In Vitro and Ex Vivo Investigation of the Antibacterial Effects of Methylene Blue against Methicillin-Resistant Staphylococcus aureus

Methylene blue (MB) is a water-soluble dye that has a number of medical applications. Methicillin-resistant Staphylococcus aureus (MRSA) was selected as a subject for research due to the numerous serious clinical diseases it might cause and because there is a significant global resistance challenge. Our main goal was to determine and analyze the antibacterial effects of MB against S. aureus both in vitro and ex vivo to enhance treatment options. A total of 104 MRSA isolates recovered from various clinical specimens were included in this study. Minimum inhibitory concentration (MIC) values of MB against MRSA isolates were determined by the agar dilution method. One randomly selected MRSA isolate and a methicillin-susceptible S. aureus strain (S. aureus ATCC 25923) were employed for further evaluation of the antibacterial effects of MB in in vitro and ex vivo time-kill assays. A disc diffusion method-based MB + antibiotic synergy assay was performed to analyze the subinhibitory effects of MB on ten isolates. MICs of MB against 104 MRSA isolates, detected by the agar dilution method, ranged between 16 and 64 µg/mL. MB concentrations of 4 and 16 µg/mL showed a bactericidal effect at 24 h in the ex vivo time-kill assays and in vitro time-kill assays, respectively. We observed a significant synergy between cefoxitin and methylene blue at a concentration of 1-2 μg/mL in two (20%) test isolates. Employing MB, which has well-defined pharmacokinetics, bioavailability, and safety profiles, for the treatment of MRSA infections and nasal decolonization could be a good strategy.

Enhancement of the Photosensitizing Properties of 6-Carboxypterin through Covalent Binding to the pH-Responsive and Biocompatible Poly(allylamine Hydrochloride)

A polymeric photosensitizer was synthesized through covalent attachment of the natural photosensitizer 6-carboxypterin (Cap) to a poly(allylamine hydrochloride) (PAH) polymer. The optimization of the functionalization steps and purification procedure is described. The overall yield of the functionalization reaction was 67% to generate the modified polymer (PAH-Cap), featuring a Cap substitution degree of approximately 1% and advantageous spectroscopic properties. Photosensitizing properties of PAH-Cap were observed to occur via both photooxidation mechanisms, i.e., type I and type II. This feature was demonstrated using a biologically relevant target molecule, 2'-deoxyguanosine (dG). The spectroscopic, photophysical, and photochemical behaviors in aqueous environments were studied and compared to Cap. To explore possible further relevant biological applications, experiments with PAH-Cap and dG were carried out at physiological pH. PAH-Cap can generate singlet molecular oxygen and initiate an electron transfer process at pH 7 in air-saturated solutions upon UVA irradiation. Moreover, based on its spectroscopic features, visible light can be used to initiate the photooxidation of biological compounds in water, with many interesting advantages compared to free Cap and other related pteridines. These advantages include an enhancement of the photosensitizing effect at physiological pH and the potential of PAH-Cap for its use as a building block in supramolecular assemblies. The functionalization strategy hereby described can be employed for the preparation of robust photoactive polymers with great potential for its application in photodynamic therapy (PDT) and disinfection technologies.

Recyclable and Environmentally Friendly Magnetic Nanoparticles with Aggregation-Induced Emission Photosensitizer for Sustainable Bacterial Inactivation in Water

Bacterial photodynamic inactivation based on the combined actions of photosensitizers, light, and oxygen presents a promising alternative for eliminating bacteria compared to conventional water disinfection methods. However, a significant challenge in this approach is the inability to retrieve photosensitizers after phototreatment, posing potential adverse environmental impacts. Additionally, conventional photosensitizers often exhibit limited photostability and photodynamic efficiency. This study addresses these challenges by employing an aggregation-induced emission (AIE) photosensitizer, iron oxide magnetic nanoparticles (Fe3O4 MNPs), and Pluronic F127 to fabricate AIE magnetic nanoparticles (AIE MNPs). AIE MNPs not only exhibit fluorescence imaging capabilities and superior photosensitizing ability but also demonstrate broad-spectrum bactericidal activities against both Gram-positive and Gram-negative bacteria. The controlled release of TPA-Py-PhMe and magnetic characteristics of the AIE MNPs facilitate reuse and recycling for multiple cycles of bacterial inactivation in water. Our findings contribute valuable insights into developing environmentally friendly disinfectants, emphasizing the full potential of AIE photosensitizers in photodynamic inactivation beyond biomedical applications.

Domestic LED bulb induced photodynamic effect of Toluidine Blue O-embedded silicone catheters against urinary tract infection

BACKGROUND

Novel combination of Toluidine Blue O (TBO) embedded silicone catheter with domestic/household LED bulb has a potential in clinical infection such as prevention of multi drug resistant catheter-associated urinary tract infections (CAUTIs) through photodynamic therapy.

MATERIAL AND METHODS

Preliminarily, TBO was entrapped into silicone catheter by swell-encapsulation-shrink method. Further, in vitro study was carried out to check the antimicrobial photodynamic efficacy of TBO with domestic/household LED light. Antibiofilm activity was evaluated by scanning electron microscopy.

RESULTS

The results showed that these modified TBO embedded silicone catheters showed significant antimicrobial and antibiofilm activity against vancomycin resistant Staphylococcus aureus VRSA. Small piece (1 cm) of TBO-embedded silicone catheter (700 µM) showed 6 log₁₀ reduction in the viable count when exposed for only 5 min of domestic/household LED bulb, while 1 cm piece of 500 µM and 700 µM concentration of TBO-embedded catheter eradicated all bacterial load when exposed to 15 min of light. Segment of medical grade TBO-embedded silicone catheters were used to carry out investigation of reactive oxygen species generation mainly singlet oxygen that contributes to type II phototoxicity.

CONCLUSION

These modified catheter provides cost effective, easy to manage and less time consuming therapy to eliminate CAUTIs.

Optimization of PVDF-TrFE Based Electro-Conductive Nanofibers: Morphology and In Vitro Response

In this study, morphology and in vitro response of electroconductive composite nanofibers were explored for biomedical use. The composite nanofibers were prepared by blending the piezoelectric polymer poly(vinylidene fluoride-trifluorethylene) (PVDF-TrFE) and electroconductive materials with different physical and chemical properties such as copper oxide (CuO), poly(3-hexylthiophene) (P3HT), copper phthalocyanine (CuPc), and methylene blue (MB) resulting in unique combinations of electrical conductivity, biocompatibility, and other desirable properties. Morphological investigation via SEM analysis has remarked some differences in fiber size as a function of the electroconductive phase used, with a reduction of fiber diameters for the composite fibers of 12.43% for CuO, 32.87% for CuPc, 36.46% for P3HT, and 63% for MB. This effect is related to the peculiar electroconductive behavior of fibers: measurements of electrical properties showed the highest ability to transport charges of methylene blue, in accordance with the lowest fibers diameters, while P3HT poorly conducts in air but improves charge transfer during the fiber formation. In vitro assays showed a tunable response of fibers in terms of viability, underlining a preferential interaction of fibroblast cells to P3HT-loaded fibers that can be considered the most suitable for use in biomedical applications. These results provide valuable information for future studies to be addressed at optimizing the properties of composite nanofibers for potential applications in bioengineering and bioelectronics.

Sophorolipid-toluidine blue conjugates for improved antibacterial photodynamic therapy through high accumulation

Anti-bacterial photodynamic therapy is the most promising treatment protocol for bacterial infection, but low accumulation of photosensitizers has seriously hindered their development in clinical application. Here, with inherent outstanding affinity to bacterial cell envelope, sophorolipid produced from Candida bombicola has been conjugated to toluidine blue (SL-TB) through amidation reaction. The structure of SL-TB conjugates was identified by ¹H-NMR, FT-IR and ESI-HRMS. The interfacial assembly and photophysical properties of SL-TB conjugates have been disclosed through surface tension, micro-polarity, electronic and fluorescence spectra. After light irradiation, the log₁₀ (reduced CFU) of free toluidine blue to P. aeruginosa and S. aureus were 4.5 and 7.9, respectively. In contrast, SL-TB conjugates showed a higher bactericidal activity, with a reduction of 6.3 and 9.7 log₁₀ units of CFU against P. aeruginosa and S. aureus, respectively. The fluorescence quantitative results showed that SL-TB could accumulate 2850 nmol/10¹¹ cells and 4360 nmol/10¹¹ cells by P. aeruginosa and S. aureus, which was much higher than the accumulation of 462 nmol/10¹¹ cells and 827 nmol/10¹¹ cells of free toluidine blue. Through the cooperation of triple factors, including sophorose affinity to bacterial cells, hydrophobic association with plasma membrane, and electrostatic attraction, higher SL-TB accumulation was acquired, which has enhanced antibacterial photodynamic efficiencies.

Electrochemically Deposited Zinc (Tetraamino)phthalocyanine as a Light-activated Antimicrobial Coating Effective against S. aureus

Light-activated antimicrobial coatings are currently considered to be a promising approach for the prevention of nosocomial infections. In this work, we present a straightforward strategy for the deposition of a photoactive biocidal organic layer of zinc (tetraamino)phthalocyanine (ZnPcNH₂) in an electrochemical oxidative process. The chemical structure and morphology of the resulting layer are widely characterized by microscopic and spectroscopic techniques, while its ability to photogenerate reactive oxygen species (ROS) is investigated in situ by UV–Vis spectroscopy with α-terpinene or 1,3-diphenylisobenzofuran as a chemical trap. It is shown that the ZnPcNH₂ photosensitizer retained its photoactivity after immobilization, and that the reported light-activated coating exhibits promising antimicrobial properties towards Staphyloccocus aureus (S. aureus).

Physically Switchable Antimicrobial Surfaces and Coatings: General Concept and Recent Achievements

Bacterial environmental colonization and subsequent biofilm formation on surfaces represents a significant and alarming problem in various fields, ranging from contamination of medical devices up to safe food packaging. Therefore, the development of surfaces resistant to bacterial colonization is a challenging and actively solved task. In this field, the current promising direction is the design and creation of nanostructured smart surfaces with on-demand activated amicrobial protection. Various surface activation methods have been described recently. In this review article, we focused on the "physical" activation of nanostructured surfaces. In the first part of the review, we briefly describe the basic principles and common approaches of external stimulus application and surface activation, including the temperature-, light-, electric- or magnetic-field-based surface triggering, as well as mechanically induced surface antimicrobial protection. In the latter part, the recent achievements in the field of smart antimicrobial surfaces with physical activation are discussed, with special attention on multiresponsive or multifunctional physically activated coatings. In particular, we mainly discussed the multistimuli surface triggering, which ensures a better degree of surface properties control, as well as simultaneous utilization of several strategies for surface protection, based on a principally different mechanism of antimicrobial action. We also mentioned several recent trends, including the development of the to-detect and to-kill hybrid approach, which ensures the surface activation in a right place at a right time.

Surfactin-methylene blue complex under LED illumination for antibacterial photodynamic therapy: Enhanced methylene blue transcellular accumulation assisted by surfactin

Recently, increased attention has been focused on antibacterial photodynamic therapy (APDT) to treat multidrug-resistant bacterial infection due to the antibiotic abuse. Methylene blue has been used as a kind of efficient and cheap commercial photosensitizer in APDT. However, due to high hydrophilicity, methylene blue is not able to be transcellular intaken and accumulated efficiently. To promote accumulation and APDT efficiency of methylene blue, lipopeptide surfactin-methylene blue complex has been prepared through electrostatic interaction. The complex under LED irradiation was found to effectively reduce 5.0 Log₁₀ CFU and 7.6 Log₁₀ CFU for P. aeruginosa and S. aureus, respectively. The bacterial reduction efficiency is slightly higher than free methylene blue. The photosensitizers accumulation and APDT targeting protein have been characterized by fluorescence spectroscopy, fluorescence microscopy and protein electrophoresis techniques. These results demonstrated that more surfactin-methylene blue complex could be accumulated more into the cell, and inactivate bacteria through destroying intracellular protein under LED illumination. In comparison, free methylene blue under light could inactivate bacteria through destroying membrane protein and lipid structures. These results would provide valuable insight for developing advanced clinical medicine and designing photo-drug for photodynamic therapy.

Covalent Immobilization of Organic Photosensitizers on the Glass Surface: Toward the Formation of the Light-Activated Antimicrobial Nanocoating

Two highly efficient commercial organic photosensitizers—azure A (AA) and 5-(4-aminophenyl)-10,15,20-(triphenyl)porphyrin (APTPP)—were covalently attached to the glass surface to form a photoactive monolayer. The proposed straightforward strategy consists of three steps, i.e., the initial chemical grafting of 3-aminopropyltriethoxysilane (APTES) followed by two chemical postmodification steps. The chemical structure of the resulting mixed monolayer (MIX_TC_APTES@glass) was widely characterized by X-ray photoelectron (XPS) and Raman spectroscopies, while its photoactive properties were investigated in situ by UV–Vis spectroscopy with α-terpinene as a chemical trap. It was shown that both photosensitizers retain their activity toward light-activated generation of reactive oxygen species (ROS) after immobilization on the glassy surface and that the resulting nanolayer shows high stability. Thanks to the complementarity of the spectral properties of AA and APTPP, the effectiveness of the ROS photogeneration under broadband illumination can be optimized. The reported light-activated nanocoating demonstrated promising antimicrobial activity toward Escherichia coli (E. coli), by reducing the number of adhered bacteria compared to the unmodified glass surface.

A study of the interaction of cationic dyes with gold nanostructures

The interaction of methylene blue and crystal violet dyes with a range of gold nanoparticles (AuNPs), gold nanoclusters and gold/silver nanoclusters is reported.

Photoactive rose bengal-based latex via RAFT emulsion polymerization-induced self-assembly

Rose bengal shell- or core-functionalized acrylic latex synthesized by RAFT emulsion PISA: interfacial photosensitized ¹O₂ production under visible light.

Hot-melt extrusion of photodynamic antimicrobial polymers for prevention of microbial contamination

Infectious disease outbreaks within healthcare facilities can exacerbate patient illness and, in some cases, can be fatal. Contaminated surfaces and medical devices can act as a reservoir for transmission of pathogens and have been linked to the rising incidence of healthcare-acquired infections. Antimicrobial surfaces can reduce microbial contamination and transmission and have emerged as a crucial component in healthcare infection control in recent years. The aim of this study was to manufacture antimicrobial polymer surfaces containing the photosensitiser, toluidine blue O (TBO), using hot-melt extrusion (HME). Several concentrations of TBO were combined with a range of medically relevant polymers via HME. TBO-polymer extrudates displayed no significant differences in thermal properties and surface wettability relative to non-loaded polymers. Minimal leaching of TBO from the surface was confirmed through in vitro release studies. Antibacterial activity was observed to vary according to the polymer and concentration of incorporated TBO, with PEBAX® polymers modified with 0.1% w/w TBO demonstrating promising reductions of >99.9% in viable bacterial adherence of a range of common nosocomial pathogens, including Staphylococcus aureus, Staphylococcus epidermidis, Acinetobacter baumannii and Escherichia coli. This study demonstrates the use of HME as a facile alternative method to common encapsulation strategies for the production of light-activated antimicrobial polymer surfaces. This method can be easily translated to large-scale manufacture and, in addition, the polymers constitute promising antimicrobial base materials for the rapidly growing additive manufacturing industries.

Effect of long-term methylene blue treatment on the composition of mouse gut microbiome and its relationship with the cognitive abilities of mice

In recent years, methylene blue (MB) has attracted considerable interest as a potential drug for the treatment of methemoglobinemia and neurodegenerative diseases. MB is active against microorganisms from various taxonomic groups. However, no studies have yet been conducted on the effect of MB on the intestinal microbiome of model animals. The aim of this work was to study the effect of different concentrations of MB on the mouse gut microbiome and its relationship with the cognitive abilities of mice. We showed that a low MB concentration (15 mg/kg/day) did not cause significant changes in the microbiome composition. The Bacteroidetes/Firmicutes ratio decreased relative to the control on the 2nd and 3rd weeks. A slight decrease in the levels Actinobacteria was detected on the 3rd week of the experiment. Changes in the content of Delta, Gamma, and Epsilonproteobacteria have been also observed. We did not find significant alterations in the composition of intestinal microbiome, which could be an indication of the development of dysbiosis or other gut dysfunction. At the same time, a high concentration of MB (50 mg/kg/day) led to pronounced changes, primarily an increase in the levels of Delta, Gamma and Epsilonproteobacteria. Over 4 weeks of therapy, the treatment with high MB concentration has led to an increase in the median content of Proteobacteria to 7.49% vs. 1.61% in the control group. Finally, we found that MB at a concentration of 15 mg/kg/day improved the cognitive abilities of mice, while negative correlation between the content of Deferribacteres and cognitive parameters was revealed. Our data expand the understanding of the relationship between MB, cognitive abilities, and gut microbiome in respect to the antibacterial properties of MB.

Photobactericidal activity activated by thiolated gold nanoclusters at low flux levels of white light

The emergence of antibiotic resistant bacteria is a major threat to the practice of modern medicine. Photobactericidal agents have obtained significant attention as promising candidates to kill bacteria, and they have been extensively studied. However, to obtain photobactericidal activity, an intense white light source or UV-activation is usually required. Here we report a photobactericidal polymer containing crystal violet (CV) and thiolated gold nanocluster ([Au25(Cys)18]) activated at a low flux levels of white light. It was shown that the polymer encapsulated with CV do not have photobactericidal activity under white light illumination of an average 312 lux. However, encapsulation of [Au25(Cys)18] and CV into the polymer activates potent photobactericidal activity. The study of the photobactericidal mechanism shows that additional encapsulation of [Au25(Cys)18] into the CV treated polymer promotes redox reactions through generation of alternative electron transfer pathways, while it reduces photochemical reaction type-ІІ pathways resulting in promotion of hydrogen peroxide (H2O2) production.

Antibacterial photodynamic activity of carbon quantum dots/polydimethylsiloxane nanocomposites against Staphylococcus aureus, Escherichia coli and Klebsiella pneumoniae

Despite great efforts, the design of antibacterial surfaces is still a challenge. In this work, results of structural, mechanical, cytotoxic and antibacterial activities of hydrophobic carbon quantum dots/polydimethylsiloxane surfaces are presented. Antibacterial action of this surface is based on the generation of reactive oxygen species which cause bacteria damage by oxidative stress. At the same time, this surface was not cytotoxic towards the NIH/3T3 cells. Swelling-encapsulation-shrink method is applied for encapsulation of hydrophobic carbon quantum dots in medical grade silicone-polydimethylsiloxane. XPS and photoluminescence spectroscopy analyses confirm that hydrophobic carbon quantum dots have been encapsulated successfully into polydimethylsiloxane polymer matrix. Based on stress-strain test the improvement of mechanical properties of these nanocomposites is established. It is shown by electron paramagnetic resonance spectroscopy and luminescence method that nanocomposite generates singlet oxygen initiated by 470 nm blue light irradiation. Antibacterial testing shows the nanocomposite in the form of foil kills Staphylococcus aureus, Escherichia coli and Klebsiella pneumoniae and is very effective after only a 15 min irradiation.

Zinc phthalocyanine activated by conventional indoor light makes a highly efficient antimicrobial material from regular cellulose

A phthalocyanine-cellulose material quickly inactivates drug-resistant microbes under indoor light.

Carbon Quantum Dots Modified Polyurethane Nanocomposite as Effective Photocatalytic and Antibacterial Agents

Development of new types of antibacterial coatings or nanocomposites is of great importance due to widespread multidrug-resistant infections including bacterial infections. Herein, we investigated biocompatibility as well as structural, photocatalytic, and antibacterial properties of photoactive hydrophobic carbon quantum dots/polyurethane nanocomposite. The swell-encapsulation-shrink method was applied for production of these nanocomposites. Hydrophobic carbon quantum dots/polyurethane nanocomposites were found to be highly effective generator of singlet oxygen upon irradiation by low-power blue light. Analysis of conducted antibacterial tests on Staphyloccocus aureus and Escherichia coli showed 5-log bactericidal effect of these nanocomposites within 60 min of irradiation. Very powerful degradation of dye (rose bengal) was observed within 180 min of blue light irradiation of the nanocomposites. Biocompatibility studies revealed that nanocomposites were not cytotoxic against mouse embryonic fibroblast cell line, whereas they showed moderate cytotoxicity toward adenocarcinomic human epithelial cell line. Minor hemolytic effect of these nanocomposites toward red blood cells was revealed.

Superhydrophobic and White Light-Activated Bactericidal Surface through a Simple Coating

Bacterial adhesion and proliferation on surfaces are a challenge in medical and industrial fields. Here, a simple one-step technique is reported to fabricate self-cleaning and bactericidal surfaces. White, blue, and violet paints were produced using titanium dioxide nanoparticles, 1H,1H,2H,2H-perfluorooctyltriethoxysilane, crystal violet, toluidine Blue O, and ethanol solution. All of the painted surfaces showed superhydrophobicity in air, and even after hexadecane oil contamination, they retained water repellency and self-cleaning properties. In an assay of bacterial adhesion, significant reductions (>99.8%) in the number of adherent bacteria were observed for all the painted surfaces. In bactericidal tests, the painted surfaces not only demonstrated bactericidal activity against Staphylococcus aureus and Escherichia coli in the dark but also induced very potent photosensitization (>4.4 log reduction in the number of viable bacteria on the violet painted surface) under white light illumination. The technique that we developed here is general and can be used on a wide range of substrates such as paper, glass, polymers, and others.

Photoactive antimicrobial nanomaterials

Nanomaterials for killing pathogenic bacteria under light irradiation.

Thiol-Capped Gold Nanoparticles Swell-Encapsulated into Polyurethane as Powerful Antibacterial Surfaces Under Dark and Light Conditions

A simple procedure to develop antibacterial surfaces using thiol-capped gold nanoparticles (AuNPs) is shown, which effectively kill bacteria under dark and light conditions. The effect of AuNP size and concentration on photo-activated antibacterial surfaces is reported and we show significant size effects, as well as bactericidal activity with crystal violet (CV) coated polyurethane. These materials have been proven to be powerful antibacterial surfaces against both Gram-positive and Gram-negative bacteria. AuNPs of 2, 3 or 5 nm diameter were swell-encapsulated into PU before a coating of CV was applied (known as PU-AuNPs-CV). The antibacterial activity of PU-AuNPs-CV samples was tested against Staphylococcus aureus and Escherichia coli as representative Gram-positive and Gram-negative bacteria under dark and light conditions. All light conditions in this study simulated a typical white-light hospital environment. This work demonstrates that the antibacterial activity of PU-AuNPs-CV samples and the synergistic enhancement of photoactivity of triarylmethane type dyes is highly dependent on nanoparticle size and concentration. The most powerful PU-AuNPs-CV antibacterial surfaces were achieved using 1.0 mg mL-1 swell encapsulation concentrations of 2 nm AuNPs. After two hours, Gram-positive and Gram-negative bacteria were reduced to below the detection limit (>4 log) under dark and light conditions.

The bactericidal activity of glutaraldehyde-impregnated polyurethane

Although glutaraldehyde is known to be bactericidal in solution, its potential use to create novel antibacterial polymers suitable for use in healthcare environments has not been evaluated. Here, novel materials were prepared in which glutaraldehyde was either incorporated into polyurethane using a simple "swell-encapsulation-shrink" method (hereafter referred to as "glutaraldehyde-impregnated polyurethane"), or simply applied to the polymer surface (hereafter referred to as "glutaraldehyde-coated polyurethane"). The antibacterial activity of glutaraldehyde-impregnated and glutaraldehyde-coated polyurethane samples was tested against Escherichia coli and Staphylococcus aureus. Glutaraldehyde-impregnated polyurethane resulted in a 99.9% reduction in the numbers of E. coli within 2 h and a similar reduction of S. aureus within 1 h, whereas only a minimal reduction in bacterial numbers was observed when the biocide was bound to the polymer surface. After 15 days, however, the bactericidal activity of the impregnated material was substantially reduced presumably due to polymerization of glutaraldehyde. Thus, although glutaraldehyde retains antibacterial activity when impregnated into polyurethane, activity is not maintained for extended periods of time. Future work should examine the potential of chemical modification of glutaraldehyde and/or polyurethane to improve the useful lifespan of this novel antibacterial polymer.

Enhancing the Antibacterial Activity of Light-Activated Surfaces Containing Crystal Violet and ZnO Nanoparticles: Investigation of Nanoparticle Size, Capping Ligand, and Dopants

Healthcare-associated infections pose a serious risk for patients, staff, and visitors and are a severe burden on the National Health Service, costing at least £1 billion annually. Antimicrobial surfaces significantly contribute toward reducing the incidence of infections as they prevent bacterial adhesion and cause bacterial cell death. Using a simple, easily upscalable swell-encapsulation-shrink method, novel antimicrobial surfaces have been developed by incorporating metal oxide nanoparticles (NPs) and crystal violet (CV) dye into medical-grade polyurethane sheets. This study compares the bactericidal effects of polyurethane incorporating ZnO, Mg-doped ZnO, and MgO. All metal oxide NPs are well defined, with average diameters ranging from 2 to 18 nm. These materials demonstrate potent bactericidal activity when tested against clinically relevant bacteria such as Escherichia coli and Staphylococcus aureus. Additionally, these composites are tested against an epidemic strain of methicillin-resistant Staphylococcus aureus (MRSA) that is rife in hospitals throughout the UK. Furthermore, we have tested these materials using a low light intensity (∼500 lx), similar to that present in many clinical environments. The highest activity is achieved from polymer composites incorporating CV and ∼3 nm ZnO NPs, and the different performances of the metal oxides have been discussed.

White Light-Activated Antimicrobial Paint using Crystal Violet

Crystal violet (CV) was incorporated into acrylic latex to produce white-light-activated antimicrobial paint (WLAAP). Measurement of the water contact angle of the WLAAP showed that the water contact angle increased with increasing CV concentration. In a leaching test over 120 h, the amount of CV that leached from the WLAAPs was close to the detection limit (<0.03%). The WLAAPs were used to coat samples of polyurethane, and these showed bactericidal activity against Escherichia coli, which is a key causative agent of healthcare-associated infections (HAIs). A reduction in the numbers of viable bacteria was observed on the painted coated polyurethane after 6 h in the dark, and the bactericidal activity increased with increasing CV concentration (P < 0.1). After 6 h of white light exposure, all of coated polyurethanes demonstrated a potent photobactericidal activity, and it was statistically confirmed that the WLAAP showed better activity in white light than in the dark (P < 0.05). At the highest CV concentration, the numbers of viable bacteria fell below the detection limit (<10(3) CFU/mL) after 6 h of white light exposure. The difference in antimicrobial activity between the materials in the light and dark was 0.48 log at CV 250 ppm, and it increased by 0.43 log at each increment of CV 250 ppm. The difference was the highest (>1.8 log) at the highest CV concentration (1000 ppm). These WLAAPs are promising candidates for use in healthcare facilities to reduce HAIs.

Synthesis, characterization and biological evaluation of a new photoactive hydrogel against Gram-positive and Gram-negative bacteria

Development of a cheap material active against both Gram-positive and Gram-negative bacteria to be used as a novel water-sterilizing device.

White light-activated antimicrobial surfaces: effect of nanoparticles type on activity

Toluidine blue O (TBO) dye together with either silver (Ag) nanoparticles (NPs), gold (Au) NPs, or a mixture of Ag and Au NPs (Mix Ag–Au NPs) were incorporated into polyurethane to make antimicrobial surfaces using a swell-encapsulation-shrink process.

Comparative study of singlet oxygen production by photosensitiser dyes encapsulated in silicone: towards rational design of anti-microbial surfaces

Theoretical and experimental toolbox for the rational design of light-activated antimicrobial surfaces.

Methylene Blue Doped Films of Wool Keratin with Antimicrobial Photodynamic Activity

In this work, keratin films doped with different amounts of methylene blue (MB) were developed in order to prepare new biodegradable and biocompatible materials for tissue engineering and wound healing, able to exert antimicrobial photodynamic activity upon irradiation with visible light. Preliminary results indicated that the swelling ratio, as well as the MB release, increases by increasing the pH. Moreover, the generation of reactive oxygen species (ROS) and singlet oxygen can be easily triggered and controlled by a fine-tuning of the irradiation time and MB concentration in the films. As concerns the photodynamic effects on keratin, the ROS attack does not induce any significant photodegradation on the protein, even if a slight photo-oxidation of sulfonated amino acids occurs. Finally, the film with the highest MB concentration (400 μg per gram of keratin) displays a significant photobactericidal activity against Staphylococcus aureus with a bacterial reduction that increases by increasing the irradiation time. In particular, the irradiation of KFMB400 film incubated with S. aureus at a concentration of 10(8) cfu mL(-1) determined the 99.9% killing rate and the killing effect increased proportionally with irradiation time.

Chitosan finishing nonwoven textiles loaded with silver and iodide for antibacterial wound dressing applications

Polyethylene terephtalate (PET) and Polypropylene (PP) textiles are widely used in biomedical application such as wound dressings and implants. The aim of this work was to develop an antibacterial chitosan (CHT) coating activated by silver or by iodine. Chitosan was immobilized onto PET and PP supports using citric acid (CTR) as a crosslinking agent through a pad-dry-cure textile finishing process. Interestingly, depending on the CHT/CTR molar ratio, two different systems were obtained: rich in cationic ammonium groups when the CTR concentration was 1%w/v, and rich in anionic carboxylate groups when the CTR concentration was 10%w/v. As a consequence, such samples could be selectively loaded with iodine and silver nitrate, respectively.Both types of coatings were analyzed using SEM and FTIR, their sorption capacities were evaluated toward iodide/iodate anions (I(-)/IO3(-)) and the silver cations (Ag(+)) were evaluated using elemental analysis. Finally, in vitro evaluations were carried out to evaluate the cytocompatibility on the epithelial cell line. The silver loaded textile reported a stronger antibacterial effect against E.coli (5 log10 reduction) than toward S. aureus (3 log10) while the antibacterial effect of the iodide loaded textiles was limited to 1 log10 to 2 log10 on both strains.

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

Bactericidal polymer surfaces were prepared by crystal violet and ZnO nanoparticle encapsulation, demonstrating 99.9% dark kill ofE. coli.

The interaction of bacteria with engineered nanostructured polymeric materials: a review

Bacterial infections are a leading cause of morbidity and mortality worldwide. In spite of great advances in biomaterials research and development, a significant proportion of medical devices undergo bacterial colonization and become the target of an implant-related infection. We present a review of the two major classes of antibacterial nanostructured materials: polymeric nanocomposites and surface-engineered materials. The paper describes antibacterial effects due to the induced material properties, along with the principles of bacterial adhesion and the biofilm formation process. Methods for antimicrobial modifications of polymers using a nanocomposite approach as well as surface modification procedures are surveyed and discussed, followed by a concise examination of techniques used in estimating bacteria/material interactions. Finally, we present an outline of future sceneries and perspectives on antibacterial applications of nanostructured materials to resist or counteract implant infections.

The antibacterial properties of light-activated polydimethylsiloxane containing crystal violet

Crystal violet was incorporated into polydimethylsiloxane (PDMS) by a swell–encapsulation–shrink method using chloroform as a swelling solvent.

Light-activated antimicrobial surfaces with enhanced efficacy induced by a dark-activated mechanism

We report a potent antimicrobial polymer demonstrating an enhanced bactericidal activity upon white light illumination.