Microscale Electric Fields Induced by Galvanically Coupled Ti-Mg Metal-Metal Composites Promote Antibacterial Activity

Implant-associated infections still represent major challenge to successful implantation. Titanium and its alloys are attractive implant materials for orthopedic applications. However, they lack of effective antibacterial activities against bacterial infection. Heterogeneous metallic materials can induce galvanic corrosion in physiological solution, and this phenomenon can also induce antibacterial action. In this work, we fabricated Ti-Mg metal-metal composites (MMCs) with different contents of Mg-Zn alloy by spark plasma sintering (SPS). We quantitatively evidenced that microscale electric fields formed between Ti and Mg area in MMCs by using atomic force microscopy (AFM). The formation of microscale electric fields effectively inhibited the adhesion and growth of Gram-positive Staphylococcus aureus (S. aureus) and Gram-negative Escherichia coli (E. coli) on Ti-Mg MMCs. Moreover, the antibacterial behavior could be controlled by tuning microscale electric fields, revealing the effect of the electron transfer in the antibacterial process. The electron transfer between the Mg-rich area and titanium matrix could induce local alkaline environment leading to bacterial death. Moreover, the presence of microscale electric fields could induce burst of reactive oxygen species (ROS) in bacteria, which also caused bacterial death by inducing intracellular oxidation, membrane potential variation, and the release of cellular contents. The findings can provide new insights for understanding the antibacterial action of Ti-Mg MMCs that exhibit great potential as orthopedic implants. The results also offer new concepts for designing metal-metal composite implants with non-antibiotic solution for combatting infections by controlling microscale electric fields.