Using Neutron Reflectometry to Discern the Structure of Fibrinogen Adsorption at the Stainless Steel/Aqueous Interface

Abstract

Neutron reflectometry has been successfully used to study adsorption on a stainless steel surface by means of depositing a thin steel film on silicon. The film was characterized using XPS (X-ray photoelectron spectroscopy), TOF-SIMS (time-of-flight secondary ion mass spectrometry) and GIXRD (grazing incidence X-ray diffraction), demonstrating the retention both of austenitic phase and of the required composition for 316L stainless steel. The adsorption of fibrinogen from a physiologically-relevant solution onto the steel surface was studied using neutron reflectometry and QCM (quartz crystal microbalance) and compared to that on a deposited chromium oxide surface. It was found that the protein forms an irreversibly-bound layer at low concentrations, with maximum protein concentration a distance of around 20 Å from the surface. Evidence for a further diffuse reversibly-bound layer forming at higher concentrations was also observed. Both the structure of the layer revealed by the neutron reflectometry data and the high water retention predicted by the QCM data suggest that there is a significant extent of protein unfolding upon adsorption. A lower extent of adsorption was seen on the chromium surfaces, although the adsorbed layer structures were similar, suggesting comparable adsorption mechanisms.

Bovine Serum Albumin and Fibrinogen Adsorption at the 316L Stainless Steel/Aqueous Interface

“…The NR data and model fits for the untreated stainless steel sample are shown in Figure 2; the stainless steel film under PBS/water could be modelled with a metal layer of thickness 214 Å (+ 2 Å), roughness 15 Å and SLD 5.42 x 10 -6 Å -2 , and an oxide layer of thickness 30 Å (+ 3 Å) and SLD 6.15 x 10 -6 Å -2 . The thicknesses are in good agreement with the XRR data (the increase in oxide thickness is attributed to the UV/ozone cleaning prior to NR measurements) and the SLD values are similar to those seen previously 25 , with the oxide SLD consistent with that expected for a mixture of iron and chromium oxides (values for pure Cr 2 O 3 and Fe 2 O 3 would be 5.11 and 7.17 x 10 -6 Å -2, respectively). While the SLD of 316L stainless steel should theoretically be closer to 7 x 10 -6 Å -2 , an increased amount of Mn (which has a very low SLD) was previously observed in the deposited films, hence decreasing the overall SLD 25 .…”

“…The thicknesses are in good agreement with the XRR data (the increase in oxide thickness is attributed to the UV/ozone cleaning prior to NR measurements) and the SLD values are similar to those seen previously 25 , with the oxide SLD consistent with that expected for a mixture of iron and chromium oxides (values for pure Cr 2 O 3 and Fe 2 O 3 would be 5.11 and 7.17 x 10 -6 Å -2, respectively). While the SLD of 316L stainless steel should theoretically be closer to 7 x 10 -6 Å -2 , an increased amount of Mn (which has a very low SLD) was previously observed in the deposited films, hence decreasing the overall SLD 25 . Up to and including 3000 ppm BSA, a simple Langmuir model was sufficient to fit the data; however, the data point at 30,000 ppm did not fit this trend.…”

“…The NR data are modelled to give a profile of the scattering length density (SLD) as a function of the distance along the surface normal, z. SLD values of the materials of interest in this work are given in Table 1. We have previously demonstrated that by using an electron-beam deposition technique, a film of stainless steel can be successfully deposited onto a silicon substrate to provide a model stainless steel surface that is suitable for NR experiments 25 . Here, we extend the technique to a more complex protein system.…”

Neutron Reflectometry for Studying Corrosion and Corrosion Inhibition

“…This has been successfully applied to a range of materials, such as iron [65,73,74], copper [10], titanium [41], nickel [75], chromium [76], zirconium [77], ITO [78], stainless steel [76] and various other alloys [79][80][81][82]. Care should be taken during deposition and subsequent handling to ensure that the final surface represents the material desired: for example to what extent it oxidises upon exposure to air.…”

“…The direct study of steel alloys is slightly more challenging due to the necessity of preparing thin (to ensure neutron transmission) and very flat films, although recent work has demonstrated that representative stainless steel films can be prepared using electron-beam deposition at low pressures [76].…”