Biocidal Materials Research Articles

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".

Polymeric microspheres containing silver nanoparticles as a bactericidal agent for water disinfection

A facile methodology has been developed by anchoring silver nanoparticles on to the macroporous methacrylic acid copolymer beads for disinfection of water in this study. Methacrylic acid copolymer beads are prepared by suspension polymerization technique. Silver nanoparticles formed on these copolymer beads by chemical reduction method are stable and are not washed away by water washing. Their stability is due to the interaction of nanoparticles with the carboxylic functional group on the copolymer beads. Copolymer beads containing silver nanoparticles are tested for their antibacterial activity against two gram positive and two gram negative bacteria. Antibacterial activity tested shows that they can be a potent biocidal material for water disinfection as they are highly effective against both gram positive and gram negative bacteria tested. The silver nanoparticles bound copolymer beads performed efficiently in bringing down the bacterial count to zero for all the strains tested except spore forming Bacillus subtilis which showed 99.9% reduction. There is no bacterial adsorption/adhesion on the copolymer beads containing silver nanoparticles proving them as effective water disinfectant.

Synthesis of antibacterial silver nanoparticles by γ-irradiation

Silver nanoparticles (Ag NPs) were synthesized by γ-irradiation of silver ions in aqueous solutions containing polyvinyl pyrrolidone (PVP). Increasing of γ-irradiation doses from 1 to 5 kGy enhanced the concentration of Ag NPs, indicated by UV–vis analysis. The XRD and the TEM measurements showed the production of face-centered cubic (fcc) Ag NPs with a mean size of about 16 nm. The produced nanoparticles were effectively stabilized by PVP through interactions, confirmed by the FT-IR. The relatively higher antibacterial activities of Ag NPs, synthesized through γ-irradiation method, against E. coli indicate their potential for practical applications as biocidal materials.

TLC retention behavior of brodifacoum, bromadiolone, and coumatetralyl and their impurities on different adsorbents

The chromatographic behavior of three biocidal technical materials, rodenticide active ingredients brodifacoum, bromadiolone, and coumatetralyl, and impurities present in the technical material was investigated by both normal-phase (NP) and reversed-phase (RP) planar chromatography. The research was carried out using thinlayers of silica gel, alumina, cellulose, and C 18 silica. Several solvents on their own or in various combinations and proportions were used for separation. The optimum chromatographic systems for separation of the substances from each other and from their impurities were selected. Under reversed-phase chromatographic (RPC) conditions a linear correlation between R M values and mobile phase composition was established. From results obtained, the lipophilicity R M ° and C 0 were determined. Possible separation mechanisms are discussed on the basis of the established retention behavior.

Polyurethane-based leukocyte-inspired biocidal materials

During the neutrophil respiratory burst myeloperoxidase uses hydrogen peroxide and chloride ion to generate hypochlorite which kills pathogens. Synthetic antimicrobial materials based on this chemistry are described herein. The oxidizing enzymes glucose oxidase (GOX) and horseradish peroxidase (HRP) catalyze two reactions in tandem using glucose, hydrogen peroxide and sodium halide (iodide or bromide). The final product of these two consecutive enzymatic reactions is either iodine or bromine. HRP, acting as haloperoxidase, utilizes the H 2O 2 generated by GOX to oxidize halide ions into free halogens. Typically, 15 units/ml HRP and 25 units/ml GOX reacted with 0.8 m m NaI and 5 m m glucose to generate 5–7 ppm free iodine within 30 min. Medical grade polyurethane ChronoFlex AR (CF) was electrospun together with GOX and HRP. The electrospun fibers were collected as a uniform, water-insoluble, flexible elastomeric matrix with an average fiber diameter of 1 ± 0.2 μm. Biocidal activity of CF/enzyme fibers resulted in >6-log unit reduction of both Escherichia coli and Staphylococcus aureus challenges. A time-course of biocidal activity displayed a 3–4 log reduction of E. coli and S. aureus within the first 5 min and complete kill (>6 logs) within 15 min. A dose–response study of fiber weight (0.5–30 mg/ml) exhibited complete kill of E. coli (>6 logs) and at least 99.99% S. aureus kill (>4 logs) with as little as 1 mg fiber. The fibers were reusable with slightly less activity on the second use and significant activity after continuous soaking in buffer for up to 7 days. Electrospun CF/GOX/HRP fibers adhered to a thin film with embedded NaI and glucose caused a complete kill of E. coli (>7-log units) and MRSA (6-log unit reduction) within 1 h at 37 °C.

Synthesis and antimicrobial properties of polymerizable quaternary ammoniums

Introduction of biocide monomers during the process of polymerization is a promising approach in the development of new permanent non leaching biocide materials. Two series of surfactants monomers, with a quaternary ammonium group as polar head and an acrylic function as the polymerizable moiety, were synthesized and tested to evaluate their surface active properties alongside with their antibacterial and antifungal properties. Four microbial strains were used to perform the study: Pseudomonas aeruginosa, Staphylococcus aureus, Candida albicans and Aspergillus niger. The biocidal efficacy measured by bacterial and fungal growth inhibition expressed as MIC (Minimal Inhibitory Concentration) and MLC (Minimal Lethal Concentration) values was discussed as a function of molecular parameters. All the synthesized surfactant monomers presented bactericidal and fungicidal activities. Increasing the spacer between the acrylic part and the ammonium group has a favourable effect on the MIC and MLC results.

Polymerizable semi-fluorinated gemini surfactants designed for antimicrobial materials

Introduction of biocide monomers during the process of polymerization is one of promising approaches in the development of new permanent non leaching biocide materials. In this perspective, new polymerizable semi-fluorinated gemini surfactants, with quaternary ammonium groups as polar heads and an acrylic function as the polymerizable moiety, were synthesized and tested to evaluate their surface active properties alongside with their antibacterial and antifungal properties. Four microbial strains, known for their implication in nosocomial infections, were used to perform the study: Pseudomonas aeruginosa, Staphylococcus aureus, Candida albicans and Aspergillus niger. The biocide efficacy measured by bacterial and fungal growth inhibition expressed as MIC (minimal inhibitory concentration) and MLC (minimal lethal concentration) values was discussed as a function of molecular parameters. As compared to homologue compounds without acrylic part, this study shows that even the introduction of a polymerizable moiety allows to keep remarkable both surfactant and bacteriostatic activities, and allows us to envisage the use of these surfactant monomers to build up advanced biocide materials. Moreover, semi-fluorinated gemini surfactant monomers with an amide connector came out as broad spectrum biocides (against Gram positive and negative bacteria and fungi).

Electrospun polyacrylonitrile nanofibrous biomaterials

An N-halamine precursor, 3-(5'-methyl-5'-hydantoinyl)acetanilide (I), was synthesized in our laboratory and loaded onto electrospun polyacrylonitrile fiber to prepare nanosized biocidal materials, which could be rendered antimicrobial by exposure to household bleach. Differential scanning calorimetry was used to study the thermal properties of the nanofibers with and without the N-halamine precursor and its chlorinated derivative loaded. Scanning electron microscopy demonstrated that the ultrafine fibers formed with diameters from 250 to 600 nm. Chlorinated nanofibrous mats composed of the fibers were challenged with Staphylococcus aureus (ATCC 6538) and Escherichia coli O157:H7 (ATCC 43895); they showed promising inactivation efficacies against the two bacterial species within 5 minutes of contact. Potential uses of the antimicrobial fibers include filters for industrial water and air disinfection and protective clothing.

Kinetic aspects of the silver ion release from antimicrobial polyamide/silver nanocomposites

Spherical silver nanoparticles were grown in situ in different polyamides by a thermal reduction of silver acetate during melt processing of the polymers. Most of the particles have a diameter of about 20 nm. The absolute amount as well as the kinetics of the silver ion release from the various polyamide/silver nanocomposites differ strongly, although the filler content in all materials is the same (1.5 wt. %) and the morphologies of the silver particles are not very different. One result of the investigations was that the absolute amount of the long-term silver ion release increases exponentially with the maximum water absorption of the polymers used as matrix materials, because silver ions are formed from elemental silver particles in the presence of water, only. Moreover, it was also found that the long-term silver ion release increases with a growing diffusion coefficient of water in the polymer. The water absorption properties of the polymers govern the kinetics of the silver ion release, too: for strong hydrophilic polyamides like PA6 or PA6.6, which are plasticized by water, the silver ion release is a zero-order process. For nanocomposites with less hydrophilic polyamides like a cycloaliphatic polyamide or a P12 modified with polytetrahydrofurane (PA12-poly-THF), the silver ion release is governed by diffusion. As expected from the efficacy of the silver ion release, PA6, PA6.6, PA12 and PA12 modified with polytetrahydrofurane and a cycloaliphatic polyamide filled with 1.5 wt. % of silver nanoparticles are active against Escherichia coli. But, only nanocomposites with PA6, PA6.6 and P12-poly-THF as matrix materials are suitable as long-term biocidal materials.

Why Does Kevlar Decompose, while Nomex Does Not, When Treated with Aqueous Chlorine Solutions?

Kevlar and Nomex are high-performance polymers which have wide varieties of applications in daily life. Recently, they have been proposed to be biocidal materials when reacted with household bleach (sodium hypochlorite solution) because they contain amide moieties which can be chlorinated to generate biocidal N-halamine functional groups. Although Nomex can be chlorinated without any significant decomposition, Kevlar decomposes under the same chlorination conditions. In this study, two mimics for each of the polymers were synthesized to simulate the carboxylate and diaminophenylene components of the materials. It was found that the p-diaminophenylene component of the Kevlar mimic is oxidized to a quinone-type structure upon treatment with hypochlorous acid, which then decomposes. However, such a mechanism for the Nomex mimic is not possible. In this paper, based upon these observations, a plausible answer will be provided to the title question.

Durable and Regenerable Biocidal Polymers: Acyclic N-Halamine Cotton Cellulose

As a continued study on halamine biocidal materials, acyclic halamine cotton cellulose was prepared by graft reaction of amide monomers onto cellulose and subsequent chlorination of the grafted materials. Two acyclic vinyl amide monomers, acrylamide (AM) and methacrylamide (MAA), were employed in the reaction successfully. The grafting reaction was implemented by a free radical polymerization process. Several radical initiators were able to abstract hydrogen atoms on the polymers and generate macromolecular radicals to react with the monomers. Similar to cyclic halamines, the resulted acyclic ones were able to provide durable and rechargeable biocidal functions. However, acyclic halamine structures are more vulnerable to hydrolysis compared to the cyclic halamines.

Mechanism of Formation of Biocidal Imidazolidin-4-one Derivatives: An Ab Initio Density-Functional Theory Study

N-halamine chemistry has been a research topic of considerable importance in these laboratories for over 2 decades because N-halamine compounds are very useful in preparing biocidal materials. To understand the utility of these compounds, the stabilities and mechanism of halogenation of cyclic N-halamine compounds should be resolved. The important precursor biocidal compound, 2,2,5,5-tetramethylimidazolidin-4-one (TMIO) was considered as a model in this theoretical study. The thermodynamic and kinetic products of monohalogenation were investigated along with tautomerization of TMIO and succinimide theoretically at the level of B3LYP/6-311+G(2d,p). Solvation effects (water and chloroform) were included using the CPCM solvation model with UAKS cavities. Several mechanisms have been proposed for the chlorine migration from the 3-position (kinetic product) to the 1-position (thermodynamic product) of the TMIO ring. The results are in agreement with experimental NMR data.

The Stabilities of N-Cl Bonds in Biocidal Materials.

N-halamine chemistry has been a research topic of considerable importance in these laboratories for over two decades. N-halamine compounds are useful in preparing biocidal materials. There are three N-Cl moieties available in cyclic N-halamine compounds: imide, amide, and amine. The stabilities toward the release of free halogen have been experimentally shown to decrease in the order amine > amide > imide. In this work, this generalization has been tested theoretically at the level of B3LYP/6-31+G(d) and using the conductor-like polarizable continuum aqueous solvation model with UAKS cavities. Excellent accord was observed between theory and experiment. It was also found that the imide and amide N-halamine stabilities on hydantoin rings could be reversed with substitution patterns at the 5 position.

Preparation of MgO and Fe nanostructure in Mg matrix composite by reaction sintering

MgO, Fe and FeO were in situ formed in the Mg matrix when the green compact containing 20 wt% Fe 3O 4 was sintered at 450 °C. All the Fe 3O 4 phase in the sample were converted to Fe nanoparticle and MgO nanowire, and uniformly distributed in the Mg matrix at 630 °C. It is identified that the average size of Fe nanoparticle is about 50 nm, and the MgO nanowire is single crystals with a diameter of about 25 nm and a length of about 300 nm. The crystal growth of MgO nanowire is controlled by the VS mechanism. A model of in situ reactions and Gibbs free energy in the sample have been proposed and confirmed in the experiments. In our work, these newly in situ formed MgO nanowire and Fe nanoparticle can act as potential biocidal action materials for antibacterial properties. Meanwhile, they also improve the strength and CTE property in the sample. At final, the potential application of this Mg–MMC for electronic packaging materials has been discussed.

Novel N-halamine siloxane monomers and polymers for preparing biocidal coatings

Precursor N-halamine siloxane monomers and polymers have been prepared for the purpose of functionalising the surfaces of materials in order to render them biocidal upon exposure to oxidative halogen solutions. The biocidal function can be imparted to the N-halamine moiety either before or after siloxane bonding or adhesion to the surface or material. The biocidal surfaces and materials can then be used to inactivate pathogenic micro-organisms such as bacteria, fungi and yeasts, as well as virus particles, which can cause infectious diseases, and those micro-organisms which cause noxious odours and unpleasant colouring such as mildew. Examples of surfaces and materials which can be rendered biocidal with the N-halamine siloxanes include cellulose, synthetic fibres, ceramics, plastics, polyurethanes and metals. Preparation procedures and some biocidal efficacy data on paper, cotton and polyurethane paint are discussed.

Chemistry of Durable and Regenerable Biocidal Textiles

Unlike the widely used slow-releasing biocidal mechanism now employed in biocidal textiles, a novel regenerable process, based on a regeneration principle and halamine chemistry, has been developed in antimicrobial finishing of textiles. Halamine-modified textile materials demonstrate durable and regenerable antimicrobial functions and execute rapid inactivation of a broad spectrum of microorganisms by contact without yielding drug resistance. The unique properties of the products render them useful materials for medical-use and hygienic textiles. The chemistry of the biocidal materials is be discussed.

The antibacterial activities of hydrophilic-modified nonwoven PET

The hydrophobic surface of nonwoven PET with surface inertia has limited the practical bioapplications. In this study, nonwoven PET was activated by argon gas plasma and subsequently water-soluble monomers (acrylamide and itaconic acid) were grafted onto the PET by UV-induced surface graft polymerization. After the plasma activation and/or grafting, the hydrophobic surface of nonwoven was modified into a hydrophilic surface. To improve wound healing, the following three biocides have been used in this study: (1) AgNO 3 solution complexes, (2) Vinyl quarternary ammonium salt (VQAS) and (3) chitosan. For Ag + ion impregnation and VQAS grafting, the amount of these biocidal materials on the surface increases when the monomer concentration increases. However, for the chitosan immobilization, the chitosan amounts seemingly decrease with an increase in the chitosan concentration. For biocidal properties, the Ag + ions produce best result. However, the VQAS grafting is most durable against the flushing water.

Fabrication and properties of biocidal fibre materials

The conditions for fabricating biocidal material based on strongly basic VION AS-1 fibre containing iodine were elaborated. The elevated biocidal activity of the mateiral allows using it as the filtering component in filters for purification of drinking water with a high concentration of microorganisms which cause dangerous gastrointestinal diseases.

The treatment of biological growths on stone: a conservator's viewpoint

Recognition of the importance of microbiological factors in the deterioration of stone in buildings and monuments is comparatively recent, with attention focusing on the growths and the kinds of deterioration they cause, rather than on their elimination. This paper outlines considerations in the development of treatments for the elimination of microbiological growths from building stone. The goals of biocidal treatment in the context of architectural conservation are delineated, and limitations in the selection and application of biocidal treatments for architecture are discussed; conditions of work in the USA are emphasized. Directions for future work that would be of interest to architectural conservators are suggested, including evaluation of commonly used biocidal materials and development of comprehensive literature reviews.

Newly made antibacterial braided nylon sutures. I. In vitro qualitative and in vivo preliminary biocompatibility study.

A new type of braided nylon thread with a silver compound coating was made for the purpose of designing a biocidal suture material. The study used standard bacterial culture techniques to evaluate the antibacterial property of the new Ag-coated nylon thread. Seven types of bacterial species were tested; S. aureus, E. coli, P. aeruginosa, K. pneumoniae, S. dysenteriae, S. maruslens, and P. mirabilis. The commercial size 2/0 Nurolon suture from Ethicon served as the control. A weak direct current ranging from 0.4-400 microA was applied to the specimens to examine whether the biocidal property of silver could be enhanced by current. The antibacterial property was evaluated by the width and sterility of the clear zone in the bacterial culture plates. It was found that the new nylon thread exhibited very good to moderate bactericidal property toward these seven bacterial species. P. aeruginosa was the most sensitive species, while P. mirabilis was the least sensitive one. Application of direct current through the Ag-coated specimens positively enhanced their antibacterial property and the degree of enhancement depended on the direct current level. The material also exhibited an antibacterial property toward well-established bacterial colonies, but the effect was less strong than the case when direct current was applied simultaneously with incubation. Silver ions released from the coated nylon thread were responsible for the observed antibacterial property; and the application of a weak direct current to the material enhanced this effect. A preliminary biocompatibility study of this new material in rat gluteal muscle indicated that the new material caused less inflammatory reaction than the control Nurolon suture up to 60 days after implantation.