TiO2 surfaces are generally recognized as excellent biocompatible interfaces with a high stability and corrosion resistance, antibacterial properties and wetting ability. Among various TiO2 nanostructured surfaces that show very good cell interactions and osseointegration, self-organized TiO2 nanotube (TNT) layers, grown by anodization of Ti, have emerged as extremely suitable substrates. Studies showed that anodization is a very viable tool for nanostructuring of various biomedical alloys, including TiAlV. Pioneering work by Schmuki et al. demonstrated that TNT layers with diameter of 15 nm are the most suitable for cell growth. However, despite advances, Ti-based implants still face challenges like poor osseointegration, bacterial infections, and alloy cytotoxicity.
This doctoral thesis demonstrates the influence of ultrathin coatings of different oxides (incl. TiO2, ZrO2 and V2O5) on TNT layers on the enhancement of the cell growth and adhesion. These coatings were deposited using Atomic Layer Deposition (ALD) on reference Ti, TiAlV foils and anodized TNT layers with a distinct tube diameter of 12 nm (TNT 12), 15 nm (TNT 15), 30 nm (TNT 30), 50 nm (TNT 50) and 100 nm (TNT 100). Different cell cultures (incl. MG-63, hGFs, WI-38/MRC-5, SH-SY5Y, A549 and U-87 MG) were investigated in detail for the proliferation and growth. TNT layers with smaller diameters appear to be the most suitable for cell growth in general and the larger diameters are used for comparisons. The shaping, adhesion, proliferation, and cell density on these substrates are also studied. Moreover, the single-cell adhesion of the cells to the TNT layers was studied by the Bio-atomic force microscopy (Bio-AMF) technique.
Additional ALD TiO2 coatings mildly improved the biocompatibility of the Ti foils and TNT layers for the cells investigated. The growth of hGFs increased by ∼8% on coated TNT 15 compared to the uncoated (0c) ones. The single-cell adhesion measured by Bio-AFM (in terms of Young's Modulus) of all the 5c ALD TiO2 coated TNT layers increased by 25% compared to the uncoated (0c) ones and on the 5c ALD TiO2 coated Ti foils, it increased by∼6% compared to uncoated (0c) ones. The coated surfaces were evaluated in terms of the effect of tube diameter, crystallinity, roughness, wettability, and surface chemistry on cell growth and elongation. The cell proliferation in WI-38, A549, MRC-5, and U-87 MG cell lines for TiAlV foil surfaces showed a significant increase on TiAlV foils coated with 1c ALD TiO2 compared with uncoated ones. TNT 30 and TNT 100 coated with 5c ALD V2O5, low cell densities on these surfaces were observed due to the adverse effect of V species. TNT 15 coated with 5c ALD ZrO2 assisted MG-63 cells to exhibit a well-developed cytoskeleton structure compared to those grown on uncoated TNT 15. These findings establish ALD as a versatile tool for atomic-scale optimization of Ti via atomic-scale surface modifications, for improved implant performance and patient outcomes in diverse clinical contexts.