What is the role of lipopolysaccharide on the tribocorrosive behavior of titanium?

In an oral environment, titanium dental implants are exposed to a complex degradation process which is predominantly influenced by the intermittent mechanical events (mastication), continuous exposure to varying chemical solutions (saliva and food) and formation of microbiological (biofilm). Several studies have investigated the chemical corrosion and mechanical resistance of titanium; however, very few attempted to report on the effects of combined chemical, mechanical and microbiological interactions, which simulates the oral environment. A new multi-disciplinary research area, "tribocorrosion" (a combined study of wear and corrosion), was used to address such issues. The tribocorrosive nature of titanium in artificial saliva (pH 6.5) with lipopolysaccharide (LPS) was investigated. Twenty-four titanium discs (12 mm diameter, 7 mm thickness), were divided into 8 groups (n=3) as a function of material (commercially pure titanium (cpTi) and titanium-aluminum-vanadium (TiAlV) alloy) and LPS concentrations (0, 0.15, 15 and 150 μg/ml). Sliding duration (2000 cycles), frequency (1.2 Hz) and load (20 N) parameters mimicked the daily mastication process. Electrochemical impedance spectroscopy was conducted before and after tribocorrosion to comprehend the changes in corrosion kinetics. Worn surfaces were examined using white-light-interferometry and scanning electron microscopy. Total weight loss and roughness values were calculated. LPS affected the tribocorrosive behavior of both titanium types. LPS statistically accelerated the ion exchange between titanium and saliva, and reduced the resistance of the titanium surface against corrosion (p<.05). Sliding events decreased the protectiveness of the titanium surface. In general, TiAlV exhibited better corrosion behavior, but both titanium types showed similar in total weight loss (p>.05). LPS significantly increased the cpTi weight loss (p=.041), and the roughness of the surface (p<.001). In summary, LPS negatively affected the corrosion/wear behavior of titanium, which may contribute to the failure of dental implants.