rat, no detectable F_P peak was observed, suggesting unimpeded pial penetration. Conclusions: A tapered probe geometry and vibration-assisted insertion can reduce F_max and F_P while enhancing the insertion success rate for probe penetration in rat brain. These strategies are generally applicable to long-shank MEA insertions in brain and may inform design and insertion strategies.