Bactericidal Surfaces Research Articles

Hierarchical polymer coating for optimizing the antifouling and bactericidal efficacies

The bacteria-repellent and bactericidal functionalities in a single system are generally need to be carefully optimized in order to obtain the highest antibacterial performance. In this study, the controlled SI-PIMP strategy was developed for creating hierarchical polymer brushes possessing the bacteria-repellent and bactericidal functionalities. To obtain a bactericidal surface with minimal interference to its nonfouling property, optimization studies were conducted by facilely tailoring the surface density of the quaternary ammonium compound moieties through control over the monomer concentration. An optimal hierarchical polymer coating showed potent protein and bacteria repellence as well as certain bactericidal property. The longlasting antibacterial performance was also achieved due to the good balance between the dual functionalities. The tenability of the hierarchical polymer coating is applicable to surface chemistries for biosensors, molecular imaging, and biomedical applications.

Integrated antifouling and bactericidal polymer membranes through bioinspired polydopamine/poly(N-vinyl pyrrolidone) coating

Polypropylene (PP) non-woven has been widely used as wound dressing; however, the hydrophobic nature of PP can initiate bacterial attachment and subsequent biofilm formation. Herein, we propose a facile approach to functionalize PP non-woven with poly(ethylene glycol) (PEG) and poly(N-vinyl pyrrolidone)-iodine complex (PVP-I). PVP and PEG were successively tethered onto PP non-woven surface via versatile bioinspired dopamine (DA) chemistry, followed by complexing iodine with PVP moieties. It was demonstrated through the field emission scanning electron microscope (SEM) and spread plate method that the as-modified PP non-woven integrated both antifouling property of PEG for suppressing bacterial adhesion, and bactericidal property of PVP-I for killing the few adherent bacteria. Meanwhile, it could greatly resist platelet and red blood cell adhesion. The integrated antifouling and bactericidal PP non-woven surfaces might have great potential in various wound dressing applications.

Construction of a temperature-responsive terpolymer coating with recyclable bactericidal and self-cleaning antimicrobial properties.

Once a biomedical implant is implanted into a human body, proteins and bacteria can easily colonize the implant, and subsequently, a biofilm can grow on the surface. A biofilm can protect the inhabiting bacteria against macrophages and neutrophil cell attack from the host immune system. The most important issue for artificial antibacterial surfaces is the accumulation of the bacteria corpse after they are killed by contact, which promotes further adhesion of bacteria and biofilm formation. Therefore, we constructed a novel multifunctional bactericidal and fouling release antibacterial surface through the combination of temperature-responsive N-vinylcaprolactam (VCL), hydrophilic 2-methacryloyloxyethyl phosphorylcholine (MPC) and a bactericidal quaternary ammonium salt (2-(dimethylamino)-ethyl methacrylate (DMAEMA+)). The terpolymer coating was prepared through surface-initiated reversible addition-fragmentation chain-transfer (RAFT) polymerization and characterized using water contact angle measurements, atomic force microscopy and spectroscopic ellipsometry. At a temperature above the lower critical solution temperature (LCST), the P(VCL-co-DMAEMA+-co-MPC) terpolymer coating was in a compressed and hydrophobic state with low moisture content, which displayed bactericidal efficiency against Gram-positive Staphylococcus aureus. The coating could be switched into a relatively hydrophilic surface at a temperature below the LCST, which showed self-cleaning properties against both bacteria and bovine serum albumin. The functionalized surface showed good biocompatibility against human lens epithelial cells as evaluated by morphology studies and activity measurements.

Diamond-coated 'black silicon' as a promising material for high-surface-area electrochemical electrodes and antibacterial surfaces.

This report describes a method to fabricate high-surface-area boron-doped diamond (BDD) electrodes using so-called 'black silicon' (bSi) as a substrate. This is a synthetic nanostructured material that contains high-aspect-ratio nano-protrusions, such as spikes or needles, on the Si surface produced via plasma etching. We now show that coating a bSi surface composed of 15 μm-high needles conformably with BDD produces a robust electrochemical electrode with high sensitivity and high electroactive area. A clinically relevant demonstration of the efficacy of these electrodes is shown by measuring their sensitivity for detection of dopamine (DA) in the presence of an excess of uric acid (UA). Finally, the nanostructured surface of bSi has recently been found to generate a mechanical bactericidal effect, killing both Gram-negative and Gram-positive bacteria at high rates. We will show that BDD-coated bSi also acts as an effective antibacterial surface, with the added advantage that being diamond-coated it is far more robust and less likely to become damaged than Si.

Modification of medical grade PVC with N-vinylimidazole to obtain bactericidal surface

Abstract N-vinylimidazole (VIm) was grafted onto medical-grade poly(vinyl chloride) (PVC) catheters in order to provide a bactericidal surface that make them less susceptible to microbial colonization. The grafting of VIm was carried out by means of gamma rays using the direct method, which demonstrated to be an efficient and fast procedure for obtaining PVC-g-VIm copolymers. These copolymers could be quaternized in a second step using methyl iodide (CH 3 I). The effects of solvent nature, absorbed dose, and monomer concentration on the grafting yield were investigated. Modified PVC catheters were characterized by means of Fourier transform infrared spectroscopy (FT-IR), thermogravimetry (TGA), and swelling studies. PVC-g-VIm copolymers both before and after quaternization showed good hemocompatibility, while quaternization was required to inhibit the growth of Staphylococcus aureus .

Nanopatterned polymer surfaces with bactericidal properties.

Bacteria that adhere to the surfaces of implanted medical devices can cause catastrophic infection. Since chemical modifications of materials' surfaces have poor long-term performance in preventing bacterial buildup, approaches using bactericidal physical surface topography have been investigated. The authors used Nanoimprint Lithography was used to fabricate a library of biomimetic nanopillars on the surfaces of poly(methyl methacrylate) (PMMA) films. After incubation of Escherichia coli (E. coli) on the structured PMMA surfaces, pillared surfaces were found to have lower densities of adherent cells compared to flat films (67%-91% of densities on flat films). Moreover, of the E. coli that did adhere a greater fraction of them were dead on pillared surfaces (16%-141% higher dead fraction than on flat films). Smaller more closely spaced nanopillars had better performance. The smallest most closely spaced nanopillars were found to reduce the bacterial load in contaminated aqueous suspensions by 50% over a 24-h period compared to flat controls. Through quantitative analysis of cell orientation data, it was determined that the minimum threshold for optimal nanopillar spacing is between 130 and 380 nm. Measurements of bacterial cell length indicate that nanopillars adversely affect E. coli morphology, eliciting a filamentous response. Taken together, this work shows that imprinted polymer nanostructures with precisely defined geometries can kill bacteria without any chemical modifications. These results effectively translate bactericidal nanopillar topographies to PMMA, an important polymer used for medical devices.

Synthesis of Ag ion-implanted TiO2 thin films for antibacterial application and photocatalytic performance

TiO2 thin films were deposited by spin coating method. Silver ions were implanted into the films using a Metal Vapor Vacuum Arc implanter. The antibacterial ability of implanted films was tested using Escherichia coli removal under fluorescent irradiation and in the dark. The concentration of E. coli was evaluated by plating technique. The photocatalytic efficiency of the implanted films was studied by degradation of methyl orange under fluorescent illumination. The surface free energy of the implanted TiO2 films was calculated by contact angle testing. Vitamin C was used as radical scavengers to explore the antibacterial mechanism of the films. The results supported the model that both generation of reactive oxygen species and release of silver ions played critical roles in the toxic effect of implanted films against E. coli. XPS experimental results demonstrated that a portion of the Ag(Ag3+) ions were doped into the crystalline lattice of TiO2. As demonstrated by density functional theory calculations, the impurity energy level of subtitutional Ag was responsible for enhanced absorption of visible light. Ag ion-implanted TiO2 films with excellent antibacterial efficiency against bacteria and decomposed ability against organic pollutants could be potent bactericidal surface in moist environment.

Antibiofilm Activity of Epoxy/Ag-TiO2 Polymer Nanocomposite Coatings against Staphylococcus Aureus and Escherichia Coli

Dispersion of functional inorganic nano-fillers like TiO2 within polymer matrix is known to impart excellent photobactericidal activity to the composite. Epoxy resin systems with Ag+ ion doped TiO2 can have combination of excellent biocidal characteristics of silver and the photocatalytic properties of TiO2. The inorganic antimicrobial incorporation into an epoxy polymeric matrix was achieved by sonicating laboratory-made nano-scale anatase TiO2 and Ag-TiO2 into the industrial grade epoxy resin. The resulting epoxy composite had ratios of 0.5–2.0 wt% of nano-filler content. The process of dispersion of Ag-TiO2 in the epoxy resin resulted in concomitant in situ synthesis of silver nanoparticles due to photoreduction of Ag+ ion. The composite materials were characterized by DSC and SEM. The glass transition temperature (Tg) increased with the incorporation of the nanofillers over the neat polymer. The materials synthesized were coated on glass petri dish. Anti-biofilm property of coated material due to combined release of biocide, and photocatalytic activity under static conditions in petri dish was evaluated against Staphylococcus aureus ATCC6538 and Escherichia coli K-12 under UV irradiation using a crystal violet binding assay. Prepared composite showed significant inhibition of biofilm development in both the organisms. Our studies indicate that the effective dispersion and optimal release of biocidal agents was responsible for anti-biofilm activity of the surface. The reported thermoset coating materials can be used as bactericidal surfaces either in industrial or healthcare settings to reduce the microbial loads.

Dual‐Mechanism Antimicrobial Polymer–ZnO Nanoparticle and Crystal Violet‐Encapsulated Silicone

The prevalence of healthcare‐associated infection caused by multidrug‐resistant bacteria is of critical concern worldwide. It is reported on the development of a bactericidal surface prepared by use of a simple, upscalable, two‐step dipping strategy to incorporate crystal violet and di(octyl)­phosphinic‐ acid‐capped zinc oxide nanoparticles into medical grade silicone, as a strategy to reduce the risk of infection. The material is characterized by UV–vis absorbance spectroscopy, X‐ray photoelectron spectroscopy (XPS), inductively coupled plasma‐optical emission spectroscopy (ICP‐OES) and transmission electron microscopy (TEM) and confirmed the incorporation of the ZnO nanoparticles in the polymer. The novel system proves to be a highly versatile bactericidal material when tested against both Staphylococcus aureus and Escherichia coli, key causative micro‐organisms for hospital‐acquired infection (HAI). Potent antimicrobial activity is noted under dark conditions, with a significant enhancement exhibits when the surfaces are illuminated with a standard hospital light source. This polymer has the potential to decrease the risk of HAI, by killing bacteria in contact with the surface.

Lethal photosensitisation of Staphylococcus aureus and Escherichia coli using crystal violet and zinc oxide-encapsulated polyurethane.

Crystal violet and zinc oxide nanoparticles (CVZnO) were incorporated into medical grade polyurethane polymers by a two-step dipping procedure to prepare novel bactericidal surfaces. The photobactericidal activity of CVZnO polyurethane samples was tested against the Gram-positive bacterium, Staphylococcus aureus and the Gram-negative bacterium, Escherichia coli. Exposure of the polymer samples to white light induced the lethal photosensitisation of both S. aureus and E. coli. In addition, this novel system demonstrated significant antibacterial activity under dark conditions against S. aureus within 2 hours, but more remarkably, a 99.9% reduction in the numbers of E. coli within 4 hours in the dark. This is, to the best of our knowledge, the most potent 'dark-kill' by a light activated antimicrobial agent ever reported. The singlet oxygen quenchers, bovine serum albumin and l-histidine, and an enzyme which catalyses the decomposition of hydrogen peroxide, bovine catalase, were incorporated into the antibacterial assays to determine if the mechanism of E. coli kill involved a Type 1 or a Type 2 light-activated process.

Recent advances in engineering topography mediated antibacterial surfaces.

The tendency of bacterial cells to adhere and colonize a material surface leading to biofilm formation is a fundamental challenge underlying many different applications including microbial infections associated with biomedical devices and products. Although, bacterial attachment to surfaces has been extensively studied in the past, the effect of surface topography on bacteria-material interactions has received little attention until more recently. We review the recent progress in surface topography based approaches for engineering antibacterial surfaces. Biomimicry of antibacterial surfaces in nature is a popular strategy. Whereas earlier endeavors in the field aimed at minimizing cell attachment, more recent efforts have focused on developing bactericidal surfaces. However, not all such topography mediated bactericidal surfaces are necessarily cytocompatible thus underscoring the need for continued efforts for research in this area for developing antibacterial and yet cytocompatible surfaces for use in implantable biomedical applications. This mini-review provides a brief overview of the current strategies and challenges in the emerging field of topography mediated antibacterial surfaces.

Comparative Study of Antibacterial Efficiency of M-TiO<sub>2</sub> (M = Ag, Cu) Thin Films Grown by CVD

M-TiO2 (M = Ag, Cu) nanocomposite layers were grown by pulsed direct liquid injection chemical vapor deposition (DLICVD) on various substrates to produce bactericidal surfaces with long term activity. Monodisperse Ag nanoparticles (NPs) with an average size of 5-10 nm are embedded in an anatase matrix. A bactericidal behavior determined by the JIS Z 2801 standard test was found for Ag-TiO2 films for Ag ≤ 1 at. % and above. Higher Ag content is not necessary since efficiency is already at its maximum (relative activity 100%). By contrast, using Cu as antibacterial agent, a larger size distribution of metal particles was found (20 to 400 nm). Cu-TiO2 films exhibit a bactericidal behavior if their thickness is higher than 100 nm and Cu content ≥ 3.5 at. %. These coatings are still antibacterial after 5 months of aging and their efficiency has decreased by only 35%.

Evaluation of new in vitro efficacy test for antimicrobial surface activity reflecting UK hospital conditions

Antimicrobial surfaces aim to reduce microbial bioburden and improve hygiene. The current antimicrobial surface efficacy test (ISO22196) is an initial screening test but its conditions, high temperature (37°C) and relative humidity (RH) (100%) bear little relationship to in-use conditions. To develop an antimicrobial surface efficacy test providing a realistic second-tier test, simulating in-use conditions. Surface relative humidity, temperature and soiling were measured over one year at a UK hospital, enabling realistic parameters to be set for our surface efficacy test. A nebulizer, connected to a cascade impactor, aerosolized and uniformly deposited a Staphylococcus aureus suspension over test copper alloys and control stainless steel surfaces. Bacteria were enumerated following nebulization, and after a range of contact times, under [20°C, 50% RH] and [20°C, 40% RH] parameters reflecting in-use conditions; [37°C, 100% RH] was employed to reflect conditions used in ISO22196. All copper alloys produced a >4 log10 reduction after 24h under all conditions tested. Copper alloys were more effective at [37°C, 100% RH] showing a >4 log10 reduction after 30 min than at in-use conditions [20°C, 50% RH and 20°C, 40% RH], for which 60 min was required to achieve the same level of kill, for most but not all alloys. The use of the nebulizer to deposit bacterial inocula on surfaces showed little variability in results. Our method was more discriminatory than the ISO22196 enabling distinction between the bactericidal surface activity, which allows for a more rigorous selection of antimicrobial surfaces for potential use in healthcare settings.

Antibacterial properties of TiO2–Cu composite thin films grown by a one step DLICVD process

The correlations between microstructural features, chemical compositions and antibacterial properties of coatings containing metallic Cu particles embedded in a titanium dioxide matrix have been determined. A Direct Liquid Injection Chemical Vapor Deposition (DLICVD) process was used for the one step growth of TiO2–Cu composite coatings on various substrates. Titanium tetra-iso-propoxide (TTIP) and copper bis(2,2,6,6-tetramethyl-3,5-heptationate) (Cu(tmhd)2) were used as titanium and copper molecular sources, respectively. This growth process allows a good control of the quantity of metalorganic precursors injected into the CVD reactor and thus of the coating composition. The deposition occurs at 683K under low pressure (800Pa). The influence of the main features of the coatings on their antibacterial properties was investigated in order to produce bactericidal surfaces that are durable, non-toxic and containing a minimum amount of active agent. The antibacterial activity on Staphylococcus aureus without any photon activation was measured according to the JIS Z 2801:2000 standard method. An antibacterial activity was detected for a low metal content of ca. 1at.% Cu, and was found to increase with the Cu content. It was maximal for 3.5at.% Cu, i.e. TiO2–Cu composite coatings exhibit bactericidal behavior against S. aureus for this optimal composition (relative activity=100%). In order to better characterize the microbiological behavior of the coatings more discriminating methods derived from the literature were tested to assess the performances of these CVD coatings in terms of efficiency, release of antibacterial agent and accelerated aging.

Design of self-disinfecting PVC surfaces using the click chemistry

Novel bactericidal PVC surfaces were developed. Cationic copolymers containing alkyne groups and quaternary ammonium or phosphonium groups were successfully synthesized and characterized. These polymers were grafted by click chemistry on PVC surfaces bearing azide groups (PVC-N3). The modified surfaces exhibited higher polarity and hydrophilicity in comparison with non grafted surfaces. Accessible surface charge densities varied from 1.1×1014 to 6.5×1014 chargecm−2. In these conditions, bactericidal effects of the cationic surfaces against Escherichia coli and Staphylococcus epidermidis were evidenced by the Live and Dead fluorescent assay.

Immobilized silver nanoparticles enhance contact killing and show highest efficacy: elucidation of the mechanism of bactericidal action of silver

Antimicrobial materials with immobilized/entrapped silver nanoparticles (AgNPs) are of considerable interest. There is significant debate on the mode of bactericidal action of AgNPs, and both contact killing and/or ion mediated killing have been proposed. In this study, AgNPs were immobilized on an amine-functionalized silica surface and their bactericidal activity was studied concurrently with the silver release profile over time. This was compared with similar studies performed using colloidal AgNPs and AgCl surfaces that released Ag ions. We conclude that contact killing is the predominant bactericidal mechanism and surface immobilized nanoparticles show greater efficacy than colloidal AgNPs, as well as a higher concentration of silver ions in solution. In addition, the AgNP immobilized substrate was used multiple times with good efficacy, indicating this immobilization protocol is effective for retaining AgNPs while maintaining their disinfection potential. The antibacterial surface was found to be extremely stable in aqueous medium and no significant leaching (∼1.15% of total silver deposited) of the AgNPs was observed. Thus, immobilization of AgNPs on a surface may promote reuse, reduce environmental risks associated with leaching of AgNPs and enhance cost effectiveness.

Electrochemical analysis of the UV treated bactericidal Ti6Al4V surfaces

This research investigates in detail the bactericidal effect exhibited by the surface of the biomaterial Ti6Al4V after being subjected to UV-C light. It has been recently hypothesized that small surface currents, occurring as a consequence of the electron–hole pair recombination taking place after the excitation process, are behind the bactericidal properties displayed by this UV-treated material. To corroborate this hypothesis we have used different electrochemical techniques, such as electrochemical impedance spectroscopy (EIS), potentiodynamic polarization plots and Mott–Schottky plots. EIS and Mott–Schottky plots have shown that UV-C treatment causes an initial increase on the surface electrical conduction of this material. In addition, EIS and polarization plots demonstrated that higher corrosion currents occur at the UV treated than at the non-irradiated samples. Despite this increase in the corrosion currents, EIS has also shown that such currents are not likely to affect the good stability of this material oxide film since the irradiated samples completely recovered the control values after being stored in dark conditions for a period not longer than 24h. These results agree with the already-published in vitro transitory behavior of the bactericidal effect, which was shown to be present at initial times after the biomaterial implantation, a crucial moment to avoid a large number of biomaterial associated infections.

Selective bactericidal activity of nanopatterned superhydrophobic cicada Psaltoda claripennis wing surfaces

The nanopattern on the surface of Clanger cicada (Psaltoda claripennis) wings represents the first example of a new class of biomaterials that can kill bacteria on contact based solely on its physical surface structure. As such, they provide a model for the development of novel functional surfaces that possess an increased resistance to bacterial contamination and infection. Their effectiveness against a wide spectrum of bacteria, however, is yet to be established. Here, the bactericidal properties of the wings were tested against several bacterial species, possessing a range of combinations of morphology and cell wall type. The tested species were primarily pathogens, and included Bacillus subtilis, Branhamella catarrhalis, Escherichia coli, Planococcus maritimus, Pseudomonas aeruginosa, Pseudomonas fluorescens, and Staphylococcus aureus. The wings were found to consistently kill Gram-negative cells (i.e., B. catarrhalis, E. coli, P. aeruginosa, and P. fluorescens), while Gram-positive cells (B. subtilis, P. maritimus, and S. aureus) remained resistant. The morphology of the cells did not appear to play any role in determining cell susceptibility. The bactericidal activity of the wing was also found to be quite efficient; 6.1 ± 1.5 × 10(6) P. aeruginosa cells in suspension were inactivated per square centimeter of wing surface after 30-min incubation. These findings demonstrate the potential for the development of selective bactericidal surfaces incorporating cicada wing nanopatterns into the design.

Copper as an antimicrobial agent against opportunistic pathogenic and multidrug resistant Enterobacter bacteria

Infections by Enterobacter species are common and are multidrug resistant. The use of bactericidal surface materials such as copper has lately gained attention as an effective antimicrobial agent due to its deadly effects on bacteria, yeast, and viruses. The aim of the current study was to assess the antibacterial activity of copper surfaces against Enterobacter species. The antibacterial activity of copper surfaces was tested by overlying 5×10(6) CFU/ml suspensions of representative Enterobacter strains and comparing bacterial survival counts on copper surfaces at room temperature. Iron, stainless steel, and polyvinylchloride (PVC) were used as controls. The mechanisms responsible for bacterial killing on copper surfaces were investigated by a mutagenicity assay of the D-cycloserin (cyclA gene), single cell gel electrophoresis, a staining technique, and inductively coupled plasma mass spectroscopy. Copper yielded a significant decrease in the viable bacterial counts at 2 h exposure and a highly significant decrease at 4 h. Loss of cell integrity and a significantly higher influx of copper into bacterial cells exposed to copper surfaces, as compared to those exposed to the controls, were documented. There was no increase in mutation rate and DNA damage indicating that copper contributes to bacterial killing by adversely affecting cellular structure without directly targeting the genomic DNA. These findings suggest that copper's antibacterial activity against Enterobacter species could be utilized in health care facilities and in food processing plants to reduce the bioburden, which would increase protection for susceptible members of the community.

A Highly Luminescent Hexanuclear Molybdenum Cluster – A Promising Candidate toward Photoactive Materials

AbstractA new Mo6 cluster complex and its silica and polyurethane composites have been synthesized and characterized. These materials are highly luminescent with emission above 650 nm, produce singlet oxygen with high efficiency, are photostable, and can be excited up to 580 nm. These properties are desirable for the construction of luminescent probes of oxygen, photoactive materials for oxidation reactions with easily separable active carriers, and bactericidal textile surfaces upon daylight irradiation.