Figure 5. Chronic implant impedances.

(a) Impedance values (mean ± standard error of the mean) for each probe type across time. Both electrode types saw an approximately 2 MΩ increase in impedance within the first two weeks. Values for the carbon fibers then leveled off while the silicon electrode values dropped before leveling off. Impedance values for 177 um² silicon sites coated with PEDOT are shown in green [53]. The number of channels used for impedance analysis at each time point can be seen in figure S1. (b) Impedance values scaled by geometric surface area (mean ± standard error of the mean) for each probe type across time. Carbon fibers increased to approximately 80,000 kΩ·μm² before leveling off, while the silicon electrode values peaked at about 650,000 kΩ·μm² before steadying at approximately 500,000 kΩ·μm². Similar to (a), values for 177 um² silicon sites coated with PEDOT are shown in green [53].