Synergistic microbiologically influenced corrosion of SLM TC4 by co-culture of Streptococcus mutans and Veillonella dispar

Ti-6Al-4V (TC4) is extensively utilized for oral implants due to its excellent mechanical properties and biocompatibility. In the oral environment, microbiologically influenced corrosion (MIC) is typically driven by multispecies biofilms. Here, electrochemical, surface, and corrosion product analyses were used to investigate the MIC of selective laser melted (SLM) TC4 induced by mono- or dual-species biofilms of Streptococcus mutans ( S. mutans ) and Veillonella dispar ( V. dispar ). The dual-species biofilm was thicker, denser, and produced more extracellular polymeric substances (EPS) than mono-species biofilms, resulting in higher corrosion current density and lower charge transfer resistance. Although S. mutans dominated the interaction, V. dispar alone accelerated corrosion mainly via extracellular electron transfer (EET), as confirmed by riboflavin addition. The co-culture system’s overall pH increased, ruling out acid-induced corrosion as the main mechanism. Instead, their synergy promoted EET-MIC, further enhanced by riboflavin as an electron shuttle. Corrosion product analysis showed that under dual-species conditions, TiO 2 in the passive film decreased significantly, while Ti, Al, and V ion release increased, indicating lower corrosion resistance. Cytotoxicity and cytoskeletal staining revealed that the dual-species biofilm corrosion solution more strongly stimulated cell growth and proliferation. Our findings offer new insights into oral MIC mechanisms and strategies for developing corrosion-resistant oral materials.