Antibacterial Ti-Mn-Cu alloys for biomedical applications

Abstract

Titanium alloys are common biomedical materials due to their biocompatibility and mechanical performance. However, titanium alloys are expensive and, unless surface treated, generally cannot prevent surgical infections related to bacteria which can damage the integrity of the implant. In this study, new titanium alloys were developed via powder metallurgy and the addition of manganese and copper, respectively, aiming to limit the manufacturing costs and induce new functionality on the materials including antibacterial response. The addition of manganese and copper to titanium significantly changes the behaviour of the Ti-Mn-Cu alloys leading to the successful stabilization of the beta titanium phase, great refinement of the typical lamellar structure, and achievement of materials with low level of porosity. Consequently, it is found that the mechanical performance and the antibacterial efficacy are enhanced by the addition of a higher amount of alloying elements. The manufactured Ti-Mn-Cu alloys fulfil the requirements for structural biomedical implants and have antibacterial response making them potential candidates for permanent medical implants.

Keywords: E. coli (Escherichia coli); antibacterial activity; homogeneous microstructure; mechanical properties; powder metallurgy; titanium alloys.

Figure 1.

Phase diagram showing the expected type of Ti alloy, for the Ti-Mn-Cu alloys, as a function of the molecular orbital calculation of electronic structures (adapted from [25]).

Figure 2.

XRD diffractograms of the sintered Ti-Mn-Cu alloys.

Figure 3.

Optical micrographs of the sintered Ti-Mn-Cu alloys showing the microstructural features present (phases and porosity). (a) Ti-0.5Mn-0.25Cu, (b) Ti-1Mn-0.5Cu, (c) Ti-2Mn-1Cu, (d) Ti-3.5Mn-1.75Cu and (e) Ti-5Mn-2.5Cu; and f): SE-SEM micrograph of the Ti₂Cu intermetallic compound precipitated at the at the lamellar boundaries in the Ti-5Mn-2.5Cu alloy.

Figure 4.

Values of the density/porosity (a) and of the hardness (b) of the sintered Ti-Mn-Cu alloys.

Figure 5.

Representative tensile behaviour of the sintered Ti-Mn-Cu alloys: (a) stress-strain curves, fracture surface of the (b) Ti-0.5Mn-0.25Cu, (c) Ti-1Mn-0.5Cu, (d) Ti-2Mn-1Cu, (e) Ti-3.5Mn-1.75Cu and (f) Ti-5Mn-2.5Cu alloys, (g) average tensile properties and (h) comparison with other antibacterial Ti-based alloys [19, 30–34].

Figure 6.

Digital images of the E. coli colonies found on the surface of the sintered Ti-Mn-Cu alloys: (a) Ti-0.5Mn-0.25Cu, (b) Ti-1Mn-0.5Cu, (c) Ti-2Mn-1Cu, (d) Ti-3.5Mn-1.75Cu, (e) Ti-5Mn-2.5Cu and (f) comparison of the antibacterial efficacy with literature [36–39].