nanofibers by electrospinning

nanofibers by electrospinning

Materials Letters 63 (2009) 658–660 Contents lists available at ScienceDirect Materials Letters j o u r n a l h o m e p a g e : w w w. e l s e v i e...

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Materials Letters 63 (2009) 658–660

Contents lists available at ScienceDirect

Materials Letters j o u r n a l h o m e p a g e : w w w. e l s e v i e r. c o m / l o c a t e / m a t l e t

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

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Article history: Received 3 February 2008 Accepted 11 December 2008 Available online 25 December 2008 Keywords: Electrospinning Nanofiber Chitosan PLA

a b s t r a c t The chitosan/PLA blend micro/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 blend solutions in various ratios were studied for electrospinning into micro/nanofibers. The morphology of the fibers was shown by scanning electron microscope (SEM). It was found that the average diameter of the chitosan/PLA blend fibers became larger, and the morphology of the fibers became finer with the content of PLA increasing. To show the molecular interactions, chitosan/PLA fibers were characterized by Fourier transform infrared spectroscopy (FTIR). The spun micro/nanofibers are expected to be used in the native extracellular matrix for tissue engineering. © 2008 Elsevier B.V. All rights reserved.

1. Introduction Electropinning is a simple and low-cost method for manufacturing nanoscale polymer fibers [1]. The micro/nanofibers produced by electrospinning method have showed amazing characteristics such as very large surface area-to-volume ratio and high porosity with very small pore size [2], so they are used in the biomedical area, including wound dressings [3], drug delivery [4], tissue engineering scaffolds [5], and so on. For the tissue engineering scaffold, a highly porous microstructure with interconnected pores and large surface area is conducive to tissue ingrowth. The collected non-woven fibers mats just meet these requirements. The topology of these electrospun scaffolds closely mimics that of native extracellular matrix (ECM) [6]. Many materials, including natural macromolecule [7,8], synthetic polymer [9,10] and their mixture [11], were manufactured into tissue engineering scaffold by electrospinning. Among these materials, chitosan (poly-1, 4-Dglucosamine), a partially deacetylated derivative from chitin, is chemically similar to glycosaminoglycan (GAG) [12] and has many desirable properties as tissue engineering scaffolds [13]. Nevertheless, just as other natural macromolecules, chitosan has a poor mechanical property for supporting tissue cells. With the development of synthetic polymer/natural macromolecule composite material in tissue engineering, the mixing of chitosan and synthetic polymer which has a good mechanical property can improve the mechanical property. In the previous report, chitosan-based nanofibers have been successfully electrospun from chitosan solutions blended with poly (ethylene oxide) (PEO) [14], poly (vinyl alcohol) (PVA) [15,16]. PLA was a biocompatible synthetic polymer which was approved by the Food and Drug Administration for specific human clinical applications, such

⁎ Corresponding author. Tel.: +86 431 85168470 4; fax: +86 431 85168420. E-mail address: jfl[email protected] (J. Li). 0167-577X/$ – see front matter © 2008 Elsevier B.V. All rights reserved. doi:10.1016/j.matlet.2008.12.014

as surgical sutures and some implantable devices. Most importantly, PLA has eximious mechanical property [17] and is a perfect material to prepare composite material with chitosan. Many researchers have investigated manufacture of chitosan/PLA composite material by electrospinning. Peesan et al. [18] had successfully prepared hexanoyl chitosan/PLA blend fibers by electrospinning. A fly in the ointment was sacrificing many amino and hydroxyls in chitosan which were very useful signal to be identified by cells. Duan et al. [19] had prepared PLGA/ chitosan hybrid nanofiber membranes by collecting PLGA nanofibers and chitosan nanofibers on one rotary drum. In this study, a very convenient method of using a single syringe was introduced for the preparation of chitosan/PLA blend fibers and trifluoroacetic acid was the co-solvent. Chitosan and PLA were blended in 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 Institute of Applied Chemistry (China)), Trifluoroacetic acid (TFA, Tianjin Fuchen 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, the spinning 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, the polymer solution was placed into a 2 ml glass syringe with the tip of inner diameter of 1 mm. A clamp connected with high voltage power

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

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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.

supplier (0–30 kV) was attached to the glass syringe. As grounded collector, a piece of aluminum foil was placed towards the tip at the distance of 22 cm. The polymer fibers generated from the tip by high voltage flied to the grounded collector and formed the micro/ nanofiber mesh. The apparatus for the electrospinning experiments was similar to previous report [20]. 2.3. Instruments The morphology of the electrospun fibers were observed under a Scanning Electron Microscope (SHIMADZU SSX-550) at an accelerating voltage of 15 kV. FT–IR spectra were recorded on a Nicolet Instruments Research series 5PC Fourier Transform Infrared spectrometer. The transmission electron microscopy (TEM) images were recorded on a JEM-2000EX microscopy.

to 2.4 wt.%. Comparing with other concentrations, the fibers spun by the solution of 1.77 wt.% (0.18 g chitosan, 10 g TFA) were more homogeneous and smooth. So, this content was used in confecting chitosan/PLA blend solution. Fig. 1 (A–F) showed SEM micrographs of the micro/nanofibers which were spun from the chitosan/PLA solutions with different content of PLA. It was observed that the fiber diameter distribution of each sample was wide. With the increasing content of PLA, the beads were decreasing and the average diameter was increasing (Fig. 2). TEM image (Fig. 1 (I)) showed that chitosan and PLA were well blended in the fiber. It was also found that some branches like Fig. 1 (B) insert image occurred in each samples. In Previous report, Zhao et al. [23] attributed this phenomenon to the nonuniform dispersion of charges and low molecular weight. The nonuniform dispersion of charges could cause the electrostatic repulsion forces to overcome the surface tension in some areas, and the lower viscosity of the lower molecular weight polymer may allow for the split of the jet. Jessica D. Schiffman et al. [24] also gave another possible explanation

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 the solution could not be spun into fibers by electrospinning. Concentrated acetic acid solution could dissolve and electrospin chitosan [21], but it could not dissolve PLA. So finding a proper solvent to dissolve both chitosan and PLA became tough work. That's why the electrospinning of chitosan/PLA blend has never been reported. TFA was a suitable solvent for chitosan electrospinning [22]. Basing on this, we tried to dissolve PLA into TFA, and spun it into fibers for the first time successfully. The smooth fibers were obtained between the concentration of 15% and 29% of the solution. Fig. 1 (F) shows the SEM images of typical PLA micro/nanofibers. It explains that TFA is a good solvent of PLA for electrospinning. So according to this, TFA was selected as cosolvent of chitosan/PLA. 3.2. Electrospinning For the sake of electrospinning chitosan/PLA, the behavior of chitosan was studied first. It was found that chitosan can be spun into fibers with the concentration from 1.2

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

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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.

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 nonbranched fibers 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 contained chitosan had branches, but pure PLA fibers (Fig. 1 (H)) had no branching. It may be explained that different polymers have different limiting values in humidity and molecular 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 branched fibers were created. When the content of PLA was inundatory, the morphology of fibers was mainly contributed by PLA. Fig. 1 (G) showed SEM micrograph of the chitosan/PLA blend fibers which were spun from 17.4 wt.% (the weight ratio of chitosan and PLA is 1:20) blend solution. Obviously, the fibers were homogeneous and smooth without any branching. 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 the electrospun pure chitosan and pure PLA fibers. Chitosan fibers displayed characteristic absorption bands at 1680 and 1540 cm− 1 which represent the amide I and II characteristic absorption bands respectively. A weak peak at 1324 cm− 1 is the amide III characteristic absorption band as shown in Fig. 3 A (a). The FTIR spectrum of PLA fibers (Fig. 3 A (b)) depicted characteristic absorption bands at 1759, 1185, 1130 and 1089 cm− 1, which represent the backbone ester group of PLA. Fig. 3 (B) displays the FTIR spectra of the electrospun chitosan/PLA blend fibers with different ratios. Obviously, with the increase of PLA, the relative strength of peak at 1759 cm− 1 which belongs to carbonyl group in PLA was increased, and the relative strength of peak at 1680 cm− 1 which represent the amide I absorption band of chitosan was decreased. The peaks position of these spectra almost didn't change. It may be explained that the molecular interaction between chitosan and PLA was weak because PLA does not have enough −OH groups to form hydrogen bonds with −OH groups and −NH2 groups in chitosan.

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

chitosan/PLA blended fibers. With the increasing of content of PLA, the beads gradually disappeared and the morphology of fibers became finer. The result of FTIR indicated that the molecular interaction between chitosan and PLA was weak. It was assumed that the production would have a great potential application in the tissue engineering. References [1] [2] [3] [4]

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