Tap water is one of the most commonly used water resources in our daily life. However, the increasing water contamination and the health risk caused by pathogenic bacteria, such as Staphylococcus aureus and Escherichia coli have attracted more attention. The mutualism of different pathogenic bacteria may diminish antibacterial effect of antibacterial agents. It was found that materials used for making pipe and tap played one of the most important roles in promoting bacterial growth. This paper is to report the performance of an innovative type 304 Cu-bearing stainless steel(304Cu SS) against microbes in tap water. The investigation methodologies involved were means of heterotrophic plate count, contact angle measurements, scanning electron microscopy for observing the cell and subtract surface morphology,atomic absorption spectrometry for copper ions release study, and confocal laser scanning microscopy used for examining live/dead bacteria on normal 304 stainless steel and 304 Cu SS. It was found that the surface free energy varied after being immersed in tap water with polar component and Cu ions release.The results showed 304 Cu SS could effectively kill most of the planktonic bacteria(max 95.9% antibacterial rate), and consequently inhibit bacterial biofilms formation on the surface, contributing to the reduction of pathogenic risk to the surrounding environments.
Escherichia coli(E.coli)and Staphylococcus aureus(S.aureus)are the most typical pathogenic bacteria with a significantly high risk of bio-contamination,widely existing in hospital and public places.Recent studies on antibacterial materials and the related mechanisms have attracted more interests of researchers.However,the antibacterial behavior of materials is usually evaluated separately on the single bacterial strain,which is far from the practical condition.Actually,the interaction between the polymicrobial communities can promote the growing profile of bacteria,which may weaken the antibacterial effect of materials.In this work,a 420 copper-bearing martensitic stainless steel(420 CuSS)was studied with respect to its antibacterial activity and the underlying mechanism in a co-culturing infection model using both E.coli and S.au reus.Observed via plating and counting colony forming units(CFU),Cu releasing,and material characterization,420 CuSS was proved to present excellent antibacterial performance against the mixed bacteria with an approximately 99.4%of antibacterial rate.In addition,420 CuSS could effectively inhibit the biofilm formation on its surfaces,resulting from a synergistic antibacterial effect of Cu ions,Fe ions,reactive oxygen species(ROS),and proton consumption of bacteria.
Mingjun LiLi NanChunyong LiangZiqing SunLei YangKe Yang
The antibacterial Cu-bearing 304 L stainless steel is a new kind of structural and functional integrated metal material. In this work, evolution behavior of passive film of different heat treated Cu-bearing 304 L stainless steel immersed in 0.5 M H2SO4 solution was investigated by using electrochemical measurements, atomic force microscopy（AFM） observation and X-ray photoelectron spectroscopy（XPS） analysis.The results show that the solution and aging treated samples have the similar polarization behaviors. The passive film impedance experiences an initial decrease within 7 days followed by a subsequent increase,while the defect density of passive film presents the opposite trend. Meanwhile, the evolution of surface morphology and the estimated thickness of the passive film confirm that it experiences initial dissolution and follow-up repair. Furthermore, the Cr^3＋ content in passive film undergoes sequential reduction to increase, however the variation tendency of Cu^2＋ content is just opposite, indicating that the content variation of Cr and Cu in passive film reflects the competitive process of film dissolution and repair. In addition, compared with solution treated samples, aged samples have a bigger icorrvalue and the rougher passive film. This indicates that the passive film of solution treated steel is more compact and stable.
Xinrui ZhangJinlong ZhaoTong XiM.Babar ShahzadChunguang YangKe Yang
Cu-bearing stainless steel has been found to have obvious inhibition performance against encrustation in vitro. This study was aiming to further investigate the inhibitory effect of a Cu-bearing stainless steel（316 L-Cu SS） on the infectious encrustation based on its antimicrobial activity. The encrustation in presence of bacteria, antibacterial performance, urease production and Ca and Mg precipitation were examined by scanning electron microscopy, antibacterial assay, enzyme-linked immunosorbent assay and inductively coupled plasma-mass spectrometry, respectively. It was found that 316 L-Cu SS could inhibit the formation of bacterial biofilm due to the release of Cu^（2＋） ions and then decrease the urease amount splitting by bacteria, which produced a neutral environment with pH around 7. However, more encrustations coupled with bacterial biofilms on the surface of comparison stainless steel（316 L SS） with an alkaline environment were recorded. It can thus be seen that the 316 L-Cu SS highlights prominent superiority against encrustation in the presence of microorganisms.
Jing ZhaoLing RenBingchun ZhangZhiqiang CaoKe Yang
Pathogen microorganisms exist in various environments such as dairy processing facilities. They are not easily eliminated, and significantly raise the risk of bacterial contamination. The inhibition ability of a novel type 304 Cu-bearing stainless steel （304CUSS） with nano-sized Cu-rich precipitates against Staph-ylococcus aureus （S. aureus） and Pseudomonas aeruginosa （P. aeruginosa） added whole milk was investigated in this study. The results showed that after 24 h contact, the inhibition rates of the 304CUSS against S. aureus and P. aeruginosa added whole milk reached 99.2% ± 0.3% and 99.3% ± 0.2%, respectively, in contrast with the 304SS. In the plain whole milk, the inhibition rate of the 304CUSS also reached 66.9% ± 2.0% compared with the 304SS. The results demonstrated that the 304CUSS killed majority of the planktonic bacteria, and inhibited sessile bacteria adherence to the steel surface in the whole milk with and without bacteria addition, significantly reducing the bacterial growth rate. These research outcomes explicitly show an application potential of this novel antibacterial stainless steel in the dairy related food industry.
