Titanium alloys with varying surface micro-area potential differences have antibacterial abilities and a favorable cellular response

Abstract

Objectives: Surface micro-area potential difference (MAPD) can achieve bacteriostatic performance independent of metal ion dissolution. To study the influence of MAPD on antibacterial properties and the cellular response, Ti-Ag alloys with different surface potentials were designed and prepared by changing the preparation and heat treatment processes.

Materials and methods: Ti-Ag alloys (T4, T6, and S) were prepared by vacuum arc smelting, water quenching, and sintering. Cp-Ti was set as a control group in this work. The microstructures and surface potential distributions of the Ti-Ag alloys were analyzed by SEM and energy dispersive spectrometry. Plate counting and live/dead staining methods were used to evaluate the antibacterial properties of the alloys, and the mitochondrial function, ATP levels, and apoptosis were assessed in MC3T3-E1 cells to analyze the cellular response.

Results: Due to the formation of the Ti-Ag intermetallic phase in the Ti-Ag alloys, Ti-Ag (T4) without the Ti-Ag phase had the lowest MAPD, Ti-Ag (T6) with a fine Ti₂Ag phase had a moderate MAPD, and Ti-Ag (S) with a Ti-Ag intermetallic phase had the highest MAPD. The primary results demonstrated that the Ti-Ag samples with different MAPDs exhibited different bacteriostatic effects, ROS expression levels, and apoptosis-related protein expression levels in cells. The alloy with a high MAPD exhibited a strong antibacterial effect. A moderate MAPD stimulated cellular antioxidant regulation (GSH/GSSG) and downregulated the expression of intracellular ROS. MAPD could also promote the transformation of the inactive mitochondria to biologically active mitochondria by increasing the ΔΨ_m and reducing apoptosis.

Conclusion: The results here indicated that moderate MAPD not only had bacteriostatic effects but also promoted mitochondrial function and inhibited cell apoptosis, which provides a new strategy to improve the surface bioactivity of titanium alloys and a new idea for titanium alloy design.

Clinical relevance: There are some limitations of the mechanism of MAPD. However, researchers will become increasingly aware of the advantages and disadvantages of MAPD and MAPD might provide an affordable solution of peri-implantitis.

Keywords: Antibacterial ability; Apoptosis; MAPD; Mitochondrial function; Ti-Ag alloy.