Kaitlynn Olczak

Although the potential for intracortical implanted microelectrodes has been demonstrated, successful clinical translation has been hindered by their inability to function over clinically relevant time-points (years to decades). Failure of implanted microelectrode arrays (MEA's) has been highly correlated with the foreign body response which progressively encapsulates the MEA's in a glial sheath, isolating them from the surrounding microenvironment. To mitigate this response, drug delivery has been implemented to release therapeutics from the device surface. This has allowed limited success at acute time points; however, challenges in maintaining long-term therapeutic dosages has resulted in an inability to mitigate chronic inflammation. A recent publication has demonstrated the use of multi-layer film composed of dextran-sulfate, minocycline hydrochloride (MH), and gelatin type A, assembled via layer-by-layer technology, capable of providing sustained release of MH for several weeks; however, their impact on functionality has not yet been analyzed. We found that after being coated with 20 layers NeuroNexus devices exhibited significantly increased impedance at 100Hz, 1kHz, and 10kHz, though this was significantly reduced after 24-hours of incubation in PBS. Charge carrying capacity also significantly increased after incubation in PBS. It can be concluded that these coatings do influence MEA's immediately after coating, but is less impactful over time as the coating degrades.

Intracortical microelectrode arrays (MEAs) are a valuable tool for neuroscience research, and their potential clinical use has been demonstrated. However, their inability to function reliably over chronic timepoints has limited their clinical translation. MEA failure is highly correlated with the foreign body response (FBR) and therapeutics have been used to reduce the FBR and improve device function, with drugs such as minocycline showing promising results in vivo. To avoid issues associated with systemic drug delivery, device coatings can be used to for therapeutic delivery. One method to locally deliver minocycline is a layer-by-layer (LBL) coating that consists of multiple trilayers of gelatin type A, minocycline, and dextran sulfate; however, the coating’s impact on device function was previously unknown. This work characterized 10, 20, and 30 trilayer coatings then evaluated their effect on device function. Cumulative minocycline release and coating thickness increased with the number of trilayers, agreeing with observations in previous studies. Atomic force microscopy images were used to calculate surface roughness of the coatings, which significantly increased from 10 to 20 trilayers, then remained relatively constant upon increasing to 30 trilayers. Scanning electron microscopy images confirmed trilayers coated the MEAs. Electrochemical impedance spectroscopy (EIS) and charge carrying capacity (CCC), were used to evaluate the coating’s effect on MEA electrochemical behavior over 3 weeks while the coated MEAs soaked in PBS. The 10 trilayer coatings slightly decreased CCC, while 20 and 30 trilayers initially increased CCC. CCC of all trilayers gradually increased as the MEAs soaked
in PBS. All trilayers initially increased MEA impedance magnitude and reduced the phase angle at low frequencies. Impedance magnitude at 1 kHz and 15 kHz decreased towards their initial precoated values for all trilayers as the MEAs soaked in PBS. Overall, these results show that the LBL
coatings did not significantly impact MEA function.