Chronic recording and electrochemical performance of amorphous silicon carbide-coated Utah electrode arrays implanted in rat motor cortex.

Clinical applications of implantable microelectrode arrays are currently limited by device failure due to, in part, mechanical and electrochemical failure modes. To overcome this challenge, there is significant research interest in the exploration of novel array architectures and encapsulation materials. Amorphous silicon carbide (a-SiC) is biocompatible and corrosion resistant, and has recently been employed as a coating on biomedical devices including planar microelectrode arrays. However, to date, the three-dimensional Utah electrode array (UEA) is the only array architecture which has been approved by the FDA for long-term human trials. Here, we demonstrate, for the first time, that UEAs can be fabricated with a-SiC encapsulation and sputtered iridium oxide film (SIROF) electrode coatings, and that such arrays are capable of single-unit recordings over a 30 week implantation period in rat motor cortex. Over the same period, we carried out electrochemical measurements, including voltage transients, cyclic voltammetry, and electrochemical impedance spectroscopy, to evaluate potential failure modes. Furthermore, we evaluated chronic foreign body response via fluorescence immunohistochemistry following device explantation. During the indwelling period, we observed a reduction in active electrode yield percentage from 94.6 ± 5.4 (week 1) to 16.4 ± 11.5 % (week 30). While the average active electrode yield showed a steady reduction, it is noteworthy that 3 out of 8 UEAs recorded greater than 60% active electrode yield at all times through 24 weeks and 1 out of 8 UEAs recorded greater than 60% active electrode yield at all times through the whole implantation period. In total, these findings further suggest that a-SiC may serve as a mechanically and electrochemically stable device encapsulation alternative to polymeric coatings such as Parylene-C.