Indoor Light Enhanced Photocatalytic Ultra-Thin Films on Flexible Non-Heat Resistant Substrates Reducing Bacterial Infection Risks

Photocatalytic antibacterial sol-gel coated substrates have been reported to kill bacteria under light or in the dark. These coatings showed non-uniform distribution, poor adhesion to the substrate and short effective lifetime as antibacterial surfaces. These serious limitations to the performance/stability retard the potential application of antibacterial films on a wide range of surfaces in hospital facilities and public places. Here, the preparation, testing and performance of flexible ultra-thin films prepared by direct current magnetron sputtering (DCMS) at different energies are reviewed. This review reports the recent advancements in the preparation of highly adhesive photocatalytic coatings prepared by up to date sputtering technology: High Power Impulse Magnetron Sputtering (HIPIMS). These latter films demonstrated an accelerated antibacterial capability compared to thicker films prepared by DCMS leading to materials saving. Nanoparticulates of Ti and Cu have been shown during the last decades to possess high oxidative redox potentials leading to bacterial inactivation kinetics in the minute range. In the case of TiO2-CuOx films, the kinetics of abatement of Escherichia coli (E. coli) and methicillin resistant Staphylococcus aureus (MRSA) were enhanced under indoor visible light and were perceived to occur within few minutes. Oligodynamic effect was seen to be responsible for bacterial inactivation by the small amount of released material in the dark and/or under light as detected by inductively-coupled plasma mass spectrometry (ICP-MS). The spectral absorbance (detected by Diffuse Reflectance Spectroscopy (DRS)) was also seen to slightly shift to the visible region based on the preparation method

Thin films for Healthcare Acquired Infections (HAIs) prevention:materials preparation, testing and characterization

This thesis addresses the preparation of antibacterial surfaces for hospital facilities taking biomedical thin polymer films, textiles and catheter as probes. Magnetron sputtering is used to apply the coatings leading to fast bacterial inactivation in the dark and under low intensity light on the selected substrates. These coating are designed and prepared to achieve fast bacterial inactivation to avoid biofilm formation on textiles and polymer films and later on the catheter surface. The infection due to catheters is one of the major problem leading to catheter associated infections (CAIs). The design, preparation, testing and the characterization of the surface properties of uniform and adhesive TiO2,TiO2/Cu, Ag, Cu-films presenting fast bacterial inactivation kinetics on textiles and catheters by up to date HIPIMS and DCMS/DCPMS has been addressed very sparsely until now mainly on 3D objects. No evidence for Ag-Cu coating applied by sputtering covering uniformly the entire catheter surface has been reported up to this date. A modification of the sputtering unit was carried out to coat 3D objects and is one of the main novelties reported in this thesis. The antimicrobial activity was tested on antibiotic resistant bacteria Methycillin resistant Staphylococcus aureus (MRSA) and Escherichia coli (E. coli) alone or jointly representing an important focus of infection by themselves or in the form of pathogenic biofilms in hospital facilities. The bacterial inactivation kinetics was investigated in details under low intensity light and in the dark. The active part of the catheter remains under the patient skin (in the dark). Ag/Cu-has been selected since fast bacterial inactivation proceeds in with a quasi-instantaneous kinetics inducing a cytotoxicity below the limit authorized by the sanitary regulations for mammalian cells. These coatings are also well tolerated by osteoblasts. The sputtered films leading to fast bacterial inactivation and showing low cytotoxicity consisted mainly of TiO2, Cu-TiO2, and Ag/Cu films on 2D surfaces and on catheters with 3D-geometry. This is the first report for materials of this kind, their evaluation and surface properties

Continuous Photocatalytic Antibacterial Activity of AgNPs doped TiO2 Digital Printed on Commercial Porcelain-grès Tiles

Photocatalytic finishing materials, such as tiles or paints, are a productive as well as scientific reality. One of the most interesting photocatalytic material currently on the market is the porcelain stoneware which combines the beauty of a design product with hardness and absence of porosity and thus used for both floors and walls. The Ag- micrometric TiO2 allowed active ceramic slabs to be active under LED lights, bypassing the problem of the UVA radiation. SEM/TEM images in Fig. 1 indicate the full coverage of the porcelain surface (left image), besides a nanometric though heterogenous spreading of the AgNPs on top of the TiO2 matrix (right image). Figure 1. HR-SEM of the Active ceramic surface (left), TEM image of 8% AgNPs-TiO2(center); possible photocatalytic mechanistic pathways in Ag doped TiO2 system (right) An important question concerns the antibacterial action: in fact, today the role of silver is unknown when the metal is physically blocked on a surface and cannot penetrate and therefore interfere at the DNA level in the cellular barrier. The prepared porcelain Ag-TiO2 printed surfaces were tested against E. coli under solar and visible illumination and in the dark. To differenciate the semicondutor behavior and the ions mediated bacterial inactivation mechanism, porinless E. coli were used under band-gap irradiation. Stereomicroscopy analysis showed dead bacteria within 180 and 240 min respectively for normal E. coli and porinless E. coli. Using appropriate quenchers, the bacterial inactivation mechanisms under solar and visible light are proposed

Recent Developments in Accelerated Antibacterial Inactivation on 2D Cu-Titania Surfaces under Indoor Visible Light

This review focuses on Cu/TiO2 sequentially sputtered and Cu-TiO2 co-sputtered catalytic/photocatalytic surfaces that lead to bacterial inactivation, discussing their stability, synthesis, adhesion, and antibacterial kinetics. The intervention of TiO2, Cu, and the synergic effect of Cu and TiO2 on films prepared by a colloidal sol-gel method leading to bacterial inactivation is reviewed. Processes in aerobic and anaerobic media leading to bacterial loss of viability in multidrug resistant (MDR) pathogens, Gram-negative, and Gram-positive bacteria are described. Insight is provided for the interfacial charge transfer mechanism under solar irradiation occurring between TiO2 and Cu. Surface properties of 2D TiO2/Cu and TiO2-Cu films are correlated with the bacterial inactivation kinetics in dark and under light conditions. The intervention of these antibacterial sputtered surfaces in health-care facilities, leading to Methicillin-resistant Staphylococcus Aureus (MRSA)-isolates inactivation, is described in dark and under actinic light conditions. The synergic intervention of the Cu and TiO2 films leading to bacterial inactivation prepared by direct current magnetron sputtering (DCMS), pulsed direct current magnetron sputtering (DCMSP), and high power impulse magnetron sputtering (HIPIMS) is reported in a detailed manner

Polystyrene CuO/Cu2O uniform films inducing MB-degradation under sunlight

This study reports on a Cu-sputtered film on polystyrene (PS) leading to the discoloration/degradation of methylene blue (MB) under low intensity solar simulated irradiation. Direct current magnetron sputtering (DCMS) was used to graft uniform, adhesive Cu/Cu oxides on the polystyrene substrate. The kinetics of Cu-PS mediated MB-discoloration adding H2O2 was observed to take place within 90-120 min. The surface potential and pH variation was followed on the Cu-PS surface during MB-discoloration. Insight is provided for the observed changes relating them to the dye discoloration mechanism. The concentration, mean-free path and lifetime of the oxidative radical leading to MB-degradation were estimated. The Cu/Cu-oxides on the PS were characterized by X-ray diffraction (XRD). X-ray photoelectron spectroscopy (XPS) evidence for redox catalysis involving Cu(I)/Cu(II)-species was detected during MB-discoloration. Also by XPS the surface atomic percentage concentration was determined for the topmost Cu-PS layers. The Cu-PS coatings were also investigated for their optical and crystallographic properties. (C) 2016 Elsevier B.V. All rights reserved

New evidence for Cu-decorated binary-oxides mediating bacterial inactivation/mineralization in aerobic media

Binary oxide semiconductors TiO2-ZrO2 and Cu-decorated TiO2-ZrO2 (TiO2-ZrO2-Cu) uniform films were sputtered on polyester (PES). These films were irradiated under low intensity solar simulated light and led to bacterial inactivation in aerobic and anaerobic media as evaluated by CFU-plate counting. But bacterial mineralization was only induced by TiO2-ZrO2-Cu in aerobic media. The highly oxidative radicals generated on the films surface under light were identified by the use of appropriate scavengers. The hole generated on the TiO2-ZrO2 films is shown to be the main specie leading to bacterial inactivation. TiO2-ZrO2 and Cu-decorated TiO2-ZrO2 films release Zr and Ti< 1ppb and Cu 4.6 ppb/cm2 as determined by inductively coupled plasma mass spectrometry (ICP-MS) This level is far below the citotoxicity permitted level allowed for mammalian cells suggesting that bacterial disinfection proceeds through an oligodynamic effect. By Fourier transform attenuated infrared spectroscopy (ATR-FTIR) the systematic shift of the predominating vs(CH2) vibrational-rotational peak making up most of the bacterial cell-wall content in C was monitored. Based on this evidence a mechanism suggested leading to C-H bond stretching followed by cell lysis and cell death. Bacterial inactivation cycling was observed on TiO2-ZrO2-Cu showing the stability of these films leading to bacterial inactivation

Evidence for TiON sputtered surfaces showing accelerated antibacterial activity under simulated solar irradiation

New evidence is reported for TiON sputtered polyester surfaces activated by sunlight irradiation leading to the accelerated bacterial inactivation in the minute range. The absorption in Kubelka-Munk units of the TiON film was observed to be directly proportional to the time of Escherichia coil inactivation as detected by diffuse reflection spectroscopy (DRS). TiON layers were characterized by electron microscopy and by high angle angular dark field (HAADF) showing the continuous coverage of the polyester fibers by the TiON film. Ti4+/Ti3+ redox catalysis was detected on the TiON surface by the XPS shifts during the bacteria inactivation process. Production of HO radicals on TiON polyester as a function of sunlight irradiation was determined following the fluorescence of 2-hydroxyterephthalic acid. Release of Na and K-ions was determined by ICP-MS and provides the evidence that cell wall damage is a preceding step leading the bacterial inactivation. A stable performance of the TiON films was observed during repetitive bacterial inactivation. (C) 2013 Elsevier Ltd. All rights reserved

Accelerated self-cleaning by Cu promoted semiconductor binary-oxides under low intensity sunlight irradiation

Uniform adhesive TiO2–ZrO2 films co-sputtered on polyester (PES) under low intensity sunlight irradiation discolored methylene blue (MB) within 120 min. The discoloration kinetics was seen to be accelerated by a factor four by TiO2–ZrO2–Cu containing ∼0.01% Cu, as determined by X-ray fluorescence (XRF). TiO2–ZrO2–Cu also increased also accelerated by a factor the discoloration of MB compared to TiO2/Cu(PES). MB discoloration was also monitored under visible light in the solar cavity by using a 400 nm cutoff filter. Photocatalyst surfaces were characterized by spectroscopic methods showing the film optical absorption and by X-ray photoelectron spectroscopy (XPS), the surface atomic percentage concentration up to 120 nm (∼600 layers). The band-gaps of TiO2–ZrO2 and TiO2–ZrO2–Cu were estimated for films co-sputtered for different times. By Fourier transform attenuated infrared spectroscopy (ATR-FTIR), the systematic shift of the predominating νs(CH2) vibration-rotational MB bands was monitored up to complete MB discoloration under low intensity solar simulated light. Evidence is presented for the OHradical dot generation by TiO2–ZrO2–Cu participating in the self-cleaning mechanism. The photo-induced interfacial charge transfer (IFCT) on the TiO2–ZrO2–Cu is discussed in terms of the electronic band positions of the binary oxides and Cu intra-gap states. This study presents the first evidence for a Cu-promoted composed of two binary oxide semiconductors accelerating the self-cleaning performance

Innovative semi-transparent nanocomposite films presenting photo-switchable behavior and leading to a reduction of the risk of infection under sunlight

Novel sputtered polyethylene-TiO2 (PE-TiO2) thin films induce fast bacterial inactivation with concomitant photo-switchable hydrophobic to hydrophilic transition under light. RF-plasma pretreatments allowed an increased TiO2 loading on PE, favorably affecting the photocatalyst performance. ATR-FTIR spectroscopy shows that the increase in the cell lipid-layer fluidity leads to cell wall scission/bacterial inactivation

Accelerated bacterial inactivation obtained by HIPIMS sputtering on low cost surfaces with concomitant reduction in the metal/semiconductor content

Novel ultrathin TiO2-Cu nanoparticulate films sputtered by highly ionized pulsed plasma magnetron sputtering (HIPIMS) lead to faster bacterial inactivation compared to more traditional sputtering approaches with an appreciable metal saving. HIPIMS sputtering induces a strong interaction of the TiO2-Cu-ions (M+) with the polyester surface due to the high fraction and density of M+-ions interacting with the biased substrate