In situ preparation of silver nanocomposites on cellulosic fibers – Microwave vs. conventional heating

A Facile Green Fabrication and Characterization of Cellulose-Silver Nanoparticle Composite Sheets for an Antimicrobial Food Packaging

The present study focused on a facile and green approach for the one-step synthesis of silver nanoparticles (AgNPs) embedded in hard wood bleached kraft fiber. The hydroxyl groups on the cellulose chain induced ionic silver reduction with additional hydrothermal energy, allowing for the in situ formation and deposition of AgNPs on the cellulose fiber. The white color of the bleached fiber transformed to yellow due to the formation of AgNPs. UV-Vis spectroscopy, scanning electron microscopy, and X-ray photoelectron spectroscopy revealed that the AgNPs were uniformly distributed across the surface of the obtained cellulose fibers. The results indicated that the formation and distribution of AgNPs on surface of cellulose fibers was significantly influenced by the amount and concentration of silver nitrate (AgNO3). The antimicrobial activity of the cellulose-AgNP composite sheet against Escherichia coli was found to be inhibiting. These findings imply that cellulose-AgNP composite sheets can be feasibly used as antimicrobial paper for food packaging.

Adsorption Characteristics of Ag Nanoparticles on Cellulose Nanofibrils with Different Chemical Compositions

The adsorption characteristics of silver nanoparticles (AgNPs) on cellulose nanofibrils (CNFs) were investigated herein with different chemical compositions. Pure cellulose nanofibers (PCNFs), lignocellulose nanofibers (LCNFs) with different lignin contents (LCNF-20% and LCNF-31%), and holocellulose nanofibers (HCNFs) with hemicellulose were used in this study. Furthermore, CNFs and silver nitrate were mixed and reacted at different temperatures, and NaBH4 was used as the reducing agent. First, the effect of temperature on the adsorption of AgNPs on PCNF was studied. At an optimal temperature (45 °C), the effect of the chemical composition of CNF was studied. The overall properties were analyzed using UV-vis spectroscopy, transmission electron microscopy, X-ray diffraction, Fourier-transform infrared spectroscopy, and X-ray photoelectron spectroscopy. The AgNPs were found to be spherical under all conditions with average diameter of 5.3 nm (PCNF), 5.6 nm (HCNF), 6.3 nm (LCNF-20%) and 6.6 nm (LCNF-31%). The amount of AgNPs adsorbed on the CNF was observed to vary, based on the chemical composition of the CNF. The adsorption amount of AgNPs was observed to increase in the order of LCNF-20% > PCNF > LCNF-31% > HCNF. The results indicated that phenolic hydroxyl groups present in LCNF significantly affected the adsorption of AgNPs.

Synthesis and Characterization of Silver Nanoparticles on Orthodontic Brackets: A New Alternative in the Prevention of White Spots

Silver nanoparticles (AgNPs) are used for their powerful antibacterial effect and their ability to adhere to surfaces due to their size; they are used in different areas of life, mainly in the area of health as medicine. More recently, in dentistry, the synthesis and characterization of AgNPs attracted significant attention due to their antibacterial properties. In this study, the AgNPs were synthesized using the most effective method on different orthodontic brackets (metallic and esthetic) and characterized by scanning electron microscopy/energy-dispersive spectroscopy (SEM/EDS) and transmission electron microscopy (TEM). Their antimicrobial effect was tested against the widely used standard human pathogens Staphylococcus aureus (Gram-negative) and Escherichia coli (Gram-positive). Our results showed that, via a simple chemical method, AgNPs can be synthesized on the surface of orthodontic brackets with good antimicrobial activity and the possibility of reducing dental decay, periodontal disease and white spots generated during orthodontic treatment.

Bactericidal and Cytotoxic Properties of Silver Nanoparticles

Silver nanoparticles (AgNPs) can be synthesized from a variety of techniques including physical, chemical and biological routes. They have been widely used as nanomaterials for manufacturing cosmetic and healthcare products, antimicrobial textiles, wound dressings, antitumor drug carriers, etc. due to their excellent antimicrobial properties. Accordingly, AgNPs have gained access into our daily life, and the inevitable human exposure to these nanoparticles has raised concerns about their potential hazards to the environment, health, and safety in recent years. From in vitro cell cultivation tests, AgNPs have been reported to be toxic to several human cell lines including human bronchial epithelial cells, human umbilical vein endothelial cells, red blood cells, human peripheral blood mononuclear cells, immortal human keratinocytes, liver cells, etc. AgNPs induce a dose-, size- and time-dependent cytotoxicity, particularly for those with sizes ≤10 nm. Furthermore, AgNPs can cross the brain blood barrier of mice through the circulation system on the basis of in vivo animal tests. AgNPs tend to accumulate in mice organs such as liver, spleen, kidney and brain following intravenous, intraperitoneal, and intratracheal routes of administration. In this respect, AgNPs are considered a double-edged sword that can eliminate microorganisms but induce cytotoxicity in mammalian cells. This article provides a state-of-the-art review on the synthesis of AgNPs, and their applications in antimicrobial textile fabrics, food packaging films, and wound dressings. Particular attention is paid to the bactericidal activity and cytotoxic effect in mammalian cells.

Green Procedure to Manufacture Nanoparticle-Decorated Paper Substrates

For this study, a paper impregnated with silver nanoparticles (AgNPs) was prepared. To prepare the substrates, aqueous suspensions of pulp fines, a side product from the paper production, were mixed with AgNP suspensions. The nanoparticle (NP) synthesis was then carried out via laser ablation of pure Ag in water. After the sheet formation process, the leaching of the AgNPs was determined to be low while the sheets exhibited antimicrobial activity toward Escherichia coli (E. coli).

Synthesis and antimicrobial effects of highly dispersed, cellulose-stabilized silver/cellulose nanocomposites

Small, spherical silver nanoclusters were synthesised on the surface of paper as a model cellulosic fibre substrate by a standard chemical reduction method. The concentration of the silver nanoclusters on the substrate surface is roughly proportional to the initial silver salt concentration. However, there is a noticeable degree of nanocluster aggregation to larger agglomerates. The addition of small amounts of α-cellulose, carboxymethyl cellulose or aminocellulose during the synthesis of the silver/cellulose nanocomposites suppresses this aggregation and significantly increases the concentration of the silver nanoclusters on the surface of the fibres of cellulose. These small, surface-stabilised silver nanoclusters, with the desired size and morphology, deposited from aqueous solutions on the surface of cellulosic cotton fibres, show enhanced antibacterial activity against MRSA compared to that of the corresponding silver/cotton nanocomposites prepared in the absence of a cellulosic surface stabiliser.

Silver/cellulose nanocomposite fibres, prepared using a simple reduction method, exhibit significant and competitive antibacterial activity against strains of bacteria, such as MRSA, which are proving resistant to broad-spectrum antibacterial agents.

Injectable methylcellulose hydrogel containing silver oxide nanoparticles for burn wound healing

A thermo-sensitive methylcellulose (MC) hydrogel containing silver oxide nanoparticles (NPs) was prepared via one-pot synthesis in which a silver acetate precursor salt (CH₃COOAg) induces a salt-out effect in the MC solution. The silver oxide NPs were synthesized in situ from Ag⁺ ions during the MC hydrogelation, and the residual CH₃COO^- ions decreased the gelation temperature of the MC solution through the salt-out effect. The gelation behavior of the MC solution varied according to the CH₃COOAg content and was monitored. Also, the formation and structure of the silver oxide NPs in the MC hydrogel was confirmed. From the results, silver oxide NPs was successfully incorporated in MC hydrogels, simultaneously, acetate ion which was counter ion of Ag was affected gelation behavior of Ag. Finally, the antimicrobial activity and wound healing effect was examined using the shaking flask method and burn wound test, respectively. The MC hydrogel with silver oxide NPs showed excellent antimicrobial activity and burn wound healing. Therefore, this thermo-responsive MC hydrogel has great potential as an injectable hydrogel for wound regeneration.

Plasma treatments of dressings for wound healing: a review

This review covers the use of plasma technology relevant to the preparation of dressings for wound healing. The current state of knowledge of plasma treatments that have potential to provide enhanced functional surfaces for rapid and effective healing is summarized. Dressings that are specialized to the needs of individual cases of chronic wounds such as diabetic ulcers are a special focus. A summary of the biology of wound healing and a discussion of the various types of plasmas that are suitable for the customizing of wound dressings are given. Plasma treatment allows the surface energy and air permeability of the dressing to be controlled, to ensure optimum interaction with the wound. Plasmas also provide control over the surface chemistry and in cases where the plasma creates energetic ion bombardment, activation with long-lived radicals that can bind therapeutic molecules covalently to the surface of the dressing. Therapeutic innovations enabled by plasma treatment include the attachment of microRNA or antimicrobial peptides. Bioactive molecules that promote subsequent cell adhesion and proliferation can also be bound, leading to the recruitment of cells to the dressing that may be stem cells or patient-derived cells. The presence of a communicating cell population expressing factors promotes healing.

Biosynthesis of Silver Nanoparticles on Orthodontic Elastomeric Modules: Evaluation of Mechanical and Antibacterial Properties

In the present study, silver nanoparticles (AgNPs) were synthesized in situ on orthodontic elastomeric modules (OEM) using silver nitrate salts as metal-ion precursors and extract of the plant Hetheroteca inuloides (H. inuloides) as bioreductant via a simple and eco-friendly method. The synthesized AgNPs were characterized by UV-visible spectroscopy; scanning electron microscopy-energy-dispersive spectroscopy (SEM-EDS) and transmission electron microscopy (TEM). The surface plasmon resonance peak found at 472 nm confirmed the formation of AgNPs. SEM and TEM images reveal that the particles are quasi-spherical. The EDS analysis of the AgNPs confirmed the presence of elemental silver. The antibacterial properties of OEM with AgNPs were evaluated against the clinical isolates Streptococcus mutans, Lactobacillus casei, Staphylococcus aureus and Escherichia coli using agar diffusion tests. The physical properties were evaluated by a universal testing machine. OEM with AgNPs had shown inhibition halos for all microorganisms in comparison with OEM control. Physical properties increased with respect to the control group. The results suggest the potential of the material to combat dental biofilm and in turn decrease the incidence of demineralization in dental enamel, ensuring their performance in patients with orthodontic treatment.

Fabrication of cellulose fine fiber based membranes embedded with silver nanoparticles via Forcespinning

This study presents the successful development of cellulose fiber based membranes embedded with silver nanoparticles. These fine fiber membranes were developed utilizing the Forcespinning (FS) technique followed by alkaline hydrolysis treatment. The fiber morphology, homogeneity and yield were optimized by varying spinning parameters such as polymer concentration and angular velocity of the spinnerets. The structure, thermal and mechanical properties, and water absorption capability of the developed membranes were investigated. The cellulose acetate (CA) present in the membrane was converted to cellulose in the presence of embedded silver nanoparticles by alkaline hydrolysis. The silver nanoparticles embedded cellulose membrane exhibits outstanding water absorption capacity with fast uptake rate. Its high porosity, three-dimensional network structure with well-interconnected pores, as well as the intrinsically highly hydrophilic nature of cellulose material greatly favor its potential application as wound dressings. The antimicrobial activity was evaluated by the disk diffusion method. The composite membranes exhibit excellent antimicrobial activity against Gram-negative bacteria Escherichia coli and Pseudomonas aeruginosa, and Gram-positive Staphylococcus aureus, owing to the slow and sustained release of embedded silver nanoparticles.

Rapid continuous microwave-assisted synthesis of silver nanoparticles to achieve very high productivity and full yield: from mechanistic study to optimal fabrication strategy

Systematic studies of silver nanoparticle synthesis in a continuous-flow single-mode microwave reactor using polyol process were performed, revealing that the synthesis is exceptionally effective to give very small metal particles at full reaction yield and very high productivity. Inlet concentration of silver nitrate or silver acetate, applied as metal precursors, varied between 10 and 50 mM, and flow rates ranged from 0.635 to 2.5 dm³/h, to give 3-24 s reaction time. Owing to its much higher reactivity, silver acetate was shown to be far superior substrate for the synthesis of small (10-20 nm) spherical silver nanoparticles within a few seconds. Its restricted solubility in ethylene glycol, applied as the solvent and reducing agent, appeared to be vital for effective separation of the stage of particle growth from its nucleation to enable rapid synthesis of small particles in a highly loaded system. This was not possible to obtain using silver nitrate. All the observations could perfectly be explained by a classical LaMer-Dinegar model of NPs' formation, but taking into account also nonisothermal character of the continuous-flow process and acetate dissolution in the reaction system. The performed studies indicate an optimal strategy for the high-yield fabrication of metal particles using polyol method.

Gold nanoparticles in the engineering of antibacterial and anticoagulant surfaces

Simultaneous antibacterial and anticoagulant surfaces have been prepared by immobilization of engineered gold nanoparticles onto different kinds of surfaces. The gold nanoparticle core is surrounded by a hemocompatible, anticoagulant polysaccharide, 6-O chitosan sulfate, which serves as reduction and stabilizing agent for the generation of gold nanoparticles in a microwave mediated reaction. The particle suspension shows anticoagulant activity, which is investigated by aPTT and PT testing on citrated blood samples of three patients suffering from congenital or acquired bleeding disorders. The amount of nanoparticles deposited on the surfaces is quantified by a quartz crystal microbalance with dissipation unit. All gold containing surfaces exhibit excellent antimicrobial properties against the chosen model organism, Escherichia coli MG 1655 [R1-16]. Moreover, blood plasma coagulation times of the surfaces are increased after deposition of the engineered nanoparticles as demonstrated by QCM-D.

Microwave-assisted incorporation of silver nanoparticles in paper for point-of-use water purification

This work reports an environmentally benign method for the in situ preparation of silver nanoparticles (AgNPs) in paper using microwave irradiation. Through thermal evaporation, microwave heating with an excess of glucose relative to the silver ion precursor yields nanoparticles on the surface of cellulose fibers within three minutes. Paper sheets were characterized by electron microscopy, UV-Visible reflectance spectroscopy, and atomic absorption spectroscopy. Antibacterial activity and silver release from the AgNP sheets were assessed for model Escherichia coli and Enterococci faecalis bacteria in deionized water and in suspensions that also contained with various influent solution chemistries, i.e. with natural organic matter, salts, and proteins. The paper sheets containing silver nanoparticles were effective in inactivating the test bacteria as they passed through the paper.

A Critical Investigation on the Existence of Selective Microwave Absorption in the Synthesis of CdSe Quantum Dots

The existence of selective microwave absorption phenomena in the synthesis of CdSe quantum dots has been investigated. These types of microwave effects involving selective microwave absorption by specific reagents have recently been proposed in the microwave-assisted synthesis of various nanoparticles. In the present study, the microwave synthesis of CdSe quantum dots was investigated according to a protocol published by Washington and Strouse to clarify the presence of selective microwave heating. Importantly, control experiments involving conventional conductive heating were executed under otherwise (except for the heating mode) identical conditions, ensuring the same heating and cooling profiles, stirring rates, and reactor geometries. Comparison of powder X-ray diffraction, UV-vis, photoluminescence, and transmission electron microscopy data of the obtained CdSe quantum dots reveals that identical types of nanoparticles are obtained independently of the heating mode. Therefore, no evidence for a selective microwave absorption phenomenon could be obtained.

Nanostructural Features of Silver Nanoparticles Powder Synthesized through Concurrent Formation of the Nanosized Particles of Both Starch and Silver

Green innovative strategy was developed to accomplish silver nanoparticles formation of starch-silver nanoparticles (St-AgNPs) in the powder form. Thus, St-AgNPs were synthesized through concurrent formation of the nanosized particles of both starch and silver. The alkali dissolved starch acts as reducing agent for silver ions and as stabilizing agent for the formed AgNPs. The chemical reduction process occurred in water bath under high-speed homogenizer. After completion of the reaction, the colloidal solution of AgNPs coated with alkali dissolved starch was cooled and precipitated using ethanol. The powder precipitate was collected by centrifugation, then washed, and dried; St-AgNPs powder was characterized using state-of-the-art facilities including UV-vis spectroscopy, Transmission Electron Microscopy (TEM), particle size analyzer (PS), Polydispersity index (PdI), Zeta potential (ZP), XRD, FT-IR, EDX, and TGA. TEM and XRD indicate that the average size of pure AgNPs does not exceed 20 nm with spherical shape and high concentration of AgNPs (30000 ppm). The results obtained from TGA indicates that the higher thermal stability of starch coated AgNPS than that of starch nanoparticles alone. In addition to the data obtained from EDX which reveals the presence of AgNPs and the data obtained from particle size analyzer and zeta potential determination indicate that the good uniformity and the highly stability of St-AgNPs).