Chronic intracortical implantation of saccharose-coated flexible shaft electrodes into the cortex of rats

Within this study, polyimide based shaft electrodes were fabricated and dip-coated in molten saccharose to stiffen them for insertion into the brain tissue. These electrodes were then implanted successfully into the cortex of whistar rats and the insertion force during implantation was recorded. Electrochemical impedance spectroscopy was performed immediately after implantation and in regular time intervals up to 201 days after implantation to monitor the tissue response to the implanted electrodes. Depending on the measured electrode pairs and the rats, the impedance spectra behaved different over time. Either they showed a constant decrease in impedance at 1 kHz, or they showed an initial decrease to increase again later. Furthermore, physiological signal recording was performed by stimulating the rats with acoustic signals and simultaneously recording the response on the different electrode sites. Multi-unit activity was detected until 37 days after implantation with an averaged signal-to-noise ratio of 2 to 4.