Fig. 1. Characterization of the Nb-Cu powders and the as-sintered Nb-Cu alloys. (a-c) XRD patterns of the starting powder mixtures, 12 h-ball-milled powders, and the spark-plasma-sintered alloys, respectively. (d-f) SEM images, EBSD grain orientation maps and corresponding phase maps of Nb, Nb-0.5Cu and Nb-3Cu, respectively.

Fig. 2. (a) Representative compressive stress-strain and (b) magnetic hysteresis curves of Nb, Nb-0.5Cu and Nb-3Cu alloys.

Fig. 3. (a) Potentiodynamic polarization curves, (b) Nyquist plots under OCP and (c) Bode plots of Nb, Nb-0.5Cu and Nb-3Cu alloys.

Fig. 4. Cumulative Nb2+ (a) and Cu2+ (b) concentrations of Nb, Nb-0.5Cu and Nb-3Cu alloys during immersion in Hank's solution at 37 ℃ for 21 days.

Fig. 5. Antibacterial evaluation of Nb, Nb-0.5Cu and Nb-3Cu alloys after 24 h of incubation. (a) Representative photographs of colonies of E. coli and S. aureus. (b, c) Statistical analysis of total colony-forming units. (d) SEM micrographs of the bacteria morphology. The data were followed by one-way ANOVA with post-hoc test. **** p < 0.0001.

Fig. 6. In vitro biocompatibility evaluation of Nb, Nb-0.5Cu and Nb-3Cu alloys. (a) MC3T3-E1 pre-osteoblasts proliferation. (b) Live (green)/Dead (red) staining of the MC3T3-E1 cells after 24 h of incubation with Nb, Nb-0.5Cu and Nb-3Cu, respectively.

Fig. 7. Cell adhesion on the Nb, Nb-0.5Cu and Nb-3Cu alloys. (a) SEM and (b) confocal laser scanning microscope (CLSM) images of MC3T3-E1 cells after 24 h of incubation. The actin filaments (red) and the nuclei (blue) were stained with Alexa Fluor 568 phalloidin and Hoechst, respectively.

Fig. 8. Quantification of in vitro osteogenic potential of Nb, Nb-0.5Cu and Nb-3Cu alloys. (a) ALP activity. (b) Statistical stained area. (c) Representative images of alizarin red staining of MC3T3-E1 cells after 14 days of incubation. (d, e) Relative expression of osteogenesis-related genes (RUNX2, ALP, COLA1 and OCN) after 7 and 14 days of incubation, respectively. Note: these values are expressed as mean ± standard deviation. The data were followed by one-way ANOVA with post-hoc test. * p < 0.05, ** p < 0.01, *** p < 0.001, and **** p < 0.0001.

Fig. 9. (a) Micro-CT 3D reconstruction of skull bones after implantation for 2 months. (b) Bone mineral density. (c) Bone volume fraction (BV/TV). (d) Optical images of the Hematoxylin-eosin (HE) stained histological sections of peri-implant after 12 weeks of skull implantation. Notes: HS, Haversian structure; ob, osteoblast; fb, fibroblast. Note: these values are expressed as mean ± standard deviation. The data were followed by a one-way ANOVA with post-hoc test. * p < 0.05, ** p < 0.01, *** p < 0.001.

Fig. 10. Optical images of the methylene blue/basic fuchsin-stained histological sections of peri-implants after 12 weeks of implantation in femur with (a) Nb, (b) Nb-0.5Cu and (c) Nb-3Cu bone screws. Notes: HS, Haversian structure; NBF, new bone formation.