Spectroscopic Investigations of 316L Stainless Steel under Simulated Inflammatory Conditions for Implant Applications: The Effect of Tryptophan as Corrosion Inhibitor/Hydrophobicity Marker

Dominika Święch,Ewa Pięta,Aleksandra Szkudlarek,Natalia Piergies,Czesława Paluszkiewicz,Gaetano Palumbo

doi:10.3390/coatings11091097

Abstract

In this paper, the conformational changes of tryptophan (Trp) on the corroded 316 L stainless steel (SS) surface obtained under controlled simulated inflammatory conditions have been studied by Raman (RS) and Fourier-transform infrared (FT-IR) spectroscopy methods. The corrosion behavior and protective efficiency of the investigated samples were performed using the potentiodynamic polarization (PDP) technique in phosphate-buffered saline (PBS) solution acidified to pH 3.0 at 37 °C in the presence and absence of 10−2 M Trp, with different immersion times (2 h and 24 h). The amino acid is adsorbed onto the corroded SS surface mainly through the lone electron pair of the nitrogen atom of the indole ring, which adopts a more/less tilted orientation, and the protonated amine group. The visible differences in the intensity of the Fermi doublet upon adsorption of Trp onto the corroded SS surface, which is a sensitive marker of the local environment, suggested that a stronger hydrophobic environment is observed. This may result in an improvement of the corrosion resistance, after 2 h than 24 h of exposure time. The electrochemical results confirm this statement—the inhibition efficiency of Trp, acting as a mixed-type inhibitor, is made drastically higher after a short period of immersion.

Highlights

In recent years, as witnessed in a number of publications, stainless steel (SS) has been widely used as a metallic biomaterial, i.e., as a significant component of biomedical implements, treatments for orthopedic, dental, and cardiovascular implants [1,2,3,4,5,6,7,8,9,10]
The active domain corresponds to the metal dissolution (i.e., Fe in the matrix is oxidized to Fe2+, Equation (2) [44]), and the lower current density observed for the metal in the presence of Trp is likely ascribed to its adsorption on the SS surface fully protecting its surface and hindering its dissolution before anodic passivation
This study presents the comprehensive investigation behavior of Trp on the corroded

Summary

Introduction

As witnessed in a number of publications, stainless steel (SS) has been widely used as a metallic biomaterial, i.e., as a significant component of biomedical implements (i.e., dental extraction forceps, thoracic retractors), treatments for orthopedic, dental, and cardiovascular implants [1,2,3,4,5,6,7,8,9,10]. The corrosion resistance of this material is due to the formation of a thin oxide film on the surface (of approximately a few nanometers) [11]. It protects the material from corrosion, but it creates a very good interface with the tissue [12]. Many factors can influence the corrosion process of a material, such as the presence of chloride ions and other ions, surface topography, pH, alloying elements, etc. Upon implantation, the local pH around the metallic biomaterial decreases what it causes by surrounding it with fibrin and chlorine ions, for example [14,15,16]. The decrease in the surrounding pH can be associated with infections [15,17] or cancer development, which results in the phenomenon of extracellular acidification observed around the cancer cells [18]

Methods

Results

Conclusion