Materials Science and Engineering C 33 (2013) 446–452

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Effect of the La alloying addition on the antibacterial capability of 316L stainless steel J.P. Yuan a, b, W. Li a,⁎, C. Wang b a b

Material science and engineering department, Jinan University, Guangzhou 510632, China Jewelry Institute of Guangzhou Panyu Polytechnic, Guangzhou 511483, China

a r t i c l e

i n f o

Article history: Received 8 July 2012 Received in revised form 16 August 2012 Accepted 17 September 2012 Available online 24 September 2012 Keywords: La 316L stainless steel Corrosion resistance Antibacterial capability Processability

a b s t r a c t 316L stainless steel is widely used for fashion jewelry but it can carry a large number of bacteria and cause the potential risk of infection since it has no antimicrobial ability. In this paper, La is used as an alloying addition. The antibacterial capability, corrosion resistance and processability of the La-modified 316L are investigated by microscopic observation, thin-film adhering quantitative bacteriostasis, electrochemical measurement and mechanical test. The investigations reveal that the La-containing 316L exhibits the Hormesis effect against Staphylococcus aureus ATCC 25923 and Escherichia coli DH5α, 0.05 wt.% La stimulates their growth, as La increases, the modified 316L exhibits the improved antibacterial effect. The more amount of La is added, the better antibacterial ability is achieved, and 0.42 wt.% La shows excellent antibacterial efficacy. No more than 0.11 wt.% La addition improves slightly the corrosion resistance in artificial sweat and has no observable impact on the processability of 316L, while a larger La content degrades them. Therefore, the addition of La alone in 316L is difficult to obtain the optimal combination of corrosion resistance, antibacterial capability and processability. In spite of that, 0.15 wt.% La around is inferred to be the trade-off for the best overall performance. © 2012 Elsevier B.V. All rights reserved.

1. Introduction 316L stainless steel is one of the main materials for fashion jewelry but it has no antibacterial efficacy [1]. Since jewelries often carry a large number of bacteria and give rise to the risk of infection [2,3], it is important to improve the 316L's antimicrobial performance. Antibacterial stainless steel has become one research hotspot in biomaterial field and the alloying method is an important approach. So far, most of the work has been focused on Cu-containing stainless steel, by adding 1–5 wt.% copper into stainless steel and taking special heat treatment, ε-Cu phase could precipitate in the matrix [4–7]. When the treated materials contact with bacteria, Cu ions would release from ε-Cu phase and gave play to antibacterial function [8]. The antibacterial effect depended on the antibacterial phase's quantity, shape and size, in order to acquire good antibacterial performance, the precipitated ε-Cu phase should not be lower than 0.5% [9]. On the whole, Cu-containing antibacterial steels had to be kept at 700–900 °C for a long time since the precipitation of ε-Cu phase was controlled by the diffusion mechanism [10,11]. This complicated the technological process and increased production cost, and the long-time preservation at the sensitized interval would degrade the material's corrosion resistance more or less. Silver is an excellent antibacterial agent and it has also been tried for antibacterial stainless steel. Yokota et al. [12] found that silver-containing stainless steel could acquire excellent antibacterial properties by adding vanadium, restricting ⁎ Corresponding author. Tel./fax: +86 20 85222167. E-mail address: [email protected] (W. Li). 0928-4931/$ – see front matter © 2012 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.msec.2012.09.012

sulphur content and controlling speed, Liao et al. [13] reported that the microstructure of 304 stainless steel consisted of α + γ + Ag-riched phase, and the modified steel showed excellent antibacterial effect against Escherichia coli. Huang et al. [14] also reported that ≥0.2 wt.% Ag in AISI 316L alloy would have excellent antibacterial properties against both Staphylococcus aureus and E. coli. However, silver is quite prone to form severe segregation since its solubility in stainless steel is very limited, and it will markedly increase the cost. As is known, the compounds or of rare earth have antibacterial, sterilization and anti-inflammatory effect [15–17], and Cerium has been tried as an antibacterial agent in stainless steel. Jing et al. [18] reported that 0.05–4.5 wt.% Ce-bearing 304 stainless steel could show excellent antibacterial effect with no need for special heat treatment. Wang et al. [19] reported that the bactericidal activity of Cerium-doped TiO2 film on 304 stainless steel was better than pure TiO2 film. However, there is no further report about Cerium-bearing stainless steel, and there is no any report about La as an antibacterial agent in stainless steel up till now. Therefore, the effects of La on the antibacterial property, corrosion resistance and processability of 316L stainless steel were investigated in this paper.

2. Experimental 2.1. Materials preparation 30 wt.% La\Fe master alloy was prefabricated with pure La and pure iron by using a WK-vaccum arc furnace, then commercial 316L

J.P. Yuan et al. / Materials Science and Engineering C 33 (2013) 446–452 Table 1 The actual amounts of La in the samples, wt.%. Sample No.

Amount of La

La0 La1 La2 La3 La4

– 0.05 0.11 0.19 0.42

stainless steel strips and La\Fe alloy were used to prepare the testing samples, after the charging materials were melted uniformly, small button ingots were made in water-cooled copper crucible. The actual amounts of La in the ingots were determined by using Thermo ARL Quant' X spectrum analyzer and were listed in Table 1. The ingots were hot forged into sheets of about 2 mm thick and were solid solution treated at 1050 °C for 30 min. Dics (ϕ25 mm) or square (5 × 5 mm) specimens were machined from them, polished with 1200# sand papers and cleaned with an ultrasound cleaner. 2.2. Experimental methods 2.2.1. Antibacterial experiment The samples were sterilized in a 121 °C autoclave for 40 min and then sterilized once again under an ultraviolet sterilamp for 30 min. Bacterial colony of S. aureus ATCC 25923 and E. coli DH5α (taken from College of life science, Jinan University) was inoculated respectively into a 15 ml nutrient broth (produced by MDBio Inc., which contained peptone 10.0 g/l, NaCl 5.0 g/l and beef extract 5.0 g/l) as the test strain. The broth was shaken in wave bed for 20 h at 37 °C. The suspension of bacteria was diluted to 1 × 10 6 CFU/ml with a PBS buffer solution (KH2PO4 0.27 g/l, Na2HPO4 1.42 g/l, NaCl 8 g/l, KCl 0.2 g/l, Twain-20 0.05 ml/l, PH7.4). Inhibition zone test [20] and thin-film adhering quantitative bacteriostasis test [21] were used to examine antibacterial properties. In inhibition zone test, 500 μl of the diluted suspension was evenly smeared on agar plate, and sterilized disc samples were closely stuck on the surface of the plate respectively. After cultured at 37 °C for 24 h, the inhibition zone was directly observed. In thin-film adhering quantitative bacteriostasis test, 50 μl of the diluent was dropped on each sterilized disc sample. The samples were covered with a sterile thin film for the bacteria to spread over uniformly and kept in a test chamber for 24 h at the constant temperature of 37 °C and in the relative humidity of over 90%. Each sample was then

Fig. 1. The inhibition zone of sample La4 against Staphylococcus aureus.

Fig. 2. The antibacterial effect against Staphylococcus aureus of each sample.

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Table 2 The sterilization rates against Staphylococcus aureus and Escherichia coli, %. Sample No.

Average antibacterial rate against Staphylococcus aureus

average antibacterial rate against Escherichia coli

La0 La1 La2 La3 La4

– −15 54 78 99.6

– −9 62 89 >99.9

washed thoroughly with the PBS buffer solution and the solution was diluted in multiple times. The agar plate method was used to culture and count live bacteria. All experiments were performed three times. The relative sterilizing rate of the bacteria was calculated: Rð% Þ ¼ ðC−AÞ=C  100%

ð1Þ

Where R was the relative sterilizing rate, C was the mean number of bacteria on the control sample, and A was the mean number of bacteria on the analyzed sample. Following the antibacterial experiment, the samples were cleaned in de-ionized water under ultrasonic vibration for 5 min, Hitachi S3400N SEM and Bruker Quanta'X 200 EDS were used to analyze the surface topography and micro-zone composition. To determine the antibacterial activity of La-containing stainless steel, Sample La4 was also examined by thin-film adhering quantitative bacteriostasis test but the acting time with suspensions of E. coli was every 3 h. 2.2.2. Electrochemical experiment The potentiodynamic polarization analysis was carried out with a LK2005 electrochemical workstation. Three-electroded system was used, the sample surface as the working electrode, the saturated calomel electrode (SCE) as the reference electrode, and the platinum foil as the counter electrode, respectively. The electrolyte was artificial sweat, which consisted of 1.00 g/l of urea, 5.00 g/l of sodium chloride, 940 ml/l of lactic acid. It had a pH value of 6.50. After immersed in artificial sweat for 10 min to attain a stable open circuit potential, the samples were examined in the potential range of − 1000 to 1000 mV and at a scan rate of 5 mV/s. To study the effects of La and microbial environment on corrosion resistance, two groups of samples were prepared. Group 1 was in the original state. Group 2 was soaked in the 1 × 10 6 CFU/ml suspension of S. aureus, kept at 37 °C for 24 h and ultrasonic cleaned in de-ionized water for 5 min. Following that, their polarization curves of both groups were measured. 3. Results and analysis 3.1. The effect of La on antibacterial property of 316L Fig. 1 shows the inhibition zone test results, as can be seen, the inhibition zone of sample La4 to S. aureus on ordinary nutrition agar plate was just only recognizable and no obvious antimicrobial efficacy was showed. Fig. 2 shows the micrographs of S. aureus on the agar plates for the tested samples. Through counting the bacterial colony number of each antibacterial test, the average antibacterial rate against S. aureus and E. coli are calculated and listed in Table 2. As can be seen in Fig. 2 and Table 2, there are distinct differences in antibacterial ability for the test samples with different La contents. The modified 316L stainless steel does not exhibit any improvement in antibacterial ability when the La content is 0.05 wt.% (Sample La1). Instead, the La increases the growth rate of S. aureus and E. coli to some degree. As the La content increases, the antibacterial efficacy of the modified 316L steel gradually increases. The higher the La

Fig. 3. The surface topographies after the antibacterial test against Staphylococcus aureus.

J.P. Yuan et al. / Materials Science and Engineering C 33 (2013) 446–452

Fig. 4. The micro-zone topography of La4 at high magnification.

content, the better the antibacterial efficacy. When La content is close to 0.42 wt.% (Sample La4), the average sterilization rates against both kinds of bacteria are more than 99%, indicating the excellent antibacterial efficacy. Therefore, the results demonstrate that the La alloying addition enables the stainless steels to develop the Hormesis effect [22] against S. aureus and E. coli. After cleaned in de-ionized water under ultrasonic vibration, the surface topographies of the test samples against S. aureus are showed in Fig. 3. Again, there are distinct differences between the samples with different La contents. No distinct sediments are observed on Samples La0 and La1. However, both the samples contain obvious corrosion pits and the number of pits on Sample La1 is more than La0. In contrast, there are large areas of sediments on Samples La3 and La4, with no obvious pits observed. Two zones are selected randomly from Sample La4 for composition analysis by EDS, as shown in Fig. 4. Zone 1 in the area has no sediment while Zone 2 does. The analysis results are summarized in Table 3. It is seen that there are large O contents at both zones, but the amounts of P, N, S, and Ca in Zone 2 are much more than those in Zone 1. Since these elements are the basic constituents of biological tissue in bacteria, it is inferred that these sediments are actually the debris of killed bacteria. Meanwhile, there is a larger amount of La in Zone 2. It may imply that La has something to do with the death of bacteria. Fig. 5 shows the antibacterial efficacy of Sample La4 after it contacts with suspension of E. coli for various times. When the acting time is less than 3 h, no obvious antibacterial effect is observed. As the acting time extends, the antibacterial effect improves rapidly, when the acting time reaches 12 h, the antibacterial rate is over 99%. It demonstrates that La-containing 316L stainless steel is a mild antibacterial material by comparing with other common inorganic antibiosis, it needs a certain time to take effect. Comparing with the results of two antibacterial test methods, it is seen that Sample La4 does not show rudimentary antibacterial property in the inhibition zone test, while it displays excellent antibacterial efficacy in thin-film adhering test. It indicates that only through direct contacting with bacteria can La-containing stainless steel really realize antibacterial efficacy. As is known, 316L stainless steel can form compact passive film, which is the root cause of its excellent corrosion

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resistance. While in La-containing stainless steel, it is inevitable to form La-riched phases when La content exceeds its limit solid solubility (see Fig. 9 later), these La-riched phases may disperse randomly in the base of stainless steel, including embedded in the passive film. When stainless steel contacts with the suspension of bacteria, Bacteria adhere to the surface in a short time and the adherence is a dynamic process [23,24]. The metabolism of bacteria forms concentration cells on the surface of stainless steel, promoting corrosion [25]. Because the 316L stainless steel itself has no antimicrobial efficacy, no debris from killed bacteria deposit on its surface. When the La-modified 316L steel contacts the suspension of bacteria, it releases La ions into the solution, as shown in the schematic diagram (Fig. 6). The cell wall and membrane of S. aureus are negatively charged. The electropositive La ions are attracted to the cell wall due to the electrostatic attraction [26,27]. According to the basic toxicology theories of rare earth [28,29], it is supposed that these La ions would play the role of promoting or suppressing the growth of S. aureus. As is known, the cell wall of S. aureus consists of peptidoglycan and teichoic acid mainly. La ions can react with their organic functional groups, leading to the change of the conformation [30]. The concentration of La ions from Sample La1 is very low. The incomplete reaction makes the cell wall flabby and leaves certain gaps, which is beneficial for nutrients to penetrate into bacteria through the wall. As a result, the metabolism and growth of bacteria is promoted (see La1 in Table 2). With the increasing of the La content, the concentration of La ions is increased. The reaction between La ions and the organic functional groups of peptidoglycan or teichoic acid happens more completely. It changes the conformation of the cell wall thoroughly and forms the channel, resulting in extravasation of the inclusions in bacteria [31–33]. Meanwhile, the La ions can hinder the normal physiological metabolism of bacteria by interacting with DNA, enzyme, protein or other biological molecules, leading to the loss of Ca ions of bacteria by replacing them [34,35], as shown in Table 3. Finally, bacteria are killed. As can also be seen in Table 2 that the average antibacterial rates against E. coli are a little higher than against S. aureus on the whole, this phenomenon can be understood from the difference of the cell walls between these two strains. E. coli belongs to Gram-positive bacteria, its cell wall mainly consists of peptidoglycan and the wall thickness is thin, while S. aureus belongs to Gram-negative bacteria, its cell wall consists of peptidoglycan and teichoic acid, and the wall thickness is relatively thicker, which makes the mesh structure of peptidoglycan in S. aureus is more compact than that in E. coli [36,37]. It demonstrates that S. aureus is more difficult to be killed than E. coli, and therefore the antibacterial rate against S. aureus is a little lower than that against E. coli under the same conditions. 3.2. The effect of La on corrosion resistance of 316L Fig. 7 is the polarization curves of the tested samples in artificial sweat, where the suffix of 1 represents the result obtained before immersing in suspension of bacteria, and the suffix of 2 represents one after immersing. The self corrosion potential and pitting potential are calculated according to their respective curves, as shown in Fig. 8, where SCP and PP represents self corrosion potential and pitting potential, respectively. When comparing the corrosion potentials before immersing in the suspension of bacteria, it is found that the self corrosion potentials of Samples La1 and La2 are close to the value of La0 (316L without La) while their pitting potentials are slightly higher than the La0's. This

Table 3 The micro-zone compositions of La4 after the antibacterial test, wt.%. Micro-zone

C

N

O

P

S

Si

Ca

Cr

Mn

Fe

Ni

Mo

La

1 2

0 0.04

0.27 1.13

22.54 23.82

0.03 1.05

0.03 0.16

0.44 0.3

0 0.11

11.9 11.08

0.31 0.92

56.27 50.15

6.38 6.92

1.67 1.28

0.16 3.04

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Fig. 5. The relationship between antibacterial rate against Escherichia coli and acting time.

indicates that a small La addition is good for improving the corrosion resistance of 316L. With the increasing amount of La, both of the potentials continually decrease. When La content reaches the La level of La4, the potentials become significantly lower than La0's and the corrosion currents are obviously higher. This indicates that, when the amount of La exceeds a certain value, it deteriorates the corrosion resistance of 316L in a non microbial environment. The higher the La content, the worse the corrosion resistance. After immersing in the suspension of S. aureus for 24 h, the potential of each sample changes in a different way. Both the self corrosion potentials and pitting potentials of La0, La1 and La2 decrease and the reduction extent of La1 is the largest, La0's follows, and La2's is smaller. By contrast, the pitting potential of La3 increases to a certain degree, while both the potentials of La4 improve obviously. This indicates that a higher content of La is beneficial for the microbiological corrosion resistance. It is derived from Fig. 8 that the cusp in the varying trend of pitting potential happens to about 0.14 wt.% La before and after immersing in the suspension of bacteria, while the turning point for self corrosion potential occurs at about 0.31 wt.% La. This phenomenon is attributed to the synergistic effect of La and microbial environment. As aforementioned, when the sample is soaked in the suspension of S. aureus, bacteria adhere to its surface. Their metabolism activity can modify the micro environment on the sample surface, which lowers the corrosion potentials, affects the stability of the passive film and promotes microbiological corrosion accordingly [38–41]. When a sample has the antimicrobial effect, the adhered bacteria can be killed or suppressed and sedimentary film forms on the surface. As a result, microbiological corrosion can be hindered. After ultrasonic cleaning, live bacteria are desorbed. If those solid sediments of killed bacteria continue to cover the sample surface as a barrier, the corrosion potentials of La3 and La4 will increase significantly in the electrochemical test. 3.3. The effect of La on processability of 316L stainless steel

Fig. 7. The polarization curves in artificial sweat.

that La is prone to segregate if the amount exceeds a certain value. Then, an increase in the La content becomes harmful to corrosion resistance and processability. In fact, under the same hot-forging condition, Samples La0, La1 and La2 can be processed smoothly without cracking. By comparison, Sample La3 is observed to have small cracks in the edge while Sample La4 suffers serious crack, as shown in Fig. 10. Therefore, from the viewpoint of processability, the La content in 316L should be controlled below 0.19 wt.%. Otherwise, the processability will deteriorate severely. By considering the comprehensive influences of La on the corrosion resistance, antibacterial efficacy and processability of 316L, it is inferred that the addition of 0.15 wt.% La around is an optimal trade-off. 4. Conclusions (1) 0.05 wt.% of La addition can slightly improve the corrosion resistance of 316L stainless steel in artificial sweat. With the further increasing of La content, the corrosion resistance deteriorates continually. (2) The original 316L or the 0.05 wt.% La-containing 316L suffer obvious corrosion in the 1 × 106 CFU/ml suspension of S. aureus and E. coli for at 37 °C, 24 h while the 316L alloyed with 0.11 wt.% or more La has an improved microbiological corrosion resistance.

Fig. 9 shows the distribution of La in Samples La1 to La4, it is seen that the distribution of La is uniform in Sample La1 and La2 on the whole. By contrast, small clusters of La are observed in Sample La3 while the segregation in Sample La4 is quite severe. This indicates

Fig. 6. The antibacterial schematic diagram of La-containing stainless steel.

Fig. 8. The relationship between La content and corrosion potential.

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Fig. 10. Serious cracks formed during hot-forging in sample La4.

(3) The La-modified 316L exhibits the Hormesis effect against S. aureus and E. coli. The 316L with 0.05 wt.% La stimulates the growth of S. aureus and E. coli. With a further increase in the La content, the modified 316L demonstrates the antibiotic effect, the higher the amount of La, the better the antibacterial performance. When the La content is close to about 0.42 wt.%, the sterilization rate exceeds 99%. (4) A low content of La had no observable impact on the processability of 316L while the large La amount is harmful. The deterioration degree increases with the amount of La. (5) As a whole, when 316L is modified with La alone, it is difficult to obtain the optimal combination of corrosion resistance, antibacterial performance and processability simultaneously. The addition of 0.15 wt.% La around is inferred to be the best trade-off. Acknowledgements The authors would like to thank Qingzhou Xu and Haiming Hu for their valuable assistance in the revision of the manuscript. References

Fig. 9. The distribution of La in Sample La1 to La4.

[1] J.P. Yuan, W. Li, C. Wang, C.Y. Ma, Adv. Mater. Res. 399-401 (2011) 1540–1546. [2] I. Yildirim, M. Ceyhan, A.B. Cengiz, A. Bagdat, C. Barin, T. Kutluk, D. Gur, Int. J. Nurs. Stud. 45 (2008) 1572–1576. [3] M.D. Wongworawat, S.G. Jones, Infect. Control Hosp. Epidemiol. 28 (2007) 351–353. [4] H.W. Chai, L. Guo, X.T. Wang, Y.P. Fu, J.L. Guan, L.L. Tan, L. Ren, K. Yang, J. Mater. Sci. Mater. Med. 22 (2011) 2525–2535. [5] J. Kielemoes, W. Verstraete, Lett. Appl. Microbiol. 33 (2001) 148–152. [6] I.T. Hong, C.H. Koo, Mater. Sci. Eng. A 393 (2005) 213–222. [7] L. Ren, K. Yang, L. Guo, H.W. Chai, Mat. Sci. Eng. C-Bio. S 32 (2012) 1204–1209. [8] L. Nan, K. Yang, J. Mater. Sci. Technol. 26 (2010) 941–944. [9] Z.X. Zhang. Ph. D. Thesis, School of Material Science and Engineering, Shanghai JiaoTong University, 2007. (in Chinese). [10] Z.X. Zhang, G. Lin, Z. Xu, J. Mater. Sci. Technol. 24 (2008) 775–780. [11] L. Ren, L. Nan, K. Yang, Mater. Des. 32 (2011) 2374–2379. [12] T. Yokota, M. Tochibara, M. Ohta, in: Silver dispersed stainless steel with antibacterial property[R], Kawasaki steel technical report, Tokyo, 46, 2002, pp. 37–41. [13] K.H. Liao, K.L. Ou, H.C. Cheng, C.T. Lin, P.W. Peng, Appl. Surf. Sci. 256 (2010) 3642–3646. [14] C.F. Huang, H.J. Chiang, W.C. Lan, H.H. Chou, K.L. Ou, C.H. Yu, Biofouling 29 (2011) 449–457. [15] F.J. Jing, N. Huang, Y.W. Liu, W. Zhang, X.B. Zhao, R.K. Fu, J.B. Wang, Z.Y. Shao, J.Y. Chen, Y.X. Leng, X.Y. Liu, P.K. Chu, J. Biomed. Mater. Res. A 87 (2008) 1027–1033. [16] P. Liu, Y. Liu, Z.X. Lu, J.C. Zhu, J.X. Dong, D.W. Pang, P. Shen, S.S. Qu, J. Inorg. Biochem. 98 (2004) 68–72. [17] D. De, S.M. Mandal, S.S. Gauri, S. Samiran, R. Bhattacharya, S. Ram, S.K. Roy, J. Biomed. Nanotechnol. 6 (2010) 138–144. [18] H.M. Jing, X.Q. Wu, Y.Q. Liu, M.Q. LÜ, K. Yang, Z.M. Yao, W. Ke, J. Mater. Sci. 42 (2007) 5118–5122. [19] H.F. Wang, Z.Q. Wang, H.X. Hong, Y.S. Yin, Mater. Chem. Phys. 124 (2010) 791–794. [20] DIN 58940-9-2007, Medical microbiology-Susceptibility testing of microbial pathogens to antimicrobial agents-Part 9: Regression line analysis for the correlation of inhibition zone diameter (IZD) and minimum inhibitory concentration (MIC)[S], DIN, Berlin, 2007. published by.

452

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[21] JIS Z2801:2000, Antimicrobial products test for antimicrobial activity and efficacy [S], Japanese Standard Association, Tokyo, 2001. published by. [22] A.R.D. Stebbing, Sci. Total. Environ. 22 (1982) 213–234. [23] P.M. Stanley, Can. J. Microbiol. 29 (1983) 1493–1499. [24] M. Katsikogianni, Y.F. Missirlis, Eur. Cells Mater. 8 (2004) 37–57. [25] I.B. Beech, J. Sunner, Curr. Opin. Biotechnol. 15 (2004) 181–186. [26] S.H. Chen, M.Q. Lü, J.D. Zhang, J.S. Dong, K. Yang, Acta Metall. Sin. 40 (2004) 314–318. [27] L. Nan, Y.Q. Liu, M.Q. Lü, K. Yang, J. Mater. Sci. Mater. Med. 19 (2008) 3057–3062. [28] D.W. Bruce, B.E. Hietbrink, K.P. DuBois, Toxicol. Appl. Pharmacol. 5 (1963) 750–759. [29] S.K. Kazy, S.K. Das, P. Sar, J. Ind. Microbiol. Biotechnol. 33 (2006) 773–783. [30] G.J. Tortora, B.R. Funke, C.L. Case, Microbiology: An Introduction, Books a la Carte Edition (10th Edition)[M], Benjamin/Cummings Publishing Co, CA, 2009. [31] A.X. Hou, Y. Liu, W.G. Liu, Z. Xue, S.S. Qu, Acta Chim. Sin. 61 (2003) 1382–1387.

[32] A.M. Chen, Q.S. Shi, Y.S. Ouyang, B.Y. Chen, S.Z. Tan, Microbiology 36 (2009) 90–96. [33] P. Liu, H.Y. Xiao, X. Li, C.C. Zhang, Y. Liu, Biol. Trace Elem. Res. 11 (2006) 293–300. [34] T. Dudev, L.Y. Chang, C. Lim, J. Am. Chem. Soc. 127 (2005) 4091–4103. [35] J. Hatae, Jpn. J. Physiol. 32 (1982) 609–625. [36] Q.L. Feng, J. Wu, G.Q. Chen, F.Z. Cui, T.N. Kim, J.O. Kim, J. Biomed. Mater. Res. 52 (2000) 662–668. [37] W. Vollmer, D. Blanot, M.A. De Pedro, FEMS Microbiol. Rev. 32 (2008) 149–167. [38] K. Xu, S.C. Dexter, G.W. Luther, Corrosion 54 (1998) 814–823. [39] M. Geiser, R. Avci, Z. Lewandowski, Int. Biodeterior. Biodegrad. 49 (2002) 235–243. [40] J.J. de Damborenea, A.B. Cristóbal, M.A. Arenas, V. López, A. Conde, Mater. Lett. 61 (2007) 821–823. [41] R.C. Newman, W.P. Wong, A. Garner, Corrosion 42 (1986) 489–491.

Effect of the La alloying addition on the antibacterial capability of 316L stainless steel.

316L stainless steel is widely used for fashion jewelry but it can carry a large number of bacteria and cause the potential risk of infection since it...
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