Effect of aging treatments on mechanical, chemical, and antibacterial properties of a β-type Ti-Nb-Cu alloy for implant applications

Bacterial infections are one major cause of metallic implant failure. A metastable beta-type 96(Ti-45Nb)-4Cu alloy was developed for potential load-bearing implant applications with tailored antibacterial properties. The cast alloy was initially subjected to homogenization (1000 degrees C, 24 h, water-quenched), and then aged at two temperatures (425 degrees C, 640 degrees C, 8 h). The influence of aged microstructures on structural (XRD, SEM, APT), mechanical (microhardness, tensile tests), and corrosion (potentiodynamic polarization, ion release) behaviour, as well as on macrophage cytocompatibility and antibacterial properties, was studied. The homogenized microstructure consists of a single-phase beta, which partially decomposes into beta+omega (aging at 425 degrees C), and into three phases, beta+Ti2Cu+alpha (aging at 640 degrees C). The omega phase leads to a drastic increase in yield strength (sigma(y) > 1 GPa), and concomitant decrease in elongation (epsilon(max) = 2 %). The three-phase alloy shows a moderate yield strength (sigma(y) = 578 MPa), acceptable elongation (epsilon(max) = 10 %), and low Young's modulus (E = 78 GPa). All three alloys exhibit, in simulated physiological solution, low free corrosion and direct transfer to stable anodic passivity, similar to Ti-6Al-4V. The alloy aged at 425 degrees C exhibits enhanced corrosion activity in the higher anodic polarization regime due to omega precipitates in the beta matrix. The three-phase alloy shows good cytocompatibility with THP-1 macrophages at 24 h. Moreover, it exhibits antibacterial effect against S. aureus at 4 h. In conclusion, the aged alloy containing Ti2Cu precipitates exhibits a good combination of properties: high strength and elongation, low Young's modulus, excellent corrosion resistance, good biocompatibility, and antibacterial properties.