Poster sasithorn nongnut

The International Istanbul Textile Congress 2013 May 30th to June 1th 2013, Istanbul, Turkey

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PREPARATION OF SILK FIBROIN ELECTROSPUN FIBRES VIA NEEDLELESS ELECTROSPINNING

Nongnut Sasithorn1 and Lenka Martinová2

1Technical University of Liberec, Faculty of Textile Engineering, Department of Nonwovens,

Studentská 2 Liberec 46117 Czech Republic 2Technical University of Liberec, Institute for Nanomaterials, Advanced Technology and Innovation

Studentská 1402/2 Liberec 46117 Czech Republic Corresponding author [email protected]

Abstract:

Electrospinning is a simple method capable of producing nanofibres for biomedical applications. Silk fibroin is one of the candidate materials for biomedical application because it has good biocompatibility and minimal inflammatory reaction. This study was focused on the preparation of regenerated silk fibroin fibres from Bombyx mori silk with a needleless electrospinning technique. The effects of spinning parameters (e.g., spinning solution concentration, viscosity and surface tension) and morphology of obtained silk fibroin fibres were studied. A variety of concentrations of silk fibroin in a mixture of formic acid and calcium chloride were successfully electrospun with a roller electrospinning. It was observed that concentration of spinning solution played an important role in spinning ability of silk fibroin solution and the diameter of obtained fibres. Average diameter of electrospun fibres were increased by increasing the silk fibroin concentration. The silk electrospun fibres had diameters ranging from 200 to 5600 nm.

Keywords: silk fibroin, electrospun fibres, needleless electrospinning 1. Introduction

Silk fibroin is the protein that forms filaments of silkworm and gives high mechanical strength, elasticity and softness. In addition to the outstanding mechanical properties, silk fibroin is a candidate material for biomedical application because it has a good biological compatibility, good oxygen and water vapour permeability, biodegradability and minimal inflammatory reaction. Silk fibroin can be used in surgery as implant material as well as for tissue engineering applications in the form of non-woven membranes and fibres or in the form of woven membranes and fibres. It has been demonstrated that silk fibroin-derived scaffolds may have a wide range of applications in the fabrication of replacement tissue [1, 2]. In recent years, polymer nanofibres have gained considerable attention as promising materials with many possible areas of application, due to their unique properties such as a high specific surface area, small pore diameters, high surface to weight ratio, and good barrier characteristics against microorganisms [3, 4]. They can be used as filters, wound dressings and tissue engineering scaffolds. There are several methods to produce fibres at a nanoscale, electrospinning is one of these methods that have gained much attention because it is an effective method to manufacture ultrafine fibres or fibrous structures from both synthetic and natural polymers with diameter in the range from several micrometres down to tens of nanometres [5].

Electrospinning technology can be divided into two branches as needle electrospinning and needleless electrospinning. Needle electrospinning is based on less productive needle/capillary spinners with a low production rate. Needleless electrospinning technologies are based on highly productive jet creation from free liquid surfaces by self-organization. For example, roller electrospinning, known under the name NanospiderTM was developed by Jirsak et al (Jirsak et al., 2005). In the needleless electrospinning device contains a roller spinning electrode partially immersed in the reservoir with a polymer solution and slowly rotates, the polymer solution was loaded onto the upper roller surface. Upon applying a high voltage to the electrospinning system, many Taylor cones are simultaneously formed on the surface of the rotating spinning electrode, which makes the technology highly productive and makes the process industrially interesting [6,7].

In this work focused on preparation electrospun fibres from Bombyx mori silk with roller electrospinning technique. The experiment intensively concentrated on the effects of concentration of silk solution and applied voltage on spinning ability and fibre morphology.

The International Istanbul Textile Congress 2013 May 30th to June 1th 2013, Istanbul, Turkey

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2. Experiment

2.1 Materials

The raw silk cocoon used in this experiment was Bombyx mori Linn. (Nang-Noi Srisakate 1) from Amphoe Mueang Chan, Si Sa Ket Province, Thailand. AATCC 1993 Standard Reference Detergent (Atlas Material Testing Technology, USA) was used as soaping agent for degumming process. Calcium chloride (Fluka AG, Switzerland) and 98% formic acid (Penta, Czech Republic) were used as the solvent for spinning solution preparation

2.2 Preparation of spinning solutions

Raw silk cocoons were degummed twice with 1% sodium carbonate and 0.5% soaping agent at 100 OC for 30 minutes (the ratio of raw silk cocoon over degumming solution was 1:30), then rinsed with warm water in order to remove the sericin from the surface of the fibre and then dried at room temperature. Silk solutions were prepared by dissolving the silk fibroin (SF) in a mixture of 98% formic acid and calcium chloride. The silk fibroin concentration was varied from 8, 10, 12, 14 and 16 wt%. All the solutions were mixed by magnetic stirring at room temperature for 20 hours. Conductivity and surface tension of the solutions were measured by CON 510 Bench Conductivity/TDS Meter and a tensiometer (Krüss K9) at room temperature. The rheological measurements of the solution were performed on a HAKKE RotoVisco RV1.

2.3 Electrospinning process

A schematic representation of the equipment used in the experiment is illustrated in Figure 1. A high voltage in the range of 20 kV to 50 kV was applied to the spinning solution. The electrospun fibres were collected on a collector which was placed at a distance of 10 centimetres from the roller spinning electrode with 8.5 centimetres in length and 1.8 centimetres in diameter. Electrospinning was carried out at the temperature 221 OC and relative humidity was 402%. The morphological appearance of the electrospun fibres was observed by a scanning electron microscope (SEM, Phenom FEI). Fibre diameter was determined by using NIS-Elements AR software. About 100 randomly selected fibres were used to determine the average fibre diameter and their distribution.

Figure 1. Schematic of a roller electrospinning experiment

3. Results and Discussion

3.1 Effect of silk fibroin concentration on morphology of electrospun fibres

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In electrospinning process, various properties of solution (e.g. conductivity, surface tension, viscosity) play an important role in the morphology of the obtained electrospun fibres. The conductivity, surface tension and rheological properties of spinning solutions at various concentration are shown in Table 1 and Figure 2, respectively. The results show that the variation of silk fibroin concentration had a less significant effect on the surface tension, but produces an influence on viscosity and conductivity of the spinning solutions. All of silk fibroin solution can be spun into fibres sheet with roller electrospinning.

Figure 3 shows scanning electron micrographs of electrospun fibre from a silk fibroin solution at the 45 kV electric field. It was found that an increase in the concentration of silk solution produces a significant effect on the average fibre diameter and the uniform fibre diameter distribution of the obtained electrospun fibre (as shown in Table 2 and Figure 4). It was noticed that the average fibre diameter and the non-uniform fibre diameter distribution increased with increasing concentration of silk solutions. It is possible that an increased in the concentration of silk solution will result in greater polymer chains entanglement in the solution. During electrospinning, there may be multiple jet formations from the main electrospinning jet, which is stable enough to yield fibres of smaller diameter would provide non-uniform fibre distribution and broad fibre diameter distribution. [9]

Table 1. Conductivity and surface tension of silk fibroin solution at various concentrations

Silk fibroin concentration (%wt) Conductivity (mS/cm) Surface tension (mN/m)

SF 08 5.67 36.3

SF 10 6.33 36.9

SF 12 8.14 37.4

SF 14 9.65 38.5

SF 16 11.04 39.1

Figure 2. Rheological behaviour of silk fibroin solution at various concentrations

Table 2. Effect of concentrations of silk fibroin solution on average fibre diameter of silk electrospun fibres

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Silk fibroin concentration (%wt)

Average fibre diameter (nm) S.D. Minimum

(nm) Maximum

(nm)

SF 08 330 70 215 525

SF 10 565 110 335 857

SF 12 660 142 392 1135

SF 14 1425 400 752 2534

SF 16 3310 872 1206 5640

Figure 3. SEM micrograph of silk electrospun fibres prepared from silk fibroin solution at various concentrations by a) 8 wt%; b) 10 wt%; c) 12 wt%; d) 14 wt%; e) 16 wt%

c b a

d e

c b a

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Figure 4. Histogram of silk electrospun fibres prepared from silk fibroin solution at various concentrations by a) 8 wt%; b) 10 wt%; c) 12 wt%; d) 14 wt%; e) 16 wt%

3.2 Effect of applied voltage on morphology of electrospun fibres

In needleless electrospinning, a higher electric voltage is usually required to initiate the spinning process because Taylor cone is formed due to the wave fluctuation. A high voltage is used to create an electrically charged jet of a polymer solution [7]. In order to study the effect of the electric field on spinning ability with roller electrospinning and morphology of obtained fibre, a silk solution with the concentration of 8 wt% was electrospun with a voltage between 20 kV and 50 kV. Scanning electron micrograph at different applied voltages is shown in Figure 5. It was found that an applied voltage higher than 30 kV was successful in roller electrospinning. The results show that the variation of applied electric fields had a less significant effect on the average fibre diameter, but produces an influence on the uniform fibre distribution of the obtained nonwoven sheet. It was found that an increase in the applied voltage produces a less significant decrease in the average fibre diameter and the uniform fibre diameter distribution of the obtained electrospun fibre. It is suggested that a higher voltage will lead to greater stretching of the solution due to the greater columbic forces in the jet as well as the stronger electric field. These have the effect of reducing the diameter of the fibres [9,10].

Figure 5. SEM micrograph of silk electrospun fibres prepared from roller electrospinning of silk fibroin

d e

b a

d c

The International Istanbul Textile Congress 2013 May 30th to June 1th 2013, Istanbul, Turkey

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at different applied voltage by a) 35 kV; b) 40 kV; c) 45 kV; d) 50 kV

Table 3. Effect of applied voltage on average fibre diameter of silk electrospun fibres

Applied voltage (kV)

Average fiber diameter (nm) S.D. Minimum

(nm) Maximum

(nm)

35 460 73 236 571

40 425 69 260 555

45 375 67 240 535

50 335 67 168 508

4. Conclusion

The solutions of silk fibroin in a mixture of formic acid and calcium chloride were electrospun into fibre sheet by a roller electrospinning technique. Effects of concentration of silk fibroin solution and the voltage of electric field on fibre morphology were studied. All of silk fibroin solution can be spun by roller electrospinning. Concentration of silk fibroin solution played an important role on the diameter of the obtained fibres and uniform fibre diameter distribution. An increase of silk fibroin concentration leads to an increase in fibre diameter ranging from 200 to 5600 nm. Concentrations of silk fibroin in the range of 10 wt% to 12 wt% seem to be a suitable concentration for preparation of nanofibre sheet with roller electrospinning. The results show that this could be a new technique for an improvement of production rate of silk nanofibres. 5. Acknowledgements

This work was supported by the Technical University of Liberec, Faculty of Textile Engineering and Institute for Nanomaterials, Advanced Technology and Innovation. 6. References [1] Veparia, C.; Kaplana D.L.: Silk as a biomaterial, Progress in Polymer Science, Vol. 32 (2007) pp. 991 -

100. [2] Amiraliana, N.; Nouri, M.; Kishb, M.H.: An Experimental study on Electrospinning of silk fibroin,

http://www.docstoc.com/docs/26292086. Accessed: 2011-05-02. [3] Nerem R.M.; Sambanis A.: From Biology to Biological Substitutes, Tissue Engineering, Vol. 1 (2007),

pp. 3 - 13. [4] Stankus J.J.; Soletti L.; Fujimoto K.: Fabrication of Cell Microintegrated Blood Vessel Constructs

Through Electrohydrodynamic Atomization, Biomaterials, Vol. 28 (2007), pp. 2738 - 2746. [5] Amiraliana, N.; Nouri, M.; Kishb, M.H.: Effects of Some Electrospinning Parameters on Morphology of

Natural Silk-Based Nanofibers, Journal of Applied Polymer Science, Vol. 113 (2009) pp. 226 - 234. [6] Lukáš, D.; Sarkar A.; Martinová, L.; Vodsedálková, K.; Lubasová, D.; Chaloupek, J.; Pokorný, P.; Mikeš,

P.; Chvojka, J. & Komárek M.: Physical principles of electrospinning (Electrospinning as a nano-scale technology of the twenty-first century), Textile Progress, Vol. 41 (2009) Issue 2 pp. pages 59-140.

[7] Niu, H.; Wang, X. Lin, T.: Needleless Electrospinning : Developments and Performances, http://cdn.intechopen.com/pdfs/23290/InTech-Needleless_electrospinning_developments_and_

performances.pdf. Accessed: 2012-05-16. [8] Armato,U.;, Pra, I.D.; Migliaresi, C.; Motta, A,; Kesenci, K.: Method for the Preparation of a Non-Woven

Silk Fibroin Fabrics. US Patent 7285637, October 23, 2007 [9] Ramakrishna, S.; Fujihara, K.; Teo, W.E.; Lim, T.C.; Ma Z.: An Introduction to Electrospinning and

Nanofibers, ISBN 981-256-415-2, World Scientific Publishing Co. Pte. Ltd., Singapore. [10] Andrady, A.L.: Science and Technology of Polymer Nanofibers, John Wiley & Sons, Inc., ISBN 978-0-

471-79059-4, the United States of America (2008).