5.4. Encapsule membrane thickness

The overall capsule thickness was time-dependent, and generally decreased over time. There was, however, an increase in thickness with NiTi at 8 weeks (mean ± 1 SD: NiTi 62 ± 25 µm vs. StSt 41 ± 8 µm vs. Ti-6Al-4V 48 ± 12 µm) and with Ti-6Al-4V at 12 weeks (NiTi 45 ± 10 µm vs. StSt 38 ± 15 µm vs. Ti-6Al-4V 57 ± 31 µm) compared to stainless steel. These differences were not found to be statistically different, as the number of animals in each time group was not considered sufficient. The stainless steel capsule was thickest at 2 weeks (NiTi 70 ± 19 µm vs. StSt 84 ± 28 µm vs. Ti-6Al-4V, 69 ± 49 µm). At 4 weeks, there were no clear differences (NiTi 52 ± 12 µm vs. StSt 55 ± 16 µm vs. Ti-6Al-4V 54 ± 16 µm). At 26 weeks, all capsules around the test implants in the different groups were found to be equally thin, about 4 - 8 cell layers (NiTi 37 ± 9 µm vs. StSt 35 ± 8 µm vs. Ti-6Al-4V 37 ± 12 µm), and the morphologies were also similar (Figure 5-8). There were some variations in capsule thickness between the samples taken from a given material group at the same time point, as there were also between individual samples of different materials. The capsule was thicker at the ends of the implant. That was the reason for taking the measurements at mid-region.