Dextran Nanofiber Production by Needleless Electrospinning Process

DOI 10.1515/epoly-2013-0021 e-Polymers 2014; 14(1): 5–13

Funda Cengiz-Çallıoğlu* Dextran nanofiber production by needleless electrospinning process

Abstract: This article presents the formation of a dextran for biomedical applications. Most natural polymers that nanofibrous layer by needleless electrospinning. Opti- have been electrospun are proteins and polysaccharides mum process parameters such as polymer solution and (1). Dextran is a bacterial polysaccharide that consists of addition (surfactant) concentration, voltage, distance, etc. α-1,6-linked d-glucopyranose residues with some α-1,2-, α- were determined to obtain uniform and smooth dextran 1,3- or α-1,4-linked side chains (10). Dextran has biocom- nanofibers. It was not possible to produce nanofibers from patibility and biodegradability characteristics, which are pure dextran/water solution. Instead, solution drops were very important properties in biomedical applications such deposited on the collector; therefore, anionic surfactant as drug delivery (11, 12) and scaffolds (13). was added in various concentrations to start the nanofiber In the literature, there has been very little work done production. Also, the effects of surfactant concentration on dextran nanofiber production by electrospinning. on the solution properties, spinnability and fiber proper- Jiang et al. prepared uniform dextran nanofibrous mem- ties were determined. Generally, uniform and fine nanofib- branes by electrospinning (10). They used various solvent ers were obtained from the rod electrospinning method. mixtures such as water, dimethyl sulfoxide (DMSO)/ The value of 2 wt% surfactant concentration was chosen as water and DMSO/dimethylformamide (DMF) to produce the optimum concentration to produce a dextran nanofi- dextran nanofibers. When water was used as a solvent, brous layer by roller electrospinning. According to the up to 10% of bovine serum albumin or lysozyme could be results, spinning performance was 0.6726 g/min per meter, directly incorporated into the dextran membrane without average fiber diameter was 162 nm, diameter uniformity compromising its morphology. Composite electrospun coefficient was 1.03 and the nonfibrous area was 0.5%. In membranes consisting of polylactic-co-glycolic acid and conclusion, this methodology resulted in the production dextran were obtained using DMSO/DMF (50:50) sol- of good product properties such as good spinnability, fine vents. Also, the effects of various process parameters on and uniform nanofibers and high fiber density. the membrane properties were investigated, and no significant effect of the electrospinning process on lysozyme Keywords: dextran; nanofibers; needleless electrospin- activity was observed (10). In another study, Ritcharoen ning; polymer solution; surfactant. et al. researched the effects of solution concentration and applied electric field on the morphological appear- ance and size of the electrospun dextran fibers. They *Corresponding author: Funda Cengiz-Çallıoğlu, Engineering observed that fiber diameter increased with increasing Faculty, Textile Engineering Department, Süleyman Demirel University, 32260, Çünür, Isparta, Turkey, electric field and solution concentration. Also, the effects e-mail: [email protected] of curing temperature, curing time and MgCl2 catalyst addition were investigated for cross-linking dextran membranes with glutaraldehyde. According to the results, cross-linking did not affect the membrane morphology 1 Introduction and only slightly decreased fiber diameter. Swelling and weight loss in water of the cross-linked dextran mem- Electrospinning is the most common method of producing branes decrease with increasing curing temperature, nanofibers, and one of the greatest potential uses of elec- curing time and MgCl2 addition (14). Shawki et al. studied trospun fiber is in the area of bioengineering (1). For many the fabrication of antimicrobial dextran nanofibers by biomedical applications, natural polymers are often used electrospinning (15). They used water as a solvent and because of their high biocompatible and biofunctional loaded moxifloxacin antibiotic on the dextran nanofib- properties. Several natural polymers such as collagen ers. They investigated moxifloxacin release from dex- (2), DNA (3), silk (4), chitosan (5, 6), gelatin (7), cellulose tran-moxifloxacin and its antimicrobial effectiveness. (8, 9) and dextran (10) were used to produce nanofib- They found that dextran-moxifloxacin nanofibrous mats ers by the electrospinning method to develop products showed very high and rapid antibacterial activity against 6 F. Cengiz-Çallıoğlu: Dextran nanofiber production by needleless electrospinning process

Staphylococcus aureus and Escherichia coli strains and addition of nonionic surfactant did not eliminate the fiber reported that dextran-moxifloxacin nanofibrous mats can beads but reduced the bead numbers and changed the fiber be used in a wide range of biomedical applications (15). morphology. Also, nonionic surfactant addition slightly In recent years, Spano and Massaro obtained aligned dex- improved the solution conductivity and had a minor effect tran-based nanofibers using a special collector of electro- on the surface tension but no effect on the viscosity (33). In spinning (16). Again in 2012, Unnithan et al. prepared an another study, Kriegel et al. suggested that surfactants may antibacterial scaffold by electrospinning of a solution that modulate polymer-polymer interactions, therefore affect- includes dextran, polyurethane and ciprofloxacin HCl ing the fiber morphology and composition of deposited drug. They specified that dextran addition into the poly nanostructures. They specified that pure chitosan did not urethane increased the cell attachment and viability (17). form fibers and was instead deposited as beads. After the Kim et al. proposed a new type of smart nanofibers with addition of poly(ethylene oxide) and an increase of the sur- adjustable properties for the “on-off” controlled release factant concentration, electrospinnability was enhanced, of the dextran. According to the results, this study will be yielding a larger fiber diameter (34). useful to provide a platform for on-off drug delivery (18). The objective of this study is to produce a dextran All of the studies mentioned above achieved their nanofibrous layer by needleless electrospinning with the results by the needle electrospinning method. There are aim of developing the techniques used for the industrial currently no studies in the literature that cover dextran production of biomedical products. nanofiber production by needleless electrospinning at an industrial scale. Therefore, this paper aimed to fill the current knowledge gap through studying dextran nanofibrous layer production by the needleless electrospinning 2 Materials and methods method. Needleless electrospinning concerns self-organization of polymeric jets on free liquid surfaces and is a 2.1 Materials result of electrohydrodynamics in the liquid surface (19).

Up to now, many needleless electrospinning methods are Dextran 70 was used as a polymer [Mw, 70,000 Da (g/ being developed to prevent production problems such mol)], distilled water was used as a solvent and anionic as needle clogging, low throughput, etc. (20–25). In this synferol was used as a surfactant. Dextran was obtained study, rod and roller electrospinning methods were used from Pharma Cosmos (Denmark) and anionic synferol to provide optimization of dextran nanofiber production surfactant was purchased from Enaspol (Czech Republic). at an industrial scale. To date, only a few studies have All solutions include 0.75 g/ml (0.75 g of dextran powder been completed with needleless electrospinning (rod in 1 ml of distilled water) dextran and were prepared at and roller) using common polymer/solvent systems such various anionic synferol concentrations: 0, 2, 4, and 6 as poly(vinyl alcohol), polyurethane, poly(vinyl butyral), wt% surfactant. The aim of using this surfactant was to etc. (26–30), and in the literature, this study will be the increase the electrospinnability of dextran solution. first to obtain dextran nanofibrous layers by needleless electrospinning. This study also investigated the effects of surfactant concentration on the electrospinning process 2.2 Methods and dextran nanofiber morphology. From the literature, it is well known that addition of surfactant can enhance All solutions were prepared under the same conditions electrospinnability. Wang et al. used nonionic surfactants (room temperature, stirring time, the same day, etc.). It is to enhance electrospinnability of poly(vinyl pyrrolidone). well known that polymer solution properties play a criti- They found that surfactant addition increased spinnabil- cal role in electrospinning and resultant fiber morphol- ity while decreasing solution surface tension and fiber ogy (26, 35–37). Therefore, the solution properties such diameter (31). Talwar et al. also reported that addition of as conductivity, surface tension and viscosity were deter- nonionic surfactant provides defect-free fibers and a sig- mined. Conductivity and surface tension properties were nificant improvement in nanofiber morphology, such as determined by a conductivity meter (Radelkis, OK-102/1) reduced beading (32). In 2004, Lin et al. found that small (Budapest, Hungary) and the Wilhelmy method (Krüss) amounts of cationic surfactant stopped the formation of (Germany) using a platinum plate and a high-precision beaded electrospun polystyrene fibers. They highlighted electronic balance, respectively. The viscosity of the solu- that cationic surfactant addition increased solution con- tions was measured using a HAAKE RotoVisco 1 rheom- ductivity but had no effect on the viscosity. However, eter (Germany) at 25°C with a shear rate of 200 s-1. F. Cengiz-Çallıoğlu: Dextran nanofiber production by needleless electrospinning process 7

Grounded A collector electrode B Dextran nanofiber Nano web

Solution droplet

Rod

High voltage supplier

Figure 1 (A) Schematic diagram of rod electrospinning. (B) Picture of solution jets on the rod surface.

In this work, first, the rod electrospinning method Roller electrospinning is another needleless method was used to optimize nanofiber production from dextran used to produce nanofibrous layers at an industrial scale. solutions. This method is a needleless electrospinning This method was invented by Jirsak et al. from the Tech- process invented by Lukas (24). As a main principle of rod nical University of Liberec (25) and commercialized by electrospinning, a steel rod and collector are used to spin the Elmarco Company (http://www.elmarco.cz. Accessed solutions directly from the solution surface (Figure 1A). 2012). Roller electrospinning consists of a roller and a A high-voltage supplier is connected to the rod and the movable collector electrode. The roller slowly rotates in collector electrode. An electrostatic field forms between a tank filled with a polymer solution. The electrostatic the rod and the collector electrode. The collector elec- field organized between the roller and the oblong collec- trode is grounded, and the setup is placed in a chamber to tor enables the self-organization of jets along the upper control the relative humidity and temperature. surface of the roller (19). Then, a high voltage is connected A droplet of dextran solution was placed on the rod to the roller and collector electrode while the collector electrode before the source of voltage was switched on electrode is grounded. Various shapes of rollers can be and 30 kV was applied to the solution. Rod diameter is used in roller electrospinning such as plain cylindrical, an important parameter for the Taylor cone number and tine roller or barbed roller (39). For this study, a barbed the productivity of electrospinning. If the rod diameter is roller was used, which has six rows of barbs, and each 3 mm or less, only one Taylor cone occurs on the surface. row has nine barbs on it (a total of 54 barbs). A picture of One to six Taylor cones usually formed on the rod’s surface the barbed roller during the spinning process is shown in during electrospinning if the rod diameter is higher than Figure 2B. 8 mm (38) (Figure 1B). To obtain several Taylor cones on While rotating, the barbed roller is covered by a film the rod surface, the rod diameter was adjusted to 10 mm of dextran polymer solution, and many Taylor cones (40) for this study. The process parameters of the rod electro- are created after the voltage is switched on. The jets of spinning method are shown in Table 1. polymer solution move toward the collector electrode and After the rod electrospinning process, an optimum settle down on the supporting material as solid nanofib- solution (2 wt% surfactant concentration) was chosen ers owing to rapid solvent evaporation before reaching and spun by barbed roller electrospinning (Nanospider) the collector electrode. The optimum process parameters (Figure 2). of the roller electrospinning applied during the spinning experiments are presented in Table 2. Table 1 Process parameters of rod electrospinning. Conditioned air is blown into the spinning device from a suitable air conditioner. The air conditioner is Rod Distance between Voltage Temperature Relative able to keep the relative humidity between 18% and 60% diameter rod and collector (kV) (°C) humidity (%) (mm) (cm) and the temperature between 18°C and 30°C. Inside the chamber, optimum values of relative humidity and tem- 10 10 30 24 25 perature for spinning dextran nanofibers by barbed roller 8 F. Cengiz-Çallıoğlu: Dextran nanofiber production by needleless electrospinning process

A Supporting Output of Collector Take-up material air cylinder electrode B

Nano web Air Dextran nanofiber Rotating barbed roller High voltage Solution Input of supplier tank conditioned air

Figure 2 (A) Schematic diagram of the barbed roller electrospinning method. (B) Barbed roller. electrospinning are 35% and 24°C, respectively, which Average fiber diameter was calculated using 100 different were determined from the preliminary experiments. diameter values for each sample. The fiber diameter uni- Dextran nanofibers were collected on polypropylene formity coefficient was calculated using the number and spunbond nonwoven antistatic material. weight average calculation method. Number average has After the dextran nanofibrous layers were obtained by been used as an arithmetic mean in mathematical science, barbed roller electrospinning, the spinning performance and the method that was used to calculate the uniformity (SP) value, which is the most important parameter of coefficient has the same principle as the molar mass dis- the roller electrospinning method, was calculated. SP, or tribution in macromolecular chemistry (28). Both of these polymer throughput, is the amount of nanofiber material in values were calculated using Eqs. (2) and (3): grams per minute produced using a 1-m-long roller (g/min ∑nd per meter). The equation of spinning performance is given A = ii(numberaverage) [2] n ∑n as (41): i VW××M SP = g/min per meter [1] ∑nd2 l = ii Aw (weightaverage) [3] ∑nd ii where SP is the spinning performance (g/min per meter),

V is the take-up cylinder speed (m/min), W is the width of where di is the fiber diameter and ni is the fiber number. nanofiber web on collected nonwoven material (m), M is The fiber diameter uniformity coefficient (FDUC) was the area weight of nanofiber web (g/m2) and l is the length determined using Eq. (4); the optimum value should be of the spinning roller (m). very close to 1 for uniform fibers. The fiber morphology and diameter of the dextran A nanofibers were analyzed with fiber pictures under FDUC= w [4] A 1000 × and 10,000 × magnification by scanning electron n microscopy (SEM) (TESCAN) (Czech Republic). From the SEM pictures, average fiber diameter (nm), diameter uni- In addition, the NFA percentage value was calculated formity and nonfibrous area (NFA) percentage (%) were from SEM pictures of nanofibers under 1000 × magni- determined with the aid of Lucia 32G computer software. fication. The NFA percentage refers to the quality of the

Table 2 Process parameters of roller electrospinning.

Roller Roller Roller Take-up Distance Voltage Temperature Relative length diameter speed cylinder speed between (kV) (°C) humidity (cm) (cm) (rpm) (cm/min) electrodes (%) (cm)

14.5 2 7 10 15 60 24 35 F. Cengiz-Çallıoğlu: Dextran nanofiber production by needleless electrospinning process 9

800

600 y=234.5x-221.68 R2=0.9996 400

200

Conductivity (microS/cm) 0 0246 Surfactant concentration (%)

Figure 3 Effect of surfactant concentration on the conductivity of dextran solution.

spinning process. NFA is the area fraction of nonfibrous the surface tension was found to be statistically signifi- area in a membrane in relation to the total area of product cant using a one-way analysis of variance (ANOVA) test. (27). The equation is given below: NFA = (total area of nonfibrous area/total area of nanofibrous membrane) × 100 [5] 3.2 Spinning and analysis of fiber properties

Dextran nanofibrous layers were fabricated by needleless rod and roller electrospinning methods. It was not possible to produce nanofibers from pure dextran/water 3 Results and discussion solution by needleless electrospinning because solution drops were deposited on the collector. As has been previ- 3.1 Results of solution properties ously shown in the literature, surfactants may modulate polymer-polymer interactions to enhance electrospin- Measurement of solution properties (conductivity, surface nability and influence fiber morphology (34). Therefore, tension, viscosity, etc.) showed that the polymer-solvent anionic surfactant was added in various concentrations and polymer-polymer interactions are key factors in the to start the nanofiber production process. First, the rod electrospinning process and that surfactants are able to electrospinning method was used to obtain dextran nano adjust these interactions via electrostatic or hydrophobic fibers at various surfactant concentrations to determine interactions as well as hydrogen bonding (34). Therefore, the optimum surfactant value for roller electrospinning. dextran solution properties such as conductivity, surface Figure 5 shows the SEM images and diameter distributions tension and viscosity at various surfactant concentrations of the dextran nanofibers that were obtained by the rod were determined. Figure 3 shows the effect of surfactant electrospinning method. concentration on the solution conductivity. As can be seen in Figure 5, uniform and very fine nano The conductivity of the dextran solution increased fibers and also smooth fiber morphology were obtained from with surfactant concentration and there was a high linear the dextran solution at various surfactant concentrations. In regression between the conductivity and the surfactant concentration. In the literature, similar results were also observed (33). 80 1.6 Surface tension (mN/m) When the effect of surfactant concentration on the Viscosity (Pas) solution surface tension and viscosity was analyzed, it 60 1.2 was observed that the surface tension decreased with sur- 40 factant, whereas viscosity was not affected by surfactant 0.8 concentration (Figure 4). 20 0.4 Viscosity (Pas) It is well known in the literature that solution surface Surface tension (mN/m) tension decreases with surfactant addition (34, 42). Also, 0 0 surfactant addition has no effect on viscosity, and this 0246 Surfactant concentration (%) result is concordant with the literature (33). Therefore, these results confirm what has been previously observed Figure 4 Effect of surfactant concentration on the surface tension by other groups. The effect of surfactant concentration on and viscosity of dextran solution (shear rate: 200 s-1). 10 F. Cengiz-Çallıoğlu: Dextran nanofiber production by needleless electrospinning process

A Mean=186.52 12.5 Std. Dev.=34.43 N=100 10.0 7.5

Frequency 5.0 2.5 0 100 150 200 250 300 Fiber diameter (nm) (2% surfactant)

50 µm 10 µm

B Mean=194.48 12.5 Std. Dev.=32.698 N=100 10.0 7.5 5.0 Frequency 2.5 0 100 150 200 250 300 Fiber diameter (nm) (4% surfactant)

50 µm 10 µm

C 20 Mean=231.24 Std. Dev.=51.063 15 N=100

Frequency 5

0 100 150 200 250 300 350 400 Fiber diameter (nm) (6% surfactant)

50 µm 10 µm

Figure 5 SEM images and diameter distributions of dextran nanofibers at various surfactant concentrations by rod electrospinning: (A) 2 wt% surfactant, (B) 4 wt% surfactant, (C) 6 wt% surfactant (1000 × and 10,000 × magnification).

particular, the nanoweb structure of dextran at 2 wt% sur- fiber properties. Also, fiber diagram histograms were factant was very smooth and without fiber stickiness. The obtained and analyzed (Figure 5). Generally, uniform and 2 wt% surfactant solution was the chosen optimum for the unimodal curves were obtained from all histograms. Fiber roller electrospinning method because of its excellent diameter range was between 102 and 357 nm. F. Cengiz-Çallıoğlu: Dextran nanofiber production by needleless electrospinning process 11

300 1.06 Table 3 Product properties of dextran nanofibers from roller Fiber diameter (nm) electrospinning. 225 Fiber diameter uniformity 1.05 1.05 150 1.04 Dextran solution Product properties 1.03 1.03 75 1.03 Spinning Fiber Fiber NFA (%)

Fiber diameter (nm) performance diameter diameter

0 1.02 Fiber diameter uniformity (g/min per (nm) uniformity 246 Surfactant concentration (%) meter) coefficient 2 wt% surfactant 0.6726 162 1.03 0.5 Figure 6 Effect of surfactant concentration on the fiber diameter and diameter uniformity.

obtained. The fibers obtained from this method were very The effect of the surfactant concentration on the fine compared to previous findings in the literature (10, dextran nanofiber diameter and diameter uniformity coef- 14–16). Table 3 shows the product properties of dextran ficient is given in Figure 6. nanofibers from roller electrospinning. According to Figure 6, fiber diameter and diameter From this table, spinning performance, which is the uniformity increased with surfactant concentration. Fiber most important parameter for a roller electrospinning diameter uniformity coefficient values were very close to 1. system, is 0.6726 g/min per meter, average fiber diameter Therefore, it can be said that uniform dextran nanofibers is 162 nm, fiber diameter uniformity coefficient is 1.03 and were obtained from the rod electrospinning method. Also, NFA percentage is 0.5%. Therefore, it can be said that good the effect of surfactant concentration on the fiber diam- product properties were obtained. Lastly; when the fiber eter was statistically significant, whereas uniformity coef- properties were compared for rod and roller methods, it ficient was not (ANOVA test). is possible to explain that finer fibers were obtained from Spinning nanofibers by the barbed roller electrospin- roller electrospinning, whereas fiber morphology and ning technique using the dextran solution with 2 wt% sur- fiber diameter uniformity are similar. factant was tried. The SEM images of dextran nanofibers produced by roller electrospinning at 1000 × and 10,000 × magnifications are given in Figure 7. As can be seen from Figure 7, there is high fiber 4 Conclusions density and low NFA under 1000 × magnification. Also, very fine and uniform nanofibers were obtained. Average In this study, formation of dextran nanofibrous layers by fiber diameter was 162 nm as shown in the fiber diame- needleless electrospinning was achieved successfully. ter histogram. The lowest fiber diameter was 91 nm and First, solution properties such as polymer concentration, the highest value was 243 nm, and a unimodal curve was surfactant concentration, conductivity, surface tension

20 Mean=162.1 Std. Dev.=29.584 15 N=100

5 Frequency

0 50 100 150 200 250 Fiber diameter (nm) (roller electrospinning)

50 µm 10 µm

1000x10,000x

Figure 7 SEM images and diameter distribution of dextran nanofibers including 2 wt% surfactant produced by roller electrospinning (1000 × and 10,000 × magnification). 12 F. Cengiz-Çallıoğlu: Dextran nanofiber production by needleless electrospinning process and viscosity were determined. Then, optimum process spinning performance, 0.6726 g/min per meter; average parameters for rod and roller electrospinning, such as fiber diameter, 162 nm; fiber diameter uniformity coeffi- voltage, distance, humidity, etc., were determined to cient, 1.03; and NFA percentage, 0.5%. In summary, it can obtain uniform and smooth dextran nanofibers. It was be said that good product properties such as good spin- not possible to produce nanofiber from a pure dextran/ nability, very fine and uniform nanofibers, and high fiber water solution. Instead, solution drops were deposited on density were obtained. The results obtained in this study the collector, so anionic surfactant was added in various have potential future implications in the production of concentrations to start nanofiber production. In addition, biomedical materials and should be investigated further the effect of surfactant concentration on solution proper- at the industrial scale. ties such as conductivity, surface tension and viscosity was determined. According to the results, conductivity Acknowledgments: The author would like to thank the increased while surface tension decreased with increas- Nonwoven Department of the Textile Engineering Faculty, ing surfactant concentration. However, solution viscosity Technical University of Liberec in the Czech Republic for was not affected by the surfactant concentration. Uniform providing work facilities. Thanks are also offered to Fatma and very fine nanofibers were obtained from the rod elec- Yener, Baturalp Yalçınkaya and Prof. Dr. Oldrich Jirsak for trospinning method. The value of 2 wt% surfactant con- their assistance. centration was chosen as the optimum for producing a dextran nanofibrous layer by roller electrospinning. The product properties of roller electrospinning are as follows: Received October 3, 2013; accepted November 5, 2013

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