Materials Letters 63 (2009) 658–660

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Materials Letters

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Preparation of chitosan/PLA blend micro/nanofibers by electrospinning

Jia Xu, Jinhui Zhang, Weiquan Gao, Hongwei Liang, Hongyan Wang, Junfeng Li ⁎College of Chemistry, Jilin University, Changchun, 130012, People's Republic of China

⁎ Corresponding author. Tel.: +86 431 85168470 4; faxE-mail address: jfli@jlu.edu.cn (J. Li).

0167-577X/$ – see front matter © 2008 Elsevier B.V. Aldoi:10.1016/j.matlet.2008.12.014

a b s t r a c t

a r t i c l e i n f o

Article history:

The chitosan/PLA blend m Received 3 February 2008Accepted 11 December 2008Available online 25 December 2008

Keywords:ElectrospinningNanofiberChitosanPLA

icro/nanofibers have been prepared for the first time by electrospinning.Trifluoroacetic acid (TFA) was found to be the co-solvent for electrospinning. The chitosan/PLA blendsolutions in various ratios were studied for electrospinning into micro/nanofibers. The morphology of thefibers was shown by scanning electron microscope (SEM). It was found that the average diameter of thechitosan/PLA blend fibers became larger, and the morphology of the fibers became finer with the content ofPLA increasing. To show the molecular interactions, chitosan/PLA fibers were characterized by Fouriertransform infrared spectroscopy (FTIR). The spun micro/nanofibers are expected to be used in the nativeextracellular matrix for tissue engineering.

© 2008 Elsevier B.V. All rights reserved.

1. Introduction

Electropinning is a simple and low-cost method for manufacturingnanoscale polymer fibers [1]. The micro/nanofibers produced byelectrospinning method have showed amazing characteristics such asvery large surface area-to-volume ratio and high porosity with verysmall pore size [2], so they are used in the biomedical area, includingwound dressings [3], drug delivery [4], tissue engineering scaffolds [5],and so on. For the tissue engineering scaffold, a highly porous micro-structure with interconnected pores and large surface area is conduciveto tissue ingrowth. The collected non-wovenfibersmats justmeet theserequirements. The topology of these electrospun scaffolds closelymimics that of native extracellular matrix (ECM) [6]. Many materials,including natural macromolecule [7,8], synthetic polymer [9,10] andtheir mixture [11], were manufactured into tissue engineering scaffoldby electrospinning. Among these materials, chitosan (poly-1, 4-D-glucosamine), a partially deacetylated derivative from chitin, ischemically similar to glycosaminoglycan (GAG) [12] and has manydesirable properties as tissue engineering scaffolds [13]. Nevertheless,just as other natural macromolecules, chitosan has a poor mechanicalproperty for supporting tissue cells. With the development of syntheticpolymer/natural macromolecule composite material in tissue engineer-ing, the mixing of chitosan and synthetic polymer which has a goodmechanical property can improve the mechanical property. In theprevious report, chitosan-based nanofibers have been successfullyelectrospun from chitosan solutions blended with poly (ethyleneoxide) (PEO) [14], poly (vinyl alcohol) (PVA) [15,16]. PLA was abiocompatible synthetic polymer which was approved by the Foodand Drug Administration for specific human clinical applications, such

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as surgical sutures and some implantabledevices.Most importantly, PLAhas eximious mechanical property [17] and is a perfect material toprepare composite material with chitosan. Many researchers haveinvestigated manufacture of chitosan/PLA composite material byelectrospinning. Peesan et al. [18] had successfully prepared hexanoylchitosan/PLA blend fibers by electrospinning. A fly in the ointment wassacrificing many amino and hydroxyls in chitosan which were veryuseful signal to be identified by cells. Duan et al. [19] had prepared PLGA/chitosan hybrid nanofiber membranes by collecting PLGA nanofibersand chitosan nanofibers on one rotary drum.

In this study, a very convenient method of using a single syringewas introduced for the preparation of chitosan/PLA blend fibers andtrifluoroacetic acidwas the co-solvent. Chitosan and PLAwere blendedin at molecular level, which maintained both of their advantages.

2. Experimental

2.1. Materials

Chitosan (Mw=8000–20,000, Sinopharm Chemical Reagent Co.,Ltd (China)), Poly(L-lactic acid) (PLA, Mw=5000, Changchun Instituteof Applied Chemistry (China)), Trifluoroacetic acid (TFA, TianjinFuchen Chemical Reagents Factory (China)).

2.2. Electrospinning

Different weights of PLA (0.02, 0.09, 0.18, 0.27, 0.36 and 0.72 g)were added into 10 g TFA respectively together with 0.18 g chitosan,the mixtures were stirred for 24 h at room temperature. Then, thespinning solutions with different ratios by weight (chitosan/PLA: 9/1,2/1, 1/1, 1/1.5, 1/2 and 1/4) were prepared. At room temperature, thepolymer solution was placed into a 2 ml glass syringe with the tip ofinner diameter of 1 mm. A clamp connected with high voltage power

Fig. 1. SEM image of the chitosan/PLA blend fibers in different weight ratios. (A) 9/1; (B) 2/1; (C) 1/1; (D) 1/1.5; (E) 1/2; (F) 1/4; (G) 1/20; (H) pure PLA. TEM image (I) of the chitosan/PLA blend fiber in 1/1.5 weight ratio.

Fig. 2. The relationship between PLA content and fiber average diameter.

659J. Xu et al. / Materials Letters 63 (2009) 658–660

supplier (0–30 kV) was attached to the glass syringe. As groundedcollector, a piece of aluminum foil was placed towards the tip at thedistance of 22 cm. The polymer fibers generated from the tip by highvoltage flied to the grounded collector and formed the micro/nanofiber mesh. The apparatus for the electrospinning experimentswas similar to previous report [20].

2.3. Instruments

The morphology of the electrospun fibers were observed under aScanning Electron Microscope (SHIMADZU SSX-550) at an accelerat-ing voltage of 15 kV. FT–IR spectra were recorded on a NicoletInstruments Research series 5PC Fourier Transform Infrared spectro-meter. The transmission electron microscopy (TEM) images wererecorded on a JEM-2000EX microscopy.

3. Results and discussion

3.1. Selection of a solution

It is easy to find a solvent which could dissolve chitosan, such as dilute acid, but thesolution could not be spun into fibers by electrospinning. Concentrated acetic acidsolution could dissolve and electrospin chitosan [21], but it could not dissolve PLA. Sofinding a proper solvent to dissolve both chitosan and PLA became tough work. That'swhy the electrospinning of chitosan/PLA blend has never been reported.

TFAwas a suitable solvent for chitosan electrospinning [22]. Basing on this, we triedto dissolve PLA into TFA, and spun it into fibers for the first time successfully. Thesmooth fibers were obtained between the concentration of 15% and 29% of the solution.Fig. 1 (F) shows the SEM images of typical PLAmicro/nanofibers. It explains that TFA is agood solvent of PLA for electrospinning. So according to this, TFA was selected as co-solvent of chitosan/PLA.

3.2. Electrospinning

For the sake of electrospinning chitosan/PLA, the behavior of chitosan was studiedfirst. It was found that chitosan can be spun into fibers with the concentration from 1.2

to 2.4 wt.%. Comparing with other concentrations, the fibers spun by the solution of1.77 wt.% (0.18 g chitosan, 10 g TFA) were more homogeneous and smooth. So, thiscontent was used in confecting chitosan/PLA blend solution. Fig. 1 (A–F) showed SEMmicrographs of the micro/nanofibers which were spun from the chitosan/PLA solutionswith different content of PLA. It was observed that the fiber diameter distribution ofeach sample was wide. With the increasing content of PLA, the beads were decreasingand the average diameter was increasing (Fig. 2). TEM image (Fig. 1 (I)) showed thatchitosan and PLA were well blended in the fiber. It was also found that some brancheslike Fig. 1 (B) insert image occurred in each samples.

In Previous report, Zhao et al. [23] attributed this phenomenon to the nonuniformdispersion of charges and lowmolecular weight. The nonuniform dispersion of chargescould cause the electrostatic repulsion forces to overcome the surface tension in someareas, and the lower viscosity of the lower molecular weight polymer may allow for thesplit of the jet. Jessica D. Schiffman et al. [24] also gave another possible explanation

Fig. 3. FTIR spectra of chitosan, PLA and chitosan/PLA blend fibers. (A) chitosan (a) and PLA (b); (B) chitosan/PLA blend fibers in different weight ratios. (c) 9/1; (d) 2/1; (e) 1/1; (f) 1/1.5;(g) 1/2; (h) 1/4.

660 J. Xu et al. / Materials Letters 63 (2009) 658–660

that the appearance of branching caused by low percent humidity. In their experiment,the branched fibers were created in the 20–25% humidity range while the nonbranchedfibers were spun when the humidity was twice as high, 40–45% humidity.

In our experiment, both of chitosan (Mw=8000–20,000) and PLA (Mw=5000)were low molecular weight polymer. At the same humidity, the fibers which containedchitosan had branches, but pure PLA fibers (Fig. 1 (H)) had no branching. It may beexplained that different polymers have different limiting values in humidity andmolecular weight for occurring branches.

When the difference between the contents of chitosan and PLA was not very large,the morphology of fibers had the property of chitosan as well as PLA, so the branchedfibers were created. When the content of PLAwas inundatory, the morphology of fiberswas mainly contributed by PLA. Fig. 1 (G) showed SEM micrograph of the chitosan/PLAblend fibers which were spun from 17.4 wt.% (the weight ratio of chitosan and PLA is1:20) blend solution. Obviously, the fibers were homogeneous and smooth without anybranching. It was just the same as pure PLA fibers (Fig. 1 (H)).

3.3. Study of Fourier transform infrared spectroscopy

Fig. 3 (A) displays the Fourier transform infrared spectroscopy (FTIR) spectra of theelectrospun pure chitosan and pure PLA fibers. Chitosan fibers displayed characteristicabsorption bands at 1680 and 1540 cm−1 which represent the amide I and IIcharacteristic absorption bands respectively. A weak peak at 1324 cm−1 is the amideIII characteristic absorption band as shown in Fig. 3 A (a).

The FTIR spectrum of PLA fibers (Fig. 3 A (b)) depicted characteristic absorptionbands at 1759, 1185, 1130 and 1089 cm−1, which represent the backbone ester group ofPLA.

Fig. 3 (B) displays the FTIR spectra of the electrospun chitosan/PLA blend fibers withdifferent ratios. Obviously, with the increase of PLA, the relative strength of peak at1759 cm−1 which belongs to carbonyl group in PLA was increased, and the relativestrength of peak at 1680 cm−1 which represent the amide I absorption band of chitosanwas decreased.

The peaks position of these spectra almost didn't change. It may be explained thatthe molecular interaction between chitosan and PLA was weak because PLA does nothave enough −OH groups to form hydrogen bonds with −OH groups and −NH2 groupsin chitosan.

4. Conclusion

In this study, we succeeded for the first time in preparing chitosan/PLA blended fibers by an electrospinning technique. We find thattrifluoroacetic acid is a suitable solvent for the electrospinning of

chitosan/PLA blended fibers.With the increasing of content of PLA, thebeads gradually disappeared and the morphology of fibers becamefiner. The result of FTIR indicated that the molecular interactionbetween chitosan and PLA was weak. It was assumed that theproduction would have a great potential application in the tissueengineering.

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