Lipopolysaccharide inhibits or accelerates biomedical titanium corrosion depending on environmental acidity

Titanium and its alloys are routinely used as biomedical implants and are usually considered to be corrosion resistant under physiological conditions. However, during inflammation, chemical modifications of the peri-implant environment including acidification occur. In addition certain biomolecules including lipopolysaccharide (LPS), a component of Gram-negative bacterial cell walls and driver of inflammation have been shown to interact strongly with Ti and modify its corrosion resistance. Gram-negative microbes are abundant in biofilms which form on dental implants. The objective was to investigate the influence of LPS on the corrosion properties of relevant biomedical Ti substrates as a function of environmental acidity. Inductively coupled plasma mass spectrometry was used to quantify Ti dissolution following immersion testing in physiological saline for three common biomedical grades of Ti (ASTM Grade 2, Grade 4 and Grade 5). Complementary electrochemical tests including anodic and cathodic polarisation experiments and potentiostatic measurements were also conducted. All three Ti alloys were observed to behave similarly and ion release was sensitive to pH of the immersion solution. However, LPS significantly inhibited Ti release under the most acidic conditions (pH 2), which may develop in localized corrosion sites, but promoted dissolution at pH 4–7, which would be more commonly encountered physiologically. The observed pattern of sensitivity to environmental acidity of the effect of LPS on Ti corrosion has not previously been reported. LPS is found extensively on the surfaces of skin and mucosal penetrating Ti implants and the findings are therefore relevant when considering the chemical stability of Ti implant surfaces in vivo. Bacterial lipopolysaccharide (LPS) can accelerate or inhibit the corrosion of titanium implants depending on the acidity of the environment. These contrasting effects were demonstrated by Owen Addison and colleagues from Birmingham University, UK. Titanium and its alloys are used in biomedical implants and are generally resistant to corrosion under normal physiological conditions. Inflammation and bacterial activity can, however, modify the local environment in the biofilms around dental implants. The researchers therefore investigated the effects of LPS from bacterial cell walls on corrosion. At normal acidity levels corrosion increased in the presence of LPS, but in the more acidic conditions associated with inflammation corrosion was inhibited. Increased acidity in the absence of LPS increases corrosion. The effects of LPS may influence the long-term stability of many implants.