Since the aim was to investigate the impact of size and fixation mode of the implant on the tissue response, we compared a 200 µm to a 50 µm implant diameter, and a tethered to an un-tethered fixation mode.
Taken together, these findings underscore the need for a study systematically comparing the two fixation modes by evaluating the overall elicited tissue reactions and specifically addressing in quantitative terms the issue of neuronal numbers close to the implants over rather long evaluation periods.
Independently of electrode diameter, time-point after implantation, distance and depth of section, the un-tethered fixation mode resulted in significantly lower GFAP (F 1, 256) = 38.24, p<.0001, partial η2 = .13) and ED1 (F(1, 256) = 4.52, p<.05, partial η2 = .02) than did tethered.
Notably, the relative importance of implant size and fixation mode, and the possible interplay between the two factors have not been established or quantified.
However, although there seems to be consensus that un-tethered implants elicit a smaller tissue reaction than tethered ones, it is still unclear if the actual neuronal numbers differ between the two fixation modes.
Considering the robust effects of both electrode fixation mode and diameter on the tissue reaction we proceeded, in the second round of analysis, to test the effects of each actual electrode type separately.
The present study focused on basic properties of implanted electrodes, and could demonstrate that both size and fixation mode of the implant influence tissue trauma and healing.
The use of these four implants provides data for a full factorial design for the study (implant diameter: 200 µm vs. 50 µm, fixation mode: tethered vs. un-tethered), which allows the assessment of effects of fixation mode and implant size independently of each other, as well as the evaluation of the different implant configurations.
Fixation mode did not affect the density of neurons (Figure 2 and Table 1).
Also the shapes and sizes of the cavities made by the implants demonstrated different characteristic properties depending on implant fixation mode.
