Carbon-based composite rod as a potential electrode for stimulation of neural tissue: Electrochemical, biological, and stability evaluation

The aim of this study was to evaluate the electrochemical performance, biocompatibility, and degradation resistance of novel carbon composite electrodes as potential materials for neural tissue stimulation and treatments of neurodegenerative diseases i.e. deep brain stimulation (DBS). The CF/PyC/CNT-OH electrodes were fabricated through direct heating of carbon fiber (CF) bundle in methane, followed by CVD synthesis of pyrocarbon (PyC), and subsequent deposition of hydroxyl-terminated carbon nanotubes (CNT-OH). Measurements of voltage transient characteristics showed that the fabricated electrodes exhibited a charge injection capacity of 91.1 μC·cm −2 ·ph −1 , which was as good as the reference Pt electrode, and nearly 250 % higher than for non-modified electrodes. Additionally, surface modification enhanced the current response during standard pulse stimulation by stabilizing the signal and reducing current spikes caused by undesirable capacitive effects. Biological tests were carried out using a unique cell model not previously employed in biocompatibility studies of biomaterials namely, primary dopaminergic neuronal cultures derived from the ventral midbrain of Albino Swiss mouse embryos. The performed tests did not show a negative impact of materials on the biological response of cells and showed some pro-survival effects especially for the CF/PyC/CNT-OH electrodes. Furthermore, the CNT-OH deposit significantly enhanced stability of the electrodes under both standard and accelerated degradation-aging conditions. Summarizing, the use of CNT-OH resulted in excellent electrode performance with exceptional operational stability in terms of charge-storage capacity, double-layer capacitance, and working potential. These results are of great importance for the development of innovative stimulation electrodes, and other research on the electrodes intended for biological applications. • Novel CF/PyC/CNT-OH electrodes charge injection capacity 2.5 times vs. unmodified • Electrodes show stable electrochemical behavior and reduced capacitive artifacts • Primary dopaminergic neurons show no cytotoxicity on functionalized CNT surfaces • Durability tests show excellent electrode stability after aging, supporting DBS use