Functional Antimicrobial Surfaces by Ultrafine Powder Coating

The modem era of technology has amplified the significance of coated materials as well as their potential relevance and opportunity. With microbial infection arising as one of North America’s biggest public concerns, by the ongoing spread o f harmful microorganisms, the need for a marketably simple and durable antimicrobial surface has arisen for applications including inanimate objects and/or biomaterials. Antimicrobial surfaces cater to public safety by protection/prevention of infectious disease by the reduction of transmission of harmful microorganisms and the intervention of microorganism contamination. This study exhibits the development of various powder coating formulation efficacies against Escherichia coli and corresponding bacterial reductions of over 99% after only hours of exposure on metallic substrates. The most effective formulations recognize differences in the inorganic active agent concentrations of silver ion or nano silver metal and accompanied additive percentages of corresponding carrier materials of natural chabazite zeolite or silica gel. As an additional advantage to functional antimicrobial coatings, ultrafine powder coating is an environmentally friendly green technological coating, since it eliminates the use of toxic solvents that are responsible for the hazardous emissions of volatile organic compound

Protective Properties of Functionalised Tetrazine on an Aerospace Aluminium Alloy (AA 2024-T3)

Environmental health concerns over conventional chromium based surface treatments on aluminium substrates are well known. Current research efforts have concentrated on developing protective technologies for multiple applications. Such properties would enable manufacturers to address both corrosion and bacterial threats in areas such as fuel tanks and delivery systems. The present study explores the anticorrosion properties of 1,2-dihydro 1, 2, 4, 5 tetrazine-3, 6-dicarboxylic acid (H2DCTZ) on a copper rich aerospace aluminium alloy (AA 2024-T3). Furthermore the antimicrobial activity of the tetrazine is evaluated against Gram-positive and Gram-negative bacteria, both capable of inducing corrosion. The protective action of the tetrazine was investigated at different concentrations in a chloride ion rich environment (3.5% (w/v) NaCl) utilising electrochemical impedance spectroscopy (EIS). Results over a 72 h period proved that an optimum concentration was 500 ppm. FTIR and SEM elemental mapping of the surface confirmed the nitrogen rich tetrazine affinity for the copper rich intermetallic sites, through coordinate bonds, which delayed corrosion onset and reduced pit formation. Moderate antibacterial tetrazine activity was observed against Escherichia coli and 100% efficacy against Staphylococcus aureus at 250 ppm was achieved. The damage of the bacterial cell envelope at the critical concentrations (250 ppm) is proposed as a possible mechanism for antibacterial action

The modification of Laponite® with silver or copper and investigation of their antibacterial activity

A thesis submitted in partial fulfilment of the requirements of the University of Wolverhampton for the degree of Doctor of Philosophy.Silver and copper modified Laponite® RD were synthesised either by ion exchange or isomorphous substitution into Laponite® RD sheet. Six different concentrations of silver-exchanged Laponite® RD (AGLAP1-6) or copper exchanged Laponite® RD (CULAP1-6) were produced in this work via ion exchange and three different concentrations of silver incorporated Laponite® RD (AL1-3) and a concentration of copper incorporated Laponite® RD (CL1) were synthesized via isomorphous substitution. The silver or copper modified Laponite® RD were characterised with X-ray diffraction (XRD), Fourier transformed infrared spectroscopy (FTIR), energy dispersive X-ray spectroscopy (EDX), thermogravimetric analysis (TGA), magic angle spinning nuclear magnetic resonance (MAS NMR), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The XRD showed changes in the phase purity of pure and modified Laponite® RD. The amount of silver or copper exchanged or incorporated into Laponite® RD interlayer or sheet were determined by EDX. The TEM image analysis indicated that the Ag+ and Cu2+ ions were in the nanometer range with a modal size of 13±1 and 15±1nm for silver and copper-exchanged Laponite® RD, 10 and 18nm for silver and copper incorporated Laponite® RD respectively. The antibacterial activity was investigated by exposing Escherichia coli K12W-T, Staphylococcus aureus NCIM B6571 and Pseudomonas aeruginosa NCIMB8295 in tryptone soya broth to the different silver-Laponite® RD and copper-Laponite® RD nanocomposites for a period of 72 hours. All concentrations of silver-Laponite® RD and copper-Laponite® RD reduced the growth of all the bacterial spcies. There was no growth of P. aeruginosa after 6 hours, E. coli after 8 hours and S. aureus after 24 hours with silver-exchanged Laponite® RD containing 2.35 wt. % Ag (AGLAP6); P. aeruginosa after 8 hours, E. coli iv after 24 hours and S. aureus after 24 hours with silver-exchnaged Laponite® RD containing 1.76 wt. % Ag (AGLAP4). Similarly total inhibition was obtained in the medium supplemented with silver incorporated Laponite® RD containing 1.10 wt. % Ag (AL3) for P. aeruginosa at 6 hours, both E. coli and S. aureus at 8 hours; with silver incorporated Laponite® RD 0.58 wt. % Ag (AL2) for P. aeruginosa at 8 hours, both E. coli and S. aureus at 24 hours. To access the persistency and slow release of the antibacterial agents the release profile was compared with AgNO3 and CuSO4. While all the silver-Laponite® RD and copper-Laponite® RD showed slow and consistent release over the whole investigation period, AgNO3 and CuSO4 were abrupt, signifying that Laponite® RD is an efficient slow release material. In addition, silver ions eluted more quickly from the silver incorporated Laponite® RD than the silver-exchanged Laponite® RD. Unmodified Laponite® RD showed no antibacterial property to any of the bacteria tested, but was responsible for the consistent and controlled slow release of the metal nanoparticles into the tryptone soya broth, a phenomenon potentially utilizable in bandages where release for long duration is crucial

Formulation and Optimization of Antimicrobial Surfaces Via Ultra-Fine Powder Coating

In a health care environment, surface bio-contamination is a constant risk and contributes to outbreaks of community-acquired and nosocominal infections. Faster surface die-off of pathogens on a surface can reduce the average surface population of these pathogens. Antimicrobial ultra-fine powder coated surfaces with high antimicrobial longevity including efficiency is a good option to reduce the surface bio-contamination. Different formulations were prepared with the additives containing silver as an active agent and a chosen type of metal ions as a protective agent incorporated into zeolites and their antimicrobial activity was analyzed against Escherichia coli (E.coli). Two natural zeolites, known as chabazites (named LBC and LBN), were accustomed to enhance their sodium content as well as ion exchange characteristics by conditioning and was functionalized by using different combinations of the Ag and the other metal ions. No significant changes were observed during XRD and TGA analysis. Elemental analysis by ICP-OES confirmed the enhancement of silver ions after functionalization due to the conditioning process. Color analysis indicated that the other metal helped to maintain the color of the coated surface. These coated surfaces have shown consistent antibacterial properties with excellent durability against E.coli for an extended longevity. Antimicrobial efficiency of that coated surface was also proven by toxicity analysis through the production of lactate dehydrogenase (LDH). Synthetic zeolite A (LTA) was used as a carrier for active agents in different experiments in this study. Optimum concentration of these cations were obtained by ion exchange. TGA, XRD, XPS and FTIR analysis were used for further characterization of these additives. The reduction of Ag+ can be controlled by the addition of the other metal ions and that surface was found to be very efficient since the coated surface showed 100% reduction of microorganisms within 2 hrs of exposure. Auger parameter confirmed that copper prevented silver from being reduced during the curing period. The transfer efficiency of the additives in the resin system during the spraying was improved by increasing the aggregated particle size of the final powder from 20µm to 30µm using aggregating, grinding and sieving processes. The effects of low curing additives on surface properties were analyzed based on the ASTM standards for powder coating and found comparable with the surface cured at higher temperature. The release rate of the active components from the surface was further controlled by resin encapsulation on the additive and this process was found to provide an effective antimicrobial surface for prolonged periods. Finally, a special polymer blend was found to be the best combination for encapsulation. Encapsulation of additives was proven through antimicrobial efficiency analysis. The final formulated surface was also found to be active against microorganism after autoclave and UV treatment, which was proved by toxicity analysis

Characterisation of strontium-containing apatite-wollastonite porous scaffolds

Porous strontium-doped apatite-wollastonite scaffolds were evaluated as potential substitutes for enhanced bone regeneration and the prevention of peri-prosthetic infections. Parent glasses of composition 35.5SiO2-7.1MgO-0.4CaF2-7.1P2O5-(49.9-x)CaO-xSrO mol%, where x = 0, 6.2, 12.5, 18.7, 24.9 or 37.4, were produced via the melt-quench route, ground and sieved <45 μm. Porous scaffolds were obtained following the foam-replication method and heat-treated at 1050 °C for 2 h for controlled nucleation and growth of the crystal phases. All six glasses produced were amorphous. Differential scanning calorimetry showed that the formation of the calcium silicate phase strongly depended on the amount of strontium contained in the parent glass, linearly moving to higher temperatures with increasing strontium. Morphological evaluation (scanning electron microscopy and micro-computed tomography) proved that the obtained scaffold porosity, about 55 vol%, did not depend on the strontium content. X-ray diffraction showed that strontium preferentially substituted in apatite, while only higher strontium compositions formed a strontium magnesium calcium silicate phase. Compressive and biaxial flexural strength were both comparable to cancellous bone. Compositions containing 0 %, 6.2 % and 12.5 % strontium showed excellent apatite forming ability when submerged in simulated body fluid, which then decreased with increasing strontium for the three higher-strontium compositions. Microbiological tests carried out on strontium-containing salts showed no effective antibacterial properties for strontium as a free element. Amongst the six strontium-containing glasses, only the 37.4 % strontium oxide glass showed antimicrobial effects against Pseudomonas aeruginosa in broth dilution tests. Proliferation and osteogenic differentiation of porous scaffolds were tested on human bone cells. No conclusive results were obtained for the G292 cell line. When scaffolds were tested with human primary mesenchymal stromal cells, an increase in DNA content was observed with increasing strontium, while enhanced alkaline phosphatase activity and increased collagen production were found for low strontium compositions

Growth, inhibition and pathogenicity of microorganisms in enteral nutrient solutions

Enteral nutrient solutions (ENS) which are contaminated with microorganisms from exogenous sources or from the microbial flora of the patient's own gastrointestinal tract are associated with bacteraemia, diarrhoea, respiratory infections and septicaemia. These infections seriously undermine some of the advantages of enteral feeding by increasing patient morbidity, mortality and lengthening hospital stay. The strategies which have been employed to prevent contamination of enteral feeding systems and the subsequent incidence of disease have been shown to be ineffective or impractical in a clinical environment. Therefore, this thesis investigated the possibilities of using novel antimicrobial agents (oil of fennel and parabens) to inhibit the growth of microorganisms that commonly contaminate ENS and/or to alter the expression of products which mediate in their pathogenicity. In order to achieve this, the study of growth and the virulence determinants of microorganisms in enteral feeding solutions was necessary. Gram-negative bacteria are the most important group of microorganisms that contaminate ENS and therefore this group of bacteria and lipopolysaccharide, an important Gram-negative bacterial virulence determinant, were particularly singled out for study. The results showed that the growth of all test strains of microorganisms was similar in milk-based enteral nutrient solutions and laboratory media, while only Candida albicans and Klebsiella aerogenes grew in the "fruit-based" ENS. None of microbial strains were inhibited in milk-based ENS by the concentrations of oil of fennel or parabens used singly. However, oil of fennel and parabens used in combination had synergistic antimicrobial activity and inhibited the growth of all microbial strains. Growth in milk-based enteral nutrient solutions was found to alter the phenotypic expression and biological activity of lipopolysaccharide. Results showed differences in the O-polysaccharide portion of the lipopolysaccharide of bacteria cultured in milk-based enteral nutrient solutions compared to those cultured in laboratory media. Bacteria cultured in milk-based enteral feeds had increased serum resistance and also induced a significantly greater release of nitric oxide from a human monocyte cell line than bacteria cultured in laboratory media. The concentrations of oil of fennel and methyl parabens used in experiments did not alter the expression of O-polysacchande. Enteral nutrient solutions can therefore, not only support the growth of microorganisms but alter virulence determinants. This could have important consequences for immunocompromised patients who receive ENS

Antibacterial Metallic Touch Surfaces

Our aim is to present a comprehensive review of the development of modern antibacterial metallic materials as touch surfaces in healthcare settings. Initially we compare Japanese, European and US standards for the assessment of antimicrobial activity. The variations in methodologies defined in these standards are highlighted. Our review will also cover the most relevant factors that define the antimicrobial performance of metals, namely, the effect of humidity, material geometry, chemistry, physical properties and oxidation of the material. The state of the art in contact-killing materials will be described. Finally, the effect of cleaning products, including disinfectants, on the antimicrobial performance, either by direct contact or by altering the touch surface chemistry on which the microbes attach, will be discussed. We offer our outlook, identifying research areas that require further development and an overview of potential future directions of this exciting field

Micromotors for Environmental Applications

[eng] Scarce supply of clean water and rising water pollution are key global challenges for water sustainability. Much of the wastewater generated by human agricultural and industrial activity is left untreated. Nanotechnological materials and systems have emerged as new tools for improving the efficiency of water treatment. Among those, self-propelled micromotors have shown several advantageous characteristics. Micromotors are autonomously propelled systems which either use chemical energy present in their environment or are propelled via external force fields. Diverse designs, materials composition and mechanisms of propulsion are reported for micromotors found in the literature. Among them, bubble-propelled micromotors, which move due to the generation and release of gas bubbles from their surface, are the main type of motors used for water remediation applications. In addition to the motion in fluids, the bubbles generated by the motors, also contribute with additional mixing of the fluid and enhance the mass transfer between active material and pollutant at the microscale. Additionally, the structure of micromotors can be modified to target a wide variety of pollutants, almost on demand. The micromotors that we synthesized during the research work for this thesis can remove organic and heavy metal pollutants, as well as exhibit bactericidal activity. We studied Iron/Platinum (Fe/Pt) micromotors for their reusability, effect of sizes, swimming behaviors and catalytic properties. These micromotors were fabricated by spontaneous roll-up of iron and platinum nanomembranes, deposited on the pre-fabricated patterns of a photoresist substrate. The iron layer present as the outer surface of these micromotors can degrade organic pollutants via Fenton-like reaction and the inner platinum layer acts as the engine decomposing hydrogen peroxide to oxygen for bubble propulsion. We observed that Fe/Pt micromotors can swim continuously for hours, and can be stored for weeks before reuse, without sacrificing much of their activity. The results suggested that Fe/Pt micromotors act as a heterogeneous catalyst due to in situ generated iron oxide species on the surface, without leaching high concentration of iron in the media. We developed graphene oxide-based micromotors (GOx-micromotors) for heavy metal removal, consisting of nanosized multilayers of graphene oxide, nickel, and platinum. These micromotors can capture, transfer, and remove heavy metals (i.e. lead) from contaminated water. GOx-micromotors are synthesized by electrodepositions of electro-reducible graphene oxide, nickel and platinum layers in the polycarbonate porous templates. The outer layer of graphene oxide captures lead on their surface, and the inner layer of platinum provides self-propulsion in hydrogen peroxide, while the middle layer of nickel enables external magnetic control of the micromotors. We observed that the mobile GOx-micromotors can remove lead 10 times more efficiently than non-motile GOx-micromotors, cleaning water from 1000 ppb down to below 50 ppb. We have demonstrated control of their motion and directionality in a proof of concept microfluidic system. Silver nanoparticles (AgNPs) decorated Magnesium Janus micromotors were designed for disinfection and remove of Escherichia coli (E. coli) bacteria from contaminated water. Magnesium present in the micromotors functions as both, the template for the spherical shape and propulsion source by producing hydrogen bubbles while in contact with water. The inner layer of iron provides functionality for the magnetic remote guidance, and an outer AgNP coated gold layer facilitates adhesion of bacteria and gives bactericidal properties to the micromotors. We observed that the AgNPs-coated Au cap of the micromotors shows dual capabilities, capturing bacteria and killing them. In our efforts to develop multifunctional micromotors and scalable synthesis methods, we developed two types of micromotors. (i) Mesoporous silica-based micromotors with manganese dioxide (MnO2) layer on the inner surface and coated with γ-Fe2O3 nanoparticles (FeSiMnOx micromotors). These micromotors can remove both organic and heavy metal pollutants, and they are synthesized using only template-assisted chemical methods. (ii) Cobalt ferrite micromotors (CFO micromotors) synthesized by template-free chemical synthesis approach. They are made up of aggregated cobalt ferrite nanoparticles, which act as the catalyst for propulsion and for Fenton-like reactions. We qualitatively measured the generation of hydroxyl radicals by CFO micromotors and studied the effect of surfactants on the degradation efficiency of CFO micromotors. We hope that such approach of synthesizing micromotors via relatively facile methods will push the use of micromotors towards commercially practical solutions for water treatment. Overall, our results show that the multifunctional self-propelled micromotors have potential to become an effective tool for water remediation in the near future.[spa] El escaso suministro de agua limpia y el aumento de la contaminación del agua son desafíos globales clave para la sostenibilidad del agua, sobre todo teniendo en cuenta que gran parte del agua residual generada por la actividad agrícola e industrial humana no se trata. Los materiales y sistemas nanotecnológicos han surgido como nuevas herramientas para mejorar la eficiencia del tratamiento de aguas. Entre ellos, los micromotores autopropulsados han mostrado varias características ventajosas. Los micromotores son sistemas de propulsión autónoma que utilizan energía química presente en su entorno o pueden también ser propulsadas a través de campos de fuerzas aplicadas externamente. Varios diseños, composición de materiales y mecanismos de propulsión se han sido reportados en el campo de los micromotores. Entre ellos, principalmente los micromotores propulsados por burbujas, los cuales se mueven debido a la generación y liberación de burbujas de gas de su superficie, se utilizan como una herramienta para aplicaciones de remediación de aguas. Esto se debe a la eficacia añadida de la transferencia de masa a la microescala, que se origina a partir de su movimiento y el movimiento de las burbujas liberadas. Además, la estructura de los micromotores se puede modificar para dirigirse a una amplia variedad de contaminantes, según los requerimientos. Los micromotores que sintetizamos durante el trabajo de investigación para esta tesis pueden eliminar contaminantes orgánicos y metales pesados, así como exhibir actividad anti bactericida. Estudiamos micromotores de hierro / platino (Fe / Pt) por su reutilización, efecto de tamaños, su comportamiento durante su movimiento y propiedades catalíticas. Estos micromotores se fabricaron mediante enrollamiento espontáneo de nanomembranas de hierro y platino, depositadas en los patrones prefabricados definidos en una capa sacrificial fotorresistente. La capa de hierro presente como superficie externa de estos micromotores puede degradar los contaminantes orgánicos a través de la reacción tipo Fenton y la capa interna de platino actúa como el motor, siendo el catalizador que descompone el peróxido de hidrógeno en oxígeno para generar una propulsión por burbujas. Observamos que los micromotores Fe / Pt pueden nadar continuamente durante horas y pueden almacenarse durante semanas antes de volver a ser usados, sin que esto repercuta de manera significativa en su actividad. Los resultados de nuestros experimentos sobre el análisis de superficie de micromotores, estudio de nanoindentación y liberación de hierro sugirieron que los micromotores Fe / Pt actúan como un catalizador heterogéneo debido a las especies de óxido de hierro generadas in situ en la superficie, sin lixiviación de alta concentración de hierro en los medios. Desarrollamos micromotores basados en óxido de grafeno (micromotores GOx) para la eliminación de metales pesados que consisten en multicapas nanométricas de óxido de grafeno, níquel y platino. Estos micromotores pueden capturar, transferir y eliminar metales pesados (es decir, plomo) del agua contaminada. Los micromotores GOx se sintetizan mediante electrodeposiciones de capas de óxido de grafeno, níquel y platino, los cuales son electroreducidos en la parte interior de membranas de policarbonato porosas. La capa externa de óxido de grafeno captura el plomo en su superficie, y la capa interna de platino proporciona autopropulsión en presencia de peróxido de hidrógeno, mientras que la capa intermedia de níquel permite el control magnético externo de los micromotores. Observamos que los micromotores móviles GOx pueden eliminar el plomo hasta 10 veces más que los micromotores GOx no móviles (Figura 1B), limpiando el plomo en agua de 1000 ppb a menos de 50 ppb en menos de 60 min. Hemos demostrado el control de su movimiento y direccionalidad en un sistema microfluídico como prueba de concepto. Diseñamos también micromotores tipo Janus decorados con nanopartículas de plata (AgNP) para la desinfección y eliminación de la bacteria Escherichia coli (E. coli) en agua contaminada. Los micromotores Janus se sintetizaron recubriendo un lado de una micro-partícula de magnesio con capas de hierro y oro, las cuales posteriormente se funcionalizaron con AgNP. El magnesio presente en los micromotores funciona no sólo como estructura principal para conseguir una forma esférica, sino también como fuente de propulsión mediante la producción de burbujas de hidrógeno al entrar en contacto con el agua. La capa interna de hierro proporciona la funcionalidad requerida para el posterior control magnético externo, mientras que la capa de oro externa decorada con AgNPs promueve la adhesión de bacterias y dota de propiedades bactericidas a los micromotores. En nuestro esfuerzo por desarrollar micromotores multifuncionales y métodos de síntesis escalables, desarrollamos dos tipos de micromotores. (i) Micromotores mesoporosos basados en sílice con una capa de dióxido de manganeso (MnO2) en la superficie interna y recubiertos con nanopartículas γ-Fe2O3 (micromotores FeSiMnOx). Estos micromotores pueden eliminar contaminantes orgánicos y metales pesados, y se sintetizan utilizando solo métodos químicos asistidos por un molde (por ejemplo, una membrana porosa). (ii) Los micromotores de ferrita de cobalto (micromotores CFO) fueron sintetizados sin necesidad de utilizar ningún molde. Están formados por nanopartículas de ferrita de cobalto agregadas, que actúan como catalizadores para la propulsión y para reacciones tipo Fenton. Medimos cualitativamente la generación de radicales hidroxilos por micromotores CFO y estudiamos el efecto de los tensioactivos sobre la eficiencia de degradación de los micromotores CFO. Esperamos que la síntesis de micromotores a través de métodos relativamente fáciles empuje la implementación de micromotores en soluciones comercialmente prácticas para el tratamiento del agua. En general, nuestros resultados muestran que los micromotores autopropulsados multifuncionales tienen el potencial de convertirse en una herramienta efectiva para la limpieza de aguas en el futuro