Silver/Graphene Oxide Nanostructured Coatings for Modulating the Microbial Susceptibility of Fixation Devices Used in Knee Surgery.

Exploring silver-based and carbon-based nanomaterials' excellent intrinsic antipathogenic effects represents an attractive alternative for fabricating anti-infective formulations. Using chemical synthesis protocols, stearate-conjugated silver (Ag@C18) nanoparticles and graphene oxide nanosheets (nGOs) were herein obtained and investigated in terms of composition and microstructure. Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) characterizations revealed the formation of nanomaterials with desirable physical properties, while X-ray diffraction (XRD) analyses confirmed the high purity of synthesized nanomaterials. Further, laser-processed Ag@C18-nGO coatings were developed, optimized, and evaluated in terms of biological and microbiological outcomes. The highly biocompatible Ag@C18-nGO nanostructured coatings proved suitable candidates for the local modulation of biofilm-associated periprosthetic infections.

Combining Microscopy Assays of Bacteria-Surface Interactions To Better Evaluate Antimicrobial Polymer Coatings.

Validation of the antimicrobial performance of contact-killing polymer surfaces through the experimental determination of bacterial adhesion or viability, is essential for their targeted development and application. However, there is not yet a consensus on the single most appropriate evaluation method or procedure. Combining and benchmarking previously reported assays could reduce the significant variation and misinterpretation of efficacy data obtained from different methods. In this work, we systematically investigated the response of bacterial cells to antiadhesive and antiseptic polymer coatings by combining (i) bulk solution-based, (ii) thin-film spacer-based, and (iii) direct-contact assays. In addition, we evaluated the studied assays using a five-point scoring framework that highlights key areas for improvement. Our data suggest that combined microscopy assays provide a more comprehensive representation of antimicrobial performance, thereby helping to identify effective types of antibacterial polymer coatings. IMPORTANCE We present and evaluate a combination of methods for validating the efficacy of antimicrobial surfaces. Antimicrobial surfaces/coatings based on contact-killing components can be instrumental to functionalize a wide range of products. However, there is not yet a consensus on the single, most appropriate method to evaluate their performance. By combining three microscopy methods, we were able to discern contact-killing effects at the single-cell level that were not detectable by conventional bulk microbiological analyses. The developed approach is considered advantageous for the future targeted development of robust and sustainable antimicrobial surfaces.

Loading of Polydimethylsiloxane with a Human ApoB-Derived Antimicrobial Peptide to Prevent Bacterial Infections.

BACKGROUND: medical device-induced infections affect millions of lives worldwide and innovative preventive strategies are urgently required. Antimicrobial peptides (AMPs) appear as ideal candidates to efficiently functionalize medical devices surfaces and prevent bacterial infections. In this scenario, here, we produced antimicrobial polydimethylsiloxane (PDMS) by loading this polymer with an antimicrobial peptide identified in human apolipoprotein B, r(P)ApoBLPro. METHODS: once obtained loaded PDMS, its structure, anti-infective properties, ability to release the peptide, stability, and biocompatibility were evaluated by FTIR spectroscopy, water contact angle measurements, broth microdilution method, time-killing kinetic assays, quartz crystal microbalance analyses, MTT assays, and scanning electron microscopy analyses. RESULTS: PDMS was loaded with r(P)ApoBLPro peptide which was found to be present not only in the bulk matrix of the polymer but also on its surface. ApoB-derived peptide was found to retain its antimicrobial properties once loaded into PDMS and the antimicrobial material was found to be stable upon storage at 4 °C for a prolonged time interval. A gradual and significant release (70% of the total amount) of the peptide from PDMS was also demonstrated upon 400 min incubation and the antimicrobial material was found to be endowed with anti-adhesive properties and with the ability to prevent biofilm attachment. Furthermore, PDMS loaded with r(P)ApoBLPro peptide was found not to affect the viability of eukaryotic cells. CONCLUSIONS: an easy procedure to functionalize PDMS with r(P)ApoBLPro peptide has been here developed and the obtained functionalized material has been found to be stable, antimicrobial, and biocompatible.

Development of Functional Composite Cu(II)-Polyoxometalate/PLA with Antimicrobial Properties.

Novel composite self-disinfecting films of polylactic acid (PLA) filled with nanosized particles of double sodium-copper(II) paratungstate B Na2Cu3(CuOH)2[W12O40(OH)2]·32H2O (POM) were developed. The solvent casting (POM/PLA film) and solvent-free melt extrusion methods (Extr. POM/PLA film) were applied for film preparation. The copper (II) ion release to water from both types of the films after 10 days at different temperatures demonstrated that the PLA matrix acts as a diffusion barrier, and the resulting concentration of released copper in water at room temperature remained low, at 0.79% for POM/PLA film and 0.51% for Extr. POM/PLA film. The POM-containing films reveals a significant inhibitory effect against E. coli ATCC 25922 in the agar diffusion test. The numbers of CFUs in washes of the films after incubation for 24 h were found to be 3.6 log CFU mL-1 (POM/PLA film) and 4.1 log CFU mL-1 (Extr. POM/PLA film). The films combine the antibacterial properties of POM and a bio-based polymer matrix, which makes them a prospective coating material for applications in hospital indoor environments. Excellent thermal stability of POM gives a technological advantage for industrial manufacturing to allow the processing of novel composite material in the solvent free (molten) state.

Electrochemical removal of anodic aluminium oxide templates for the production of phase-pure cuprous oxide nanorods for antimicrobial surfaces.

Antimicrobial surfaces are ones that incapacitate or kill pathogens landing on them, which could allow for self-sanitising surfaces for hospitals or implants, ensuring healthier stays and procedures. Cuprous compounds such as Cu2O are especially effective at incapacitating both viruses and bacteria, and nanorod arrays have been shown to prevent the adhesion of pathogens and mechanically deform bacteria to the point that their cell walls rupture. A Cu2O nanorod array should therefore allow for the exploitation of both of these effects. In the present work, an electrochemical method is introduced, where Cu2O nanorods formed in a substrate-supported anodic aluminium oxide (AAO) template are held at a stable electrochemical potential throughout the removal of the AAO template. This avoids the partial reduction of the nanorods from Cu2O to Cu that was observed during chemical removal of the template, which was attributed to the presence of residual aluminium from the template fabrication process that reacts with the etchant and lowers the electrochemical potential of the nanorods to a value that favours reduction. Using the electrochemical removal method, the reliable production of phase-pure, free-standing, crystalline Cu2O nanorod arrays on ITO/glass substrates is demonstrated. This simple method is compatible with nanorod arrays of any size.

DNA-Based Nanofabrication: Pathway to Applications in Surface Engineering.

This Concept provides an overview of recent developments of DNA-based nanofabrication and discusses its potential applications in the area of surface engineering. The first part of the paper discusses the strength and limitations of existing DNA-based nanofabrication methods. The second part highlights several examples of surface engineering applications involving nano- and microscale surface textures. It finishes with a discussion of the opportunities and remaining challenges of applying DNA-based nanofabrication in surface engineering applications.

Antimicrobial properties of ternary eutectic aluminum alloys.

Several Escherichia coli deletion mutants of the Keio collection were selected for analysis to better understand which genes may play a key role in copper or silver homeostasis. Each of the selected E. coli mutants had a deletion of a single gene predicted to encode proteins for homologous recombination or contained functions directly linked to copper or silver transport or transformation. The survival of these strains on pure copper surfaces, stainless steel, and alloys of aluminum, copper and/or silver was investigated. When exposed to pure copper surfaces, E. coli ΔcueO was the most sensitive, whereas E. coli ΔcopA was the most resistant amongst the different strains tested. However, we observed a different trend in sensitivities in E. coli strains upon exposure to alloys of the system Al-Ag-Cu. While minor antimicrobial effects were detected after exposure of E. coli ΔcopA and E. coli ΔrecA to Al-Ag alloys, no effect was detected after exposure to Al-Cu alloys. The release of copper ions and cell-associated copper ion concentrations were determined for E. coli ΔcopA and the wild-type E. coli after exposure to pure copper surfaces. Altogether, compared to binary alloys, ternary eutectic alloys (Al-Ag-Cu) had the highest antimicrobial effect and thus, warrant further investigation.

Potential of antimicrobial treatment of linear low-density polyethylene with poly((tert-butyl-amino)-methyl-styrene) to reduce biofilm formation in the food industry.

Antimicrobial surfaces are one approach to prevent biofilms in the food industry. The aim of this study was to investigate the effect of poly((tert-butyl-amino)-methyl-styrene) (poly(TBAMS)) incorporated into linear low-density polyethylene (LLDPE) on the formation of mono- and mixed-species biofilms. The biofilm on untreated and treated LLDPE was determined after 48 and 168 h. The comparison of the results indicated that the ability of Listeria monocytogenes to form biofilms was completely suppressed by poly(TBAMS) (Δ168 h 3.2 log10 cfu cm-2) and colonization of Staphylococcus aureus and Escherichia coli was significantly delayed, but no effect on Pseudomonas fluorescens was observed. The results of dual-species biofilms showed complex interactions between the microorganisms, but comparable effects on the individual bacteria by poly(TBAMS) were identified. Antimicrobial treatment with poly(TBAMS) shows great potential to prevent biofilms on polymeric surfaces. However, a further development of the material is necessary to reduce the colonization of strong biofilm formers.

Quaternary ammonium-based biomedical materials: State-of-the-art, toxicological aspects and antimicrobial resistance.

Microbial infections affect humans worldwide. Many quaternary ammonium compounds have been synthesized that are not only antibacterial, but also possess antifungal, antiviral and anti-matrix metalloproteinase capabilities. Incorporation of quaternary ammonium moieties into polymers represents one of the most promising strategies for preparation of antimicrobial biomaterials. Various polymerization techniques have been employed to prepare antimicrobial surfaces with quaternary ammonium functionalities; in particular, syntheses involving controlled radical polymerization techniques enable precise control over macromolecular structure, order and functionality. Although recent publications report exciting advances in the biomedical field, some of these technological developments have also been accompanied by potential toxicological and antimicrobial resistance challenges. Recent evidenced-based data on the biomedical applications of antimicrobial quaternary ammonium-containing biomaterials that are based on randomized human clinical trials, the golden standard in contemporary medicinal science, are included in the present review. This should help increase visibility, stimulate debates and spur conversations within a wider scientific community on the implications and plausibility for future developments of quaternary ammonium-based antimicrobial biomaterials.

Broad-Spectrum Supramolecularly Reloadable Antimicrobial Coatings.

Antimicrobial surfaces limit the spread of infectious diseases. To date, there is no antimicrobial coating that has widespread use because of short-lived and limited spectrum efficacy, poor resistance to organic material, and/or cost. Here, we present a paint based on waterborne latex particles that is supramolecularly associated with quaternary ammonium compounds (QACs). The optimal supramolecular pairing was first determined by immobilizing selected ions on self-assembled monolayers exposing different groups. The QAC surface loading density was then increased by using polymer brushes. These concepts were adopted to develop inexpensive paints to be applied on many different surfaces. The paint could be employed for healthcare and food production applications. Its slow release of QAC allows for long-lasting antimicrobial action, even in the presence of organic material. Its efficacy lasts for more than 90 washes, and importantly, once lost, it can readily be restored by spraying an aqueous solution of the QAC. We mainly tested cetyltrimethylammonium as QAC as it is already used in consumer care products. Our antimicrobial paint is broad spectrum as it showed excellent antimicrobial efficiency against four bacteria and four viruses.

Antibacterial activity of solid surfaces is critically dependent on relative humidity, inoculum volume, and organic soiling.

Antimicrobial surface materials potentially prevent pathogen transfer from contaminated surfaces. Efficacy of such surfaces is assessed by standard methods using wet exposure conditions known to overestimate antimicrobial activity compared to dry exposure. Some dry test formats have been proposed but semi-dry exposure scenarios e.g. oral spray or water droplets exposed to ambient environment, are less studied. We aimed to determine the impact of environmental test conditions on antibacterial activity against the model species Escherichia coli and Staphylococcus aureus. Surfaces based on copper, silver, and quaternary ammonium with known or claimed antimicrobial properties were tested in conditions mimicking microdroplet spray or larger water droplets exposed to variable relative air humidity in the presence or absence of organic soiling. All the environmental parameters critically affected antibacterial activity of the tested surfaces from no effect in high-organic dry conditions to higher effect in low-organic humid conditions but not reaching the effect size demonstrated in the ISO 22169 wet format. Copper was the most efficient antibacterial surface followed by silver and quaternary ammonium based coating. Antimicrobial testing of surfaces using small droplet contamination in application-relevant conditions could therefore be considered as one of the worst-case exposure scenarios relevant to dry use surfaces.

Temperature and pH Stimuli-Responsive System Delivers Location-Specific Antimicrobial Activity with Natural Products.

Smart materials with controlled stimuli-responsive functions are at the forefront of technological development. In this work, we present a generic strategy that combines simple components, physicochemical responses, and easy fabrication methods to achieve a dual stimuli-responsive system capable of location-specific antimicrobial cargo delivery. The encapsulated system is fabricated by combining a biocompatible inert polymeric matrix of poly(dimethylsiloxane) (PDMS) and a bioactive cargo of saturated fatty acids. We demonstrate the effectiveness of our approach to deliver antimicrobial activity for the model bacteria Escherichia coli. The system responds to two control variables, temperature and pH, delivering two levels of antimicrobial response under distinct combinations of stimuli: one response toward the planktonic media and another response directly at the surface for sessile bacteria. Spatially resolved Raman spectroscopy alongside thermal and structural material analysis reveals that the system not only exhibits ON/OFF states but can also control relocation and targeting of the active cargo toward either the surface or the liquid media, leading to different ON/OFF states for the planktonic and sessile bacteria. The approach proposed herein is technologically simple and scalable, facing low regulatory barriers within the food and healthcare sectors by using approved components and relying on fundamental chemical processes. Our results also provide a proof-of-concept platform for the design and easy fabrication of delivery systems capable of operating as Boolean logic gates, delivering different responses under different environmental conditions.

Correlating the physico-chemical properties of two conventional glazed porcelain stoneware tiles in relation to cleanability and sanitization.

Keeping surfaces clean can reduce the spread of infections. In particular, to decrease the potential for SARS CoV-2 contamination, performing disinfection of high-touching surfaces. Several ceramic tiles and porcelain stoneware tiles with antimicrobial properties are already available on the market. However, the widespread use of antimicrobial glazed stoneware tiles may require to replace the ceramic surfaces already present in many buildings. The unfeasibility of such replacement can be due to both product durability (lifetime of a tile is usually long) and/or monetary restrictions. Furthermore, as porcelain stoneware per se does not have antimicrobial activity, these materials are fabricated by adding chemical agents able to provide antimicrobial properties. This approach requires a compatibility between the antimicrobial agents and the glaze formulation, as well as a careful control of the firing cycle and the final properties of the ceramic products. It follows that the final cost of antimicrobial tiles is not competitive with that of conventional tiles. In the latter, the persistence of potential pathogens on the surfaces is a crucial problem to face: the longer a pathogen survives on a surface, the longer it may be a source of transmission and thus endanger susceptible subjects. In this work, bacteria's capacity to adhere and to be effectively removed from two conventional glazed porcelain stoneware tiles (under dirty and clean conditions) was investigated. Two different glazes were tested, one mainly glassy (glossy) and the other mainly crystalline (matt). The sanitization procedures were carried out by chemical and chemo-mechanical procedures. The results showed that chemo-mechanical sanitization was the most effective, and the best results could be obtained on the stoneware tiles coated with the mainly glassy glaze, with the lowest porosity and the lower roughness values and water contact angles, especially under clean conditions.

Interlaboratory reproducibility of a touch-transfer assay for the assessment of antimicrobial surfaces.

BACKGROUND: Various assay methods have been developed to study antimicrobial activity based on contamination of surfaces with different amounts of liquid bacterial suspensions. Since surfaces with frequent hand contact are typically touched in a dry state in clinical settings, these tests may be inappropriate at assessing effectiveness to reduce pathogen transmission. AIM: To investigate a surface previously confirmed to display antimicrobial activity even after drying of small volumes of bacterial suspension (Egger antimicrobial surfaces: EAS) under conditions modelling dry contamination using a touch-transfer method. METHODS: EAS, an antimicrobial copper alloy, as well as a negative control were examined to assess interlaboratory test reproducibility. FINDINGS: Significantly fewer bacteria on EAS after touch transfer and some differences in the touch transmission were detected between the two laboratories. However, an identical assessment of effectiveness for EAS came from both laboratories. Interestingly, despite previously detected antimicrobial efficacy of EAS and the antimicrobial copper alloy after liquid contamination, insufficient activity was observed under dry conditions during a contact time of 4 h by both laboratories. Experiments under standardized air humidity in one laboratory revealed at least for copper a strong influence of humidity on antimicrobial activity. These data indicate that procedures involving contamination of surfaces with organisms suspended in liquids are not directly comparable to dry contamination. CONCLUSION: Since, in the real world of a hospital, organisms are typically transferred between dry surfaces, further standardization of the touch-transfer method is worthwhile for a better understanding of the efficacy of such surfaces.

Activity of antimicrobial examination gloves under realistic conditions: challenge not fulfilled.

BACKGROUND: Antimicrobial materials or surfaces are advertised as part of infection prevention bundles. However, the efficacy of such antimicrobial surfaces has not been sufficiently investigated in hospitals. In this study, the antimicrobial activity of examination gloves with light-activated antimicrobial properties against Gram-positive microorganisms was investigated modelling real live conditions. METHOD: In a standardized experimental set-up with dry and realistic contamination, the antimicrobial properties of gloves claiming light dependent antimicrobial activity against Gram-positive organisms were tested in comparison with conventional examination gloves. All gloves were contaminated through a standardized activity of the test persons for construction with contaminated building blocks. For contamination suspensions of Enterococcus faecium ATCC 6057, Acinetobacter baumannii (outbreak strain), methicillin resistant Staphylococcus aureus ATCC 43300 or E. faecium (VRE) patient isolate were dried on the surfaces. After the standardized activity, the gloves were held for 10 min in the light present in the room (bright conditions) and the grade of contamination was determined subsequently by quantitative culture. In one experimental series gloves were held in a dark box after contamination as a control (dark conditions). RESULTS: The light intensity in all experiments under bright conditions was significantly above the limit value specified by the manufacturer for the activation of antimicrobial properties (> 500 lx). The mean values for experiments with antimicrobial active and non-active gloves were 955 and 935 lx, respectively. As claimed by the manufacture, the gloves showed no sufficient efficacy against A. baumannii under bright conditions. Against Gram-positive microorganisms such as E. faecium, E. faecium (VRE) and methicillin resistant S. aureus the gloves showed only very low antimicrobial activity with a reduction factor < 1 log10 even after 10 min in bright conditions. Interestingly, comparable results for experiments with A. baumannii and E. faecium were shown under dark conditions. CONCLUSION: The lack of activity of the active principle against Gram-negative microorganisms could be confirmed. The reduction factors of > 4 log10 within 5 min for Gram-positive microorganisms claimed for the product using a standard test procedure (ASTM D7907) could not be confirmed in a realistic experimental test set-up even after 10 min of light exposure. The effectiveness against Gram-positive microorganisms should be further investigated under realistic (dry) conditions, including patient care. At this stage, the use of supposedly antimicrobial gloves should not be recommended, as the belief in their efficacy may encourage the misuse of gloves.

Developing Novel Biointerfaces: Using Chlorhexidine Surface Attachment as a Method for Creating Anti-Fungal Surfaces.

There is an increasing focus in healthcare environments on combatting antimicrobial resistant infections. While bacterial infections are well reported, infections caused by fungi receive less attention, yet have a broad impact on society and can be deadly. Fungi are eukaryotes with considerable shared biology with humans, therefore limited technologies exist to combat fungal infections and hospital infrastructure is rarely designed for reducing microbial load. In this study, a novel antimicrobial surface (AMS) that is modified with the broad-spectrum biocide chlorhexidine is reported. The surfaces are shown to kill the opportunistic fungal pathogens Candida albicans and Cryptococcus neoformans very rapidly (<15 min) and are significantly more effective than current technologies available on the commercial market, such as silver and copper.

Plasma Electroless Reduction: A Green Process for Designing Metallic Nanostructure Interfaces onto Polymeric Surfaces and 3D Scaffolds.

The design of metal nanoparticle-modified polymer surfaces in a green and scalable way is both desirable and highly challenging. Herein, a new green low-temperature plasma-based in situ surface reduction strategy termed plasma electroless reduction (PER) is reported for achieving in situ metallic nanostructuring on polymer surfaces. Proof of concept for this new method was first demonstrated on hydrophilic cellulose papers. Cellulose papers were dip-coated with different metal ion (Ag+ and Au3+) solutions and then subjected to hydrogen plasma treatment for this PER process. Transmission electron microscopy (TEM) analysis has revealed that this PER process caused anisotropic growth of either gold or silver nanoparticles, resulting in the time-dependent formation of both distinct spherical nanoparticles (∼20 nm) and anisotropic 2D nanosheets. Furthermore, we have demonstrated the adaptability of this process by applying it to hydrophobic fibrous and 3D printed polymeric materials such as surgical face masks and 3D printed polylactic acid scaffolds. The PER process on these hydrophobic polymer surfaces was accomplished via a sequential combination of air plasma and hydrogen plasma treatment. The metallic nanostructuring caused by the PER process on these hydrophobic surfaces was systematically studied using different surface imaging techniques including 3D confocal laser surface scanning microscopy and scanning electron microscopy. We have also systematically optimized the PER process on the surface of 3D scaffolds via varying the concentration of the silver ion precursor and by different postprocessing methods such as sonication and medium soaking. These optimization processes were found to be very important in generating uniform metallic nanoparticle-modified 3D printed scaffolds while simultaneously improving cytocompatibility. Through joint disk diffusion and inhibitory concentration testing, the antibacterial efficacy of silver coatings on face masks and 3D scaffolds was established. Altogether, these results clearly suggest the excellent futuristic potential of this new PER method for designing metallic nanostructured interfaces for different biomedical applications.

Death at the interface: Nanotechnology's challenging frontier against microbial surface colonization.

The emergence of antimicrobial-resistant bacterial strains has led to novel approaches for combating bacterial infections and surface contamination. More specifically, efforts in combining nanotechnology and biomimetics have led to the development of next-generation antimicrobial/antifouling nanomaterials. While nature-inspired nanoscale topographies are known for minimizing bacterial attachment through surface energy and physicochemical features, few studies have investigated the combined inhibitory effects of such features in combination with chemical alterations of these surfaces. Studies describing surface alterations, such as quaternary ammonium compounds (QACs), have also gained attention due to their broad spectrum of inhibitory activity against bacterial cells. Similarly, antimicrobial peptides (AMPs) have exhibited their capacity to reduce bacterial viability. To maximize the functionality of modified surfaces, the integration of patterned surfaces and functionalized exteriors, achieved through physical and chemical surface alterations, have recently been explored as viable alternatives. Nonetheless, these modifications are prone to challenges that can reduce their efficacy considerably in the long term. Their effectiveness against a wider array of microbial cells is still a subject of investigation. This review article will explore and discuss the emerging trends in biomimetics and other antimicrobials while raising possible concerns about their limitations and discussing future implications regarding their potential combined applications.

Potentiation Effect of Iodine Species on the Antimicrobial Capability of Surfaces Coated with Electroactive Phthalocyanines.

The spreading of different infections can occur through direct contact with glass surfaces in commonly used areas. Incorporating the use of alternative therapies in these materials seems essential to reduce and also avoid bacterial resistance. In this work, the capability to kill microbes of glass surfaces coated with two electroactive metalated phthalocyanines (ZnPc-EDOT and CuPc-EDOT) is assessed. The results show that both of these materials are capable of producing reactive oxygen species; however, the polymer with Zn(II) (ZnPc-PEDOT) has a singlet oxygen quantum yield 8-fold higher than that of the Cu(II) containing analogue. This was reflected in the in vitro experiments where the effectiveness of the surfaces was tested in bacterial suspensions, monitoring single microbe inactivation upon attachment to the polymers, and eliminating mature biofilms. Furthermore, we evaluated the use of an inorganic salt (KI) to potentiate the photodynamic inactivation mediated by an electropolymerized surface. The addition of the salt improved the efficiency of phototherapy at least two times for both polymers; nevertheless, the material coated with ZnPc-PEDOT was the only one capable of eliminating >99.98% of the initial microbes loading under different circumstances.