In vitro studies on the influence of surface modification of Ni-Ti alloy on human bone cells

Formation of Nitrogen Doped Titanium Dioxide Surface Layer on NiTi Shape Memory Alloy

NiTi shape memory alloys are increasingly being used as bone and cardiac implants. The oxide layer of nanometric thickness spontaneously formed on their surface does not sufficiently protect from nickel transition into surrounding tissues, and its presence, even in a small amount, can be harmful to the human organism. In order to limit this disadvantageous phenomenon, there are several surface engineering techniques used, including oxidation methods. Due to the usually complex shapes of implants, one of the most prospective methods is low-temperature plasma oxidation. This article presents the role of cathode sputtering in the formation of a titanium dioxide surface layer, specifically rutile. The surface of the NiTi shape memory alloy was modified using low-temperature glow discharge plasma oxidation processes, which were carried out in two variants: oxidation using an argon + oxygen (80% vol.) reactive atmosphere and the less chemically active argon + air (80% vol.), but with a preliminary cathode sputtering process in the Ar + N₂ (1:1) plasma. This paper presents the structure (STEM), chemical composition (EDS, SIMS), surface topography (optical profilometer, Atomic Force Microscopy-AFM) and antibacterial properties of nanocrystalline TiO₂ diffusive surface layers. It is shown that prior cathodic sputtering in argon-nitrogen plasma almost doubled the thickness of the produced nitrogen-doped titanium dioxide layers despite using air instead of oxygen. The (TiO_xN_y)₂ diffusive surface layer showed a high level of resistance to E. coli colonization in comparison with NiTi, which indicates the possibility of using this surface layer in the modification of NiTi implants' properties.

Biocompatibility and Inflammatory Potential of Titanium Alloys Cultivated with Human Osteoblasts, Fibroblasts and Macrophages

The biomaterials used to maintain or replace functions in the human body consist mainly of metals, ceramics or polymers. In orthopedic surgery, metallic materials, especially titanium and its alloys, are the most common, due to their excellent mechanical properties, corrosion resistance, and biocompatibility. Aside from the established Ti6Al4V alloy, shape memory materials such as nickel-titanium (NiTi) have risen in importance, but are also discussed because of the adverse effects of nickel ions. These might be reduced by specific surface modifications. In the present in vitro study, the osteoblastic cell line MG-63 as well as primary human osteoblasts, fibroblasts, and macrophages were cultured on titanium alloys (forged Ti6Al4V, additive manufactured Ti6Al4V, NiTi, and Diamond-Like-Carbon (DLC)-coated NiTi) to verify their specific biocompatibility and inflammatory potential. Additive manufactured Ti6Al4V and NiTi revealed the highest levels of metabolic cell activity. DLC-coated NiTi appeared as a suitable surface for cell growth, showing the highest collagen production. None of the implant materials caused a strong inflammatory response. In general, no distinct cell-specific response could be observed for the materials and surface coating used. In summary, all tested titanium alloys seem to be biologically appropriate for application in orthopedic surgery.

Biofunctionalization of a titanium surface with a nano-sawtooth structure regulates the behavior of rat bone marrow mesenchymal stem cells

BACKGROUND

The topography of an implant surface can serve as a powerful signaling cue for attached cells and can enhance the quality of osseointegration. A series of improved implant surfaces functionalized with nanoscale structures have been fabricated using various methods.

METHODS

In this study, using an H(2)O(2) process, we fabricated two size-controllable sawtooth-like nanostructures with different dimensions on a titanium surface. The effects of the two nano-sawtooth structures on rat bone marrow mesenchymal stem cells (BMMSCs) were evaluated without the addition of osteoinductive chemical factors.

RESULTS

These new surface modifications did not adversely affect cell viability, and rat BMMSCs demonstrated a greater increase in proliferation ability on the surfaces of the nano-sawtooth structures than on a control plate. Furthermore, upregulated expression of osteogenic-related genes and proteins indicated that the nano-sawtooth structures promote osteoblastic differentiation of rat BMMSCs. Importantly, the large nano-sawtooth structure resulted in the greatest cell responses, including increased adhesion, proliferation, and differentiation.

CONCLUSION

The enhanced adhesion, proliferation, and osteogenic differentiation abilities of rat BMMSCs on the nano-sawtooth structures suggest the potential to induce improvements in bone-titanium integration in vivo. Our study reveals the key role played by the nano-sawtooth structures on a titanium surface for the fate of rat BMMSCs and provides insights into the study of stem cell-nanostructure relationships and the related design of improved biomedical implant surfaces.

In vitro biocompatibility and mechanical performance of titanium doped high calcium oxide metaphosphate-based glasses

This study challenged to produce phosphate-based glasses (PBG) for the treatment of osseous defects. The glasses contained, among other components, 40 mol% CaO and 1–5 mol% TiO₂. The mechanical performance and in vitro biocompatibility using both human osteosarcoma and primary osteoblasts were carried out. Incorporation of TiO₂ into PBG had no significant effect on strength and modulus. These glasses encouraged attachment and maintained high viability of osteosarcoma cells similar to the positive control surface. Cells grown directly (on glasses) or indirectly (in the presence of glass extracts) showed similar proliferation pattern to the positive control cells with no significant effect of TiO₂ detected. Increasing TiO₂ content, however, has a profound effect on cytoskeleton organization and spreading and maturation of primary osteoblasts. It is believed that TiO₂ might have acted as a chemical cue-modulating cells response, and hence the substrates supported maturation/mineralization of the primary osteoblasts.