Chapter 5. Results
- Table of Contents
- 5.1. Cell attachment and proliferation in the presence of NiTi
- 5.2. Soft tissue response to NiTi
- 5.3. Perineural response to NiTi
- 5.4. Encapsule membrane thickness
- 5.5. Bone response to NiTi in the regional acceleratory phenomenon (RAP) model
- 5.6. Effects of NiTi on fracture healing after intramedullary nailing
- 5.7. Peripheral quantitative computed tomography
- 5.8. Corrosion of NiTi
5.1. Cell attachment and proliferation in the presence of NiTi
5.1.1. Contact of single cells with test materials in vitro and in vivo
The contacts of single cells to material surface were quite similar between NiTi and the other implant materials in commercial use. The cell cultures showed that the cells had grown very close to the titanium and NiTi surfaces in the fibroblast cultures, but slightly less close to stainless steel in the osteoblast cultures. In this study, the toxic control composite material inhibited cell attachment prominently, as also did the white soft paraffin (Figure 5-1).
Figure 5-1. Growth of osteoblasts near the test discs after one week of incubation. Figures from left to right: Wsp = white soft paraffin, stst = stainless steel, Ti = titanium, NiTi, Control = no test disc and Comp = Silux Plus®. The black areas at the corners of the photographs are the borders and the shadows of the test discs (light microscopy, magn. 108x).
Figure 5-2. A) A FESEM image of a hard resin embedded sample with a stainless steel implant 26 weeks after operation. M= metal implant, FC= fibrous capsule with collagen fibers and fibroblast type cells, MT= muscular tissue. A similar soft tissue reaction was seen with all materials at 26 weeks (magn. 330x).
Figure 5-3. B) Fibroblast (FB) attachment to a metal (M) surface. The 15 µm gap between metal and soft tissue is due to sample preparation. A close connection, a slender cell shape and small filopodia are seen. Ti-6Al-4V 4 weeks after implantation. (FESEM, magn. 1700x).
Figure 5-4. C) Cell-metal interface of NiTi 4 weeks after implantation. Torn cell podia and membrane structures (arrows) can be seen in the under surface of the cell. Respective focal contacts to the metal surface (asterix) are also present (FESEM, magn. 5000x).
Figure 5-5. D) A closely connected focal adhesion site with ruptured cell membrane structures. The gap to the metal (M) surface is under 30 nm. NiTi 4 weeks after implantation. (FESEM, magn. 50 000x).
In study III a close contact was seen between the fibrous capsule layer, single cells and the NiTi, StSt and Ti-6Al-4V in vivo (Figure 5-2 and Figure 5-3). There was a thin interfacial ”basal lamina like” zone over the surface of NiTi, Ti-6Al-4V and stainless steel materials. It consisted of an afibrillar layer of organic amorphous material with a wavy texture. This was generally thicker over Ti-6Al-4V than NiTi or stainless steel implants. Single cells seemed to adhere via this layer with clod-like, direct-contact adhesion structures (gap < 30 nm) (Figure 5-5). These were considered to be focal cell adhesion sites with proteins and cell membrane composition. The cell surfaces had respective fibril or torn cell membrane structures (Figure 5-4).
5.1.2. Cell proliferation in vitro
The rates of fibroblast and osteoblast proliferation in cell cultures correlated well with each other. The number of cells in the control group flask of fibroblast cultures at the end of the study was 1.6 x 105 (SD 1,2 x 104). The average proliferation of fibroblasts was 134.1% (p < 0.02) in the flasks containing titanium as compared to the control flasks, and 108.3% (p < 0.136) and 106.8% (p < 0.174) in the NiTi and stainless steel flasks. The proliferation of cells was only 63.2% (p < 0.002) in the white soft paraffin flasks and 48.3% (p < 0.0001) in the composite material flasks compared to the control group.
The proliferation of osteoblasts in the control group was 1.7 x 105 (SD 1,6 x 104). The values for titanium, NiTi and stainless steel were almost the same as those for the control group: 99.5% (p < 0.483), 100.5% (p < 0.475) and 104.7% (p < 0.334), respectively. In the white soft paraffin group, the number of cells was 81.5% (p < 0.058) compared to the control group. In the composite material flasks it was even less, 53.6% (p < 0.025) (Figure 5-6).
