To enhance their longevity dental implants must be highly biocompatible and must have a low elastic modulus close to that of the bone. They must also possess a high superficial hardness and a high corrosion resistance. For these reasons a recently developed low modulus Ti-27Nb alloy with non-toxic elements was treated by gas nitriding at high temperature in this study. A very thin nitrided layer of 0.5µm in thickness followed by an enriched nitrogen zone was observed. Consequently, a very high hardness evaluated at about 1800 HV was obtained in surface, which represents an increase of 4-5 times the hardness of the non nitrided alloy. This superficial hardness was experimentally observed to decrease up to 800 nm in depth from the surface to the core. The low modulus of Ti-27Nb (evaluated at 55 GPa, which is twice lower than the commercially pure titanium) was not affected by the surface nitriding treatment. A better corrosion resistance was observed as well as a significant decrease in ion release rates for the nitrided alloy (ion release of 1.41 ng/cm 2 compared to the 163.58 ng/cm 2 obtained for the commercially pure titanium at pH=7.48 in artificial Carter-Brugirard saliva). The cytocompatibility was not compromised and the cell viability performed on human osteoblasts, fibroblastic cells and epithelial cells was enhanced on the nitrided surface in comparison with the non-nitrided surface. These combined properties make the nitrided Ti-27Nb alloy a good candidate for dental implant applications.
This study reports the in vitro biocompatibility of a composite biomaterial composed of 46S6 bioactive glass in association with chitosan (CH) by using 3D osteoblast culture of SaOS2. The 46S6 and CH composite (46S6-CH) forms small hydroxyapatite crystals on its surface after only three days immersion in the simulated body fluid. For 2D osteoblast culture, a significant increase in cell proliferation was observed after three days of contact with 46S6 or 46S6-CH-immersed media. After six days, 46S6-CH led to a significant increase in cell proliferation (128%) compared with pure 46S6 (113%) and pure CH (122%). For 3D osteoblast culture, after six days of culture, there was an increase in gene expression of markers of the early osteoblastic differentiation (RUNX2, ALP, COL1A1). Geometric structures corresponding to small apatite clusters were observed by SEM on the surface of the spheroids cultivated with 46S6 or 46S6-CH-immersed media. We showed different cellular responses depending on the 2D and 3D cell culture model. The induction of osteoblast differentiation in the 3D cell culture explained the differences of cell proliferation in contact with 46S6, CH or 46S6-CH-immersed media. This study confirmed that the 3D cell culture model is a very promising tool for in vitro biological evaluation of bone substitutes' properties.
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