Polyamide/silver antimicrobials: effect of filler types on the silver ion release

Effects of silver nitrate and silver nanoparticles on a planktonic community: general trends after short-term exposure

Among metal pollutants silver ions are one of the most toxic forms, and have thus been assigned to the highest toxicity class. Its toxicity to a wide range of microorganisms combined with its low toxicity to humans lead to the development of a wealth of silver-based products in many bactericidal applications accounting to more than 1000 nano-technology-based consumer products. Accordingly, silver is a widely distributed metal in the environment originating from its different forms of application as metal, salt and nanoparticle. A realistic assessment of silver nanoparticle toxicity in natural waters is, however, problematic and needs to be linked to experimental approaches. Here we apply metatranscriptome sequencing allowing for elucidating reactions of whole communities present in a water sample to stressors. We compared the toxicity of ionic silver and ligand-free silver nanoparticles by short term exposure on a natural community of aquatic microorganisms. We analyzed the effects of the treatments on metabolic pathways and species composition on the eukaryote metatranscriptome level in order to describe immediate molecular responses of organisms using a community approach. We found significant differences between the samples treated with 5 µg/L AgNO3 compared to the controls, but no significant differences in the samples treated with AgNP compared to the control samples. Statistical analysis yielded 126 genes (KO-IDs) with significant differential expression with a false discovery rate (FDR) <0.05 between the control (KO) and AgNO3 (NO3) groups. A KEGG pathway enrichment analysis showed significant results with a FDR below 0.05 for pathways related to photosynthesis. Our study therefore supports the view that ionic silver rather than silver nanoparticles are responsible for silver toxicity. Nevertheless, our results highlight the strength of metatranscriptome approaches for assessing metal toxicity on aquatic communities.

Adhesion behaviors on superhydrophobic surfaces

The adhesion behaviors of superhydrophobic surfaces have become an emerging topic to researchers in various fields as a vital step in the interactions between materials and organisms/materials. Controlling the chemical compositions and topological structures via various methods or technologies is essential to fabricate and modulate different adhesion properties, such as low-adhesion, high-adhesion and anisotropic adhesion on superhydrophobic surfaces. We summarize the recent developments in both natural superhydrophobic surfaces and artificial superhydrophobic surfaces with various adhesions and also pay attention to superhydrophobic surfaces switching between low- and high-adhesion. The methods to regulate or translate the adhesion of superhydrophobic surfaces can be considered from two perspectives. One is to control the chemical composition and change the surface geometric structure on the surfaces, respectively or simultaneously. The other is to provide external stimulations to induce transitions, which is the most common method for obtaining switchable adhesions. Additionally, adhesion behaviors on solid-solid interfaces, such as the behaviors of cells, bacteria, biomolecules and icing on superhydrophobic surfaces are also noticeable and controversial. This review is aimed at giving a brief and crucial overview of adhesion behaviors on superhydrophobic surfaces.

The effects of titania nanotubes with embedded silver oxide nanoparticles on bacteria and osteoblasts

A versatile strategy to endow biomaterials with long-term antibacterial ability without compromising the cytocompatibility is highly desirable to combat biomaterial related infection. TiO2 nanotube (NT) arrays can significantly enhance the functions of many cell types including osteoblasts thus having promising applications in orthopedics, orthodontics, as well as other biomedical fields. In this study, TiO2 NT arrays with Ag2O nanoparticle embedded in the nanotube wall (NT-Ag2O arrays) are prepared on titanium (Ti) by TiAg magnetron sputtering and anodization. Well-defined NT arrays containing Ag concentrations in a wide range from 0 to 15 at % are formed. Ag incorporation has little influence on the NT diameter, but significantly decreases the tube length. Crystallized Ag2O nanoparticles with diameters ranging from 5 nm to 20 nm are embedded in the amorphous TiO2 nanotube wall and this unique structure leads to controlled release of Ag(+) that generates adequate antibacterial activity without showing cytotoxicity. The NT-Ag2O arrays can effectively kill Escherichia coli and Staphylococcus aureus even after immersion for 28 days, demonstrating the long lasting antibacterial ability. Furthermore, the NT-Ag2O arrays have no appreciable influence on the osteoblast viability, proliferation, and differentiation compared to the Ag free TiO2 NT arrays. Ag incorporation even shows some favorable effects on promoting cell spreading. The technique reported here is a versatile approach to develop biomedical coatings with different functions.

Silica/ultrasmall Ag composite microspheres: facile synthesis, characterization and antibacterial and catalytic performance

Uniform silica/ultrasmall silver composite microspheres have been successfully prepared from silica microspheres and [Ag(NH₃)₂]⁺via a hydrothermal process. The as-prepared silica/Ag microspheres exhibit an excellent antibacterial performance towards E. coli.

Air stable magnetic bimetallic Fe-Ag nanoparticles for advanced antimicrobial treatment and phosphorus removal

We report on new magnetic bimetallic Fe-Ag nanoparticles (NPs) which exhibit significant antibacterial and antifungal activities against a variety of microorganisms including disease causing pathogens, as well as prolonged action and high efficiency of phosphorus removal. The preparation of these multifunctional hybrids, based on direct reduction of silver ions by commercially available zerovalent iron nanoparticles (nZVI) is fast, simple, feasible in a large scale with a controllable silver NP content and size. The microscopic observations (transmission electron microscopy, scanning electron microscopy/electron diffraction spectroscopy) and phase analyses (X-ray diffraction, Mössbauer spectroscopy) reveal the formation of Fe₃O₄/γ-FeOOH double shell on a "redox" active nZVI surface. This shell is probably responsible for high stability of magnetic bimetallic Fe-Ag NPs during storage in air. Silver NPs, ranging between 10 and 30 nm depending on the initial concentration of AgNO₃, are firmly bound to Fe NPs, which prevents their release even during a long-term sonication. Taking into account the possibility of easy magnetic separation of the novel bimetallic Fe-Ag NPs, they represent a highly promising material for advanced antimicrobial and reductive water treatment technologies.

Biological responses of silver-coated thermosets: an in vitro and in vivo study

Bisphenol A glycidylmethacrylate (BisGMA)/triethyleneglycol dimethacrylate (TEGDMA) thermosets are biomaterials commonly employed for orthopedic and dental applications; for both these fields, bacterial adhesion to the surface of the implant represents a major issue for the outcome of the surgical procedures. In this study, the antimicrobial properties of a nanocomposite coating formed by polysaccharide 1-deoxylactit-1-yl chitosan (Chitlac) and silver nanoparticles (nAg) on methacrylate thermosets were studied. The Chitlac-nAg system showed good anti-bacterial and anti-biofilm activity although its biocidal properties can be moderately, albeit significantly, inhibited by serum proteins. In vitro studies on the silver release kinetic in physiological conditions showed a steady metal release associated with a gradual loss of antimicrobial activity. However, after 3weeks there was still effective protection against bacterial colonization which could be accounted for by the residual silver. This time-span could be considered adequate to confer short-term protection from early peri-implant infections. Preliminary in vivo tests in a mini-pig animal model showed good biological compatibility of Chitlac-nAg-coated materials when implanted in bony tissue. The comparison was made with implants of titanium Ti6Al4V alloy and with a Chitlac-coated thermoset. Bone healing patterns and biocompatibility parameters observed for nAg-treated material were comparable with those observed for control implants.

Enhancing the fouling resistance of biocidal urethane coatings via surface chemistry modulation

A group of novel cross-linked polyurethane materials with varying ratios of hydroxyl-terminated macrodiols and tethered quaternary ammonium biocides have been prepared. The resulting materials had a wide range of thermal, mechanical, and surface properties, dictated by the macrodiol composition and biocide concentration. The complex interplay between surface chemistry and biocide concentration was shown to have a profound effect on the fouling resistance of these materials. While the combination of quaternary ammonium salt (QAS) diols with poly(tetramethylene oxide) macrodiols did not result in any enhancement of fouling resistance, addition of biocides to poly(ethylene glycol)-containing urethanes resulted in up to a 90% increase in biocidal activity compared to control materials while reducing the ability for microbes to adhere to the surface by an additional 60%. Materials prepared with polybutadiene macrodiols underwent a thermally induced oxidation, resulting in partial decomposition of the quaternary ammonium salt biocide and joint antimicrobial activity arising from remaining QAS and peroxide compounds.

Characterization of fibrous polymer silver/cobalt nanocomposite with enhanced bactericide activity

This manuscript describes the synthesis (based on the intermatrix synthesis (IMS) method), optimization, and application to bacterial disinfection of Ag@Co polymer-metal nanocomposite materials with magnetic and bactericidal properties. This material showed ideal bactericide features for being applied to bacterial disinfection of water, particularly (1) an enhanced bactericidal activity (when compared with other nanocomposites only containing Ag or Co nanoparticles), with a cell viability close to 0% for bacterial suspensions with an initial concentration below 10(5) colony forming units per milliliter (CFU/mL) after a single pass through the material, (2) capacity of killing a wide range of bacterial types (from coliforms to gram-positive bacteria), and (3) a long performance-time, with an efficiency of 100% (0% viability) up to 1 h of operation and higher than 90% during the first 24 h of continuous operation. The nanocomposite also showed a good performance when applied to water samples from natural sources with more complex matrices with efficiencies always higher than 80%.

Ion-release kinetics and ecotoxicity effects of silver nanoparticles

The environmental toxicity associated with silver nanoparticles (AgNPs) has been a major focus in nanotoxicology. The Ag(+) released from AgNPs may affect ecotoxicity, although whether the major toxic effect is governed by Ag(+) ions or by AgNPs themselves is unclear. In the present study, we have examined the ecotoxicity of AgNPs in aquatic organisms, silver ion-release kinetics of AgNPs, and their relationship. The 48-h median effective concentration (EC50) values for Daphnia magna of powder-type AgNP suspensions were 0.75 µg/L (95% confidence interval [CI] = 0.71-0.78) total Ag and 0.37 µg/L (95% CI = 0.36-0.38) dissolved Ag. For sol-type AgNP suspension, the 48-h EC50 values for D. magna were 7.98 µg/L (95% CI = 7.04-9.03) total Ag and 0.88 µg/L (95% CI = 0.80-0.97) dissolved Ag. The EC50 values for the dissolved Ag of powder-type and sol-type AgNPs for D. magna showed similar results (0.37 µg/L and 0.88 µg/L) despite their differences of EC50 values in total Ag. We observed that the first-order rate constant (k) of Ag(+) ions released from AgNPs was 0.0734/h at 0.05 mg/L total Ag at 22°C within 6 h. The kinetic experiments and the toxicity test showed that 36% and 11% of sol-type AgNPs were converted to the Ag(+) ion form under oxidation conditions, respectively. Powder-type AgNPs showed 49% conversion rate of Ag(+) ion from AgNPs. We also confirmed that Ag(+) ion concentration in AgNP suspension reaches an equilibrium concentration after 48 h, which is an exposure time of the acute aquatic toxicity test.

Fabrication of novel biofibers by coating silk fibroin with chitosan impregnated with silver nanoparticles

Nanoparticle based agents often applied as coatings on biomaterials have shown promise in delivering the improved sterility against variety of microbes. In the present study, silk fibers (SF) were coated with chitosan impregnated with silver nanoparticles (Ag-C-SF). These Ag-C-SF fibers were characterized using scanning electron microscopy (SEM) with energy dispersive X-ray analysis, atomic force microscopy (AFM), Infra Red spectroscopy, Thermogravimetric Analysis and Microbiological assay techniques. AFM studies have confirmed the nano sized silver particles in chitosan solution; SEM pictures have exhibited the coating of chitosan along with silver nanoparticles on the silk fibroin. The modified fibers have also shown anti-microbial activity and improved thermal stability. The Ag-C-SF fibers may be explored as wound dressing and tendon reconstruction material in future.

Silver distribution and release from an antimicrobial denture base resin containing silver colloidal nanoparticles

PURPOSE

The aim of this study was to evaluate a denture base resin containing silver colloidal nanoparticles through morphological analysis to check the distribution and dispersion of these particles in the polymer and by testing the silver release in deionized water at different time periods.

MATERIALS AND METHODS

A Lucitone 550 denture resin was used, and silver nanoparticles were synthesized by reduction of silver nitrate with sodium citrate. The acrylic resin was prepared in accordance with the manufacturers' instructions, and silver nanoparticle suspension was added to the acrylic resin monomer in different concentrations (0.05, 0.5, and 5 vol% silver colloidal). Controls devoid of silver nanoparticles were included. The specimens were stored in deionized water at 37°C for 7, 15, 30, 60, and 120 days, and each solution was analyzed using atomic absorption spectroscopy.

RESULTS

Silver was not detected in deionized water regardless of the silver nanoparticles added to the resin and of the storage period. Micrographs showed that with lower concentrations, the distribution of silver nanoparticles was reduced, whereas their dispersion was improved in the polymer. Moreover, after 120 days of storage, nanoparticles were mainly located on the surface of the nanocomposite specimens.

CONCLUSIONS

Incorporation of silver nanoparticles in the acrylic resin was evidenced. Moreover, silver was not detected by the detection limit of the atomic absorption spectrophotometer used in this study, even after 120 days of storage in deionized water. Silver nanoparticles are incorporated in the PMMA denture resin to attain an effective antimicrobial material to help control common infections involving oral mucosal tissues in complete denture wearers.

Applications of nanotechnology in food packaging and food safety: barrier materials, antimicrobials and sensors

In this article, several applications of nanomaterials in food packaging and food safety are reviewed, including: polymer/clay nanocomposites as high barrier packaging materials, silver nanoparticles as potent antimicrobial agents, and nanosensors and nanomaterial-based assays for the detection of food-relevant analytes (gasses, small organic molecules and food-borne pathogens). In addition to covering the technical aspects of these topics, the current commercial status and understanding of health implications of these technologies are also discussed. These applications were chosen because they do not involve direct addition of nanoparticles to consumed foods, and thus are more likely to be marketed to the public in the short term.

Silver polymeric nanocomposites as advanced antimicrobial agents: classification, synthetic paths, applications, and perspectives

Utilization of metallic nanoparticles in various biotechnological and medical applications represents one of the most extensively investigated areas of the current materials science. These advanced applications require the appropriate chemical functionalization of the nanoparticles with organic molecules or their incorporation in suitable polymer matrices. The intensified interest in polymer nanocomposites with silver nanoparticles is due to the high antimicrobial effect of nanosilver as well as the unique characteristics of polymers which include their excellent structural uniformity, multivalency, high degree of branching, miscellaneous morphologies and architectures, and highly variable chemical composition. In this review, we explore several aspects of antimicrobial polymer silver nanocomposites, giving special focus to the critical analysis of the reported synthetic routes including their advantages, drawbacks, possible improvements, and real applicability in antibacterial and antifungal therapy. A special attention is given to "green" synthetic routes exploiting the biopolymeric matrix and to the methods allowing preparing magnetically controllable antimicrobial polymers for targeting to an active place. The controversial mechanism of the action of silver against bacteria, fungi and yeasts as well as perspectives and new applications of silver polymeric nanocomposites is also briefly discussed.

Simultaneous dispersion-dissolution behavior of concentrated silver nanoparticle suspensions in the presence of model organic solutes

The premise of the nanotechnology revolution is based on the increased surface reactivity of nanometer-sized particles. Thus, these newly realized applications of noble metal nanoparticles introduce new concerns about the environmental fate of these materials if released during use or product disposal. In this paper, the focus is on silver nanoparticles, a known biocidal agent. In particular, this work explores the effect of model solutes chosen for their simple chemical structure yet their ability to simulate chemical attributes common to soil humic material: a chelating molecule, EDTA; a nonionic surfactant, Brij 35; and a large polysaccharide, alginic acid. Batch systems containing concentrated (1600 mg L(-1)) silver nanoparticle (nAg) suspensions were equilibrated with varying additions of EDTA, Brij 35, or alginic acid to solutions containing 1 or 100 mM NaNO3 background electrolyte. In general, both EDTA and alginate were shown to exhibit poor control over nAg dispersion stability, while Brij 35 served as a good dispersant of nAg particles, showing little difference in particle size with respect to electrolyte concentration. The data also show that loading of the model organic compounds resulted in the supersaturation of dissolved Ag for most of the systems. Mechanisms by which these occurred are discussed in more detail. The evidence suggests that regardless of the effect of humics on the stability of nAg dispersions in aqueous systems, polymer loading may enhance the dissolution and release of dissolved Ag into the environment.

Silver nanoparticle studded porous polyethylene scaffolds: bacteria struggle to grow on them while mammalian cells thrive

Silver nanoparticle studded scaffolds were prepared by exploiting the Ag(+) ion reducing activity of sophorolipids--a class of 'glycolipids' that cap the ensuing nanoparticles as well. To achieve this, the porous polyethylene scaffolds are subjected to N(2) + H(2) plasma treatment, in the first step. Subsequently the sophorolipids are covalently attached to the amine groups on the polymer surface through simple amide chemistry to yield sophorolipid grafted polymer scaffolds. These are then exposed to Ag(+) ions under appropriate conditions leading to the formation of silver nanoparticles immobilized on the polymer scaffolds. It has been found that while bacteria do not survive on these silver studded scaffolds, CHO-K1 cells thrive on them making them good candidates for tissue engineering and bio-implant applications.

Antibacterial nano-structured titania coating incorporated with silver nanoparticles

Titanium (Ti) implants are widely used clinically but post-operation infection remains one of the most common and serious complications. A surface boasting long-term antibacterial ability is highly desirable in order to prevent implant associated infection. In this study, titania nanotubes (TiO(2)-NTs) incorporated with silver (Ag) nanoparticles are fabricated on Ti implants to achieve this purpose. The Ag nanoparticles adhere tightly to the wall of the TiO(2)-NTs prepared by immersion in a silver nitrate solution followed by ultraviolet light radiation. The amount of Ag introduced to the NTs can be varied by changing processing parameters such as the AgNO(3) concentration and immersion time. The TiO(2)-NTs loaded with Ag nanoparticles (NT-Ag) can kill all the planktonic bacteria in the suspension during the first several days, and the ability of the NT-Ag to prevent bacterial adhesion is maintained without obvious decline for 30 days, which are normally long enough to prevent post-operation infection in the early and intermediate stages and perhaps even late infection around the implant. Although the NT-Ag structure shows some cytotoxicity, it can be reduced by controlling the Ag release rate. The NT-Ag materials are also expected to possess satisfactory osteoconductivity in addition to the good biological performance expected of TiO(2)-NTs. This controllable NT-Ag structure which provides relatively long-term antibacterial ability and good tissue integration has promising applications in orthopedics, dentistry, and other biomedical devices.

120 years of nanosilver history: implications for policy makers

Nanosilver is one nanomaterial that is currently under a lot of scrutiny. Much of the discussion is based on the assumption that nanosilver is something new that has not been seen until recently and that the advances in nanotechnology opened completely new application areas for silver. However, we show in this analysis that nanosilver in the form of colloidal silver has been used for more than 100 years and has been registered as a biocidal material in the United States since 1954. Fifty-three percent of the EPA-registered biocidal silver products likely contain nanosilver. Most of these nanosilver applications are silver-impregnated water filters, algicides, and antimicrobial additives that do not claim to contain nanoparticles. Many human health standards for silver are based on an analysis of argyria occurrence (discoloration of the skin, a cosmetic condition) from the 1930s and include studies that considered nanosilver materials. The environmental standards on the other hand are based on ionic silver and may need to be re-evaluated based on recent findings that most silver in the environment, regardless of the original silver form, is present in the form of small clusters or nanoparticles. The implications of this analysis for policy of nanosilver is that it would be a mistake for regulators to ignore the accumulated knowledge of our scientific and regulatory heritage in a bid to declare nanosilver materials as new chemicals, with unknown properties and automatically harmful simply on the basis of a change in nomenclature to the term "nano".

Reduction of the spoilage-related microflora in absorbent pads by silver nanotechnology during modified atmosphere packaging of beef meat

Silver-based antibacterial hybrid materials have been developed by in situ reduction of silver nitrate (1%) adsorbed on cellulose fibers by thermal and UV treatments. Microscopy revealed that the silver nanoparticles were dispersed and regular in shape. Migrated silver ions achieved 60 ppm in beef meat exudates. The ability of the silver-loaded absorbent pads to lower microbial contamination of exuded fluids was studied during storage of beef meat in modified atmosphere packaging. Cellulose-silver hybrid materials reduced the levels of the major microbial groups (total aerobic bacteria, lactic acid bacteria, Pseudomonas spp., and Enterobacteriaceae) present in the absorbent pads by an average of 1 log CFU/g during the entire storage period. The levels of total aerobic bacteria and Pseudomonas spp. were significantly reduced in the presence of silver ions, whereas lactic acid bacteria were less sensitive and not significantly affected. Enterobacteriaceae levels remained under the detection limit when silver was present. Neither the color of the meat nor the microbial loads were markedly affected by the presence of the silver-based antimicrobial hybrid materials.

Dissolution-accompanied aggregation kinetics of silver nanoparticles

Bare silver nanoparticles with diameters of 82 ± 1.3 nm were synthesized by the reduction of the Ag(NH(3))(2)(+) complex with D-maltose, and their morphology, crystalline structure, UV-vis spectrum, and electrophoretic mobilities were determined. Dynamic light scattering was employed to assess early stage aggregation kinetics by measuring the change in the average hydrodynamic diameter of the nanoparticles with time over a range of electrolyte types (NaCl, NaNO(3), and CaCl(2)) and concentrations. From this the critical coagulation concentration values were identified as 30, 40, and 2 mM for NaNO(3), NaCl, and CaCl(2), respectively. Although the silver nanoparticles were observed to dissolve in all three electrolyte solutions, the aggregation results were still consistent with classical Derjaguin-Landau-Verwey-Overbeek (DLVO) theory. The dissolution of the silver nanoparticles, which were coated with a layer of Ag(2)O, was highly dependent on the electrolyte type and concentration. In systems with Cl(-) a secondary precipitate, likely AgCl, also formed and produced a coating layer that incorporated the silver nanoparticles. Aggregation of the silver nanoparticles was also examined in the presence of Nordic aquatic fulvic acid and was little changed compared to that evaluated under identical fulvic acid-free conditions. These results provide a fundamental basis for further studies evaluating the environmental fate of silver nanoparticles in natural aquatic systems.

Recent progress in inorganic and composite coatings with bactericidal capability for orthopaedic applications

This review covers the most recent developments of inorganic and organic-inorganic composite coatings for orthopedic implants, providing the interface with living tissue and with potential for drug delivery to combat infections. Conventional systemic delivery of drugs is an inefficient procedure that may cause toxicity and may require a patient's hospitalization for monitoring. Local delivery of antibiotics and other bioactive molecules maximizes their effect where they are required, reduces potential systemic toxicity and increases timeliness and cost efficiency. In addition, local delivery has broad applications in combating infection-related diseases. Polymeric coatings may present some disadvantages. These disadvantages include limited chemical stability, local inflammatory reactions, uncontrolled drug-release kinetics, late thrombosis and restenosis. As a result, embedding of bioactive compounds and biomolecules within inorganic coatings (bioceramics, bioactive glasses) is attracting significant attention. Recently nanoceramics have attracted interest because surface nanostructuring allows for improved cellular adhesion, enhances osteoblast proliferation and differentiation, and increases biomineralization. Organic-inorganic composite coatings, which combine biopolymers and bioactive ceramics that mimick bone structure to induce biomineralization, with the addition of biomolecules, represent alternative systems and ideal materials for "smart" implants. In this review, emphasis is placed on materials and processing techniques developed to advance the therapeutic use of biomolecules-eluting coatings, based on nanostructured ceramics. One part of this report is dedicated to inorganic and composite coatings with antibacterial functionality.

FROM THE CLINICAL EDITOR

Inorganic and composite nanotechnology-based coating methods have recently been developed for orthopedic applications, with the main goal to provide bactericide and other enhanced properties, which may result in reduced need for pharmaceutical interventions and overall more cost effective orthopedic procedures. This review discusses key aspects of the above developments.

Differentiation of the toxicities of silver nanoparticles and silver ions to the Japanese medaka (Oryzias latipes) and the cladoceran Daphnia magna

Silver nanoparticles (AgNPs) are increasingly used in various fields. However, little is known about the environmental effects of widespread use of products containing AgNPs. The objective of this study was to determine the ecotoxicity caused by AgNPs. The 48-h effective concentration 50 (EC(50)) values for Daphnia magna of suspensions of 60 nm and 300 nm AgNPs were 1.0 (95% confidence interval [CI] = 0.1-1.3) and 1.4 (95% CI = 0.3-2.1) μg Ag/l, respectively. The 96 h LC(50) values for Oryzias latipes of 60 nm and 300 nm AgNP suspensions were 28 (95% CI = 23-34) and 67 (95% CI = 45-108) μg Ag/l, respectively. To show that toxicity is caused only by Ag(+) and not by AgNPs, Ag(+) was adsorbed onto the synthesized sorbents packed in a column and D. magna was exposed to the column-passed-300 nm AgNP suspensions. There was no acute toxicity with the AgNP suspensions not containing Ag(+).

The behavior of silver nanotextiles during washing

The widespread use of silver nanoparticles (Ag-NPs) in commercial products, especially textiles, will likely result in an unknown spread of Ag into the environment. The quantification and characterization of the Ag released from nano-Ag-products is an important parameter needed to predict the effect of Ag-NPs on the environment. The aim of this study was to determine the amount and the form of Ag released during washing from nine fabrics with different ways of silver incorporation into or onto the fibers. The effect of pH, surfactants, and oxidizing agents was evaluated. The results show that little dissolution of Ag-NPs occurs under conditions relevant to washing (pH 10) with dissolved concentrations 10 times lower than at pH 7. However, bleaching agents such as hydrogen peroxide or peracetic acid (formed by the perborate/TAED system) can greatly accelerate the dissolution of Ag. The amount and form of Ag released from the fabrics as ionic and particulate Ag depended on the type of Ag-incorporation into the textile. The percentage of the total silver emitted during one washing of the textiles varied considerably among products (from less than 1 to 45%). In the washing machine the majority of the Ag (at least 50% but mostly >75%) was released in the size fraction >450 nm, indicating the dominant role of mechanical stress. A conventional silver textile did not show any significant difference in the size distribution of the released silver compared to many of the textiles containing nano-Ag. These results have important implications for the risk assessment of Ag-textiles and also for environmental fate studies of nano-Ag, because they show that under conditions relevant to washing, primarily coarse Ag-containing particles are released.

Intracellular biogenic silver nanoparticles for the generation of carbon supported antiviral and sustained bactericidal agents

Intracellular silver nanoparticles produced by exposing silver ions to the fungus Aspergillus ochraceus were heat-treated in nitrogen environment to yield silver nanoparticles embedded in carbonaceous supports. This carbonaceous matrix embedded silver nanoparticles showed antimicrobial properties against both bacteria (Gram-positive and Gram-negative) and virus (M 13 phage virus). The bactericidal effects were noticed even after washing and repeated exposure of these carbon supported silver nanoparticles to fresh bacterial cultures, revealing their sustained activity.

Antibacterial activity of nanocomposites of silver and bacterial or vegetable cellulosic fibers

Cellulose/Ag nanocomposites were prepared using two distinct methodologies and two cellulose substrates: vegetable and bacterial cellulose. These nanocomposites were characterized in terms of their morphology and chemical composition. Detailed studies on the antibacterial activity of these materials were carried out for Bacillus subtilis, Staphylococcus aureus and Klebsiella pneumoniae. Silver nanoparticles present in the cellulosic fibers in concentrations as low as 5.0x10(-4)wt.% make these nanocomposites effective antibacterial materials. We anticipate that the versatile use of these cellulose-based nanocomposites can bring a promising strategy to produce a wide range of interesting materials where antibacterial properties are crucial.

Antimicrobial properties of a novel silver-silica nanocomposite material

Nanotechnology enables development and production of novel silver-based composite materials. We used in vitro tests to demonstrate the antimicrobial activity of a silver-silica nanocomposite compared to the activities of conventional materials, such as silver nitrate and silver zeolite. A silver-silica-containing polystyrene material was manufactured and shown to possess strong antimicrobial properties.

Embedded silver ions-containing liposomes in polyelectrolyte multilayers: cargos films for antibacterial agents

A new antibacterial coating made of poly(L-lysine)/hyaluronic acid (PLL/HA) multilayer films and liposome aggregates loaded with silver ions was designed. Liposomes filled with an AgNO 3 solution were first aggregated by the addition of PLL in solution. The obtained micrometer-sized aggregates were then deposited on a PLL/HA multilayer film, playing the role of a spacer with the support. Finally, HA/PLL/HA capping layers were deposited on top of the architecture to form a composite AgNO 3 coating. Release of encapsulated AgNO 3 from this composite coating was followed and triggered upon temperature increase over the transition temperature of vesicles, found to be equal to 34 degrees C. After determination of the minimal inhibitory concentration (MIC) of AgNO 3 in solution, the antibacterial activity of the AgNO 3 coating was investigated against Escherichia coli. A 4-log reduction in the number of viable E. coli cells was observed after contact for 120 min with a 120 ng/cm (2) AgNO 3 coating. In comparison, no bactericidal activity was found for PLL/HA films previously dipped in an AgNO 3 solution and for PLL/HA films with liposome aggregates containing no AgNO 3 solution. The strong bactericidal effect could be linked to the diffusion of silver ions out of the AgNO 3 coating, leading to an important bactericidal concentration close to the membrane of the bacteria. A simple method to prepare antibacterial coatings loaded with a high and controlled amount of AgNO 3 is therefore proposed. This procedure is far superior to that soaking AgNO 3 or Ag nanoparticles into a coating. In principle, other small bactericidal chemicals like antibiotics could be encapsulated by this method. This study opens a new route to modify surfaces with small solutes that are not permeating phospholipid membranes below the phase transition temperature.

Manufactured nanoparticles: an overview of their chemistry, interactions and potential environmental implications

The industrial scale production and wide variety of applications of manufactured nanoparticles (NPs) and their possible release in considerable amounts into the natural aquatic environment have produced an increasing concern among the nanotechnology and environmental science community. In order to address this issue, it is important to understand NP chemistry, preparation, reactivity and possible mechanisms involved in their interaction with the naturally occurring aquatic components, particularly natural colloids and NPs present in the aquatic systems. In this review, an overview of the chemistry of both manufactured and natural aquatic NPs is outlined. This review discusses the physico-chemical aspects of both type of NPs as an essential point to assess possible routes involved in manufactured NP fate in the natural aquatic environment and their toxicity. Key advances related to the characterisation of the manufactured NPs and natural colloids.