Effect of Rare−Earth Elements Microdoping on Ti−6Al−7Nb Alloys for Biomedical Application: Materials Characterization and In Vivo Biocompatibility Tests

The paper focuses on materials characterization and «in vivo» biocompatibility tests of Ti6Al7Nb alloys microdoped by 0.3 wt. % of rareearth elements (REE) to use it as perspective materials to produce personalized medical implants. All Ti6Al7Nb0.3REE alloys (REE Y, Ce, La) were produced by electric arc melting method and characterized by scanning electron microscopy (SEM), optical microscopy (OM), energy-dispersive Xray spectroscopy analysis (EDX), helium pycnometer as well as reducing/oxidation melting methods. The measured true densities increased in the order: Ti−6Al−7Nb−0.3Y (4.4563 ± 0.1075 g/cm³) < Ti−6Al−7Nb−0.3Ce (4.7255 ± 0.2853 g/cm³) < Ti−6Al−7Nb−0.3La (4.8019 ± 0.0111 g/cm³). Diffraction analysis was performed to indicate phases composition and calculate crystallites sizes, crystal orientation and lattice parameters that confirmed REEmicrodoping due to increase of lattice volume. The single-phase Ti6Al7Nb0.3Y alloy had the finest αTi crystallites (22.32 nm), the larger αTi crystallites in the dualphase Ti6Al7Nb0.3Ce and Ti6Al7Nb0.3La (30.77 nm and 29.83 nm, respectively) suggest that the presence of the βTi phase. Hardness (H) and elastic modulus (E) were indicated by nanoindentation and increased in the order: Ti−6Al−7Nb−0.3La (4.01 GPa and 17.7 GPa respectively) < Ti−6Al−7Nb−0.3Y (4.39 GPa and 137 GPa respectively ) < Ti−6Al−7Nb−0.3Ce (4,67 GPa and 146 GPa respectively). In vivo tests showed that Ti6Al7Nb0.3La alloy had statistically significant increase of local inflammation at the one-week mark needed to further research and explanation as well, that could be indicator of toxicity in comparison with other studied alloys.