The influence of albumin on the anodic dissolution of chromium present in UNS S31254 stainless steel in chloride environment

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Colloids and Surfaces A: Physicochem. Eng. Aspects 317 (2008) 760–763

Brief note

The influence of albumin on the anodic dissolution of chromium present in UNS S31254 stainless steel in chloride environment M.L.C.A. Afonso a,∗ , R.F.V. Villamil Jaimes a,b,c , E.P.G. Arˆeas a , M.R. Capri d , E. Oliveira a , S.M.L. Agostinho a a

Departamento de Qu´ımica Fundamental, Instituto de Qu´ımica, Universidade de S˜ao Paulo Avenida Professor Lineu Prestes, 748, CEP: 05508-900 S˜ao Paulo, SP, Brazil b Faculdade de Ciˆ encias, Funda¸ca˜ o Instituto Tecnol´ogico de Osasco, Avenida Ang´elica, 100, Jardim Nova Granada, 06132-380 Osasco, S˜ao Paulo, Brazil c Universidade do Grande ABC, UniABC, Avenida Industrial 3.330, Santo Andr´ e, S˜ao Paulo, Brazil d Escola de Engenharia de Lorena - Universidade de S˜ ao Paulo, Itajub´a-Lorena, Km 74,5, Caixa Postal 116, CEP: 12600-970 Lorena, SP, Brazil Received 16 August 2007; received in revised form 6 November 2007; accepted 14 November 2007 Available online 22 November 2007

Abstract The influence of bovine serum albumin (BSA) on the anodic dissolution of chromium present in UNS S31254 stainless steel (SS) in 0.15 mol L−1 NaCl at 37.0 ± 0.5 ◦ C has been studied, using anodic potentiostatic polarization curves and optical emission spectroscopy. Electrochemical results have shown that BSA has little effect on the transpassivation potential (ET ) and on the passivation current density values. However on the passivation range, BSA diminishes the intensity of the anodic wave seen at about E = 750 mV versus SCE attributed to Cr(III)/Cr(VI) oxidation. Optical emission spectroscopy results have shown that BSA prevents the anodic dissolution of chromium to occur and minimizes iron dissolution above the transpassivation potential (E = 1160 mV versus SCE). © 2007 Elsevier B.V. All rights reserved. Keywords: Bovine serum albumin; Austenitic stainless steel; UNS S31254; Corrosion; Orthopedic implants

1. Introduction Austenitic stainless steels are frequently used as internal fixation devices in orthopedic implants. Regardless of the lower corrosion resistance when compared to titanium and titanium alloys [1–3] stainless steels exhibit excellent mechanical properties [4]. These properties combined with the low cost and low osteointegration make the stainless steel a material of choice to be used in temporary internal implants [4]. For these reasons new steels are currently being studied [5–8]. This new generation of steels has a high corrosion resistance due in part to its high chromium content, principal element present as passivating oxide film. Studies performed in vivo such as, analysis of implants and tissues removed from patients and laboratory animals, have shown that the corrosion rates are lower when compared to in

∗

Corresponding author. Tel.: +55 11 30912157; fax: +55 11 38155579. E-mail address: [email protected] (M.L.C.A. Afonso).

0927-7757/$ – see front matter © 2007 Elsevier B.V. All rights reserved. doi:10.1016/j.colsurfa.2007.11.014

vitro saline solutions ([9] and references therein). Some authors have suggested that this behavior might be due to a layer of adsorbed proteins on the implant surface, since it is known that such a layer is formed immediately after metal immersion in human plasma [10–21]. Albumin is the most abundant protein in blood plasma. Bovine serum albumin (BSA) is similar in composition to human serum albumin (Table 1) particularly in the number of acidic terminal groups (aspartic and glutamic acids) [22]. Accordingly to the literature these groups are responsible for proteins binding to metallic surfaces, which explains therefore the significant amount of works in the literature that use BSA to simulate human fluids [9–21,23–27]. Some authors seem to agree that BSA diminishes the extent of corrosion of stainless steels and titanium alloys [9,21]. Other authors have reported that BSA promotes the dissolution of these alloys by forming stable complexes with the metallic components of the alloys [16,18]. Cosman et al. [28] compared the thermodynamic values of the adsorption properties of BSA onto several metallic surfaces and concluded that BSA exhibits different affinities with different metallic materi-

M.L.C.A. Afonso et al. / Colloids and Surfaces A: Physicochem. Eng. Aspects 317 (2008) 760–763

761

Table 1 Chemical composition of UNS S31254 stainless steel (wt%) Sample

ASTM (UNS designation)

C

Mn

P

S

Si

Cr

Ni

Mo

N

Cu

Nb

UNS S31254

A 276–00 (S 31254)

0.016

0.56

0.018

0.004

0.52

19.40

17.70

6.26

0.208

0.75

–

als. Wataha et al. [19] alerted to the importance to evaluate and to understand the response of each type of alloy since each alloy originates a specific answer. UNS S31254 stainless steel (55.31% Fe, 20% Cr, 17.7% Ni, 0.56% Mn and 0.21% N) was initially developed with the purpose to be used in concentrated chloride media. Nevertheless, the scientific interest in its investigation is due to several reasons: high pitting corrosion resistance in chloride media [29–31], good biocompability as shown by experiments in vivo performed in dogs [32], high content of chromium and electrochemical behavior comparable to the one observed for ISO 5832-9 stainless steel, recently used in orthopedic implants [33]. The aim of this work is to study the influence of bovine serum albumin (2, 2 × 10, 2 × 102 , 2 × 103 , 2 × 104 ) mg L−1 on the chromium dissolution present in UNS S31254 stainless steel in 0.15 mol L−1 NaCl aqueous solutions at (37.0 ± 0.5) ◦ C, using potentiostatic linear voltammetry and optical emission spectroscopy as techniques.

The optical emission experiments were carried out after a 30 min attack at E = 1160 mV versus SCE to the UNS S31254 surfaces immersed in 0.15 mol L−1 NaCl without and with 2 × 104 mg L−1 BSA. This potential value corresponds to the beginning of transpassivation region, where there is not selective oxidation of the alloy in the absence of BSA, as indicated from the optical emission experiments. After this procedure the solutions were taken for analysis. Iron and chromium solutions used for the construction of the standard curves were prepared from 1000 mg L−1 solutions (Tritisol Merck) in 0.15 mol L−1 NaCl. An ICP OES Spectro model Spectroflame Modula, sequential spectrometer was used. All the experiments were performed in triplicate with naturally aerated solutions at (37.0 ± 0.5)◦ C. The chemical composition of UNS S31254 stainless steel is presented in Table 2. 3. Results and discussion 3.1. Electrochemical experiments

2. Experimental procedure The stainless steel working electrodes were taken out from the core regions of the bars and had an area of 0.29 cm2 . A cylindrical polytetrafluoroethylene (PTFE) sleeve was fitted on the steel disk. A concentric brass rod was coupled to the steel and PTFE. The electrodes were prepared by polishing with successively finer grades of emery papers of 120, 400 and 600 mesh and then thoroughly rinsed with distilled water and ethanol and air dried prior to the experiments. Serum albumin (96% Sigma–Aldrich) and the electrolyte, NaCl (99.5% Merck) were used without further purification. All the solutions [(2, 2 × 10, 2 × 102 , 2 × 103 , 2 × 104 ) mg L−1 albumin and 0.15 mol L−1 NaCl] were prepared with doubly distilled water. Solutions were prepared within a day to minimize possible denaturation. The auxiliary electrode consisted of a platinum foil and it was cleaned with acid and flamed just before each experiment. The saturated calomel electrode (SCE) was used as reference electrode. A computer controlled EG&G PAR 273A potentiostat/galvanostat was used in the electrochemical measurements. Prior to each experiment, the electrodes were immersed in the electrolytes with and without protein, until the attainment of the stationary open circuit potential, corrosion potential (Ecorr ). The linear potentiostatic voltammetric experiments were performed after the attainment of a constant current at each potential application, starting from the open circuit potential in the anodic direction till the breakdown of the passivating film. It was assumed as criterium that this potential is reached when the current density equals to 10 ␮A cm2 .

Table 2 shows Ecorr values obtained in the absence and in the presence of BSA for UNS S31254 stainless steel. It is interesting to note that the significant effect of BSA on the corrosion potential is only seen from 2 × 10 mg L−1 to 2 × 103 mg L−1 with BSA shifting Ecorr to more negative potentials. At the lower and the higher concentrations (2 mg L−1 and 2 × 104 mg L−1 , respectively) the value of the referred parameter is similar to the one obtained in the medium without BSA. This simple technique allows to suggest that at lower concentrations, the complexing effect of albumin is predominant favoring metal dissolution and at higher concentrations the predominant effect is the adsorption of the protein on the surface; this is possible taking into account that the alloy is passivated and ion concentration on its surface is low. The anodic polarization potentiostatic curves shown in Fig. 1 reveal that UNS S31254 stainless steel exhibits a wide range of passivation, with no evidence of localized corrosion until the transpassivation potential, ET . As referred in the experTable 2 Effect of BSA concentration on the corrosion potentials (Ecorr ), transpassivation potentials (ET ) and passivation current densities (jpass ) of UNS S31254 stainless steel in 0.15 mol L−1 NaCl CBSA (mg L−1 ) 0 2 2 × 10 2 × 102 2 × 103 2 × 104

Ecorr (mV) −20 −20 −190 −145 −145 −20

± ± ± ± ± ±

7 14 14 15 8 1

ET (mV) 940 910 990 920 890 1010

± ± ± ± ± ±

1 4 1 4 7 1

jpass (E = 200 mV) (␮A cm−2 ) 1.5 1.6 1.2 1.3 1.4 1.0

± ± ± ± ± ±

0.1 0.3 0.1 0.1 0.8 0.1

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M.L.C.A. Afonso et al. / Colloids and Surfaces A: Physicochem. Eng. Aspects 317 (2008) 760–763 Table 3 Amount (mg L−1 ) and standard deviations of the elements Fe and Cr detected by ICP OES in the leaching solution of UNS S31254 stainless steel after the application of E = 1160 mV vs. ECS during 30 min in 0.15 mol L−1 NaCl without and with 2 × 104 mg L−1 BSA Elements

Fe Cr

Amount of metals (mg L−1 ) Without BSA

With BSA

0.44 ± 0.03 0.17 ± 0.03

0.23 ± 0.02 (<0.0084)

θ = 37.0 ± 0.5 ◦ C (n = 3). Note: The values in brackets are referred to the quantification limit, i.e., 10× the standard deviation of the blank solutions expressed as concentration.

Fig. 1. Linear voltammograms recorded in 0.15 mol L−1 NaCl, starting from the open circuit potential of UNS S31254 stainless steel in the absence and in the presence of (2, 2 × 10, 2 × 102 , 2 × 103 and 2 × 104 ) mg L−1 albumin. Each value of current was recorded after waiting 3 min for each potential applied. (Inset) j vs. E (E: 400–1000 mV; j: 0–10 ␮A cm−2 ). () without BSA; (䊉) BSA 2 mg L−1 ; ()BSA 2 × 10 mg L−1 ; (×) BSA 2 × 102 mg L−1 ; () 2 × 103 mg L−1 ; (*) 2 × 104 mg L−1 .

imental part this potential is defined, in the present work, as the potential where current density equals to 10 ␮A cm2 . This behavior is similar to the one observed for ISO 5832-9 stainless steel, which belongs to the last generation of stainless steels used in orthopedic implants [32]. The sharp current increase, at about 1000 mV can be assigned to the oxidation of water [28,34,35]. This result is an indicative of the absence of pitting corrosion. As can be seen in Table 2, BSA has little or none effect on both the ET and current density values obtained at a fixed potential (200 mV versus SCE) in the concentration range studied. Passivating current density values, of about 1 ␮A cm−2 confirm that UNS S31254 SS is passivated in the absence and in the presence of BSA. In order to reach to a better understanding of the chromium dissolution in UNS S31254 stainless steel/BSA, the voltammetric curves were amplified in the passivation region (inset of Fig. 1). The slight current increase seen at about 750 mV versus SCE can be ascribed to changes occurring in the passive oxide film, namely oxidation of Cr2 O3 and/or CrOOH to the soluble species CrO4 2− [34]. The effect of albumin can be observed in this region: the intensity of the anodic wave is decreased with the presence of BSA in the electrolyte. This effect is more pronounced at the higher concentration of BSA studied (2 × 104 mg L−1 ) when the passivating effect is higher than the complexing effect. However, low current density values show that the sample remains in the passive state until the oxidation of water [34].

versus SCE) to the UNS S31254 surfaces immersed in 0.15 mol L−1 NaCl without and with 2 × 104 mg L−1 BSA media. This potential is higher than ET in order to permit the anodic dissolution of all the components of the stainless steel. The results are shown in Table 3. In the absence of protein the species iron and chromium are dissolved at a 0.17/0.44 = 0.39 ratio while in the stainless steel structure this relation (see Table 1) is 20/55 = 0.36. This result suggests that the dissolution of chromium is not selective. As it can be seen only iron was detected in the leached medium with BSA (half of the amount found in the medium without albumin). The absence of chromium suggests the inhibitive effect of the protein on the anodic dissolution of these species. These results are in accordance with the ones obtained by the electrochemical results, where it was seen that the anodic wave assigned to chromium transpassivation disappears in the presence of BSA (2 × 104 mg L−1 ) in the same concentration studied by this technique (OES). 4. Conclusions The results obtained in this work permit to take the following conclusions: In the absence of protein the dissolution of chromium is not selective at potentials higher than ET . BSA diminishes the intensity of the anodic wave seen at about E = 750 mV versus SCE corresponding to Cr(III)/Cr(VI) oxidation. BSA prevents the anodic dissolution of chromium to occur and minimizes iron dissolution on the transpassivation potential (E = 1160 mV). Acknowledgements The authors would like to thank Fundac¸a˜ o de Amparo a` Pesquisa do Estado de S˜ao Paulo (FAPESP) for the financial support and to the Villares Metals industry for the samples of stainless steel.

3.2. Optical emission experiments (OES) In order to verify the hypothesis that the passivating effect of BSA is predominant at higher concentrations optical emission experiments were performed after a 30 min attack (E = 1160 mV

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