A study on the influence of Hf as part of a novel Ta-Nb-Ti based multi-component alloy system for endoprosthetic implants

• Three equimolar alloys (Ta-Nb-Ti, Nb-Ti-Hf, Ta-Nb-Ti-Hf) were developed with tunable hardness and good surface quality. • Microstructure, surface roughness and hardness were analyzed and compared to pure elements and Ti-6Al-4V. • Biocompatibility matched reference materials in cell and inflammation assays. • Strong anti-bacterial effect, outperforming all references and pure elements. In the present study, we report on our findings regarding the preparation and analysis of three equimolar alloying compositions (Ta-Nb-Ti, Nb-Ti-Hf and Ta-Nb-Ti-Hf). All alloys were produced via arc melting, microstructurally investigated and analysed regarding their surface quality after polishing. Moreover, Vickers hardness tests were performed and related to the achievable surface qualities. All experiments were also carried out on reference materials (pure Ta, Nb, Ti and Hf) and the benchmark alloy Ti-6Al-4V. Subsequently, the interaction between bacteria ( E. coli , S. capitis ) and the alloys surfaces was analysed and a biocompatibility assay (SaOs-2 attachment and mineralization and MM6 inflammatory reaction test) was performed. The obtained results show that the hardness of the alloys within the system can be adjusted by alloying, however, the surface quality can be well controlled. Moreover, all alloys tested show comparable biocompatibility to the reference material in the cell attachment and mineralization assays, as well as the inflammatory tests. In addition, the alloys observed demonstrate anti-adhesive behaviour regarding the bacteria tested, significantly exceeding the performance of the reference and the individual components. The latter in particular should be emphasised here and has not yet been presented in this form anywhere else in the literature.