Promising Materials for Wound Dressing: PVA/PAA/PVP Electrospun Nanofibers

Promising Materials for Wound Dressing: PVA/PAA/PVPElectrospun Nanofibers

Arda Aytimur1,2 and Ibrahim Uslu11Department of Chemistry Education, Gazi Faculty of Education, Gazi University, Teknikokullar,Ankara, Turkey2Department of Advanced Technologies, Institute of Science and Technology, Gazi University,Teknikokullar, Ankara, Turkey

In this study, PVA/PAA, PVA/PAA/PVP, PVA/PAA/PVP-Iand PVA/PAA/PVP/Chitosan fiber mats were prepared via electro-spinning. Synthesized nanofibers were characterized by DSC,FT-IR and SEM. DSC results showed that the nanofibers weredegraded at 400�C and 450�C. The addition of PVP-K30, PVP-Iand chitosan to PVA/PAA structure increased the thermal stabilityof the nanofibers. SEM micrographs showed that synthesized nano-fibers are linear. Fiber diameter measurements showed that averagediameters of the fibers are less than 0.5 micron. The averagediameters of PVA/PAA, PVA/PAA/PVP, PVA/PAA/PVP-I andPVA/PAA/PVP/Chitosan fibers were calculated as 458 nm,237 nm, 139 nm, and 270 nm, respectively.

Keywords Chitosan; Electrospun nanofiber; PAA; PVA; Wounddressing material

INTRODUCTION

Poly(vinyl alcohol) (PVA) and Poly(acrylic acid) (PAA)electrospun nanofibers have a great future in biomedicalapplications especially in wound dressing material due totheir good biocompatibility and high swelling capabilitycoupled with relatively good mechanical properties.[1–21]

Kim et al. noted that PVA=PAA is a typical blendsystem where molecular level miscibility is achieved byinter-polymer hydrogen-bonding interactions.[22–24] Kimet al. also mentioned that the cross-linking of thecompletely miscible blend system probably occurs viadehydration between carboxylic acid and hydroxyl groupas Chen et al. and Shin et al. reported in their articles.[25,26]

This study is related to the preparation of differentwound dressing materials by the use of PVA=PAA polymersolutions added with compounds such as chitosan,poly(vinyl pyrrolidone) (PVP) and PVP-iodine complex

(PVP-I), for which wound healing capacity have beenclinically demonstrated. For instance. chitosan was provento accelerate tensile strength of wounds by speeding the‘‘fibroblastic synthesis of collagen’’ in the first few daysof wound healing.[27]

Poly(vinyl pyrrolidone) (PVP K-30) is an importantpolymer because of its biocompatibility and low chemicaltoxicity. It has been used in cosmetics, paints, electronics,and biological engineering.[28–36] Yoo et al. argued thatPVP films may have high potential as new wound-dressingmaterials that provide and maintain the moist environmentneeded to prevent scab formation and dehydration of thewound bed.[37]

PVP interacts with iodine to produce a stable compoundwith iodophor property extensively employed as an anti-septic. The PVP-iodine complex (PVP-I) also acts as aniodophor gradually releasing active iodine which is aneffective antimicrobial agent.

In this work, the PVA=PAA fibrous mats were preparedfor wound dressing applications facilitating rapid woundhealing by the formation of normal skin growth withoutthe formation of scar tissue, which occurs in the traditionaltreatment by the use of electrospinning technique, an effi-cient, facile and cost-effective method for the fabricationof nonwoven polymer nanofibers.[9,37–40]

EXPERIMENTAL PROCEDURE

PVA (MW: 85,000–124,000 g.mol�1, 98% hydrolyzed),PAA (35% wt aqueous solution), chitosan (Mw

400,000 g.mol�1) and acetic acid were purchased fromMerck. Aqueous acetic acid (2% [v=v]) was used as asolvent. Granular polyvinyl pyrrolidone (PVP, K-30, pH,10% in water 3.48 with K value 31.41) and polyvinylpyrrolidone iodine (PVP-I) were supplied by BASF andall the solutions were prepared by the use of ultrapuredistilled water as a solvent.

Then, 10 g PVA was dissolved in water to obtain10wt.% solutions with magnetic stirring for 2 h, at a

Address correspondence to Ibrahim Uslu, Department ofChemistry Education, Gazi Faculty of Education, Gazi University,Teknikokullar, Ankara 06500, Turkey. E-mail: [email protected]

Color versions of one or more of the figures in the article can befound online at www.tandfonline.com/lpte.

Polymer-Plastics Technology and Engineering, 53: 655–660, 2014

Copyright # Taylor & Francis Group, LLC

ISSN: 0360-2559 print=1525-6111 online

DOI: 10.1080/03602559.2013.874031

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temperature of 80�C and PAA solution was diluted withwater to 10wt.%. These two solutions were mixed to pre-pare a set of PVA: PAA blend solution with a ratio of10:3. The mixture was heated at 60�C for 1 h on a waterbath with magnetic stirrer. The solutions were kept at roomtemperature for 24 h to remove air bubbles.

Components of 10% chitosan, 10% PVP-K30 (PVP) and10% PVP-I were prepared separately to be added to thissolution. Then, 10% chitosan was dissolved in aqueousacetic acid by stirring overnight at room temperature.

There were four different polymer solutions preparedfor the electrospinning process. Solution A was preparedby the mixture of PVA (from 10% solution) and PAA(from 10% solution) with a PVA: PAA ratio of 10:3. Sol-ution B was made of 60% solution A and 40% PVP-K30(from 10% solution). Solution C contained 40% solutionA, 40% PVP-K30 and 20% Chitosan. Finally, solution Dwas prepared by mixing 60% solution A and 40% PVP-I.All amounts were based on weight. The solutions werehomogenized by mixing for two hours. Figure 1 is experi-mental flow chart for electrospinning of Solution A.

The electrospinning equipment uses a variable high volt-age power supply from Gamma High Voltage Research(USA). The applied voltage can be varied from 0–40KV.The syringe needle was used as the electrode connected tothe power source.

The collector was a 20� 40 cm2 aluminum foil placedhorizontally 15 cm away from the tip of the needle. The col-lector was connected to the power supply as an electrodewith opposite polarity. A metering syringe pump fromNew Era pump systems Inc. (USA) was responsible forsupplying polymer solution at a constant rate of 0.5ml=h. Nanofiber samples were obtained by electrospinning of

four different aqueous solutions at an electrical voltageof 15–20 kV at room temperature under atmosphericpressure. Finally, nanofibers were detached from Al foilcollector and dried in the furnace at 80�C overnight undervacuum.

pH and conductivity of the solutions were measured byusing Wissenschaftlich-Technische-Werkstatten WTW and315i=SET apparatus and the viscosity of the hybrid poly-mer solutions measured with AND SV-10 viscometer.

Surface morphology of the electrospun fibers obtainedfrom solutions A-D were first coated with gold in a PolaronSC 502 Sputter Coater, and examined with a JEOL JSM6060 SEM operated at 10 kV in Gazi University (Facultyof Arts and Science, Electron Microscopy Unit, Turkey).Fiber diameters were quantitatively measured using ImageJ software, which was originally developed at the NationalInstitutes of Health (NIH).[41]

Fourier transformations infrared spectra (FT-IR) of theelectrospun fibers were obtained using a Thermo Nicolet6700 spectrophotometer with ATR module and DSCstudies of the fibers were carried out with ShimadzuDSC-60 Differential Scanning Calorimeter.

RESULTS AND DISCUSSION

Table 1 lists the pH, solution viscosity, and solutionconductivity values. Since the pH of the chitosan solutionis lower than that of PVA and PVP K-30 (PVP), theaddition of chitosan 5% and 10% solution decreased thepH of the solution to 4.08 and 3.90, respectively. PVA=PVP blending causes a considerable increase in their vis-cosity as a result of hydrogen bondings in the blendedhybrid polymer.

Chitosan solution is very viscous, and its additioncaused the viscosity of the PVA=PVP solution to increase.The conductivity of PVA=PVP solution and its fibers hasshown a considerable increase by the addition of the chit-osan as well. Increased conductivity of the solution affectedthe diameter of the final fibers because the net chargedensity carried by the jet in the electrospinning process isaffected by the conductivity of the solution. The highernet charge density increased the electrical force exertedon the jet and led to a decreased fiber diameter.

FIG. 1. Experimental flow chart for electrospinning of solution A.

TABLE 1Physical properties of polymer solutions

Sample name

Solutionviscosity(mPa � s)

Solutionconductivity(mS � cm�1) pH

PAA=PVA=PVP-K30 291 14.17 4.12PAA=PVA=PVP=Chitosan 122 16.95 3.97PAA=PVA=PVP-I 218 15.35 3.80

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The FT-IR spectra obtained are shown in Figure 2. TheIR spectrum of the cross-linked PVA=PAA fibers exhibits amoderate ester absorbance band (–CO–O–) of PAA at1712 cm�1. The addition of PVP and Chitosan decreasedthe intensity of this peak due to cross-linking reaction.Our samples’ spectrum is similar to the spectrum in thearticle written by Kim et al. (2005). Kim et al. said thatthe broad absorption peak at around 3400 cm�1 observedin fiber mats indicates that there was a significant amountof –OH group. These broad peaks were composed of vari-ous components such as hydroxyl group of unreacted PVAand carboxylic group of unreacted PAA. These -OHgroups provided sites for hydrogen bonding betweenpolymer chains and water. The peak at 1240 cm�1 arisesfrom the C-O stretch mode of in PAA and the band at920 cm�1 is the –OH (hydroxyl group) out of plane motionof the carboxylic group in PAA.[22,42,43]

Determination of the glass transition temperature, Tg,on the pure polymers and blends, was performed by differ-ential scanning calorimetry in a Shimadzu DSC-60 Differ-ential Scanning Calorimeter between room temperatureand 500�C for the pure polymers at a heating rate of10�C=min, under nitrogen atmosphere.

The thermal properties of the electrospun nanofiberswere elucidated first by heating to 200�C under nitrogenatmosphere and cooling down to room temperature. Thesamples were then heated up to 500�C at a rate of 10�C=min. The results are given in Figure 3.

As seen in the figure the melting temperatures of theall nanofibers are approximately 210�C. The fibers wereobserved to be degraded at 400�C and 450�C. The degra-dation at 400�C is the result of the breakage of cross-linking bonds (the –CO–O– bonds). The degradation

observed at 540�C corresponded to the decomposition ofmain chain of the polymer.

PVA=30% PAA nanofibers showed strong decompo-sition at 400�C. The peaks in other fibers are not as sharp,which indicates that the addition of PVP-K30, PVP-I andchitosan to PVA=PAA structure increases the thermalstability of the compound. It is clear that the most sta-bile structure is chitosan-added PVA=30% PAA with 20%PVP.

Figure 4 is the micrographs of the synthesized nano-fibers. Micrograph of the nanofibers obtained from thesolution A was given in Figure 4(a). As seen fromFigure 4(a), the nanofibers are linear and have no beadings.As seen from the micrograph of the nanofibers synthesizedfrom the solution B (Fig. 4(b)), the nanofibers are less

FIG. 2. FT-IR spectrums of the nanofibers electrospun from solution:

(a) A, (b) B, (c) C, and (d) D.

FIG. 3. DSC thermograms of electrospun nanofibers.

FIG. 4. SEM micrographs of the nanofibers electrospun from solution:

(a) A, (b) B, (c) C, and (d) D.

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linear and have a small amount of beading, but finer thanthe nanofibers obtained from the solution A. Nanofibersobtained from solution C were formed by fine and flatfibers (Fig. 4(c)). They have a lower amount of beadingcompared to fibers obtained from solution B. The nanofi-bers electrospun from solution D are not as fine and linearas in fibers obtained from solutions B and C; however, theycontains lesser amount of beading (Fig. 4(d)).

The nanofiber diameters were calculated (fibers wererandomly selected for calculation) from the SEM picturesusing the Image J software. Fiber diameter distributionof the electrospun fibers were given in Figure 5. The sizeof the fibers obtained from the solution A ranges between200 to 900 nm with an average diameter of 458 nm. Fibersamples obtained from the solution B are much more hom-ogenous than the ones obtained from solution A. However,there are occasional beadings in the structure. The averagediameter of the fibers is 237 nm. The average diameter ofthe fibers electrospun from solution C is 139 nm. The aver-age diameter of the hybrid polymeric fibers obtained fromsolution D was calculated as 270 nm.

CONCLUSIONS

In this study, PVA=PAA, PVA=PAA=PVP, PVA=PAA=PVP-I and PVA=PAA=PVP=Chitosan fiber mats wereprepared via electrospinning technique. Synthesized nano-fibers were characterized by DSC, FT-IR and SEM techni-ques. DSC results show that the nanofibers were degradedat 400�C and 450�C. The addition of PVP-K30, PVP-I andchitosan to PVA=PAA structure increased the thermalstability of the nanofibers. SEM micrographs show thatsynthesized nanofibers are linear. Fiber diameter measure-ments show that average fiber diameters of the electrospunfibers are less than 0.5 micron. The average fiberdiameters of PVA=PAA, PVA=PAA=PVP, PVA=PAA=PVP-I and PVA=PAA=PVP=Chitosan fibers were calculatedas 458nm, 237nm, 139nm, and 270nm, respectively.

FUNDING

This work was supported financially by the Scientificand Technological Research Council of Turkey (TUBI-TAK) Project by contract 106T630.

FIG. 5. Fiber diameter distribution histograms of the nanofibers electrospun from solution: (a) A, (b) B, (c) C, and (d) D.

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