Antimicrobial Cu-functionalized surfaces prepared by bipolar asymmetric DC-pulsed magnetron sputtering (DCP)

New Evidence for Ag-Sputtered Materials Inactivating Bacteria by Surface Contact without the Release of Ag Ions: End of a Long Controversy?

The study provides new evidence for Ag-coated polyester (PES) mediating Escherichia coli inactivation by way of genetically engineered E. coli (without porins, from now denoted porinless bacteria). This allows the quantification of the bactericidal kinetics induced by the Ag surface without the intervention of Ag ions. Bacterial inactivation mediated by Ag-PES was seen to be completed within 60 min. The samples were prepared by high-power impulse magnetron sputtering (HiPIMS) at different sputter powers. In anaerobic media, this process required 120 min. The amounts of ions (Ar⁺, Ag⁺, and Ag²⁺) generated during the deposition by direct current magnetron sputtering (DCMS) and HiPIMS were determined by mass spectrometry. The thickness of the Ag films sputtered on PES by DCMS (0.28 A) during 100 s was found to be 340 nm. Thicknesses of 250, 230, and 200 nm were found when sputtering with HiPIMS was tuned at 8, 17, and 30 A, respectively. By scanning transmission electron microscopy (STEM-HAADF), the atomic distribution of Ag and oxygen was detected. By X-ray photoelectron spectroscopy (XPS), a shift in the Ag oxidation state was observed within the bacterial inactivation period. This reveals redox catalysis within the time required for the total bacterial inactivation due to the interaction between the bacterial suspension and Ag-PES. Surface properties of the Ag-coated PES samples were additionally investigated by X-ray diffraction (XRD). The formation of Ag plasmon was detected by diffuse reflectance spectroscopy (DRS) and was a function of the applied sputtering energy. The indoor sunlight irradiation dose required to induce an accelerated bacterial inactivation was found to be 5-10 mW/cm².

Recent Progress in Magnetron Sputtering Technology Used on Fabrics

The applications of magnetron sputtering technology on the surface coating of fabrics have attracted more and more attention from researchers. Over the past 15 years, researches on magnetron sputtering coated fabrics have been mainly focused on electromagnetic shielding, bacterial resistance, hydrophilic and hydrophobic properties and structural color etc. In this review, recent progress of the technology is discussed in detail, and the common target materials, technologies and functions and characterization of coated fabrics are summarized and analyzed. Finally, the existing problems and future prospects of this developing field are briefly proposed and discussed.

Flexible Antibacterial Coatings

This article reviews the present state of the art in the field of flexible antibacterial coatings which efficiently kill bacteria on their surfaces. Coatings are formed using a reactive magnetron sputtering. The effect of the elemental composition and structure of the coating on its antibacterial and mechanical properties is explained. The properties of Cr–Cu–O, Al–Cu–N, and Zr–Cu–N antibacterial coatings are used as examples and described in detail. The efficiency of killing of bacteria was tested for the Escherichia coli bacterium. The principle of the formation of thick, flexible antibacterial coatings which are resistant to cracking under bending is explained. It is shown that magnetron sputtering enables production of robust, several-micrometer thick, flexible antibacterial coatings for long-term use. The antibacterial coatings produced by magnetron sputtering present huge potential for many applications.

Microstructure of Cu-Ag Uniform Nanoparticulate Films on Polyurethane 3D Catheters: Surface Properties

The preparation, characterization, and antibacterial testing of Cu-Ag sputtered polyurethane (PU) catheters are addressed in this study. PU catheters with different atomic ratios Cu:Ag have been sputtered and led to different optical properties as followed by diffuse reflectance spectroscopy (DRS) and the surface redox properties were also different for different Cu-Ag ratios as observed by X-ray photoelectron spectroscopy (XPS). The surface atomic percentage concentration of the oxidized/reduced C-species originating from bacterial cultures before and after bacterial inactivation were determined on the Cu-Ag PU catheters. The crystallographic properties were determined by X-ray diffraction (XRD). The XRD-diffractogram showed the presence of Cu2O (111), Cu (200), CuO (020), and Ag (111) indicating that Cu nanoparticles present a more crystalline character compared to Ag nanoparticles. Increasing the percentage of Ag in the Cu-Ag films, bigger Ag-particle agglomerates were detected by scanning transmission electron microscopy (STEM) microanalysis confirming the results obtained by AFM. The bacterial inactivation kinetics of the sputtered Cu-Ag films on PU catheters was investigated in detail. Quasi-instantaneous bacterial inactivation kinetics was induced by the sputtered films on PU catheters after optimization of the Cu-Ag film thickness.

Inactivation of bacteria under visible light and in the dark by Cu films. Advantages of Cu-HIPIMS-sputtered films

INTRODUCTION

The Cu polyester thin-sputtered layers on textile fabrics show an acceptable bacterial inactivation kinetics using sputtering methods.

MATERIALS AND METHODS

Direct current magnetron sputtering (DCMS) for 40 s of Cu on cotton inactivated Escherichia coli within 30 min under visible light and within 120 min in the dark. For a longer DCMS time of 180 s, the Cu content was 0.294% w/w, but the bacterial inactivation kinetics under light was observed within 30 min, as was the case for the 40-s sputtered sample.

RESULTS AND DISCUSSION

This observation suggests that Cu ionic species play a key role in the E. coli inactivation and these species were further identified by X-ray photoelectron spectroscopy (XPS). The 40-s sputtered samples present the highest amount of Cu sites held in exposed positions interacting on the cotton with E. coli. Cu DC magnetron sputtering leads to thin metallic semi-transparent gray-brown Cu coating composed by Cu nanoparticulate in the nanometer range as found by electron microscopy (EM). Cu cotton fabrics were also functionalized by bipolar asymmetric DCMSP.

CONCLUSION

Sputtering by DCMS and DCMSP for longer times lead to darker and more compact Cu films as detected by diffuse reflectance spectroscopy and EM. Cu is deposited on the polyester in the form of Cu(2)O and CuO as quantified by XPS. The redox interfacial reactions during bacterial inactivation involve changes in the Cu oxidation states and in the oxidation intermediates and were followed by XPS. High-power impulse magnetron sputtering (HIPIMS)-sputtered films show a low rugosity indicating that the texture of the Cu nanoparticulate films were smooth. The values of R (q) and R (a) were similar before and after the E. coli inactivation providing evidence for the stability of the HIPIMS-deposited Cu films. The Cu loading percentage required in the Cu films sputtered by HIPIMS to inactivate E. coli was about three times lower compared to DCMS films. This indicates a substantial Cu metal savings within the preparation of antibacterial films.

Innovative TiO2/Cu nanosurfaces inactivating bacteria in the minute range under low-intensity actinic light

The bacterial inactivation of E. coli by cotton TiO(2)/Cu DC-magnetron sputtered thin films was investigated in the dark and under low-intensity actinic light. The TiO(2)/Cu sputtered layers revealed to be sensitive to actinic light showing the spectral characteristics of Cu/CuO. This indicates that Cu does not substitute Ti(4+) in the crystal lattice. Under diffuse actinic light (4 mW/cm(2)), the hybrid composite TiO(2)/Cu sample lead to fast bacterial inactivation times <5 min. This study presents evidence for a direct relation between the film optical absorption obtained by diffuse reflectance spectroscopy (DRS) and the bacterial inactivation kinetics by the TiO(2)/Cu samples. The Cu-ions inactivating the bacteria were followed in solution by inductively plasma coupled spectroscopy (ICPS). The amounts of Cu-ions detected by ICPS provide the evidence for an oligodynamic antibacterial effect. The changes in the oxidation state of Cu during bacterial inactivation were followed by XPS. The E. coli cell viability was detected by standard coliform counting CFU methods. The TiO(2)/Cu thickness layer was determined by profilometry and the film microstructure by XPS, TEM, AFM, XRD, XRF and contact angle (CA). A mechanism of bacterial inactivation by TiO(2)/Cu samples is suggested in terms of interfacial charge transfer (IFCT) involving charge transfer between TiO(2) and Cu.

Comparison of methods for evaluation of the bactericidal activity of copper-sputtered surfaces against methicillin-resistant Staphylococcus aureus

Bacteria can survive on hospital textiles and surfaces, from which they can be disseminated, representing a source of health care-associated infections (HCAIs). Surfaces containing copper (Cu), which is known for its bactericidal properties, could be an efficient way to lower the burden of potential pathogens. The antimicrobial activity of Cu-sputtered polyester surfaces, obtained by direct-current magnetron sputtering (DCMS), against methicillin-resistant Staphylococcus aureus (MRSA) was tested. The Cu-polyester microstructure was characterized by high-resolution transmission electron microscopy to determine the microstructure of the Cu nanoparticles and by profilometry to assess the thickness of the layers. Sputtering at 300 mA for 160 s led to a Cu film thickness of 20 nm (100 Cu layers) containing 0.209% (wt/wt) polyester. The viability of MRSA strain ATCC 43300 on Cu-sputtered polyester was evaluated by four methods: (i) mechanical detachment, (ii) microcalorimetry, (iii) direct transfer onto plates, and (iv) stereomicroscopy. The low efficacy of mechanical detachment impeded bacterial viability estimations. Microcalorimetry provided only semiquantitative results. Direct transfer onto plates and stereomicroscopy seemed to be the most suitable methods to evaluate the bacterial inactivation potential of Cu-sputtered polyester surfaces, since they presented the least experimental bias. Cu-polyester samples sputtered for 160 s by DCMS were further tested against 10 clinical MRSA isolates and showed a high level of bactericidal activity, with a 4-log(10) reduction in the initial MRSA load (10(6) CFU) within 1 h. Cu-sputtered polyester surfaces might be of use to prevent the transmission of HCAI pathogens.