Facile Construction of Antimicrobial Surface via One-Step Co-Deposition of Peptide Polymer and Dopamine

The infections associated with implantable medical devices can greatly affect the therapeutic effect and impose a heavy financial burden. Therefore, it is of great significance to develop antimicrobial biomaterials for the prevention and mitigation of healthcare-associated infections. Here, a facile construction of antimicrobial surface via one-step co-deposition of peptide polymer and dopamine is reported. The co-deposition of antimicrobial peptide polymer DLL60 BLG40 with dopamine (DA) on the surface of thermoplastic polyurethane (TPU) provides peptide polymer-modified TPU surface (TPU-DLL60 BLG40 ). The antimicrobial test shows that the TPU-DLL60 BLG40 surfaces of the sheet and the catheter both exhibit potent killing of 99.9% of methicillin-resistant Staphylococcus aureus (MRSA) and Escherichia coli (E. coli). In addition, the TPU-DLL60 BLG40 surface also exhibits excellent biocompatibility. This one-step antimicrobial modification method is fast and efficient, implies promising application in surface antimicrobial modification of implantable biomaterials and medical devices.

A Two-Step Surface Modification Methodology for the Advanced Protection of a Stone Surface

The biodeterioration of the natural surface on monuments, historical buildings, and even public claddings brings to the attention of researchers and historians the issues of conservation and protection. Natural stones undergo changes in their appearance, being subjected to deterioration due to climatic variations and the destructive action of biological systems interfering with and living on them, leading to ongoing challenges in the protection of the exposed surfaces. Nanotechnology, through silver nanoparticles with strong antimicrobial effects, can provide solutions for protecting natural surfaces using specific coupling agents tailored to each substrate. In this work, surfaces of two common types of natural stone, frequently encountered in landscaping and finishing works, were modified using siloxane coupling agents with thiol groups. Through these agents, silver nanoparticles (AgNPs) were fixed, exhibiting distinct characteristics, and subjected to antimicrobial analysis. This study presents a comparative analysis of the efficiency of coupling agents that can be applied to a natural surface with porous structures, when combined with laboratory-obtained silver nanoparticles, in reducing the formation of microbial biofilms, which are a main trigger for stone biodeterioration.

Inactivation of Bacteriophage ɸ6 and SARS-CoV-2 in Antimicrobial Surface Tests

Due to the COVID-19 pandemic, researchers have focused on new preventive measures to limit the spread of SARS-CoV-2. One promising application is the usage of antimicrobial materials on often-touched surfaces to reduce the load of infectious virus particles. Since tests with in vitro-propagated SARS-CoV-2 require biosafety level 3 (BSL-3) laboratories with limited capacities and high costs, experiments with an appropriate surrogate like the bacteriophage ɸ6 are preferred in most studies. The aim of this study was to compare ɸ6 and SARS-CoV-2 within antiviral surface tests. Different concentrations of copper coatings on polyethylene terephthalate (PET) were used to determine their neutralizing activity against ɸ6 and SARS-CoV-2. The incubation on the different specimens led to similar inactivation of both SARS-CoV-2 and ɸ6. After 24 h, no infectious virus particles were evident on any of the tested samples. Shorter incubation periods on specimens with high copper concentrations also showed a complete inactivation. In contrast, the uncoated PET foils resulted only in a negligible reduced inactivation during the one-hour incubation. The similar reduction rate for ɸ6 and SARS-CoV-2 in our experiments provide further evidence that the bacteriophage ɸ6 is an adequate model organism for SARS-CoV-2 for this type of testing.

Demonstrating the In Vitro and In Situ Antimicrobial Activity of Oxide Mineral Microspheres: An Innovative Technology to Be Incorporated into Porous and Nonporous Materials

The antimicrobial activity of surfaces treated with zinc and/or magnesium mineral oxide microspheres is a patented technology that has been demonstrated in vitro against bacteria and viruses. This study aims to evaluate the efficiency and sustainability of the technology in vitro, under simulation-of-use conditions, and in situ. The tests were undertaken in vitro according to the ISO 22196:2011, ISO 20473:2013, and NF S90-700:2019 standards with adapted parameters. Simulation-of-use tests evaluated the robustness of the activity under worst-case scenarios. The in situ tests were conducted on high-touch surfaces. The in vitro results show efficient antimicrobial activity against referenced strains with a log reduction of >2. The sustainability of this effect was time-dependent and detected at lower temperatures (20 ± 2.5 °C) and humidity (46%) conditions for variable inoculum concentrations and contact times. The simulation of use proved the microsphere's efficiency under harsh mechanical and chemical tests. The in situ studies showed a higher than 90% reduction in CFU/25 cm² per treated surface versus the untreated surfaces, reaching a targeted value of <50 CFU/cm². Mineral oxide microspheres can be incorporated into unlimited surface types, including medical devices, to efficiently and sustainably prevent microbial contamination.

Nature-Inspired Surface Structures Design for Antimicrobial Applications

Surface contamination by microorganisms such as viruses and bacteria may simultaneously aggravate the biofouling of surfaces and infection of wounds and promote cross-species transmission and the rapid evolution of microbes in emerging diseases. In addition, natural surface structures with unique anti-biofouling properties may be used as guide templates for the development of functional antimicrobial surfaces. Further, these structure-related antimicrobial surfaces can be categorized into microbicidal and anti-biofouling surfaces. This review introduces the recent advances in the development of microbicidal and anti-biofouling surfaces inspired by natural structures and discusses the related antimicrobial mechanisms, surface topography design, material application, manufacturing techniques, and antimicrobial efficiencies.

Microfluidic Study of Bacterial Attachment on and Detachment from Zinc Oxide Nanopillars

Nanopillars can influence how bacterial cells attach to a surface. Herein, we investigated whether self-assembled zinc oxide (ZnO) nanopillars synthesized on glass substrates via the conventional hydrothermal route possess anti-biofouling properties either by reducing the amount of initially attached cells or promoting the detachment of cells from the surface or both. To avoid complications associated with manual intervention methods of assessing bacterial attachment on nanopillar surfaces, we implemented a microfluidic approach. In our study, we synthesized two nanopillar topographies: a low surface density of ZnO nanopillars and a high surface density of ZnO nanopillars. Next, we mounted microfluidic channels to each of these substrates. This microfluidic approach allowed us to gently flow Pseudomonas aeruginosa, Staphylococcus aureus, or Bacillus subtilis cells onto the nanopillars for initial attachment before systematically increasing the flowrate to attempt to detach remaining attached cells without introducing air-liquid interface artefacts during the assay. Generally, initial bacterial attachment was similar across all substrates. However, cells consistently detached more readily from high-surface-density nanopillars compared to low-surface-density nanopillars. Electron microscopy revealed that cells that attached to high-surface-density nanopillars rested atop the nanopillars, fully exposed to microfluidic shear, whereas many cells became trapped in the void space between neighboring low-surface-density nanopillars, shielding these cells from detachment. Our findings indicate that self-assembled ZnO nanopillars can provide anti-biofouling properties under submerged flow but only if synthesized at high surface density.

Poly(methyl methacrylate) with Oleic Acid as an Efficient Candida albicans Biofilm Repellent

Poly(methyl methacrylate) (PMMA), widely used in dentistry, is unfortunately a suitable substrate for Candida (C.) albicans colonization and biofilm formation. The key step for biofilm formation is C. albicans ability to transit from yeast to hypha (filamentation). Since oleic acid (OA), a natural compound, prevents filamentation, we modified PMMA with OA aiming the antifungal PMMA_OA materials. Physico-chemical properties of the novel PMMA_OA composites obtained by incorporation of 3%, 6%, 9%, and 12% OA into PMMA were characterized by Fourier-transform infrared spectroscopy and water contact angle measurement. To test antifungal activity, PMMA_OA composites were incubated with C. albicans and the metabolic activity of both biofilm and planktonic cells was measured with a XTT test, 0 and 6 days after composites preparation. The effect of OA on C. albicans morphology was observed after 24 h and 48 h incubation in agar loaded with 0.0125% and 0.4% OA. The results show that increase of OA significantly decreased water contact angle. Metabolic activity of both biofilm and planktonic cells were significantly decreased in the both time points. Therefore, modification of PMMA with OA is a promising strategy to reduce C. albicans biofilm formation on denture.

Surface Characterization and Anti-Biofilm Effectiveness of Hybrid Films of Polyurethane Functionalized with Saponite and Phloxine B

The main objective of this work was to synthesize composites of polyurethane (PU) with organoclays (OC) exhibiting antimicrobial properties. Layered silicate (saponite) was modified with octadecyltrimethylammonium cations (ODTMA) and functionalized with phloxine B (PhB) and used as a filler in the composites. A unique property of composite materials is the increased concentration of modifier particles on the surface of the composite membranes. Materials of different compositions were tested and investigated using physico-chemical methods, such as infrared spectroscopy, X-ray diffraction, contact angle measurements, absorption, and fluorescence spectroscopy in the visible region. The composition of an optimal material was as follows: nODTMA/mSap = 0.8 mmol g-1 and nPhB/mSap = 0.1 mmol g-1. Only about 1.5% of present PhB was released in a cultivation medium for bacteria within 24 h, which proved good stability of the composite. Anti-biofilm properties of the composite membranes were proven in experiments with resistant Staphylococcus aureus. The composites without PhB reduced the biofilm growth 100-fold compared to the control sample (non-modified PU). The composite containing PhB in combination with the photodynamic inactivation (PDI) reduced cell growth by about 10,000-fold, thus proving the significant photosensitizing effect of the membranes. Cell damage was confirmed by scanning electron microscopy. A new method of the synthesis of composite materials presented in this work opens up new possibilities for targeted modification of polymers by focusing on their surfaces. Such composite materials retain the properties of the unmodified polymer inside the matrix and only the surface of the material is changed. Although these unique materials presented in this work are based on PU, the method of surface modification can also be applied to other polymers. Such modified polymers could be useful for various applications in which special surface properties are required, for example, for materials used in medical practice.

Anti-Colonization Effect of Au Surfaces with Self-Assembled Molecular Monolayers Functionalized with Antimicrobial Peptides on S. epidermidis

Medical devices with an effective anti-colonization surface are important tools for combatting healthcare-associated infections. Here, we investigated the anti-colonization efficacy of antimicrobial peptides covalently attached to a gold model surface. The gold surface was modified by a self-assembled polyethylene glycol monolayer with an acetylene terminus. The peptides were covalently connected to the surface through a copper-catalyzed [3 + 2] azide-acetylene coupling (CuAAC). The anti-colonization efficacy of the surfaces varied as a function of the antimicrobial activity of the peptides, and very effective surfaces could be prepared with a 6 log unit reduction in bacterial colonization.

Preparation, Characterization and Antimicrobial Properties of Nanosized Silver-Containing Carbon/Silica Composites from Rice Husk Waste

Rice husk, one of the main side products in the rice production, and its sustainable management represent a challenge in many countries. Herein, we describe the use of this abundant agricultural bio-waste as feedstock for the preparation of silver-containing carbon/silica nano composites with antimicrobial properties. The synthesis was performed using a fast and cheap methodology consisting of wet impregnation followed by pyrolysis, yielding C/SiO2 composite materials doped with varying amounts of silver from 28 to 0.001 wt %. The materials were fully characterized and their antimicrobial activity against ESKAPE pathogens, namely E. faecium, S. aureus, K. pneumoniae, A. baumannii, P. aeruginosa, and E. coli, and the pathogenic yeast C. albicans was investigated. Sensitivities of these strains against the prepared materials were demonstrated, even with exceptional low amounts of 0.015 m% silver. Hence, we report a straightforward method for the synthesis of antimicrobial agents from abundant sources which addresses urgent questions like bio-waste valorization and affordable alternatives to increasingly fewer effective antibiotics.

Candida albicans Can Survive Antifungal Surface Coatings on Surfaces with Microcone Topography

This study demonstrates the ability of Candida albicans, a medically significant human fungal pathogen, to minimize contact with an antifungal surface coating that on a flat surface is lethal on contact by growing on and between micron-sized surface topographical features, thus minimizing the contact area. Scanning electron microscopy showed that cells contacting the "floor" between microcones were killed, whereas cells attached to microcones survived and formed hyphal filaments. These spanned space between cones and avoided contact with the flat surface in-between cones. Thus, fungal cells managed to attach and grow despite the antifungal coating. This ability of Candida albicans to exploit topography features to minimize surface contact yet utilize the solid surface for anchoring reduces the effectiveness of the grafted antifungal surface coating. This suggests that biomedical devices with rough surfaces might be more challenging to protect against fungal biofilm formation via application of an antifungal coating.

Practical Preparation of Infection-Resistant Biomedical Surfaces from Antimicrobial β-Peptide Polymers

Tackling microbial infection associated with biomaterial surfaces has been an urgent need. Synthetic β-peptide polymers can mimic host defense peptides and have potent antimicrobial activities without driving the bacteria to develop antimicrobial resistance. Herein, we demonstrate a plasma surface activation-based practical β-peptide polymer modification to prepare antimicrobial surfaces for biomedical materials such as thermoplastic polyurethane (TPU), polytetrafluoroethylene, polyvinyl pyrrolidone, polyvinyl chloride, and polydimethylsiloxane. The β-peptide polymer-modified surfaces demonstrated effective killing on drug-resistant Gram-positive and Gram-negative bacteria. The antibacterial function retained completely even after the β-peptide polymer-modified surfaces were stored at ambient temperature for at least 2 months. Moreover, the optimum β-peptide polymer (50:50 DM-Hex)-modified surfaces displayed no hemolysis and cytotoxicity. In vivo study using methicillin-resistant Staphylococcus aureus (MRSA)-pre-incubated TPU-50:50 DM-Hex surfaces for subcutaneous implantation revealed a 3.4-log reduction of MRSA cells after the implantation for 11 days at the surrounding tissue of implanted TPU sheet and significant suppression of infection, compared to bare TPU control. These results imply promising and practical applications of β-peptide polymer tethering to prepare infection-resistant surfaces for biomedical materials and devices.

Biofilm Forming Antibiotic Resistant Gram-Positive Pathogens Isolated From Surfaces on the International Space Station

The International Space Station (ISS) is a closed habitat in a uniquely extreme and hostile environment. Due to these special conditions, the human microflora can undergo unusual changes and may represent health risks for the crew. To address this problem, we investigated the antimicrobial activity of AGXX®, a novel surface coating consisting of micro-galvanic elements of silver and ruthenium along with examining the activity of a conventional silver coating. The antimicrobial materials were exposed on the ISS for 6, 12, and 19 months each at a place frequently visited by the crew. Bacteria that survived on the antimicrobial coatings [AGXX® and silver (Ag)] or the uncoated stainless steel carrier (V2A, control material) were recovered, phylogenetically affiliated and characterized in terms of antibiotic resistance (phenotype and genotype), plasmid content, biofilm formation capacity and antibiotic resistance transferability. On all three materials, surviving bacteria were dominated by Gram-positive bacteria and among those by Staphylococcus, Bacillus and Enterococcus spp. The novel antimicrobial surface coating proved to be highly effective. The conventional Ag coating showed only little antimicrobial activity. Microbial diversity increased with increasing exposure time on all three materials. The number of recovered bacteria decreased significantly from V2A to V2A-Ag to AGXX®. After 6 months exposure on the ISS no bacteria were recovered from AGXX®, after 12 months nine and after 19 months three isolates were obtained. Most Gram-positive pathogenic isolates were multidrug resistant (resistant to more than three antibiotics). Sulfamethoxazole, erythromycin and ampicillin resistance were most prevalent. An Enterococcus faecalis strain recovered from V2A steel after 12 months exposure exhibited the highest number of resistances (n = 9). The most prevalent resistance genes were ermC (erythromycin resistance) and tetK (tetracycline resistance). Average transfer frequency of erythromycin, tetracycline and gentamicin resistance from selected ISS isolates was 10⁻⁵ transconjugants/recipient. Most importantly, no serious human pathogens such as methicillin resistant Staphylococcus aureus (MRSA) or vancomycin-resistant Enterococci (VRE) were found on any surface. Thus, the infection risk for the crew is low, especially when antimicrobial surfaces such as AGXX® are applied to surfaces prone to microbial contamination.

Enhanced antibacterial properties and the cellular response of stainless steel through friction stir processing

Biofilm related bacterial infection is one of the primary causes of implant failure. Limiting bacterial adhesion and colonization of pathogenic bacteria is a challenging task in health care. Here, a highly simplistic processing technique for imparting antibacterial properties on a biomedical grade stainless steel is demonstrated. Low-temperature high strain-rate deformation achieved using submerged friction stir processing resulted in a nearly single phase ultra-fine grain structure. The processed stainless steel demonstrated improved antibacterial properties for both Gram-positive and Gram-negative bacteria, significantly impeding biofilm formation during the in vitro study. Also, the processed stainless steel showed better compatibility with human fibroblasts manifested through apparent cell spreading and proliferation. The substantial antibacterial properties of the processed steel are explained in terms of the favorable electronic characteristics of the metal-oxide and by using classical Derjaguin-Landau-Verwey-Overbeek (DLVO) and the extended DLVO (XDLVO) approach at the cell-substrate interface.

A Chemical Approach to Optimizing Bioactive Glass Dental Composites

The chemical microenvironment surrounding dental composites plays a crucial role in controlling the bacteria grown on these specialized surfaces. In this study, we report a scanning electrochemical microscopy (SECM)-based analytic technique to design and optimize metal ion-releasing bioactive glass (BAG) composites, which showed a significant reduction in biofilm growth. SECM allows positioning of the probe without touching the substrate while mapping the chemical parameters in 3-dimensional space above the substrate. Using SECM and a solid-state H⁺ and Ca²⁺ ion-selective microprobe, we determined that the local Ca²⁺ concentration released by different composites was 10 to 224 µM for a BAG particle size of <5 to 150 µm in the presence of artificial saliva at pH 4.5. The local pH was constant above the composites in the same saliva solution. The released amount of Ca²⁺ was determined to be maximal for particles <38 µm and a BAG volume fraction of 0.32. This optimized BAG-resin composite also showed significant inhibition of biofilm growth (24 ± 5 µm) in comparison with resin-only composites (53 ± 6 µm) after Streptococcus mutans bacteria were grown for 3 d in a basal medium mucin solution. Biofilm morphology and its subsequent volume, as determined by the SECM imaging technique, was (0.59 ± 0.38) × 10⁷ µm³ for BAG-resin composites and (1.29 ± 0.53) × 10⁷ µm³ for resin-only composites. This study thus lays the foundation for a new analytic technique for designing dental composites that are based on the chemical microenvironment created by biomaterials to which bacteria have been exposed.

Surface Modified with a Host Defense Peptide-Mimicking β-Peptide Polymer Kills Bacteria on Contact with High Efficacy

Methicillin-resistant Staphylococcus aureus (MRSA) has been one of the major nosocomial pathogens to cause frequent and serious infections that are associated with various biomedical surfaces. This study demonstrated that surface modified with host defense peptide-mimicking β-peptide polymer, has surprisingly high bactericidal activities against Escherichia coli ( E. coli) and MRSA. As surface-tethered β-peptide polymers cannot move freely to adopt the collaborative interactions with bacterial membrane and are too short to penetrate the cell envelop, we proposed a mode of action by diffusing away the cell membrane-stabilizing divalent ions, Ca²⁺ and Mg²⁺. This hypothesis was supported by our study that Ca²⁺ and Mg²⁺ supplementation in the assay medium causes up to 80% loss of bacterial killing efficacy and that the addition of divalent ion chelating ethylenediaminetetraacetic acid into the above assay medium leads to significant recovery of the bacterial killing efficacy. In addition to its potent bacterial killing efficacy, the surface-tethered β-peptide polymer also demonstrated excellent biocompatibility by displaying no hemolysis and supporting mammalian cell adhesion and growth. In conclusion, this study demonstrated the potential of β-peptide polymer-modified surface in addressing nosocomial infections that are associated with various surfaces in biomedical applications.

A Novel Antimicrobial Coating Represses Biofilm and Virulence-Related Genes in Methicillin-Resistant Staphylococcus aureus

Methicillin-resistant Staphylococcus aureus (MRSA) has become an important cause of hospital-acquired infections worldwide. It is one of the most threatening pathogens due to its multi-drug resistance and strong biofilm-forming capacity. Thus, there is an urgent need for novel alternative strategies to combat bacterial infections. Recently, we demonstrated that a novel antimicrobial surface coating, AGXX®, consisting of micro-galvanic elements of the two noble metals, silver and ruthenium, surface-conditioned with ascorbic acid, efficiently inhibits MRSA growth. In this study, we demonstrated that the antimicrobial coating caused a significant reduction in biofilm formation (46%) of the clinical MRSA isolate, S. aureus 04-02981. To understand the molecular mechanism of the antimicrobial coating, we exposed S. aureus 04-02981 for different time-periods to the coating and investigated its molecular response via next-generation RNA-sequencing. A conventional antimicrobial silver coating served as a control. RNA-sequencing demonstrated down-regulation of many biofilm-associated genes and of genes related to virulence of S. aureus. The antimicrobial substance also down-regulated the two-component quorum-sensing system agr suggesting that it might interfere with quorum-sensing while diminishing biofilm formation in S. aureus 04-02981.

Nanostructured multifunctional surface with antireflective and antimicrobial characteristics

Functional polymeric films with antireflective and hydrophobic properties have been widely used for electronic device displays. However, the design of such functional films with an antimicrobial characteristic has been a challenge. We designed a nanostructured surface using a rigorous coupled-wave analysis to obtain a period of 300 nm and an aspect ratio of 3.0 on a flat poly(methyl methacrylate) film. The fabricated nanostructure was hydrophobic and exhibited the desired optical characteristics with a reflectance of less than 0.5% over the visible wavelength range. Furthermore, the nanoimprinted polymer film exhibited antimicrobial characteristics and low adhesion when compared with the corresponding flat surface. The results suggest that the nanostructured surface designed in this study is multifunctional and should be suitable for the production of protective optical and hygienic polymer films for the displays of portable electronic devices.

Potent bactericidal efficacy of copper oxide impregnated non-porous solid surfaces

BACKGROUND

The role of fomites and the environment in nosocomial infections is becoming widely recognized. In this paper we discuss the use of Cupron copper oxide impregnated non-porous solid surface in the hospital setting and present in vitro testing data via USA Environmental Protection Agency (EPA) approved testing protocols that demonstrate the efficacy of these products to assist in reduction in environmental contamination and potentially nosocomial infections.

RESULTS

The two countertops tested passed all the acceptance criteria by the EPA (>99.9% kill within 2 hours of exposure) killing a range of bacterial pathogens on the surface of the countertops even after repeated exposure of the countertops to the pathogen, and multiple wet and dry abrasion cycles.

CONCLUSIONS

Cupron enhanced EOS countertops thus may be an important adjunct to be used in hospital settings to reduce environmental bioburden and potentially nosocomial infections.

Initial Bacterial Adhesion on Different Yttria-Stabilized Tetragonal Zirconia Implant Surfaces in Vitro

Bacterial adhesion to implant biomaterials constitutes a virulence factor leading to biofilm formation, infection and treatment failure. The aim of this study was to examine the initial bacterial adhesion on different implant materials in vitro. Four implant biomaterials were incubated with Enterococcus faecalis, Staphylococcus aureus and Candida albicans for 2 h: 3 mol % yttria-stabilized tetragonal zirconia polycrystal surface (B1a), B1a with zirconium oxide (ZrO₂) coating (B2a), B1a with zirconia-based composite coating (B1b) and B1a with zirconia-based composite and ZrO₂ coatings (B2b). Bovine enamel slabs (BES) served as control. The adherent microorganisms were quantified and visualized using scanning electron microscopy (SEM); DAPI and live/dead staining. The lowest bacterial count of E. faecalis was detected on BES and the highest on B1a. The fewest vital C. albicans strains (42.22%) were detected on B2a surfaces, while most E. faecalis and S. aureus strains (approximately 80%) were vital overall. Compared to BES; coated and uncoated zirconia substrata exhibited no anti-adhesive properties. Further improvement of the material surface characteristics is essential.