SHORT COMMUNICATION

Electrospinning fabrication and characterization of poly(vinyl alcohol)/montmorillonite/silver hybrid nanofibersfor antibacterial applications

Jae Hyeung Park & Mohammad Rezaul Karim &

In Kyo Kim & In Woo Cheong & Jong Won Kim &

Do Gyu Bae & Jin Won Cho & Jeong Hyun Yeum

Received: 18 August 2009 /Revised: 21 October 2009 /Accepted: 25 October 2009 /Published online: 20 November 2009# Springer-Verlag 2009

Abstract Poly(vinyl alcohol) (PVA)/montmorillonite clay(MMT)/silver (Ag) nanoparticles have been electrospun forfabricating PVA/MMT/Ag nanofiber in aqueous solutions.Since PVA is a water-soluble and biocompatible polymer, itis one of the best materials for preparation of antibacterialnanofiber. MMT has been used as an inorganic filler toenhance properties of homopolymeric nanofiber. The PVA/MMT/Ag nanofiber diameter increases with increasingcontents of MMT clay and Ag nanoparticles. In preservationtest, the PVA/MMT/Ag nanofiber confirms an excellentantibacterial performance, elucidating for practical uses as a

new preservative. Moreover, the PVA/MMT/Ag nanofibershows improved thermal properties.

Keywords Electrospinning . Poly(vinyl alcohol) . Silvernanoparticles .Montmorillonite . Antibacterial performance

Introduction

Electrospinning has attracted great interest among academicand industrial scientists because it is very simple, low cost,and with effective technology to produce polymer nanofiberwhich has exhibited outstanding properties such as a highspecific surface area and high porosity. These nanofiberscan be used for a wide variety of applications such asseparation filters, wound dressing materials, tissue scaffold,sensors, protective clothing, catalysis reaction, etc. [1, 2].The biomedical field is one of the important applicationareas. By utilizing electrospinning technique, this field canbe enriched widely. Different groups have recentlyreviewed the patents and worked on eletrospun biomedicalnanostructures like tissue engineering, drug delivery, andscaffold engineering [3–5]. In a typical electrospinningprocess, a high voltage is applied to create electricallycharged jets of polymer solutions. The jets dry and formnanofibers, which are collected on a target as non-wovenmat. Recently, our group has reported several cases ofelectrospun polyvinyl alcohol-blend nanofibers to makeimproved nanofibers. Blended with chitosan oligosaccha-ride, montmorillonite (MMT), pullulan, poly(vinyl alcohol)(PVA), respectively, or together, we get mechanically andthermally improved PVA blend nanofibers. During theseworks, it has been optimized in the best condition to make

J. H. Park : I. K. Kim : J. H. Yeum (*)Department of Advanced Organic Materials Science andEngineering, Kyungpook National University,Daegu 702-701, South Koreae-mail: jhyeum@knu.ac.kr

M. R. Karim (*)Center of Excellence for Research in Engineering Materials,College of Engineering, King Saud University,Riyadh 11421, Saudi Arabiae-mail: mkarim@ksu.edu.sa

I. W. CheongDepartment of Applied Chemistry,Kyungpook National University,Daegu 702-701, South Korea

J. W. KimDepartment of R&D Division, Korea Dyeing Technology Center,Daegu 703-834, Korea

D. G. Bae : J. W. ChoDepartment of Natural Fiber Science,Kyungpook National University,Daegu 702-701, Korea

Colloid Polym Sci (2010) 288:115–121DOI 10.1007/s00396-009-2147-4

PVA blend nanofiber such as electrospinning instrumentparameters including electric voltage, collector speed, andtip-collector distance (TCD), and solution parameters likepolymer concentration, viscosity, and feed mass ratio [6–11].

Silver nanoparticles are widely used as a photosensi-tive components, catalysts, and chemical analysis. Addi-tionally, due to its comparatively high safety, manyresearchers have successfully developed antibacterial

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Fig. 1 FE-SEM images of (a) pure PVA nanofibers and PVA/MMT/Ag nanofibers prepared with different Ag contents of (b) 0 wt.%,(c) 1 wt.%, (d) 3 wt.%, and (e) 5 wt.% (PVA solution concentration=

7.5%, TCD=15 cm, and applied voltage=15 kV; inset: high-magnification morphologies of related images)

116 Colloid Polym Sci (2010) 288:115–121

and disinfectant agents with silver composite usingvarious polymers. Microorganisms with resistance to theantimicrobial activity of Ag are exceedingly rare. Suchsilver has a size of nano-level, the total surface area ofthe silver becoming larger in identity volume, and theantibacterial efficiency is increased [12–15].

PVA is a semi-crystalline hydrophilic polymer with goodchemical and thermal stability. Also, it is highly biocom-

patible and non-toxic. It can be processed easily and has highwater permeability. These properties have led to the use ofPVA in a wide range of applications in medical, cosmetic,food, pharmaceutical, and packaging industries [16, 17]. PVAhas been used especially in fiber and film products for manyyears. Ultrafine PVA fibers, which may have differentpotential applications than microfibers, cannot be producedby conventional spinning techniques [17].

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Fig. 2 TEM images of (a) bulkPVA nanofibers and PVA/MMT/Ag nanofibers preparedwith different Ag contents of(b) 0 wt.%, (c) 1 wt.%,(d) 3 wt.%, and (e) 5 wt.% (PVAsolution concentration=7.5%,TCD=15 cm, and appliedvoltage=15 kV)

Colloid Polym Sci (2010) 288:115–121 117

On the other hand, many scientists incorporate ofinorganic material into polymer nanofiber using electro-spinning, and it can be exhibit the more advancedproperties than homopolymer nanofiber. MMT is one ofthings in those inorganic materials. It has been attractinggreat attention due to its remarkable improvement inmechanical, thermal, flame-retardant, and barrier propertiesof polymeric composites with small amounts (1–10 wt.%)of MMT fillers added [6]. These property improvements areattributed to the nanometric thickness and high aspect ratioof the individual clay platelets, as well as to the nano-composite morphology with the platelets being exfoliatedand well-dispersed [18]. It is regularly used for packagingand medical applications [19–21]. Feng et al. and Kwon etal. have successfully demonstrated MMT as useful forbiomedical application [19, 20].

Here, electrospun PVA/MMT/Ag hybrid nanofiber matshave been fabricated in aqueous solutions. Although manytypes of Ag [13–15] or MMT [6, 7, 11, 12, 18] containnanofibers were prepared using electrospinning technique

already, PVA nanofibers containing Ag and MMT have notbeen prepared yet. Furthermore, this article demonstratesthe effectiveness of the PVA/MMT/Ag nanofiber mats onantibacterial performance, which provides a chance todevelop a new preservative.

Experimental

Materials

PVA with Pn (number–average degree of polymerization)=1,700 [fully hydrolyzed, degree of saponification=99.9%]was obtained from DC Chemical Co., Seoul, Korea, andMMT was purchased from Kunimine Industries Co., Japan.Aqueous silver nanoparticle dispersion (AGS-WP001;10,000 ppm) with diameters ca.15–30 nm was gotten fromMiji Tech., Korea. Doubly distilled water was used as asolvent to prepare all solutions.

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Fig. 3 XRD data of (a) eletrospun bulk clay and PVA nanofibers and (b) PVA/MMT/Ag nanofibers prepared with different Ag contents of (a)0 wt.%, (b) 1 wt.%, (c) 3 wt.%, and (d) 5 wt.% (PVA solution concentration=7.5%, TCD=15 cm, and applied voltage=15 kV)

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Preparation of PVA/MMT/Ag blend solution

At first, 5 wt.% of MMT powder was dispersed in distilledwater under magnetic stirring for 1 h at room temperature.After the MMT was dispersed, PVA (7.5 wt.%) was addedto the solution. The solution was heated in a water bath at80°C under magnetic stirring for 2 h followed by cooling toroom temperature. The PVA/MMT/Ag blend solution wasprepared by mixing of PVA/MMT solution and Ag nano-particle dispersion with different concentrations of Ag (1, 3,and 5 wt.%) by stirring for another 2 h at room temperature.

Electrospinning nanofiber mats

During electrospinning, a high-voltage power (CHUNGPAEMT Co., Korea) was applied to the PVA/MMT/Ag blendsolution contained in a syringe via an alligator clip attached to

the syringe needle. The applied voltage was adjusted at 15 kV.The solution was delivered to the blunt needle tip via syringepump to control the solution flow rate. Fibers were collectedon an electrically grounded aluminum foil placed at 15 cmvertical distance to the needle tip. The above spinningconditions were found being the best condition to makePVA/MMT blend nanofiber mats in our previous report [6].

Preservation test

The preservation efficacy for the PVA/MMT/Ag nanofiberwas tested to evaluate the antimicrobial property [22].Samples were prepared by dispersing the nanofibers in aviscous aqueous solution containing 0.01 wt.% ofneutralized polyacrylic acid (Carbopol 941, NoveonInc.). A mixed culture of microorganisms, Staphylococcusaureus (ATCC6538) and Escherichia coli (ATCC25922),

Fig. 4 TGA data of (a) pure PVA nanofibers and PVA/MMT/Ag nanofibers prepared with different Ag contents of (b) 0 wt.%, (c) 1 wt.%, (d)3 wt.%, and (e) 5 wt.% (PVA solution concentration=7.5%, TCD=15 cm, and applied voltage=15 kV)

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were obtained on tryptone soya broth after 24 h incubation at32°C. Then, 20 g of samples were inoculated with 0.2 g ofthe microorganism suspensions to adjust the initial concen-tration of bacteria to 107 cfu/g. Then, the inoculant mixedhomogeneously with the samples and was stored at 32°C.The microbial counts were carried out using the pour platecount method.

Characterizations

The morphology and property characterization of electrospunPVA/MMT/Ag nanofiber mats were observed with a field-emission type scanning electron microscope (FE-SEM)(JEOL, model JSM-6380) after gold coating and a reflectiontype X-ray diffraction (XRD; Philips model X'Pert APD) withthe Cu Kα radiation with wavelength of 0.154 nm. Thescanning rate was 2°/min ranging 1.5 to 50° (2θ). Thetransmission electron microscopy (TEM) analysis wasconducted on an H-7600 model machine (HITACHI, LTD)with and accelerating voltage of 100 kV. The thermalbehavior of PVA/MMT/Ag nanofibers was studied withthermo gravimetric analysis (TGA) techniques (model Q-50)from TA instruments, USA, at the rate of 10°C/min fromroom temperature to 600°C under the nitrogen gas atmo-sphere. The antibacterial performance was investigated toexamine the biological function of PVA/MMT/Ag nanofibersby KSM 0146 (shake flask method) using ATCC 6538 (S.aureus) and ATCC 25922 (E. coli).

Results and discussion

Morphology

Figure 1 demonstrates FE-SEM images of PVA/MMT/Agnanofibers electrospun from 5 wt.% MMT solutionscontaining different amounts of Ag nanoparticles (none, 1,3, and 5 wt.%). The inset on each image is the enlarged FE-SEM image of PVA/MMT/Ag nanofibers' respectiveimages. The fiber diameters are dramatically increasedwhen MMT clay and Ag nanoparticles are added [23]. Thesilver distributions along the fiber direction and on the fibercross-section (Fig. 2) are detected by TEM. It is seen thatthe silver nanoparticles are distributed uniformly in thePVA/MMT/Ag nanofibers. The TEM image also shows thatthe number of Ag nanoparticles increases gradually in thePVA/MMT/Ag nanofibers by increasing the wt.% of Agnanoparticle content.

XRD data

The XRD pattern of PVA/MMT/Ag nanofiber mats showdiffraction peaks at 2θ of ca. 19.3°, 38.2°, and 44.6°,

respectively (Fig. 3b). The pure PVA fiber mats show asignificant crystalline peak at about 19.3°, which is becauseof the occurrence of string inter- and intramolecularhydrogen bonding (Fig. 3a). In case of a clay–polymercomposite, unexfoliated or intercalated MMT usuallyshows a peak in the range 3~9° (2θ). In exfoliatednanocomposites, generally single silicate layers (1–3 nmthick) are homogeneously dispersed in the polymer matrix,and XRD patterns with no distinct diffraction peak in therange of 3~9° (2θ) could be observed [24, 25]. Except thediffraction peaks of PVA, all the other peaks arecorresponding to the silver phase [Fig. 3b (b–d)]. Thepeaks of silver particles are enlarged with increasing thecontent of Ag nanoparticle and crystallinity of PVA/MMT(2θ=19.3°) is lower in comparison with Fig. 3b (a). Thesepeaks are corresponding to the 111 and 200 planes of the silvernanocrystals with cubic symmetry [26]. XRD results indicatethat MMT and Ag particles are well dispersed in the PVAnanofiber mats, and MMT is predominantly exfoliated. TEMimages further confirm MMT (Fig. 2b) and Ag nanoparticles[Fig. 2c–e] in the PVA/MMT/Ag nanofibers.

Thermal stability

Thermal stability of electrospun PVA/MMT/Ag nano-fibers was measured using TGA in nitrogen atmosphere.Figure 4 shows TGA thermograms of different decompo-sition temperature with Ag contents of 0, 1, 3, and 5 wt.%.The most below curve of the TGA data [Fig. 4 (a)]

Fig. 5 Preservation performance of PVA/MMT/Ag nanofibers pre-pared with different Ag contents of (a) 0 wt.%, (b) 1 wt.%, (c) 3 wt.%,and (d) 5 wt.% (PVA solution concentration=7.5%, TCD=15 cm, andapplied voltage=15 kV)

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represents the pure PVA, and the most upper curve [Fig. 4(e)] is for mass ratio of 5 wt.% of Ag nanoparticles, i.e.,the highest mass ratio of Ag contents is used in our work.Figure 4 (c, d) are displaying the middle mass ratio of Agcontents at the same trend of thermal stability like theFig. 4 (a, e). Up to 225°C, there is increase in thermalstability from the pure PVA nanofibers to PVA/MMT/Agnanofibers. The higher thermal stability might be attributed tohigher contents of Ag nanoparticles in the PVA/MMT/Agnanofibers.

Antibacterial efficacy

Silver nanoparticles have been known to have stronginhibitory and antibacterial effects as well as a broad spectrumof antimicrobial activities [27]. In this study, in order toprovide useful information for the biological function ofPVA/MMT/Ag nanofibers, the antibacterial performance ofPVA/MMT/Ag nanofibers is evaluated in viscous aqueoustest samples and shown in Fig. 5. The antibacterial activity ofPVA/MMT/Ag nanofibers is assessed by counting thenumber of bacteria in the sample with the storage time at32°C. As shown in Fig. 5, the PVA/MMT/Ag nanofiberswithout Ag fail to have the antibacterial performance. Thenumber of bacteria in the test samples remains constant for along time. On the contrary, the incorporation of the PVA/MMT/Ag nanofibers into the test samples result in aremarkable decrease in the number of bacteria. The increasein the concentration of the PVA/MMT/Ag nanofibersaccelerates diminishing in bacteria. With only a smallamount of Ag, almost all the initially inoculated bacteriacould be sterilized within a week. This indicates that thePVA/MMT/Ag nanofibers have an antibacterial activity.

Conclusions

PVA/MMT/Ag nanofibers with aqueous solution aresuccessfully electrospun and characterized by FE-SEM,TEM, XRD, and TGA. As PVA is a water-soluble andbiocompatible polymer, it may use one of the bestmaterials for the preparation of antibacterial nanofibers.The fiber diameter increases with increasing amount ofMMT clay and Ag nanoparticles added. One feature ofthese PVA/MMT/Ag nanofibers is that it has a goodantibacterial performance, which gives a suggestion forthe practical use of a new preservative. Also, PVA/MMT/

Ag nanofiber thermal properties are enhanced with theaddition of MMT and Ag nanoparticles.

Acknowledgement This research was financially supported by theMinistry of Education, Science Technology (MEST) and KoreaIndustrial Technology Foundation (KOTEF) through the HumanResource Training Project for Regional Innovation. Also, the KoreaBasic Science Institute (Daegu) is acknowledged for the TEM.

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