Alginate-nanofibers fabricated by an electrohydrodynamic process

Alginate-Nanofibers Fabricated by anElectrohydrodynamic Process

GeunHyung Kim,1 Ko-eun Park21 Department of Mechanical Engineering, Chosun University, GwangJu, Korea

2 Division of Nano-Machinery, KIMM, Daejeon, Korea

Alginate, a natural polymer, is potentially useful in bio-medical applications, because it is very similar to mac-romolecular substances, unlike synthetic polymers thatmay cause problems due to toxicity and lack of recog-nition by cells. Alginate’s processability characteristics,however, are a potential drawback to its use as a bio-medical nanofiber scaffold. To improve electrospinn-ability, alginate has been processed with various syn-thetic polymers and surfactants. Although this hasenhanced the processability of the polymer, a newapproach is required to obtain a sufficient productionrate over a short period of time. We used a multiple-nozzle electrospinning system complemented withauxiliary cylindrical electrodes. The nanofibers of algi-nate/poly(ethylene oxide) supplemented with lecithinas a surfactant were electrospun using a multiple noz-zle system. We measured the production rate and sizeuniformity of the spun fibers with and without auxiliaryelectrodes. We observed that a multiple nozzle systemwith auxiliary electrodes provided much better andmore stable processability, as well as higher mass pro-ductivity of alginate nanofibers compared with a nor-mal multiple nozzle system. The resulting nanofibermat showed potential for use as a biomedical scaffoldbased on our tests with cell-cultured human dermalfibroblasts. POLYM. ENG. SCI., 49:2242–2248, 2009. ª 2009Society of Plastics Engineers

INTRODUCTION

Electrospinning is a simple and widely used technique

for producing micrometer to nanometer-sized fibers of

various polymers. Electrospinning relies on electric

charges to form ultrafine fibers from conical droplets of

polymer solution ejected from a nozzle tip [1, 2]. Nano-

meter-sized fibers have the potential for a range of highly

useful applications, such as conductive polymeric biosen-

sors, filter membranes, biomedical scaffolds, wound dress-

ing materials, artificial organs, nanoelectronics, nanocom-

posites, and chemically protective clothing [3]. In particu-

lar, nanofibers produced by electrospinning show promise

for the production of polymeric scaffolds that mimic the

structure and biological functions of the naturally occur-

ring extracellular matrix (ECM).

Even though there are well-established manufacturing

methods for fabricating nano-sized fibers, a commercially

available mass production system with a high production

rate is another issue [4]. There has been some research

into how to achieve high throughput industrial production

by stabilizing the spun jets in single-nozzle and multiple-

nozzle systems without interrupting environmental condi-

tions [4, 5]. Zussman and coworkers [4] demonstrated

experimentally and numerically that jets from multiple

nozzles show higher repulsion to other neighboring jets

due to Columbic forces than jets spun by a single-nozzle

process. For a single-nozzle process, Deitzel et al. [5]

studied the possibilities of decreasing the whipping insta-

bility caused by charged jets. That research focused on

how to dampen the instability of spun fibers and control

the deposited area of submicron poly(ethylene oxide)

(PEO) nanofibers using a substrate with an electrostatic

lens element [5]. The results indicated an approach to

controlling or even eliminating the bending instability in-

herent in conventional single- and multiple-nozzle electro-

spinning processes.

Dosunmu et al. [6] demonstrated an electrospinning

process using multiple polymer jets projecting onto a po-

rous tubular surface. Fiber production from multiple jets

was compared with fiber production from a single-syringe

nozzle jet. Fibers deposited on the porous tube from mul-

tiple jets had a significantly greater production rate than

those from the single-nozzle jet. Yarin and Zussman [7]

introduced needleless electrospinning of multiple nanofib-

ers using a normal magnetic field to eliminate clogging of

the nozzles during multiple-jet spinning. Multiple spinner-

ets increased the production rate and offered the potential

for electrospinning bicomponent and multicomponent

nanofibers. To obtain blended nanofibers of uniform thick-

ness, a multiple-jet electrospinning device was manufac-

tured with a rotating grounded target collector.

Correspondence to: GeunHyung Kim; e-mail: [email protected]

Contract grant sponsor: Chosun University.

DOI 10.1002/pen.21472

Published online in Wiley InterScience (www.interscience.wiley.com).

VVC 2009 Society of Plastics Engineers

POLYMER ENGINEERING AND SCIENCE—-2009

To predict the stability of electrospun jets fabricated

with multiple nozzles, Kim et al. [8] introduced the elec-

tric field concentration factor (EFCF), defined as the jets’

degree of convergence to a spinning axis. The EFCF pa-

rameter is used to compare the experimental results for

single- and multiple-nozzle electrospinning processes. Sta-

bility analysis of electrospinning has demonstrated that by

using a cylindrical electrode connected to multiple noz-

zles, the initial stream line and jets of nanofibers from the

nozzles could have stable jet motion without interrupting

charged jets nearby, changing the environmental condi-

tions such as airflow or interfering with nearby dielectric

or conductive materials.

Natural polymers used as biomedical scaffolds have

the advantage of being very similar to macromolecular

substances that the biological environment can recognize

and deal with metabolically, whereas synthetic polymers

may cause problems due to toxicity and lack of recogni-

tion by cells. A potential problem with natural polymers

used as biomaterials is their processability characteristics.

If the material is to be used as the ECM of connective tis-

sues such as tendons, ligaments, skin, blood vessels, or

bone, the materials must be processed into a fiber shape.

However, according to Lu et al. [9], biopolymers such as

alginate, collagen, chitosan, silk, and eggshell membrane

are extremely difficult to fabricate in micro/nanofiber

form using an electrospinning process. To overcome these

problems, there have been some efforts to blend biopoly-

mers with biocompatible synthetic polymers, which may

enhance processability [9–11]. Although this approach

does increase the processability for electrospinning, a new

approach is required to obtain a high production rate for a

short period of time. We have applied a multiple-nozzle

electrospinning system supplemented with auxiliary cylin-

drical electrodes to achieve high productivity and stable

electrospinnability of the material system.

In this article, we used a multiple-nozzle electrospin-

ning system assisted with supporting electrodes to

improve the processability of alginate, a natural biomate-

rial that is difficult to form into nano-sized fibers. Algi-

nate has distinctive properties such as nontoxicity, bio-

compatibility, biodegradability, and hydrophilicity. It is

widely used in biomedical applications such as wound

dressings, tissue engineering scaffolds, and drug delivery

carriers [12, 13]. However, fabricating alginate-nanofibers

in a general electrospinning process is difficult because al-

ginate solution tends to congeal at very low polymer con-

centrations [10].

To enhance its electrospinnability, we mixed alginate

with PEO and lecithin as a processing agent. We used a

multiple-nozzle electrospinning system connected with

auxiliary electrodes to improve the production rate of

micro/nanofibers. To observe the effect of the electrodes

in the multiple nozzle system, we measured the produc-

tion rate and fiber size uniformity with and without the

electrodes. The electrospun alginate-fiber webs we pro-

duced showed potential for use as a biomedical scaffold.

EXPERIMENTAL

Materials

Sodium alginate (SA; made up of a-(1?4)-L-guluronic

acid (G) and b-(1?4)-D-mannuronic acid (M) plus a natu-

ral polysaccharide obtained from marine brown algae),

PEO (Mw ¼ 9,000,000) and calcium chloride were pur-

chased from Sigma-Aldrich (St. Louis, MO). The viscos-

ity of the SA was medium. Lecithin was supplied by

Doosan Biotech (Korea). Several SA/PEO solutions with

different concentration ratios were prepared by dissolving

SA and PEO in distilled water. The concentration ratios

of SA/PEO were 1/1, 2/1, 3/1, 2/1, 2/2, and 3/2 wt%. We

used the notation SaPa where ‘‘a’’ and ‘‘b’’ are the weight

percent of SA and PEO, respectively. For example, S1P1

means a solution with SA 1 wt% and PEO 1 wt%. The

SA/PEO mixtures were stirred at room temperature over-

night to obtain homogeneous solutions.

Characterization

The viscosity of the SA/PEO solutions was measured

at room temperature using a viscometer (LVDVE 230,

Brookfield Engineering Laboratories, MA) equipped with

an SC4-31 spindle and 13R chamber. We used a pH/con-

ductivity meter (Orion 4 Star, Thermo Scientific, MA) to

measure the conductivity of solutions. The fiber morphol-

ogy of the alginate nanofiber was observed with a scan-

ning electron microscope (SEM) (Nova nanoSEM 200,

FEI, Netherlands). The average fiber diameter and diame-

ter distribution were obtained by analyzing randomly

selected fibers from SEM images with a custom code

image analysis program (Scope Eye II, TDI, Korea).

Alginate nanofibers were cross-linked by soaking them

in 5 wt% (w/v) CaCl2 solution for the cell test and rinsing

them with deionized water to remove the excess CaCl2[9, 14, 15]. The nanofiber scaffolds were sterilized with

70% ethanol and prewarmed with Hank’s balanced salt

solution. Human dermal fibroblasts (HDFs) were cultured

in Dulbecco’s Modified Eagle’s Medium supplemented

with 10% fetal bovine serum. The HDFs were seeded on

the 1 3 1 cm nanofiber at a density of 6.4 3 104 cells/

nanofiber. HDFs on the nanofiber were cultured for up to

5 d at 378C in an atmosphere of 5% CO2. The cells were

fixed with 2.5% glutaraldehyde for 1 h and dehydrated

through a series of ethanol dilutions. The HDFs on the

nanofiber were sputter coated with Pt, and the morphol-

ogy of the cell attachment was observed using a SEM 3

and 5 d after seeding.

Multiple-Nozzle Electrospinning System Withan Auxiliary Electrode

In the electrospinning process, a high electric potential

is applied to a droplet of the blended solution at the tip of

DOI 10.1002/pen POLYMER ENGINEERING AND SCIENCE—-2009 2243

a syringe needle. Then nanofiber is formed by the electri-

cal repulsive force between positive charges in the droplet

on the needle tip. The multiple-nozzle electrospinning

system consisted of three nozzles (syringe needles), and

each nozzle was attached to a conical auxiliary electrode

to stabilize the Taylor cone and initial spun solution, as

shown in Fig. 1. To minimize the interference of the elec-

tric field distribution of the three nozzles, the nozzles

were placed 120 mm apart in a triangular shape. We used

several different combinations of distance from needle to

collector (15, 20, and 25 cm), voltage (0–40 kV DC), and

flow rate (0.2, 0.5, 1.0, and 1.5 ml/h) to evaluate the

effect of these parameters. All experiments for the elec-

trospinning system were carried out at 308C using S2P2

solution with 0.7 wt% lecithin added.

RESULTS AND DISCUSSION

Effect of Lecithin on the Electrospinnability of SA/PEO

In general, electrospinning is strongly dependent on the

properties of the solution. Figure 2 shows the solution vis-

cosity and conductivity as functions of the blend composi-

tion. As depicted in Fig. 2, the viscosity and conductivity

increase as the content of SA in 2 wt% PEO increases. As

Bhattarai et al. [10] observed, it is extremely difficult to

create nanofibrous structures by electrospinning alginate

solution due to its high viscosity. To overcome this proc-

essability problem, they added Triton X-100 as a surfac-

tant in an alginate/PEO solution to control sol-gel transi-

tion, and this interacted with the alginate solution to

reduce the solution’s viscosity. The electrospun alginate

nanofibers fabricated in this manner were suggested for

use as biomedical scaffolds, however, the presence of the

Triton X-100 surfactant may cause cell damage during the

cell culturing process. Esquisabel et al. [16] used lecithin

as a surfactant to prepare alginate-(poly-L-lysine) (PLL)

microcapsules, the size of which was heavily dependent

on the amount and type of lecithin. This indicates that lec-

ithin could play an effective role as a surfactant to control

the size of alginate-PLL microcapsules. On the basis of

these results, we used lecithin as a surfactant in our SA/

PEO electrospinning system.

To determine a suitable composition of PEO, various

ratios of SA/PEO solution were electrospun with lecithin.

Figure 3 shows the morphology of the electrospun webs

produced for various SA/PEO ratios. A PEO content of

1 wt% with various SA concentrations produced beads

and beaded fiber. However, electrospinning a solution

with 2 wt% PEO successfully produced nanofibers. This

shows that the composition of the PEO solution plays an

important role in forming beaded fibers and nanofibers.

The best composition of PEO in our SA/PEO blend sys-

tem was a composition ratio of S2P2. Moreover, the addi-

tion of 0.7 wt% lecithin as a surfactant decreased the

spattering of alginate droplets on the target, as shown in

Fig. 4. We used S2P2 with 0.7 wt% lecithin as an appro-

priate composition in the multiple nozzle system to attain

a high nanofiber production rate.

Effect of an Auxiliary Electrode

As other research has indicated, by controlling the

shape and strength of the macroscopic electric field

FIG. 1. (a) Schematic of the electrospinning setup with multinozzles and auxiliary electrodes and (b) three

nozzles with auxiliary electrodes.

FIG. 2. Viscosity and conductivity change according to the blending

ratios of SA and PEO of 2 wt%.

2244 POLYMER ENGINEERING AND SCIENCE—-2009 DOI 10.1002/pen

between a spinneret and a grounded target, we should be

able to control the electrospinning process through basic

electrostatic principles [5, 8]. We connected various auxil-

iary electrodes (specially designed conical-type electro-

des) to the syringe nozzles [17] to stabilize the initial

spun jet solution and the Taylor cone at a nozzle tip,

which could be important for attaining a high production

rate. Using a conical-type auxiliary electrode resulted in a

stable initial spun jet without sacrificing the high voltage

drop between the nozzle and the target electrode. In this

work, we used a conical-type electrode for each nozzle,

as shown in Fig. 1, to obtain stable processability at each

nozzle. Figure 5a shows the contours of the EFCF near

the nozzle with and without an auxiliary electrode, both

FIG. 3. The SEM images of electrospun fibers with various SA/PEO ratios: (a) S1/P1, (b) S2/P1, (c) S1/P1,

and (d) S2/P2 with lecithin of 0.7 wt%.

FIG. 4. The SEM images of electrospun S2P2 nanofibers (a) without lecithin and (b) with lecithin

of 0.7 wt%.


on the same scale. The EFCF, which was defined as the

degree of convergence of an initially spun solution to a

spinning axis, has been calculated as Er/||E||, where Er is

the r-directional component of the electric field in the cy-

lindrical coordinates and E is electrical field [8]. The fac-

tor can vary across the range 61 where a positive sign

means a divergence of the electric field at the calculated

position from the spinning axis and a negative sign means

a convergence of the electric field. From Kim et al. [8],

the meniscus of the Taylor cone at a nozzle tip can be

influenced by the shape of ellipsoidal contour of the elec-

tric field near the nozzle tip. Calculated results show that

the contour of EFCF for an auxiliary electrode exhibits a

broad region at the nozzle tip relative to a normal nozzle,

and this could lead to stabilizing the initial spun jets at a

the nozzle tip, although interference from the other nearby

charged jets and unsteady processing were present.

As shown in Fig. 5b, the electrospun jet with the auxil-

iary electrode was stable and went straight to the collector,

whereas it was unstable and easily diverted for the normal

nozzle. This indicates that the jet of the nozzle with the

auxiliary electrode was concentrated on the collector during

electrospinning because the Taylor cone with the auxiliary

electrode was more stable than the normal nozzle. There-

fore, we expect that it should be possible to increase total

production through the use of an auxiliary electrode.

Processability of Multiple Nozzles

To find suitable processing conditions for the multiple

nozzle system with or without auxiliary electrodes, we

investigated the flow rate and DC voltage with respect to

the morphology of the electrospun material. As shown in

Fig. 6, there were three regions related to beads, beaded

fibers, and nanofibers. It is well known that flow rate and

applied DC voltage play important roles in the formation

of nanofibers in electrospinning. From the figure, we esti-

mate that, regardless of the auxiliary electrode, the critical

DC voltages (from 20 to 23 kV) to stably fabricate algi-

nate/PEO nanofiber were very similar to each other.

Therefore, the auxiliary electrode used in this electrospin-

ning system could assist in the enhancement of the pro-

duction rate of electrospun alginate/PEO nanofibers with-

out an increase in the supplementary applied DC voltage.

Figure 7a and b shows SEM images of the elelectro-

spun mats of alginate/PEO nanofibers deposited on the

rectangular target. The image in Fig. 7a was obtained

using the standard electrospinning method with three noz-

zles. The distance from the nozzles to the target was

150 mm, the spinning voltage was 27.5 kV at the nozzles,

and the flow rate for each nozzle was 0.5 ml/h. The image

in Fig. 7b was obtained using a three-nozzle system with

three supplementary conical electrodes. Comparison of

these two figures shows a reduction in the diameter of the

spun fibers from 246 6 83 nm for the standard electro-

spinning in Fig. 7a to 174 6 62 nm for the modified

electrospinning in Fig. 7b. As described by Fridrikh et al.,

FIG. 5. (a) Electric field concentration factor (EFCF) near nozzle tip and (b) initial spun jet.

FIG. 6. Process diagram of electrospinning using S2P2 solution with or

without an auxiliary electrode.


the simplified diameter of the terminal jet (dt) can be

determined from the equation,

dt / ðgeÞ1=3ðQ=IÞ2=3ð1= ln kÞ1=3 (1)

where g is the surface tension, e is the dielectric constant,

Q is the flow rate, I is the current, and k is the ratio of the

initial jet length to the diameter of the nozzle [18]. In this

equation, if the current of whipped fibers in both electro-

spinning systems is similar, the size reduction for the elec-

trospinning process using an auxiliary electrode is reasona-

ble because the length of the initial spun jet for the process

using the auxiliary electrode is longer than that of the nor-

mal spinning process. However, this simple estimate is not

completely correct because the current has a complex de-

pendence on the voltage applied to the nozzles and auxil-

iary electrodes. A more detailed analysis of the reduction

in size of the electrospun fibers with the auxiliary elec-

trode will be the subject of future research. The uniform

size of spun fibers from the electrospinning process sup-

plemented by auxiliary electrodes may be the result of a

stable induced electric field condition under the conical

electrodes stabilizing the chaotic motion by guiding the

initial jets.

FIG. 8. Comparison of weight between nanofibers spun by a normal electrospinning process and the process

with an auxiliary electrode under applied electric conditions: 28 kV at a nozzle for (a) various time and (b)

distance between a multinozzle and a target.

FIG. 7. SEM photographs and diameter distributions. (a) Standard e-spin with multinozzles and (b) e-spin

with auxiliary electrodes connected with multinozzles.


To evaluate the effects of using the multiple nozzle sys-

tem supplemented with auxiliary cylindrical electrodes on

the mass production rate, the spun jets were collected on

an aluminum target foil for various times and different

nozzle-target distances. The target was 50-mm high and

300-mm wide. Figure 8a shows the weight of nanofibers

collected as a function of time; it is clear that the collec-

tion rate is larger with the auxiliary electrode than without

it. Figure 8b shows weight change of nanofiber on the col-

lector for various distances between the collector and the

needle tip. The deposited weight decreased as the distance

increased with or without the auxiliary electrode. How-

ever, the increased fraction of weight became larger as the

distance increased. This result indicates that the auxiliary

electrode makes the electrospinning stable, regardless of

distance, and dramatically improves the production rate.

For the cell experiment, the fiber strand formation of

alginate nanofiber was maintained well after the CaCl2treatment [13]. The cell morphology of the HDFs was

observed using a SEM. The HDFs cells were embedded

in the alginate nanofiber mat and maintained in the cul-

ture for 3 d. As shown in Fig. 9, the HDFs were initially

attached as round shapes; after 5 d, they had elongated

and were well spread out on the alginate nanofiber.

CONCLUSIONS

We fabricated nanofibers of SA blended with PEO and

lecithin as a surfactant by using a modified multiple-noz-

zle electrospinning system supplemented with auxiliary

conical electrodes. Alginate nanofibers with a composition

of S2P2 provided the most stable electrospinning process.

Using 0.7 wt% of lecithin as a surfactant produced good

uniform bead-free nanofibers. For scaling up the produc-

tion rate of the natural biocompatible nanofibers, the

modified multiple-nozzle electrospinning system presented

a stable initial stream line and jets of nanofibers from the

nozzles. This stable jet motion was not influenced by

nearby charged jets, environmental conditions such as air-

flow, or interference from nearby dielectric or conductive

materials. This system achieved excellent processability

and a high production rate of alginate nanofibers without

sacrificing applied voltage loss. The multiple-nozzle elec-

trospinning system with an auxiliary electrode is

extremely practical for obtaining a high production rate

for electrospun nanofibers. The cell culturing results indi-

cate that electrospun alginate-based nanofiber mats have

good potential for use as biomedical materials.

ACKNOWLEDGMENTS

The authors are grateful to Dr. S. A. Park for her

assistant of cell culturing test. This work was supported

by research funds from Chosun University, 2008.

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FIG. 9. Cell morphology of (a) 3 d and (b) 5 d for alginate/PEO electrospun mats.


Alginate-nanofibers fabricated by an electrohydrodynamic process

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