6.5. Ultrastructural features of cellular adhesion and morphology at the interface of NiTi

The general ultrastructural features of cellular adhesion and morphology at the interface of NiTi have not been studied so far. In the present study, they were analyzed using FESEM. The number of adhesion plaques, the morphological features of cells and their podia as well as the adhesion areas of single cells to the material surface have been accepted into use in the evaluation of biocompatibility (Puleo et al. 1992, Ushida et al. 1992).

Knowledge of the structure and composition of tissue-material interfaces and adhesion phenomena is important for several reasons, including the need to modify the surface of biomaterials to control and accelerate their interaction with the host tissues. The surface and substratum characteristics of materials are reflected in single cells and their structures (Sinha et al. 1996). Cell adhesion is a prerequisite for further cellular functions, such as spreading, proliferation, migration and biosynthetic activity. It is probably the most important aspect of cell interaction with a non-toxic biomaterial. The adhesion to material is mediated through preadsorbed proteins, which form focal contacts with the cell membrane (Anderson et al. 1990, Groth et al. 1994). A certain amino acid sequence of these proteins binds to cell membrane integrins, which are connected to the cytoskeleton (Pytela et al. 1985, Ruoslahti et al. 1987).

The present study demonstrated that fibroblast-like cells formed close connections with NiTi, showing good adhesion. The first organic layer on the metal surface with afibrillar wavy structures was probably made up of proteoglycans and other similar extracellular matrix components. The layer was slightly thicker with Ti-6Al-4V. The exact composition of this layer and its potential value for biocompatibility need to be clarified in the future. Within and above this layer, there were bigger adhesion clots with gaps of less than 30 nanometers, which were considered to be direct contact-forming focal cell adhesion sites with proteins and cell membrane composition (Figure 5-5D). The number and composition of adhesion sites of NiTi did not differ from the control materials, and it thus appears to be well tolerated, judging by the criteria established in the FESEM study.