Inhibitory effect of L-Threonine and L-Lysine and influence of surfactant on stainless steel corrosion in artificial body solution

Abstract

Stainless steel 316L is a biomaterial, widely used in medicine for the fabrication of implants in orthopedics and cardiovascular surgery. The human body is an extremely aggressive environment and materials used for implants need to be highly resistant to corrosion and degradation. Corrosion of steel leads to the release of ions which are toxic to humans and may cause inflammatory processes in the body. Therefore, it is very important to decrease corrosion of stainless steel implants and to find inhibitors that will not cause health effects and that can be safely used. Amino acids are biomolecules that have confirmed action as corrosion inhibitors in aggressive solutions. The aim of this study is to investigate the inhibition action of rarely studied amino acids, L-Lysine and L-Threonine, on the corrosion process of stainless steel in artificial body solution using open circuit potential measurements, potentiodynamic measurements, electrochemical impedance spectroscopy measurements, surface scanning by atomic force microscopy (AFM) and quantum chemical calculation during the investigation. In order to increase the inhibition efficiency, sodium dodecyl sulphate (SDS) was used as an agent for modification of stainless steel surface that provides effortless adsorption of L-Lysine molecules on the electrode surface. Results obtained by potentiodynamic polarization measurements reveal that L-Lysine and L-Threonine act like mixed-type inhibitors with a more pronounced influence on cathodic processes. Also, potentiodynamic curves indicate that L-Lysine and L-Threonine act through adsorption onto the steel surface without changing the mechanism of corrosion of steel. Adsorption follows the Langmuir adsorption isotherm. EIS measurements reveal that charge transfer resistance increases in the presence of amino acids and after pretreatment in SDS solution indicating an increase of protection ability of formed film on the stainless steel surface. Results achieved by AFM reveal that the steel surface becomes smoother in BM − 3 solution with the addition of L-Lysine, suggesting adsorption of the amino acid molecule on the electrode surface. AFM results also indicate that SDS facilitates adsorption of amino acid molecules onto the steel surface. DFT results provide theoretical support for the results obtained by electrochemical studies. Taken together, experimental and theoretical results reveal that tested amino acids can be used as corrosion inhibitors in artificial body solution.