Preparation And Antibacterial Properties Of PVA Matrix Nano-Ag Composite Fibers By Electrospinning

In recent years,the explosive diseases caused by pathogenic microorganism have been seriously harmful to human health.On the other hand,abuse of traditional antibiotics result in occurrence of multidrug resistant strains.Thus,it will be the main way to prevent the persecution happening through the wide use of new antibacterial materials with broad-spectrum,high-effect and durable activity.Textile fibers serve as a hotbed for germs to breed due to its rugged surface,numerous of micro groove,appropriate temperature and humidity.So,the study of fibrous mats with antibacterial properties deserves high significance in both theory and application.However,there are some obstacles in the preparation,preservation and use of antibacterial materials.Electrospinning is recognized as an efficient technique for the fabrication of submicron-sized polymer nanofibers.In terms of the flexibility of the process,electrospinning is able to fabricate continuous nanofibers from a huge range of materials.It is popular for its simple process operation,high performance in nanofiber fabrication and low in cost.Electrospinning nanofibers exhibit a lot of characteristics,for example,high surface area-to-volume ratio,small pores,high porosity,light weight and good mechanical strength,etc.Polyvinyl alcohol?PVA?is typically a non-toxic and water-soluble synthetic polymer.It is also biocompatible and degradable,which yields comparably high fiber forming.Also,considering its high mechanical strength,PVA is very fit for acting as the matrix of composite electrospun nanofibers.In this paper,we prepared Ag nanoparticles?Ag NPs?,nanowires?Ag NWs?,Ag@Cu₂O core-shell nanospheres by convenient chemical reduction method,and implanted them into PVA to form hybrid nanofibers through electrospinning.What's more,PVA electrospinning nanofibers surface-decorated with Ag NPs were also obtained by in-situ reaction.The morphology and structure of the as-synthesized composite nanofibers were characterized by various techniques,and their antibacterial properties against both Gram-positive Staphylococcus aureus?S.aureus?and Gram-negative Escherichia coli?E.coli?microorganisms were evaluated by means of inhibitory zone with filter paper,absorption and turbidity.The main contents and conclusions of this dissertation are as follows.?1?Preparation,antibacterial and SERS properties of Ag NPs embedded into PVA?Ag NPs/PVA?composite electrospinning nanofibrous filmsFirst of all,the optimum electrospinning conditions of pure PVA were found through the orthogonal experiment.It is determined as follows:solution concentration is 7⁸%,applied electric field is 14¹6kV,feed rate is 0.010⁰.015 mL/min,tip-to-collector distance is 8¹2 cm,needle is 19²1 G.The order of significance factors was found and the reason was revealed.Subsequently,Ag NPs were synthesized in liquid phase,followed by evenly dispersing in PVA solution.After electrospinning of the mixed solution at room temperature,the PVA embedded into Ag NPs?Ag/PVA?composite nanofibers were obtained.The morphologies and structures of the as-synthesized Ag NPs and Ag/PVA fibers were characterized by the techniques of transmission electron microscopy?TEM?,X-ray diffraction?XRD?,ultraviolet-visible absorption spectroscopy?UV-vis?,Fourier transform infrared spectroscopy?FTIR?,scanning electron microscopy?SEM?and energy-dispersive X-ray spectroscopy?EDX?.Ag NPs have an average diameter of13.8 nm,were found to be uniformly dispersed in PVA nanofibers.It's found Ag/PVA hybrid nanofibers are randomly overlaid on aluminum foils,and the diameters of these nanofibers are quite uniform.The average diameter of hybrid nanofibers decreased from 188 nm to 135 nm with the increasing of Ag NPs contents.The antibacterial activity of Ag/PVA nanofibers against E.coli and S.aureus was evaluated by the methods of absorption and turbidity method.The surface enhanced Raman scattering?SERS?activities of Ag/PVA nanofibers substrates using 4-hydroxy thiophenol?4-MPh?as probe molecules were evaluated on a confocal Raman spectrometer.The as-synthesized free-standing and flexible nanofibrous film mats exhibit excellent antibacterial properties and SERS activates in the same time.It's found the antibacterial ability is mainly attributed to the implanted Ag NPs,and the membranes show superior bacterial inhibition against S.aureus than that of E.coli.The high SERS sensitivity is attributed that evenly embedded Ag NPs in networked PVA nanofiber membranes,which provide high density“hot spots”.?2?Preparation and antibacterial properties of Ag NWs embedded into PVA?Ag NWs/PVA?composite electrospinning nanofibrous feltsFirstly,uniform Ag NWs were synthesized through reducing AgNO₃ in the ethylene glycol?EG?system,which plays a role of both solvent and reducing agent,and polyvinylpyrrolidone?PVP?was involved as a capping agent.Secondly,the as-synthesized Ag NWs were mixed with PVA solution for electrospinning.Lastly,Ag NWs embedded in PVA?Ag NWs/PVA?hybrid nanofibers were fabricated by electrospinning method.The morphologies and structures of Ag NWs and Ag NWs/PVA nanofibers were characterized by various techniques such as TEM,UV–vis,XRD,FTIR,SEM and EDX.Using Gram-negative bacteria of E.coli and Gram-positive bacteria of S.aureus as target species,the antibacterial activity of Ag NWs/PVA nanofibers was tested by the methods of turbidity and absorption,respectively.The structure analysis results show that Ag NWs with an average diameter of 86 nm and length up to 10?m were obtained,when the concentration of CuCl₂ is 50?M,the addition amount of PVP is 0.088 g,and the reaction temperature is 160°C,respectively.Ag NWs were demonstrated to be uniformly incorporated into PVA nanofibers,forming a core-sheath nanocable structure.The antibacterial test results indicated that the as-prepared flexible and free-standing Ag NWs/PVA nanofiber felts have excellent antimicrobial activities.Interestingly,it's demonstrated that antibacterial property is more superior for S.aureus than that of E.coli.This antibacterial activity is due to the synergistic effect of Ag NWs and PVA.Furthermore,it's suggested that the enrichment of active{111}facets present in Ag NWs is favorable for its reaction with bacterial cell and contributed to the antibacterial activities.The antibacterial mechanism is due to the release of Ag NPs from fibers,the formation of Ag⁺ions,the increasing concentration of reactive oxygen species?ROS?,and their effects with the bacteria's cell membranes and cellular content.?3?Preparation and antibacterial properties of Ag@Cu₂O/PVA multivariant composite electrospinning nanofibers matsFirstly,core-shell structure of Cu₂O deposited on the surface of Ag NPs?Ag@Cu₂O?nanospheres with an average diameter of 100¹10 nm were synthesized by a convenient and mild two-step liquid reduction method.And then,Ag@Cu₂O embedded into PVA?Ag@Cu₂O/PVA?multivariate composite nanofibers materials were fabricated via electrospinning.The structures and morphologies of the as-synthesized Ag@Cu₂O nanoshperes and Ag@Cu₂O/PVA composite nanofibers were characterized by techniques of TEM,SEM,XRD,UV–vis,and FTIR,etc.The antibacterial properties of Ag@Cu₂O and the composite electrospinning nanofibers with different Ag@Cu₂O addition amounts were tested.It's found that Ag@Cu₂O nanospheres were evenly dispersed in PVA nanofibers without obvious diameters change,but with a minor increasing of core-shell interval.The result of inhibitory zone with filter paper test shows that Ag@Cu₂O nanospheres have excellent antibacterial properties,which is due to the synergistic effect of Ag and Cu₂O NPs.Absorption and turbidity test indicate that Ag@Cu₂O/PVA multivariate composite nanofibers exhibit good antibacterial activities against both S.aureus and E.coli.However,it's especially significant on S.aureus.The antibacterial properties of Ag@Cu₂O/PVA multivariate composite nanofibers were found to be improved with the increasing of Ag@Cu₂O content.?4?Preparation and antibacterial properties of PVA electrospinning nanofibers with surface-decorated Ag NPsUnlike nanocrystals embedded into PVA nanofibers,herein,PVA nanofibers surface-decorated with Ag NPs?PVA@Ag NPs?were obtained through a convenient two-step method.Firstly,PVA nanofibers were fabricated through electrospinning.Secondly,Ag NPs were decorated on the surface of PVA nanofibers by solvothermal method.The concentration of AgNO₃ which have effects on the morphologies and loading amounts of Ag NPs was investigated.With the characterization through SEM,TEM,XRD,FTIR and UV-vis,it's found that 0.066 M is the optimal AgNO₃ concentration.Ag NPs with the smallest diameter,even size distribution,and the highest loading amounts were obtained in this condition.The possible deposition process of Ag NPs on the surface of PVA nanofibers was proposed.Absorption and turbidity method were involved to evaluate the antibacterial performance of PVA@Ag NPs composite nanofibers against S.aureus and E.coli.The results demonstrate that the as-synthesized PVA@Ag NPs composite nanofibers exhibit the highest antibacterial activities when concentration of AgNO₃ is 0.066 M.It's resulting from the smallest particles size and the largest loading amounts of Ag NPs.The as-synthesized PVA@Ag NPs composite nanofibers were proved to possess durable antibacterial properties through the determination of growth curves of bacterial.