Novel antibacterial silver-silica surface coatings prepared by chemical vapour deposition for infection control

Assessing Antimicrobial Efficacy on Plastics and Other Non-Porous Surfaces: A Closer Look at Studies Using the ISO 22196:2011 Standard

The survival and spread of foodborne and nosocomial-associated bacteria through high-touch surfaces or contamination-prone sites, in either healthcare, domestic or food industry settings, are not always prevented by the employment of sanitary hygiene protocols. Antimicrobial surface coatings have emerged as a solution to eradicate pathogenic bacteria and prevent future infections and even outbreaks. Standardised antimicrobial testing methods play a crucial role in validating the effectiveness of these materials and enabling their application in real-life settings, providing reliable results that allow for comparison between antimicrobial surfaces while assuring end-use product safety. This review provides an insight into the studies using ISO 22196, which is considered the gold standard for antimicrobial surface coatings and examines the current state of the art in antimicrobial testing methods. It primarily focuses on identifying pitfalls and how even small variations in methods can lead to different results, affecting the assessment of the antimicrobial activity of a particular product.

Creation of a Composite Bioactive Coating with Antibacterial Effect Promising for Bone Implantation

When creating titanium-containing bone implants, the bioactive coatings that promote their rapid engraftment are important. The engraftment rate of titanium implants with bone tissue depends significantly on the modification of the implant surface. It is achieved by changing either the relief or the chemical composition of the surface layer, as well as a combination of these two factors. In this work, we studied the creation of composite coatings with a two-level (the micro- and nanolevel) hierarchy of the surface relief, which have bioactive and bactericidal properties, which are promising for bone implantation. Using the developed non-lithographic template electrochemical synthesis, a composite coating on titanium with a controlled surface structure was created based on an island-type TiO₂ film, silver and hydroxyapatite (HAp). This TiO₂/Ag/HAp composite coating has a developed surface relief at the micro- and nanolevels and has a significant cytological response and the ability to accelerate osteosynthesis, and also has an antibacterial effect. Thus, the developed biomaterial is suitable for production of dental and orthopedic implants with improved biomedical properties.

Antimicrobial Photodynamic Coatings Reduce the Microbial Burden on Environmental Surfaces in Public Transportation—A Field Study in Buses

Millions of people use public transportation daily worldwide and frequently touch surfaces, thereby producing a reservoir of microorganisms on surfaces increasing the risk of transmission. Constant occupation makes sufficient cleaning difficult to achieve. Thus, an autonomous, permanent, antimicrobial coating (AMC) could keep down the microbial burden on such surfaces. A photodynamic AMC was applied to frequently touched surfaces in buses. The microbial burden (colony forming units, cfu) was determined weekly and compared to equivalent surfaces in buses without AMC (references). The microbial burden ranged from 0–209 cfu/cm² on references and from 0–54 cfu/cm² on AMC. The means were 13.4 ± 29.6 cfu/cm² on references and 4.5 ± 8.4 cfu/cm² on AMC (p < 0.001). The difference in microbial burden on AMC and references was almost constant throughout the study. Considering a hygiene benchmark of 5 cfu/cm², the data yield an absolute risk reduction of 22.6% and a relative risk reduction of 50.7%. In conclusion, photodynamic AMC kept down the microbial burden, reducing the risk of transmission of microorganisms. AMC permanently and autonomously contributes to hygienic conditions on surfaces in public transportation. Photodynamic AMC therefore are suitable for reducing the microbial load and closing hygiene gaps in public transportation.

Silver-Containing Thin Films on Transparent Polymer Foils for Antimicrobial Applications

The increasing occurrence of infections caused by pathogens found on objects of everyday use requires a variety of solutions for active disinfection. Using active materials that do not require daily maintenance has a potential advantage for their acceptance. In this contribution, transparent films, with silver as the main antimicrobial agent and a total thickness of a few tens of nm, were deposited on flexible self-adhesive polymer foils used as screen protectors. TiO2 and SiO2 were used as transparent matrix to embed the Ag nanoparticles, ensuring also their mechanical protection and controlled growth. HiPIMS (High-Power Impulse Magnetron Sputtering) was used for the sputtering of the Ag target and fine control of the Ag amount in the layer, whereas TiO2 and SiO2 were sputtered in RF (Radio Frequency) mode. The thin film surface was investigated by AFM (Atomic Force Microscopy), providing information on the topography of the coatings and their preferential growth on the textured polymer foil. XRD (X-Ray Diffraction) revealed the presence of specific Ag peaks in an amorphous oxide matrix. UV-Vis-NIR (Ultraviolet-Visible-Near Infrared) spectroscopy revealed the presence of nanostructured Ag, characterized by preferential absorption in the 400 to 500 nm spectral range. The antimicrobial properties were assessed using an antimicrobial test with the Escherichia coli strain. The highest efficiency was observed for the Ag/SiO2 combination, in the concentration range of 104–105 CFU/mL.

Facile Route to Effective Antimicrobial Aluminum Oxide Layer Realized by Co-Deposition with Silver Nitrate

The emergence and spreading of the SARS-CoV-2 pandemic has forced the focus of attention on a significant issue: the realization of antimicrobial surfaces for public spaces, which do not require extensive use of disinfectants. Silver represents one of the most used elements in this context, thanks to its excellent biocidal performance. This work describes a simple method for the realization of anodized aluminum layers, whose antimicrobial features are ensured by the co-deposition with silver nitrate. The durability and the chemical resistance of the samples were evaluated by means of several accelerated degradation tests, such as the exposure in a salt spray chamber, the contact with synthetic sweat and the scrub test, highlighting the residual influence of silver in altering the protective behavior of the alumina layers. Furthermore, the ISO 22196:2011 standard was used as the reference protocol to set up an assay to measure the effective antibacterial activity of the alumina-Ag layers against both Gram-positive (Staphylococcus aureus) and Gram-negative (Escherichia coli) bacteria, even at low concentrations of silver. Finally, the Ag-containing aluminum oxide layers exhibited excellent antimicrobial performances also following the chemical–physical degradation processes, ensuring good durability over time of the antimicrobial surfaces. Overall, this work introduces a simple route for the realization of anodized aluminum surfaces with excellent antibacterial properties.

Antimicrobial coatings for environmental surfaces in hospitals: a potential new pillar for prevention strategies in hygiene

Recent reports provide evidence that contaminated healthcare environments represent major sources for the acquisition and transmission of pathogens. Antimicrobial coatings (AMC) may permanently and autonomously reduce the contamination of such environmental surfaces complementing standard hygiene procedures. This review provides an overview of the current status of AMC and the demands to enable a rational application of AMC in health care settings. Firstly, a suitable laboratory test norm is required that adequately quantifies the efficacy of AMC. In particular, the frequently used wet testing (e.g. ISO 22196) must be replaced by testing under realistic, dry surface conditions. Secondly, field studies should be mandatory to provide evidence for antimicrobial efficacy under real-life conditions. The antimicrobial efficacy should be correlated to the rate of nosocomial transmission at least. Thirdly, the respective AMC technology should not add additional bacterial resistance development induced by the biocidal agents and co- or cross-resistance with antibiotic substances. Lastly, the biocidal substances used in AMC should be safe for humans and the environment. These measures should help to achieve a broader acceptance for AMC in healthcare settings and beyond. Technologies like the photodynamic approach already fulfil most of these AMC requirements.

Organic and inorganic antibacterial approaches in combating bacterial infection for biomedical application

In spite of antibiotics, antibacterial agents or specifically known as antiseptics are actively explored for the prevention of infection-associated medical devices. Antibacterial agents are introduced to overcome the complication of bacterial resistance which devoted by antibiotics. It can be classified into inorganic and organic, that prominently have impacted bacterial retardation in their own killing mechanism patterns. Therefore, this review paper aimed to provide information on most common used inorganic and organic antibacterial agents which have potential to be utilized in biomedical applications, thus, classifying the trends of antibacterial mechanism on Gram-negative and Gram-positive bacteria. In the beginning, infectious diseases and associated biomedical infections were stated to expose current infection scenarios on medical devices. The general view, application, susceptible bacteria and activation mechanism of inorganic (silver, copper, gold and zinc) and organic (chlorhexidine, triclosan, polyaniline and polyethylenimine) antibacterial agents that are widely proposed for biomedical area, were then gathered and reviewed. In the latter part of the study, the intact mechanisms of inorganic and organic antibacterial agents in retarding bacterial growth were classified and summarized based on its susceptibility on Gram-negative and Gram-positive bacteria. Most of inorganic antibacterial agents are in the form of metal, which release its ions to retard prominently Gram-negative bacteria. While organic antibacterial agents are susceptible to Gram-positive bacteria through organelle modification and disturbance of bio-chemical pathway. However, the antibacterial effects of each antibacterial agent are also depending on its effective mechanism and the species of bacterial strain. These compilation reviews and classification mechanisms are beneficial to assist the selection of antibacterial agents to be incorporated on/within biomaterials, based on its susceptible bacteria. Besides, the combination of several antibacterial agents with different susceptibilities will cover a wide range of antibacterial spectrum.

Novel photodynamic coating reduces the bioburden on near-patient surfaces thereby reducing the risk for onward pathogen transmission: a field study in two hospitals

BACKGROUND

Near-patient surfaces are recognized as a source for hospital-acquired infections. Such surfaces act as reservoirs for microbial contamination by which pathogens can be transmitted from colonized or infected patients to susceptible patients. Routine disinfection of surfaces only results in a temporal elimination of pathogens, and recontamination inevitably occurs shortly between disinfections.

AIM

A novel antimicrobial coating based on photodynamics was tested under laboratory conditions and subsequently in a field study in two hospitals under real-life conditions.

METHODS

Identical surfaces received a photodynamic or control coating. Bacterial counts [colony-forming units (cfu)/cm²) were assessed regularly for up to 6 months.

FINDINGS

The laboratory study revealed a mean reduction of several human pathogens of up to 4.0 ± 0.3 log₁₀. The field study in near-patient environments demonstrated mean bacterial values of 6.1 ± 24.7 cfu/cm² on all control coatings. Photodynamic coatings showed a significantly lower mean value of 1.9 ± 2.8 cfu/cm² (P<0.001). When considering benchmarks of 2.5 cfu/cm² or 5 cfu/cm², the relative risk for high bacterial counts on surfaces was reduced by 48% (odds ratio 0.38, P<0.001) or 67% (odds ratio 0.27, P<0.001), respectively.

CONCLUSION

Photodynamic coatings provide a significant and lasting reduction of bacterial counts on near-patient surfaces, particularly for high bacterial loads, in addition to routine hygiene. The promising results of this proof-of-concept study highlight the need for further studies to determine how this novel technology is correlated with the frequency of hospital-acquired infections.

Synthesis and in-vitro antibacterial properties of a functionally graded Ag impregnated composite surface

Silver is considered promising in medical devices to prevent infection due to its excellent properties of broad antibacterial spectrum and persistent antibacterial activity. Herein, silver impregnated functionally graded composite surfaces have been developed by a novel duplex plasma deposition technique, which combines the double glow sputtering process and active screen plasma nitriding process. The composite surfaces include a surface antibacterial layer and a bottom supporting layer, which are deposited simultaneously. The functionally graded structure endows the composite surfaces with antibacterial activity, combined with improved wear resistance. The multilayer structures were observed by scanning electron microscopy, and the graded distribution of silver and nitrogen was verified by glow discharge optical emission spectroscopy. X-ray diffraction and X-ray photoelectron spectroscopy were used to analyze the microstructures and chemical states of the components. Results from physical properties tests indicated that the composite surfaces have increased hardness, lower contact angles, excellent scratch resistance and wear resistance. The in-vitro antibacterial tests using the Gram-negative E. coli. NCTC 10418 also showed that over 99% of bacteria were killed after 5 h contacting with the composite surface.

Critical physiological factors influencing the outcome of antimicrobial testing according to ISO 22196 / JIS Z 2801

Bactericidal materials gained interest in the health care sector as they are capable of preventing material surfaces from microbial colonization and subsequent spread of infections. However, commercialization of antimicrobial materials requires proof of their efficacy, which is usually done using in vitro methods. The ISO 22196 standard (Japanese test method JIS Z 2801) is a method for measuring the antibacterial activity of daily goods. As it was found reliable for testing the biocidal activity of antimicrobially active materials and surface coatings most of the laboratories participating in this study used this protocol. Therefore, a round robin test for evaluating antimicrobially active biomaterials had to be established. To our knowledge, this is the first report on inaugurating a round robin test for the ISO 22196 / JIS Z 2801. The first round of testing showed that analyses in the different laboratories yielded different results, especially for materials with intermediate antibacterial effects distinctly different efficacies were noted. Scrutinizing the protocols used by the different participants and identifying the factors influencing the test outcomes the approach was unified. Four critical factors influencing the outcome of antibacterial testing were identified in a series of experiments: (1) incubation time, (2) bacteria starting concentration, (3) physiological state of bacteria (stationary or exponential phase of growth), and (4) nutrient concentration. To our knowledge, this is the first time these parameters have been analyzed for their effect on the outcome of testing according to ISO 22196 / JIS Z 2801. In conclusion, to enable assessment of the results obtained it is necessary to evaluate these single parameters in the test protocol carefully. Furthermore, uniform and robust definitions of the terms antibacterial efficacy / activity, bacteriostatic effects, and bactericidal action need to be agreed upon to simplify communication of results and also regulate expectations regarding antimicrobial tests, outcomes, and materials.

Metal-Based Antibacterial Substrates for Biomedical Applications

The interest in nanotechnology and the growing concern for the antibiotic resistance demonstrated by many microorganisms have recently stimulated many efforts in designing innovative biomaterials and substrates with antibacterial properties. Among the implemented strategies to control the incidence of infections associated with the use of biomedical device and implants, interesting routes are represented by the incorporation of bactericidal agents onto the surface of biomaterials for the prevention of bacterial adhesion and biofilm growth. Natural products and particularly bioactive metals such as silver, copper and zinc represent an interesting alternative for the development of advanced biomaterials with antimicrobial properties. This review presents an overview of recent progress in the modification of biomaterials as well as the most attractive techniques for the deposition of antimicrobial coatings on different substrates for biomedical application. Moreover, some research activities and results achieved by the authors in the development of antibacterial materials are also presented and discussed.

On the long term antibacterial features of silver-doped diamondlike carbon coatings deposited via a hybrid plasma process

Environmental surfaces are increasingly recognized as important sources of transmission of hospital-acquired infections. The use of antibacterial surface coatings may constitute an effective solution to reduce the spread of contamination in healthcare settings, provided that they exhibit sufficient stability and a long-term antibacterial effect. In this study, silver-incorporated diamondlike carbon films (Ag-DLC) were prepared in a continuous, single-step plasma process using a hybrid, inductively coupled plasma reactor combined with a very-low-frequency sputtering setup. The average Ag concentration in the films, ranging from 0 to 2.4 at. %, was controlled by varying the sputtering bias on the silver target. The authors found that the activity of Escherichia coli was reduced by 2.5 orders of magnitude, compared with the control surface, after a 4-h contact with a 2.4 at. % Ag-DLC coating. The coatings displayed slow release kinetics, with a total silver ion release in the sub-ppb range after 4 h in solution, as measured by graphite furnace-atomic absorption spectroscopy. This was confirmed by Kirby-Bauer diffusion tests, which showed limited diffusion of biocidal silver with a localized antibacterial effect. As a slow and continuous release is mandatory to ensure a lasting antibacterial effect, the newly developed Ag-DLC coatings appears as promising materials for environmental hospital surfaces.

Plasma sprayed alumina–nanosilver antibacterial coatings

Plasma sprayed Al₂O₃/Ag hydrophobic coatings with no less than 10 ppm nanosilver exhibited strong anti-adhesive and antibacterial property.

Effectiveness of an antimicrobial polymer to decrease contamination of environmental surfaces in the clinical setting

We performed a real-world, controlled intervention to investigate use of an antimicrobial surface polymer, MSDS Poly, on environmental contamination. Pathogenic bacteria were identified in 18 (90%) of 20 observations in treated rooms and 19 (83%) of 23 observations in untreated rooms (P = .67). MSDS Poly had no significant effect on environmental contamination.

Antimicrobial activity of novel nanostructured Cu-SiO2 coatings prepared by chemical vapour deposition against hospital related pathogens

There is increasing recognition that the healthcare environment acts as an important reservoir for transmission of healthcare acquired infections (HCAI). One method of reducing environmental contamination would be use of antimicrobial materials. The antimicrobial activity of thin silica-copper films prepared by chemical vapour deposition was evaluated against standard strains of bacteria used for disinfectant testing and bacteria of current interest in HCAI. The structure of the coatings was determined using Scanning Electron Microscopy and their hardness and adhesion to the substrate determined. Antimicrobial activity was tested using a method based on BS ISO 22196:2007. The coatings had a pale green-brown colour and had a similar hardness to steel. SEM showed nano-structured aggregates of Cu within a silica matrix. A log10 reduction in viability of >5 could be obtained within 4 h for the disinfectant test strains and within 6 h for producing Acinetobacter baumannii, Klebsiella pneumoniae and Stenotrophomonas maltophilia. Activity against the other hospital isolates was slower but still gave log10 reduction factors of >5 for extended spectrum β-lactamase producing Escherichia coli and >3 for vancomycin resistant Enterococcus faecium, methicillin resistant Staphylococcus aureus and Pseudomonas aeruginosa within 24 h. The results demonstrate the importance of testing antimicrobial materials destined for healthcare use against isolates of current interest in hospitals as well as standard test strains. The coatings used here can also be applied to substrates such as metals and ceramics and have potential applications where reduction of microbial environmental contamination is desirable.