Metal release from stainless steel in biological environments: A review

Abstract

Due to its beneficial corrosion resistance, stainless steel is widely used in, e.g., biomedical applications, as surfaces in food contact, and for products intended to come into skin contact. Low levels of metals can be released from the stainless steel surface into solution, even for these highly corrosion resistant alloys. This needs to be considered in risk assessment and management. This review aims to compile the different metal release mechanisms that are relevant for stainless steel when used in different biological settings. These mechanisms include corrosion-induced metal release, dissolution of the surface oxide, friction-induced metal release, and their combinations. The influence of important physicochemical surface properties, different organic species and proteins in solution, and of biofilm formation on corrosion-induced metal release is discussed. Chemical and electrochemical dissolution mechanisms of the surface oxides of stainless steel are presented with a focus on protonation, complexation/ligand-induced dissolution, and reductive dissolution by applying a perspective on surface adsorption of complexing or reducing ligands and proteins. The influence of alloy composition, microstructure, route of manufacture, and surface finish on the metal release process is furthermore discussed as well as the chemical speciation of released metals. Typical metal release patterns are summarized.

Metal assisted peptide bond hydrolysis: Chemistry, biotechnology and toxicological implications

“…Also in this case, the soluble Ni(II) species are thought to be the toxic agents [120,121]. Implants made of alloys containing nickel, such as stainless steel, give rise to both types of nickel toxicity by means of a slow release of Ni(II) ions [122,123].…”

Metal Release Mechanisms for Passive Stainless Steel in Citric Acid at Weakly Acidic pH

“…9,[12][13][14] For example, the role of solution-formed complexes versus surface complexes has not been investigated yet. Although there has been the general observation that metal release, and also corrosion in some cases, correlates with the stability constant of a metal complex, 9,[12][13][14] it has been speculated, 9,12 but not demonstrated, that the observed complexation processes take place at the stainless steel surface. Possible mechanisms that have been suggested are either controlled by solution complexation (sequestration of metal ions in solution) 13 or by surface adsorption of complexing agents, followed by surface complexation, and a detachment of the surface complex into solution.…”

“…12 This study was however conducted at pH 2.4, where metal-citrate complexation exists, but not to a large extent (except for chromium, Cr). 9 It has been debated whether complexation-induced metal release plays a major role for metal release from stainless steel in weakly or non-acidic biological environments and whether it can contribute to other mechanisms, such as corrosion or other chemical dissolution processes. 9,[12][13][14] For example, the role of solution-formed complexes versus surface complexes has not been investigated yet.…”

“…9 It has been debated whether complexation-induced metal release plays a major role for metal release from stainless steel in weakly or non-acidic biological environments and whether it can contribute to other mechanisms, such as corrosion or other chemical dissolution processes. 9,[12][13][14] For example, the role of solution-formed complexes versus surface complexes has not been investigated yet. Although there has been the general observation that metal release, and also corrosion in some cases, correlates with the stability constant of a metal complex, 9,[12][13][14] it has been speculated, 9,12 but not demonstrated, that the observed complexation processes take place at the stainless steel surface.…”

“…9 Metal release investigations are not only important for the area of risk and safety assessments, but can also be a sensitive measure of dissolution and corrosion processes for passive metals and alloys, where electrochemical activity is limited. 9 We have earlier investigated metal release from stainless steel (different grades) into citric acid containing solutions from a food safety perspective, 10,11 as citric acid is one of the food simulants suggested in a relatively new European guideline 1 for testing metals and alloys used in food contact. 10 It became clear that citric acid caused an initial metal release that results in surface passivation (hindering further release), and that the mechanism does not involve any active corrosion (metal oxidation) in solutions containing citric acid and no chlorides.…”