Antibacterial Ag containing core-shell polyvinyl alcohol-poly (lactic acid) nanofibers for biomedical applications

Core-shell-structured polyvinyl alcohol (PVA)-poly (lactic acid) (PLA) nanofibers combining the hydrophilic trait of PVA and the biocompatibility of PLA were produced using coaxial electrospinning. This allowed the incorporation of AgNO₃ in the PVA core of the distinct fibers as shown through transmission electron microscopy (TEM) and Fourier transform infrared spectroscopy (FTIR). Scanning electron microscopy (SEM) showed relatively uniform and bead-free fibers with smooth surfaces. Ag-containing fibers show significantly decreased diameters compared with Ag-free samples as a result of the increased conductivity of the spinning solutions with increasing amounts of AgNO₃. In a postsynthetic treatment, the AgNO₃ was reduced forming silver nanoparticles (Ag NPs). Ag NPs of 45 to 90 nm size were located in the PVA core but also on the surface of the core-shell fibers and as individual, agglomerated, and polymer-coated particles of 100-200 nm. Powder X-ray diffraction (PXRD), energy dispersive X-ray spectroscopy (EDX), and UV-vis absorption spectroscopy confirmed the increasing amounts of Ag in the core-shell fibers when using increasing amounts of AgNO₃ in the spinning solutions. The antibacterial activity of the nanofiber mats against two prokaryotes Escherichia coli (Gram-negative) and Staphylococcus aureus (Gram-positive) increased with increasing amounts of Ag, as expected and produces inhibition zones of 1 to 2 mm.     

Perturbation-correlation moving-window two-dimensional correlation spectroscopic studies on the heat treatment of poly(vinyl alcohol)/silver nitrate film

In this paper, poly(vinyl alcohol)/silver nitrate (PVA/AgNO₃) films were annealed at 180 °C for 1 h to prepare highly electrically conductive poly(vinyl alcohol)/silver (PVA/Ag) nanohybrids. Ultraviolet (UV)-visible absorption spectra, X-ray diffraction (XRD) scans, and scanning electronic microscopy (SEM) were applied to investigate the structures and morphology of the PVA hybrids. Differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA) were employed to study the thermal property of PVA/AgNO₃ films. Furthermore, perturbation-correlation moving-window two-dimensional (PCMW2D) correlation spectroscopy combined with temperature-dependent Fourier transform infrared (FTIR) spectroscopy was used to investigate the conversion of AgNO₃ into Ag nanoparticles in PVA matrix. The results show that the chelates for AgNO₃ coordinated with hydroxyl groups are primarily decomposed in the temperature regions of 39.7–72.6 °C and 182.7–199.6 °C. AgNO₃ is reduced into Ag⁰ and the hydroxyl groups of PVA are oxidized into carbonyl groups. The PVA-AgNO₃ chelates are very rapidly decomposed in the temperature region of 182.7–199.6 °C. Large amounts of Ag⁰ produced by the reduction of AgNO₃ are aggregated into Ag nanoparticles which are homogeneously dispersed into the PVA matrix. When the temperature increases to 212.7 °C, the unhydrolyzed acetate groups in PVA chains are sharply decomposed.     

Fabrication of antibacterial silver nanoparticle‐modified chitosan fibers using Eucalyptus extract as a reducing agent

Green chemical method could be a promising route to achieve large scale synthesis of nanostructures for biomedical applications. Here, we describe a green chemical synthesis of silver nanoparticles (Ag NPs) on chitosan‐based electrospun nanofibers using Eucalyptus leaf extract. A series of silver salt (AgNO₃) amounts were added to a certain composition of chitosan/polyethylene oxide aqueous acetic acid solution. The solutions were then electrospun to obtain nanofibrous mats and then, morphology and size of nanofibers were analyzed by scanning electron microscopy (SEM). Incubation of AgNO₃‐containing mats into Eucalyptus leaf extract led to the formation of Ag NP clusters with average diameter of 91 ± 24 nm, depicted by SEM and transmission electron microscopy. Surface enhanced Raman spectroscopy also confirmed formation of Ag NPs on the nanofibers. The mats also showed antimicrobial activity against Escherichia coli and Staphylococcus aureus bacteria with bigger inhibition zone for extract‐exposed mats against S. aureus. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 42133.     

Electrospun antibacterial nylon nanofibers through in situ synthesis of nanosilver: preparation and characteristics

A new method for production of nylon nanofibers with antibacterial properties containing silver nanoparticles (nylon nanofibers/Ag NPs) is introduced via in situ synthesis of nano-silver by reduction of silver nitrate in the polymer solution prior to electrospinning. The properties of the electrospinning solutions and the structures of the electrospun fibers were studied using scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDAX), UV?Cvis spectrophotometer and reflection spectrophotometer. Further, the antibacterial properties of the nanofibers were investigated against Escherichia coli (Gram-negative) and Staphylococcus aureus (Gram-positive) bacteria. Interestingly, an antibacterial properties has been found on nylon 6 nanofibers while the nylon nanofibers/Ag NPs showed excellent antibacterial activities against both tested bacteria. The produced nylon nanofibers/Ag NPs can be a good candidate for biomedical applications, water and air filtration.     

Studies on the electromagnetic interference shielding effectiveness of metallized PVAc‐AgNO3/PET conductive films

A metal chelate polymer (MCP) of PVAc‐AgNO₃ was prepared by adding AgNO₃ salts into the PVAc matrix and was coated on to PET substrate to form PVAc‐AgNO₃/PET films. These films were then treated with NaBH₄ aqueous solution to become the reduced metallized conductive films (RMCF) of PVAc‐AgNO₃/PET. The electromagnetic interference shielding effectiveness (EMI/SE) and the characteristics of these films were investigated. The SE value was measured by the far‐field transmission line method. The surface resistivity (Rs) of RMCF with a AgNO₃ content of 15 wt % was found to be below 5 Ω/sq, and the SE value exceeded 20 dB over the frequency range 50–900 MHz. The Rs of RMCF with a AgNO₃ content of 30 wt % was less than 1 Ω/sq, and the SE value even reached 33 dB at 550–650 MHz. It was confirmed by X‐ray and scanning electronmicroscope (SEM) analysis that the conducting network, as formed by closely deposited silver atoms on the reduced coating surface, was the dominant pathway for effective electron propagation that contributed to the excellent conductivity of these RMCF (PVAc‐AgNO₃/PET). © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 91: 270–273, 2004     

Preparation and Characterization of Gelatin Nanofibers Containing Silver Nanoparticles

Ag nanoparticles (NPs) were synthesized in formic acid aqueous solutions through chemical reduction. Formic acid was used for a reducing agent of Ag precursor and solvent of gelatin. Silver acetate, silver tetrafluoroborate, silver nitrate, and silver phosphate were used as Ag precursors. Ag⁺ ions were reduced into Ag NPs by formic acid. The formation of Ag NPs was characterized by a UV-Vis spectrophotometer. Ag NPs were quickly generated within a few minutes in silver nitrate (AgNO₃)/formic acid solution. As the water content of formic acid aqueous solution increased, more Ag NPs were generated, at a higher rate and with greater size. When gelatin was added to the AgNO₃/formic acid solution, the Ag NPs were stabilized, resulting in smaller particles. Moreover, gelatin limits further aggregation of Ag NPs, which were effectively dispersed in solution. The amount of Ag NPs formed increased with increasing concentration of AgNO₃ and aging time. Gelatin nanofibers containing Ag NPs were fabricated by electrospinning. The average diameters of gelatin nanofibers were 166.52 ± 32.72 nm, but these decreased with the addition of AgNO₃. The average diameters of the Ag NPs in gelatin nanofibers ranged between 13 and 25 nm, which was confirmed by transmission electron microscopy (TEM).     

Preparation and characterization of conductive and magnetic PPy/Fe3O4/Ag nanocomposites

In this article, conductive and magnetic nanocomposites composed of polypyrrole (PPy), magnetite (Fe₃O₄) nanoparticles (NPs), silver (Ag) NPs, have been successfully synthesized with a two step process. First, the PPy/Fe₃O₄ was prepared by the ultrasonic in situ polymerization. Next, the PPy/Fe₃O₄/Ag was synthesized through the electrostatic adsorption. The products were characterized by fourier‐transform infrared (FTIR) spectroscopy, Scanning electron microscopy (SEM), Thermogravimetric (TG), conductivity and magnetization analysis, and the results showed that the Ag NPs with the good conductivity coated uniformly on the surface of PPy/Fe₃O₄ and improved the conductivity of PPy/Fe₃O₄/Ag composites. In addition, as compared with PPy/Fe₃O₄, PPy/Fe₃O₄/Ag composites also have the excellent electro‐magnetic property and enhanced thermostability. POLYM. COMPOS., 35:450–455, 2014. © 2013 Society of Plastics Engineers     

Photocrosslinkable acid urethane dimethacrylates from renewable natural oil and their use in the design of silver/gold polymeric nanocomposites

Castor oil-based acid urethane macromers were prepared and employed for obtaining Ag/Au/polymer nanocomposites. Structure and UV induced photopolymerization of the macromers were investigated by spectral methods. The polymerization rate and the degree of conversion decreased with about 10% in the presence of 2.5 wt.% silver nanoparticles (Ag NPs). For the diacid macromer, the surface plasmon intensity increased with irradiation time (the optical density of the absorption maximum (430 nm) attained 2.3 after 600 s), whereas a diminished efficiency was found for Ag NPs in situ generated. Transmission electron microscopy and X-ray photoelectron spectroscopy confirmed uniform distribution of the spherical nanoparticles (0.6 nm (Ag NPs); 5 nm (Au NPs)) and the appearance of Ag 3d_3/2, Ag 3d_5/2, Au 4f_7/2 and Au 4f_5/2 peaks corresponding to Ag (0) or Au (0). Environmental scanning electron microscope with energy-dispersive X-ray detector, contact angle and mechanical parameters measurements complemented the above observations.     

Characterization and conductive property of polyurushiol/silver conductive coatings prepared under UV irradiation

Polyurushiol/silver (PU/Ag) composite conductive coatings were prepared from urushiol and AgNO₃ under UV irradiation by using in situ radical reduction approach. The effects of the silver nitrate loading and the irradiation time on the surface resistivity of polyurushiol/silver (PU/Ag) composite films were investigated. The result from XRD analysis showed that the formation of Ag particles, and the surface resistivity of polyurushiol/silver (PU/Ag) composite films reached the value of 0.26 Ω cm, when the content of Ag particles in composite films was 23.8 wt%, and the irradiation time 90 s. Additionally, Ag particles were well dispersed in the composite films. And the films had good thermo-stability.     

Enhancement of the photocatalytic performance of Ag-modified TiO2 photocatalyst under visible light

A highly visible-light photocatalytic active Ag-modified TiO₂ (Ag–TiO₂) was prepared by a simple sol–gel process using TiOSO₄ as the starting material, AgNO₃ as a silver doping source, and hydrazine as a reducing agent. The prepared Ag–TiO₂ samples were characterized by several techniques such as X-ray powder diffraction (XRD), BET surface area measurement, scanning electron microscopy (SEM), transmission electron microscopy (TEM), inductively coupled plasma optical emission spectroscopy (ICP-OES), energy dispersive X-ray spectrometry (EDX), X-ray absorption spectroscopy (XAS) and UV–vis diffuse reflectance spectroscopy (DRS). The Ag–TiO₂ photocatalyst, a mixture of amorphous and anatase phases, has a high surface area. The silver contents in the Ag–TiO₂ samples were determined by ICP measurements. The diffused reflectance UV–vis spectra indicated that the Ag–TiO₂ samples exhibited higher red shifts compared with the undoped TiO₂ sample. Indigo carmine degradation under visible irradiation indicated that the Ag–TiO₂ catalyst gave higher photocatalytic efficiency than those of commercial P25-TiO₂ and undoped-TiO₂ samples. The Ag–TiO₂ catalyst can be reused many times without any additional treatment.     

Formation of a liquid film of AgNO3 on a silver surface

The behavior of a AgNO₃/Ag₂O/Ag “sandwich” upon heating in vacuum was studied by in situ X‐ray photoelectron spectroscopy (XPS) and ex situ scanning electron microscopy (SEM). The AgNO₃/Ag₂O/Ag “sandwich” was prepared by exposure of a silver foil to a NO : O₂ mixture. The upper layer of the “sandwich” consists of AgNO₃ crystals of a mean size between 0.1 and 0.4 μm. Heating at 550 K in vacuum results in melting of the AgNO₃ crystals. A liquid film of AgNO₃, readily wetting the silver, covers the surface. Cooling below the melting point of AgNO₃ leads to the agglomeration of silver nitrate to long islands with a size reaching a few tens of micrometers (μm). The possible effects of AgNO₃ liquid‐phase formation on surface processes are discussed. This revised version was published online in July 2006 with corrections to the Cover Date.     

Growth of silver nanoparticles on poly(acrylic acid) brushes and their properties

A simple procedure is employed for the growth of silver nanoparticles (Ag NPs) onto the silicon substrate modified by poly(acrylic acid) (PAA) brushes, via: (1) surface-initiated ATRP of tert-butyl acrylate on Si surface to the preparation of poly(tert-butyl acrylate) brushes, (2) acid hydrolysis of PBA to the formation of PAA, and (3) in situ synthesis of Ag NPs via chemical reduction of AgNO₃ in the presence of PAA brushes. The polymer brushes are thoroughly characterized. Moreover, Ag nanoparticles are homogeneously immobilized into the brush layer and have been used to fabricate a sensor platform of surface-enhance Raman scattering for the detection of organic molecules and effectively catalyze the reduction of methylene blue by NaBH₄.     

Preparation and Characterization of Polypyrrole Silver Nanocomposites via Interfacial Polymerization

Conducting polypyrrole silver (Ppy-AgNC) nanocomposite was synthesized by an interfacial polymerization method. Ag⁺ ions from the AgNO₃ solution were taken in the formation of Ppy-AgNC. The incorporated silver was confirmed by X-ray diffraction (XRD). During the polymerization in a nitrate ion-containing solution, the impregnation leads to the formation of metallic silver. The size distribution of Ag into the polymer is confirmed by transmission electron microscopy (TEM), and proves the formation of a uniform species with spherical particles of Ag (mean diameter of 8-12 nm) branching at the border of Ppy. The thermal behavior of the material was studied by thermogravimetric measurements.     

Properties investigation on electrically conductive adhesives based on acrylate resin filled with silver microsheets and silver plating carbon fibers

The introduction of highly electrically conductive fillers (Ag microsheets and silver plating carbon fiber) can functionally improve the electrical conductivity of acrylate resin. In this study, Ag microsheets and Ag/CF were thus introduced into acrylate polymer via solution blending method under ultrasonication in order to improve the electrical conductivity of the acrylate resin. The properties and microstructures of Ag microsheets, CF, Ag/CF and ECAs were performed by scan electron microscope (SEM), X-ray diffraction analysis (XRD), etc. SEM images and XRD results illustrated that the impurities in carbon fiber could be completely removed after the adequately alkali treatment. The SEM images showed that large numbers of metallic silver particles were uniformly and densely coated on the surface of the carbon fibers and hybrid fillers (silver microsheets and Ag/CF) could homogeneously disperse in acrylate resin. Electrical conductivity measurements demonstrated that the electrical conductivity of ECAs increased with the increasing content of hybrid fillers and the percolation threshold of ECAs was 5 wt%. The electrical conductivity of ECAs at its percolation threshold was 15.79 S/cm, which was two orders of magnitude higher than that of the ECAs based on acrylate resin filled with silver microsheets. The increment in Ag/CF contents may decrease 180° peel strength and raise shear strength with low content of Ag/CF. The overall performance of ECAs was optimum with 2 wt% Ag/CF. The TGA analysis indicated that ECAs possess excellent thermal stability.     

A green method of reducing silver nanoparticles based on bagasse pulp extract for preparing ultraviolet (UV)‐curable conductive ink

The silver nanoparticles are gaining extensive attention due to their tremendous applications in conductive field. In this article, we reported a green method of preparing silver nanoparticles (AgNPs) with bagasse pulp extract acting as reducing agents. In this article, ultrasonic extraction method was adopted. This extraction method has the advantages of simple operation and less impurity content in the extract. Silver nitrate (AgNO₃) solution, bagasse extract, and polyvinyl pyrrolidone (PVP) were used as the silver precursor, reducing agent, and protection agent, respectively. Next, hyperbranched polyurethane acrylate (HPUA) as waterborne resin was mixed with AgNPs to prepare UV‐curable conductive ink. The UV‐curable conductive ink synthesized by the AgNPs showed high conductivity, and the obtained conductive ink had very low resistance (1.06 Ω) and resistivity (2.6 × 10^?5 Ω·m), good electronic stability, showing the great advantage in the field of UV‐curable conductive ink. In addition, we tested the AgNPs conductive ink of tearing resistance, rubbing fastness, and bending strength. The results showed the nanosilver conductive ink had good mechanical properties. J. VINYL ADDIT. TECHNOL., 26:90–96, 2020. © 2019 Society of Plastics Engineers     

Synthesis,characterization, and cell viability of bifunctional medical-grade polyurethane nanofiber: Functionalization by bone inducing and bacteria ablating materials

There is an extensive possibility of improving characteristics of fibers used in hard tissue engineering, being hydrophobic and less osteoconductive, resulting in the dynamic growth of new tissues. The current work focuses on the fabrication of nanofibers incorporated with titanium dioxide (TiO₂) ''as osteoconductive'' and silver (Ag) ''as self-healing'' nanoparticles (NPs). The incorporation of AgNO₃ by in situ method not only helped to impart the antibacterial activity but also changed the contact angle from 81 ± 03° in the case of pristine nanofibers to 74 ± 03°, 61 ± 03°, 50 ± 08°, and 39 ± 1.1°, in the composite scaffolds containing 0.01, 0.03, 0.05, and 0.07 M of Ag salts. The incubation in simulated body fluid at 37°C to induce mineralization on nanofiber scaffolds indicated Ca and P crystals' formation. The antibacterial activity showed significantly more toxicity toward E. coli (8.3 ± 0.9 mm) than S. aureus (1.2 ± 0.1 mm). Biocompatibility studies using MTT assay on the pre-osteoblasts showed that both TiO₂ and Ag NPs present in the nanofibers are non-toxic to the bone-like cells. However, results show that a higher concentration of Ag NPs (i.e., 0.07 M) is toxic to cells growing. Finally, all the results suggest that the nanofiber scaffolds have considerable scope for future bone tissue engineering materials.     

Studies on the preparation and properties of conductive polymers. IV. Novel method to prepare metallized plastics from metal chelates of polymides–imides

A new type of polyamide–imides (PAI) was synthesized by direct polycondensation. A series of polyamide–imide metal chelate films was prepared by the transition-metal salts (AgNO₃, CuCl₂, and CoCl₂) mixed with the polyamide–imides in NMP solution. These polyamide–imide metal chelate films were reduced by various reducing agents, and the reduced films exhibited low surface resistivity around 10⁰?10¹ Ω/cm². The surfaces of these conductive films were proved to be metallized by means of X-ray analysis. The metal adhered on the film was believed to be responsible for the improvement of electrical conductivity. The effects of kinds and concentrations of metal salts, kinds and concentrations of reducing agents, and reduction time on the conductivity of metallized films were investigated. The IR spectra and SEM observations of unreduced and reduced polymer chelate films were also studied.     

Studies on the synthesis of electrospun PAN‐Ag composite nanofibers for antibacterial application

We have successfully synthesized polyacrylonitrile (PAN) nanofibers impregnated with Ag nanoparticles by electrospinning method at room temperature. Briefly, the PAN‐Ag composite nanofibers were prepared by electrospinning PAN (10% w/v) in dimethyl formamide (DMF) solvent containing silver nitrate (AgNO₃) in the amounts of 8% by weight of PAN. The silver ions were reduced into silver particles in three different methods i.e., by refluxing the solution before electrospinning, treating with sodium borohydride (NaBH₄), as reducing agent, and heating the prepared composite nanofibers at 160°C. The prepared PAN nanofibers functionalized with Ag nanoparticles were characterized by field emission scanning electron microscopy (FESEM), SEM elemental detection X‐ray analysis (SEM‐EDAX), transmission electron microscopy (TEM), and ultraviolet‐visible spectroscopy (UV‐VIS) analytical techniques. UV‐VIS spectra analysis showed distinct absorption band at 410 nm, suggesting the formation of Ag nanoparticles. TEM micrographs confirmed homogeneous dispersion of Ag nanoparticles on the surface of PAN nanofibers, and particle diameter was found to be 5–15 nm. It was found that all the three electrospun PAN‐Ag composite nanofibers showed strong antibacterial activity toward both gram positive and gram negative bacteria. However, the antibacterial activity of PAN‐Ag composite nanofibers membrane prepared by refluxed method was most prominent against S. aureus bacteria. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Antibacterial and photocatalytic properties of Ag/TiO2/ZnO nano-flowers prepared by facile one-pot hydrothermal process

In this paper, a simple and efficient strategy of one-pot synthesis of Ag doped TiO₂/ZnO photocatalyst was developed using hydrothermal process. Simultaneous crystallization of Ag and ZnO crystals from their precursor solution containing P25 (TiO₂) NPs could form effectively bonded Ag/TiO₂/ZnO composite photocatalyst during hydrothermal treatment. Several analytical techniques, including scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD), FT-IR spectroscopy, and photoluminescence spectroscopy have been used to characterize the resulting Ag/TiO₂/ZnO photocatalyst. Results showed that ZnO nano-flowers doped with TiO₂ and Ag NPs were formed by this simple facile one-step process. The unique properties of Ag NPs on binary semiconductor composite not only provide the decreased rate of electron–hole separation but also prevent from the loss of photocatalyst during recovery due to the fixed attachment of Ag and TiO₂ NPs on the surface of flower shaped large ZnO particles. Therefore, as-synthesized composite is an economically and environmentally friendly photocatalyst.     

Double regulation of conductivity by adhesive hydrogel based on catechol-modified sodium alginate /acrylamide hydrogel with silver ions

The purpose of this study is to explore how to control the conductivity of gel conveniently and effectively through experiments. First, a kind of acrylamide-based composite with adhesion and conductivity adjustment was prepared by adding silver ions and silver monomers to the gel in one step. The semi interpenetrating network structure formed by the molecular chain of polyacrylamide and catechol modified sodium alginate in the composite is cross-connected with silver ions to form a double network structure. This change of network structure not only makes the structure of gel more stable, but also brings extraordinary conductivity. Secondly, different types of conductive ions and organic solutions were added to the gel system. Electrochemical impedance spectroscopy showed that the addition of silver enhanced the conductivity of the material; When NaNO₃ is used to replace water molecules in PAM, the ionic conductivity can be increased by 75.3% (from 2.44 × 10⁻⁵ to 20.8 × 10⁻⁵ mscm⁻¹). When PDA/PAM was soaked in AgNO₃, the ionic conductivity increased in the range of 10.4% ~ 674%. It provides a novel strategy for controlling the conductivity of composite materials.