Antibacterial activity testing methods for hydrophobic patterned surfaces

Copper Nanoparticle Decorated Multilayer Nanocoatings for Controlled Nitric Oxide Release and Antimicrobial Performance with Biosafety

Biomedical device-related bacterial infections are a leading cause of mortality, and traditional antibiotics contribute to resistance. Various surface modification strategies have been explored, but effective clinical solutions remain limited. This study introduces a novel antibacterial nanocoating with copper nanoparticles (CuNPs) that triggers localized nitric oxide (NO) release. The multilayered nanocoating is created using branched polyethylenimine (BPEI) and poly(acrylic acid) (PAA) via a Layer-by-Layer assembly method. CuNP-decorated nanocoatings are formed by reducing copper ions coordinated with amine/carboxylic acid groups. In a physiological environment, CuNPs oxidize to Cu(I), promoting NO release from endogenous NO donors. The nanocoating's thickness is adjustable to regulate amount of CuNPs and NO flux. The optimal thickness for effective NO release against Staphylococcus aureus and Pseudomonas aeruginosa is identified, preventing microbial adhesion and biofilm formation. Importantly, the coating remains cytocompatible due to minimal CuNPs, physiological NO levels, and stable coating properties under physiological conditions.

Enabling Charge Trapping with Quasi-Magnetization through Transition Metal Ion-Chelated Mesoporous Silica Particles for Wearable Antibacterial Self-Powering Sensors

Wearable self-powering sensors based on triboelectric nanogenerators (TENGs) emerging as a promising strategy for a wide range of applications, such as self-powering and energy-harvesting systems, are widely used in healthcare and displacement current are utilized as the driving force. Although the TENG theory is rooted in the displacement current equation proposed by Maxwell, the magnetic field created by this current is often overlooked in TENG research. In this work, an effective charge-trapping method based on the magnetization current induced by transition metal ion chelation is reported. The experimental results, along with a theoretical analysis of the Maxwell equation and a discussion of the charge-trapping mechanism, demonstrate that magnetic materials provide enhanced charge-trapping performance. Transition metal ions chelated to mesoporous silica particles (MSPs) can slightly assign weak paramagnetic properties owing to the formation of ligand complexes. As a result, they can generate a feeble quasi-magnetization current during the TENG cycle, which enhances the surface charge density of the Co-MSPs-based polyvinyl alcohol TENG (PVA-TENG) by 68%. In addition, it is confirmed that the MSPs chelated with transition metal ions exhibit antibacterial properties, thereby providing promising synergistic effects from the perspective of application as a wearable TENG-based antibacterial sensor system.

The Antimicrobial Efficacy of Sodium Hypochlorite and Chlorhexidine in Gutta-Percha Cone Decontamination: A Systematic Review

This systematic review aims to compare the efficacy of sodium hypochlorite (NaOCl) and chlorhexidine digluconate (CHX) in decontaminating gutta-percha (GP) cones against endodontic pathogens-Enterococcus faecalis (E. faecalis), Staphylococcus aureus (S. aureus), and Candida albicans (C. albicans)-within 0-10 min. A systematic search was conducted in six databases (PubMed, Web of Science, Cochrane Library, SCIELO, Scopus, and LILACS), supplemented by manual searches performed independently by three reviewers. No publication year restrictions were applied, and only English-language studies were included. This review followed the PRISMA statement (Preferred Reporting Items for Systematic Reviews and Meta-Analyses). The risk of bias was assessed using six parameters with a modified Cochrane risk of bias tool. Out of 309 potentially eligible studies, 216 were screened by title and abstract, 32 were selected for full-text assessments, and 7 were included. All studies had a moderate or high risk of bias. The majority of the included studies showed that higher NaOCl concentrations effectively eliminate E. faecalis and S. aureus within 1-5 min. However, data on CHX's antimicrobial effect on C. albicans were limited. The qualitative analysis suggests that NaOCl remains the most effective agent for GP decontamination, while CHX with additives shows potential against fungal species.

Quantitative Assessment of Microbial Transmission onto Environmental Surfaces Using Thermoresponsive Gelatin Hydrogels as a Finger Mimetic under In Situ-Mimicking Conditions

Surface-mediated transmission of pathogens plays a key role in healthcare-associated infections. However, proper techniques for its quantitative analysis are lacking, making it challenging to develop novel antimicrobial and anti-fouling surfaces to reduce pathogen spread via environmental surfaces. This study demonstrates a gelatin hydrogel-based touch transfer test, the HydroTouch test, to evaluate pathogen transmission on high-touch surfaces under semi-dry conditions. The HydroTouch test employs gelatin as a finger mimetic, facilitating testing with pathogenic bacteria under controlled conditions. The thermoresponsive sol-gel transition of gelatin allows easy recovery and quantification of bacteria before and after testing. The HydroTouch test demonstrates that methicillin-resistant Staphylococcus aureus has a high transmission efficiency of ≈16% onto stainless steel, compared to <3% for Escherichia coli or Pseudomonas aeruginosa. Polyurethane surfaces exhibit strong resistance to bacterial contamination with a transmission efficiency of ≈0.6%, while polytetrafluoroethylene shows a transmission efficiency approximately four times higher than polyurethane. Additionally, quaternary ammonium-based antimicrobial coatings reduce the transmission efficiency of live bacteria on stainless steel to ≈4% of the original level. The HydroTouch test provides a reliable method for assessing pathogen transmission on various surfaces under semi-dry settings, supporting the development of effective antimicrobial, anti-transmission coatings to reduce healthcare-associated infections.

Enhancing Implantable Medical Devices: Surface Functionalization of Titanium with Quaternary Ammonium Salts for Antibacterial Adhesion Properties

Bacterial colonization of titanium-based materials used in implantable medical devices represents a significant challenge in the dental and orthopedic fields, often leading to infections and implant failure. This study reports the surface modification of titanium discs with ammonium salts containing carbon atom chains of different lengths (from 6 to 12) to provide antibacterial properties to the modified metal surfaces while maintaining their biocompatibility. The chemically modified samples have been characterized by ATR-FTIR and SEM-EDX analyses and evaluated for roughness and hydrophilic behavior. This surface modification not only provides hydrophobic properties to titanium surfaces but also introduces a hindering environment for bacterial adhesion. Antibacterial tests performed against methicillin-sensitive and methicillin-resistant Staphylococcus aureus strains demonstrated a proportional increase in antibacterial activity with increasing carbon chain length. The best antibacterial performance is reported for the sample containing 12 carbon atoms (Ti-ADTEAB), which showed inhibition values of 87.5 and 86.6% for the sensitive and resistant strains, respectively. The results suggest that this surface modification could lead to a new generation of implantable medical devices with improved patient outcomes by reducing the risk of postoperative infections.

Systematic study on the evaluation method of surface antibacterial activity based on the fluorescent observation of bacterial growth

Antibacterial and antiviral coating materials have attracted increasing attention for the prevention of infections caused by frequently touched surfaces in communities and hospitals. The standard assessment procedure for antibacterial surfaces involves bacterial culture on a film-covered substrate followed by transfer onto agar for colony counting (ISO22196:2011). However, this assessment lacks temporal and spatial information regarding bacterial growth, resulting in an incomplete and inaccurate evaluation of the antibacterial activity of the surface. In this study, we develop a novel evaluation procedure for antibacterial substrates that enables in situ visualization of bacterial growth on a surface with centimeter-scale spatial information using fluorescent protein-expressing bacterial cells and an image acquisition setup. The effects of equipment parameters on bacterial growth are systematically investigated to establish the standard evaluation conditions. Based on the optimized parameters, a quantitative evaluation of the antibacterial activity of the coating material is successfully demonstrated. The proposed method is expected to be useful in investigating the spatial and temporal distribution of bacterial growth on substrates.

Rapid Antibacterial Assessments for Plastic and Textile Materials Against Escherichia coli

Background: Standard test methods for evaluating the antibacterial performance of plastic (non-porous) and textile (porous) materials are accurate and reliable, but completing a standard assessment generally requires at least several days to a week. Well-trained and experienced technicians are also required to conduct the standard tests consistently and analyse the samples and test results systemically. These costs are often not favourable for the performance assurance of antimicrobial products in industrial production, nor for meeting the fast-return demands in research and development of antimicrobial materials nowadays. Methods: In this study, "Rapid Tests" are developed to evaluate the antibacterial activities of plastic and textile materials. Results: The assessment results from Rapid Tests for plastics and textiles are highly correlated to those from the ISO 22196 and the AATCC Test Method 100, respectively, whereas the evaluation operation can be completed within one day. Based on bioluminescence technology, colony-forming units of E. coli from the inoculated specimens are determined via luminometry. Antibacterial efficacy of the treated plastic and textile samples can be examined effectively. Conclusions: By analysing antimicrobial artificial leather samples composed of hydrophilic polyurethane polymer using Rapid Tests for plastics and textiles, the applicability and scope of these tests were remarkedly recognised and verified.

A realistic approach for evaluating antimicrobial surfaces for dry surface exposure scenarios

The severe acute respiratory syndrome coronavirus 2 pandemic has raised public awareness about the importance of hygiene, leading to an increased demand for antimicrobial surfaces to minimize microbial contamination on high-touch surfaces. This is particularly relevant in public and private transportation settings, where surfaces frequently touched by individuals pose a significant, yet preventable, risk of infection transmission. Typically, the antimicrobial activity of surfaces is tested using test methods of the International Standards Organization, American Society for Testing and Materials, or Japanese Industrial Standards, which involve complete submersion in liquid, elevated temperature (37°C), and prolonged (24 h) contact periods. However, these conditions do not accurately represent real-world scenarios where surfaces are exposed to air. In this study, we propose a modified test method designed to better reflect real-life conditions in the intended end-use setting. The modifications included using deionized water instead of nutrient broth while preparing bacterial inoculum, applying a small test inoculum to the surface and allowing it to dry, maintaining ambient temperature and relative humidity throughout the contact period, and reducing the contact period to 4 h. With this modified approach, the antimicrobial activity of 20 samples was reassessed. This screening revealed that out of 20 samples, only 2 samples were effective against all species, while 8 samples demonstrated partial effectiveness against selected species, and 10 samples showed no significant effect. These findings highlight the inadequacy of the current test standard and emphasize the urgent necessity for revised and adapted testing method to ensure a reliable and accurate evaluation.IMPORTANCEThe recent severe acute respiratory syndrome coronavirus 2 pandemic has sparked increased demand for antimicrobial surfaces to mitigate the risk of fomites-transmitted infection in both indoors and confined spaces. Commonly, the antimicrobial activity of these surfaces is assessed using test standards established by national standards bodies, which do not distinguish between different application scenarios. While these test standards are suitable for surfaces intended for submerged application, they are inappropriate for antimicrobial surfaces designed for dry surface exposure. The usage of these standards can lead to an overestimation of antimicrobial efficacy. Thus, this study introduces a modified dry exposure test method aimed at better reflecting real-life conditions in the intended end-use setting. Our results revealed the subpar antimicrobial performance of numerous samples, highlighting the necessity to revise and tailor the universal test standard to real-world scenarios in order to ensure a reliable and accurate evaluation.

Isolation, characterization and antimicrobial activity study of Thymus vulgaris

Herbal medicines are important for ensuring sustainable development goals (SDGs) in healthcare, particularly in developing countries with high rates of antimicrobial resistance (AMR) and little access to medical facilities. Thymus vulgaris is a widely used herbal medicinal plant known for its secondary metabolites and antimicrobial properties. The present study involved a comprehensive examination of the isolation, characterization, and antibacterial activity of Thymus vulgaris obtained from Ethiopia. The aerial part of the plant Thymus vulgaris was successively extracted with hexane, chloroform, and methanol based on differences in polarity. Phytochemical screening tests conducted against hexane, chloroform and MeOH crude extracts indicated the presence of some secondary metabolites. Based on the thin-layer chromatography tests, the chloroform extract was subjected to column chromatography, yielding Tv-2 compounds, namely 5-isopropyl-2-methylphenol. The structures of the compounds were elucidated via spectroscopic methods (UV-Vis, FT-IR and NMR). We investigated the antibacterial properties of hexane crude extract, chloroform crude extract, MeOH crude extract, and isolated fractions derived from T. vulgaris against various bacterial strains. This study contributes to a better understanding of the bioactive components present in Thymus vulgaris crude extracts and their potential role in tackling microbial infections.

Microencapsulation, Physicochemical Characterization, and Antioxidant, Antibacterial, and Antiplasmodial Activities of Holothuria atra Microcapsule

This study provides the design of a microencapsulation formula, physicochemical characterization, and antioxidant, antibacterial, and antiplasmodial activities of Holothuria atra microcapsules. The ethanolic extract of H. atra was microencapsulated with chitosan (CHI) and sodium tripolyphosphate (Na-TPP) with various stirring times: 60 minutes (CHI60), 90 minutes (CHI90), and 120 minutes (CHI120). The microcapsules were then observed for physicochemical properties using scanning electron microscopy (SEM) and Fourier-transform infrared spectroscopy (FTIR). The microcapsules were tested for antioxidant activity and antibacterial activity against Staphylococcus aureus and Escherichia coli using the DPPH (2,2-diphenyl-1-picrylhydrazyl) method. Antiplasmodial bioactivity was assessed through in silico molecular docking. The CHI60 and CHI120 microcapsules exhibited a smaller size and an irregular spherical shape, while the same FTIR profile was observed in CHI90 and CHI120. The bioactivity tests demonstrated that CHI90 exhibited high antibacterial activity against E. coli and S. aureus, while CHI120 exhibited high antioxidant performance. Calcigeroside B and Echinoside B exhibited antiplasmodial activity against the Plasmodium falciparum dihydroorotate dehydrogenase (PfDHODH) protein, along with an artemisinin inhibition mechanism. In conclusion, the microcapsules with the CHI90 formula demonstrated the best antibacterial activity, while the CHI120 formula exhibited high antioxidant activity. Two terpenoids, Calcigeroside B and Echinoside B, exhibited the best antiplasmodial activity.

Metal-Organic Framework-Based Antimicrobial Touch Surfaces to Prevent Cross-Contamination

Infection diseases are a major threat to global public health, with nosocomial infections being of particular concern. In this context, antimicrobial coatings emerge as a promising prophylactic strategy to reduce the transmission of pathogens and control infections. Here, antimicrobial door handle covers to prevent cross-contamination are prepared by incorporating iodine-loaded UiO-66 microparticles into a potentially biodegradable polyurethane polymer (Baycusan eco E 1000). These covers incorporate MOF particles that serve as both storage reservoirs and delivery systems for the biocidal iodine. Under realistic touching conditions, the door handle covers completely inhibit the transmission of Gram-positive bacterial species (Staphylococcus aureus, and Enterococcus faecalis), Gram-negative bacterial species (Escherichia coli, Pseudomonas aeruginosa, and Acinetobacter baumannii), and fungi (Candida albicans). The covers remain effective even after undergoing multiple contamination cycles, after being cleaned, and when tinted to improve discretion and usability. Furthermore, as the release of iodine from the door handle covers follow hindered Fickian diffusion, their antimicrobial lifetime is calculated to be as long as approximately two years. Together, these results demonstrate the potential of these antimicrobial door handle covers to prevent cross-contamination, and underline the efficacy of integrating MOFs into innovative technologies.

Recent advances and biomedical application of 3D printed nanocellulose-based adhesive hydrogels: A review

Nanocellulose-based tissue adhesives show promise for achieving rapid hemostasis and effective wound healing. Conventional methods, such as sutures and staples, have limitations, prompting the exploration of bioadhesives for direct wound adhesion and minimal tissue damage. Nanocellulose, a hydrolysis product of cellulose, exhibits superior biocompatibility and multifunctional properties, gaining interest as a base material for bioadhesive development. This study explores the potential of nanocellulose-based adhesives for hemostasis and wound healing using 3D printing techniques. Nanocellulose enables the creation of biodegradable adhesives with minimal adverse effects and opens avenues for advanced wound healing and complex tissue regeneration, such as skin, blood vessels, lungs, cartilage, and muscle. This study reviews recent trends in various nanocellulose-based 3D printed hydrogel patches for tissue engineering applications. The review also introduces various types of nanocellulose and their synthesis, surface modification, and bioadhesive fabrication techniques via 3D printing for smart wound healing.

Sustainable Strategies for Synthesizing Lignin-Incorporated Bio-Based Waterborne Polyurethane with Tunable Characteristics

In this study, we introduce a novel approach for synthesizing lignin-incorporated castor-oil-based cationic waterborne polyurethane (CWPU-LX), diverging significantly from conventional waterborne polyurethane dispersion synthesis methods. Our innovative method efficiently reduces the required solvent quantity for CWPU-LX synthesis to approximately 50% of that employed in traditional WBPU experimental procedures. By incorporating lignin into the polyurethane matrix using this efficient and reduced-solvent method, CWPU-LX demonstrates enhanced properties, rendering it a promising material for diverse applications. Dynamic interactions between lignin and polyurethane molecules contribute to improved mechanical properties, enhanced thermal stability, and increased solvent resistance. Dynamic interactions between lignin and polyurethane molecules contribute to improved tensile strength, up to 250% compared to CWPU samples. Furthermore, the inclusion of lignin enhanced thermal stability, showcasing a 4.6% increase in thermal decomposition temperature compared to conventional samples and increased solvent resistance to ethanol. Moreover, CWPU-LX exhibits desirable characteristics such as protection against ultraviolet light and antibacterial properties. These unique properties can be attributed to the presence of the polyphenolic group and the three-dimensional structure of lignin, further highlighting the versatility and potential of this material in various application domains. The integration of lignin, a renewable and abundant resource, into CWPU-LX exemplifies the commitment to environmentally conscious practices and underscores the significance of greener materials in achieving a more sustainable future.

Bacterial-Nanocellulose-Based Biointerfaces and Biomimetic Constructs for Blood-Contacting Medical Applications

Understanding the interaction between biomaterials and blood is critical in the design of novel biomaterials for use in biomedical applications. Depending on the application, biomaterials can be designed to promote hemostasis, slow or stop bleeding in an internal or external wound, or prevent thrombosis for use in permanent or temporary medical implants. Bacterial nanocellulose (BNC) is a natural, biocompatible biopolymer that has recently gained interest for its potential use in blood-contacting biomedical applications (e.g., artificial vascular grafts), due to its high porosity, shapeability, and tissue-like properties. To promote hemostasis, BNC has been modified through oxidation or functionalization with various peptides, proteins, polysaccharides, and minerals that interact with the coagulation cascade. For use as an artificial vascular graft or to promote vascularization, BNC has been extensively researched, with studies investigating different modification techniques to enhance endothelialization such as functionalizing with adhesion peptides or extracellular matrix (ECM) proteins as well as tuning the structural properties of BNC such as surface roughness, pore size, and fiber size. While BNC inherently exhibits comparable mechanical characteristics to endogenous blood vessels, these mechanical properties can be enhanced through chemical functionalization or through altering the fabrication method. In this review, we provide a comprehensive overview of the various modification techniques that have been implemented to enhance the suitability of BNC for blood-contacting biomedical applications and different testing techniques that can be applied to evaluate their performance. Initially, we focused on the modification techniques that have been applied to BNC for hemostatic applications. Subsequently, we outline the different methods used for the production of BNC-based artificial vascular grafts and to generate vasculature in tissue engineered constructs. This sequential organization enables a clear and concise discussion of the various modifications of BNC for different blood-contacting biomedical applications and highlights the diverse and versatile nature of BNC as a natural biomaterial.

Antiviral and antibacterial activity of sodium alginate/poly(diallyldimethylammonium chloride) polyelectrolyte film for packaging applications

Pathogen agents, such as bacteria and virus, can contaminate plastic surfaces, particularly those used in food packaging. This study proposed to prepare a polyelectrolyte film with antiviral and antibacterial activity based on sodium alginate (SA) and poly(diallyldimethylammonium chloride) (PDADMAC), a cationic polymer with sanitizing properties. In addition, the physicochemical properties of the polyelectrolyte films were also evaluated. The polyelectrolyte films showed continuous, compact, and crack-free structures. The FTIR analysis confirmed the ionic interaction between SA and PDADMAC. Adding PDADMAC significantly affected the mechanical properties of the films (p < 0.05), increasing the maximum tensile strength (from 8.66 ± 1.55 MPa to 18.1 ± 1.77 MPa). However, polyelectrolyte films showed higher water vapor permeability values due to the strong hydrophilicity of PDADMAC, representing a 43 % average increase compared with the control film. Also, thermal stability improved with the incorporation of PDADMAC. The selected polyelectrolyte film inactivated 99.8 % of SARS-CoV-2 after 1 min in direct contact with the virus, in addition to having an inhibitory effect against Staphylococcus aureus and Escherichia coli bacteria. Therefore, this study demonstrated the efficacy of using PDADMAC in the preparation of polyelectrolyte sodium alginate-based films with improvements in physicochemical properties and especially with antiviral activity against SARS-CoV-2.

Investigating the Properties and Characterization of a Hybrid 3D Printed Antimicrobial Composite Material Using FFF Process: Innovative and Swift

Novel strategies and materials have gained the attention of researchers due to the current pandemic, the global market high competition, and the resistance of pathogens against conventional materials. There is a dire need to develop cost-effective, environmentally friendly, and biodegradable materials to fight against bacteria using novel approaches and composites. Fused filament fabrication (FFF), also known as fused deposition modeling (FDM), is the most effective and novel fabrication method to develop these composites due to its various advantages. Compared to metallic particles alone, composites of different metallic particles have shown excellent antimicrobial properties against common Gram-positive and Gram-negative bacteria. This study investigates the antimicrobial properties of two sets of hybrid composite materials, i.e., Cu-PLA-SS and Cu-PLA-Al, are made using copper-enriched polylactide composite, one-time printed side by-side with stainless steel/PLA composite, and second-time with aluminum/PLA composite respectively. These materials have 90 wt.% of copper, 85 wt.% of SS 17-4, 65 wt.% of Al with a density of 4.7 g/cc, 3.0 g/cc, and 1.54 g/cc, respectively, and were fabricated side by side using the fused filament fabrication (FFF) printing technique. The prepared materials were tested against Gram-positive and Gram-negative bacteria such as Escherichia coli (E. coli), Staphylococcus aureus (S. aureus), Pseudomonas aeruginosa (P. aeruginosa), Salmonella Poona (S. Poona), and Enterococci during different time intervals (5 min, 10 min, 20 min, 1 h, 8 h, and 24 h). The results revealed that both samples showed excellent antimicrobial efficiency, and 99% reduction was observed after 10 min. Hence, three-dimensional (3D) printed polymeric composites enriched with metallic particles can be utilized for biomedical, food packaging, and tissue engineering applications. These composite materials can also provide sustainable solutions in public places and hospitals where the chances of touching surfaces are higher.

A novel long-acting antimicrobial nanomicelle spray

Contaminated surfaces play a major role in disease transmission to humans. The vast majority of commercial disinfectants provide short-term protection of surfaces against microbial contamination. The Covid-19 pandemic has attracted attention to the importance of long-term disinfectants as they would reduce the need for staff and save time. In this study, nanoemulsions and nanomicelles containing a combination of benzalkonium chloride (BKC; a potent disinfectant and a surfactant) and benzoyl peroxide (BPO; a stable form of peroxide that is activated upon contact with lipid/membranous material) were formulated. The prepared nanoemulsion and nanomicelle formulas were of small sizes <80 nm and high positive charge >45 mV. They showed enhanced stability and prolonged antimicrobial efficacy. The antibacterial potency was evaluated in terms of long-term disinfection on surfaces as verified by repeated bacterial inoculums. Additionally, the efficacy of killing bacteria upon contact was also investigated. A nanomicelle formula (NM-3) consisting of 0.8% BPO in acetone and 2% BKC plus 1% TX-100 in distilled water (1 : 5 volume ratio) demonstrated overall surface protection over a period of 7 weeks upon a single spray application. Furthermore, its antiviral activity was tested by the embryo chick development assay. The prepared NM-3 nanoformula spray showed strong antibacterial activities against Pseudomonas aeruginosa, Escherichia coli, and Staphylococcus aureus as well as antiviral activities against infectious bronchitis virus due to the dual effects of BKC and BPO. The prepared NM-3 spray shows great potential as an effective solution for prolonged surface protection against multiple pathogens.

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.

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.

Microbial resistance to nanotechnologies: An important but understudied consideration using antimicrobial nanotechnologies in orthopaedic implants

Microbial resistance to current antibiotics therapies is a major cause of implant failure and adverse clinical outcomes in orthopaedic surgery. Recent developments in advanced antimicrobial nanotechnologies provide numerous opportunities to effective remove resistant bacteria and prevent resistance from occurring through unique mechanisms. With tunable physicochemical properties, nanomaterials can be designed to be bactericidal, antifouling, immunomodulating, and capable of delivering antibacterial compounds to the infection region with spatiotemporal accuracy. Despite its substantial advancement, an important, but under-explored area, is potential microbial resistance to nanomaterials and how this can impact the clinical use of antimicrobial nanotechnologies. This review aims to provide a better understanding of nanomaterial-associated microbial resistance to accelerate bench-to-bedside translations of emerging nanotechnologies for effective control of implant associated infections.

Comparative Experimental Investigation of Biodegradable Antimicrobial Polymer-Based Composite Produced by 3D Printing Technology Enriched with Metallic Particles

Due to the prevailing existence of the COVID-19 pandemic, novel and practical strategies to combat pathogens are on the rise worldwide. It is estimated that, globally, around 10% of hospital patients will acquire at least one healthcare-associated infection. One of the novel strategies that has been developed is incorporating metallic particles into polymeric materials that neutralize infectious agents. Considering the broad-spectrum antimicrobial potency of some materials, the incorporation of metallic particles into the intended hybrid composite material could inherently add significant value to the final product. Therefore, this research aimed to investigate an antimicrobial polymeric PLA-based composite material enhanced with different microparticles (copper, aluminum, stainless steel, and bronze) for the antimicrobial properties of the hybrid composite. The prepared composite material samples produced with fused filament fabrication (FFF) 3D printing technology were tested for different time intervals to establish their antimicrobial activities. The results presented here depict that the sample prepared with 90% copper and 10% PLA showed the best antibacterial activity (99.5%) after just 20 min against different types of bacteria as compared to the other samples. The metallic-enriched PLA-based antibacterial sheets were remarkably effective against Staphylococcus aureus and Escherichia coli; therefore, they can be a good candidate for future biomedical, food packaging, tissue engineering, prosthetic material, textile industry, and other science and technology applications. Thus, antimicrobial sheets made from PLA mixed with metallic particles offer sustainable solutions for a wide range of applications where touching surfaces is a big concern.

Influence of Femtosecond Laser Modification on Biomechanical and Biofunctional Behavior of Porous Titanium Substrates

Bone resorption and inadequate osseointegration are considered the main problems of titanium implants. In this investigation, the texture and surface roughness of porous titanium samples obtained by the space holder technique were modified with a femtosecond Yb-doped fiber laser. Different percentages of porosity (30, 40, 50, and 60 vol.%) and particle range size (100–200 and 355–500 μm) were compared with fully-dense samples obtained by conventional powder metallurgy. After femtosecond laser treatment the formation of a rough surface with micro-columns and micro-holes occurred for all the studied substrates. The surface was covered by ripples over the micro-metric structures. This work evaluates both the influence of the macro-pores inherent to the spacer particles, as well as the micro-columns and the texture generated with the laser, on the wettability of the surface, the cell behavior (adhesion and proliferation of osteoblasts), micro-hardness (instrumented micro-indentation test, P–h curves) and scratch resistance. The titanium sample with 30 vol.% and a pore range size of 100–200 μm was the best candidate for the replacement of small damaged cortical bone tissues, based on its better biomechanical (stiffness and yield strength) and biofunctional balance (bone in-growth and in vitro osseointegration).

Laser-Assisted Nanotexturing and Silver Immobilization on Titanium Implant Surfaces to Enhance Bone Cell Mineralization and Antimicrobial Properties

Despite the great advancement and wide use of titanium (Ti) and Ti-based alloys in different orthopedic implants, device-related infections remain the major complication in modern orthopedic and trauma surgery. Most of these infections are often caused by both poor antibacterial and osteoinductive properties of the implant surface. Here, we have demonstrated a facile two-step laser nanotexturing and immobilization of silver onto the titanium implants to improve both cellular integration and antibacterial properties of Ti surfaces. The required threshold laser processing power for effective nanotexturing and osseointegration was systematically determined by the level of osteoblast cells mineralized on the laser nanotextured Ti (LN-Ti) surfaces using a neodymium-doped yttrium aluminum garnet laser (Nd:YAG, wavelength of 1.06 μm). Laser processing powers above 24 W resulted in the formation of hierarchical nanoporous structures (average pore 190 nm) on the Ti surface with a 2.5-fold increase in osseointegration as compared to the pristine Ti surface. Immobilization of silver nanoparticles onto the LN-Ti surface was conducted by dip coating in an aqueous silver ionic solution and subsequently converted to silver nanoparticles (AgNPs) by using a low power laser-assisted photocatalytic reduction process. Structural and surface morphology analysis via XRD and SEM revealed a uniform distribution of Ag and the formation of an AgTi-alloy interface on the Ti surface. The antibacterial efficacy of the LN-Ti with laser immobilized silver (LN-Ti/LI-Ag) was tested against both Gram-positive (Staphylococcus aureus) and Gram-negative (Escherichia coli) bacteria. The LN-Ti/LI-Ag surface was observed to have efficient and stable antimicrobial properties for over 6 days. In addition, it was found that the LN-Ti/LI-Ag maintained a cytocompatibility and bone cell mineralization property similar to the LN-Ti surface. The differential toxicity of the LN-Ti/LI-Ag between bacterial and cellular species qualifies this approach as a promising candidate for novel rapid surface modification of biomedical metal implants.

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.

Investigation of the Mechanical and Liquid Absorption Properties of a Rice Straw-Based Composite for Ayurvedic Treatment Tables

Managing rice crop stubble is one of the major challenges witnessed in the agricultural sector. This work attempts to investigate the physical, mechanical, and liquid absorption properties of rice straw (RS)-reinforced polymer composite for assessing its suitability to use as an ayurvedic treatment table. This material is expected to be an alternative for wooden-based ayurvedic treatment tables. The results showed that the addition of rice straw particles (RS_p) up to 60% volume in epoxy reduced the density of the composite material by 46.20% and the hardness by 15.69%. The maximum tensile and flexural strength of the RS_p composite was 17.53 MPa and 43.23 MPa, respectively. The scanning electron microscopy (SEM) analysis showed deposits of silica in the form of phytoliths in various size and shapes on the outer surface of RS. The study also revealed that the water absorption rate (WA) was less than 7.8% for the test samples with 45% volume of RS_p. Interestingly the test samples showed greater resistance to the absorption of Kottakal Dhanvantaram Thailam (<2%). In addition, the developed samples showed resistance towards bacterial and fungal growth under the exposure of treatment oils and water.

Impact of surface topography on the bacterial attachment to micro- and nano-patterned polymer films

The development of antimicrobial surfaces has become a high priority in recent times. There are two ongoing worldwide health crises: the COVID-19 pandemic provoked by the SARS-CoV-2 virus and the antibiotic-resistant diseases provoked by bacteria resistant to antibiotic-based treatments. The need for antimicrobial surfaces against bacteria and virus is a common factor to both crises. Most extended strategies to prevent bacterial associated infections rely on chemical based-approaches based on surface coatings or biocide encapsulated agents that release chemical agents. A critical limitation of these chemistry-based strategies is their limited effectiveness in time while grows the concerns about the long-term toxicity on human beings and environment pollution. An alternative strategy to prevent bacterial attachment consists in the introduction of physical modification to the surface. Pursuing this chemistry-independent strategy, we present a fabrication process of surface topographies [one-level (micro, nano) and hierarchical (micro+nano) structures] in polypropylene (PP) substrates and discuss how wettability, topography and patterns size influence on its antibacterial properties. Using nanoimprint lithography as patterning technique, we report as best results 82 and 86% reduction in the bacterial attachment of E. coli and S. aureus for hierarchically patterned samples compared to unpatterned reference surfaces. Furthermore, we benchmark the mechanical properties of the patterned PP surfaces against commercially available antimicrobial films and provide evidence for the patterned PP films to be suitable candidates for use as antibacterial functional surfaces in a hospital environment.