- Email: [email protected]
Electrospun nano-fiber mats containing cationic cellulose derivatives and poly (vinyl alcohol) with antibacterial activity
Carbohydrate Research 346 (2011) 1337–1341
Contents lists available at ScienceDirect
Carbohydrate Research journal homepage: www.elsevier.com/locate/carres
Note
Electrospun nano-fiber mats containing cationic cellulose derivatives and poly (vinyl alcohol) with antibacterial activity Baoquan Jia, Jinping Zhou ⇑, Lina Zhang Department of Chemistry, Wuhan University, Wuhan 430072, China
i n f o
Article history: Received 5 March 2011 Received in revised form 24 April 2011 Accepted 27 April 2011 Available online 3 May 2011 Keywords: Electrospinning Cationic cellulose derivatives Polyvinyl alcohol Antibacterial activity
a b s t r a c t Nano-fibrous mats have been successfully prepared by electrospinning of the blend solutions of cationic cellulose derivatives (PQ-4) and polyvinyl alcohol (PVA). Effects of the blending ratio and applied voltage on the morphology and diameter of the electrospun nano-fibers were investigated. The average diameter of the PQ-4/PVA blend fibers was in the range of 150–250 nm. The electrospinning process became instable and the fiber diameter distribution broadened with increasing PQ-4 content and applied voltage. The antibacterial activity of electrospun PQ-4/PVA blend mats against Gram-negative bacteria Escherichia coli and Gram-positive bacteria Staphylococcus aureus indicated potential for biomedical use. Ó 2011 Elsevier Ltd. All rights reserved.
nium groups, PQ-4 shows a natural attraction for some components of the skin and the hair, and particularly has applications in cosmetics and topical drug delivery devices.4,23 In the present work, nano-fibrous mats were prepared by electrospinning of the blend solutions of PQ-4 and PVA, and the morphology and antibacterial activities of the electrospun mats were investigated. Different blending ratios play a major role in the solution properties such as viscosity and conductivity, which are very important in the process of electrospinning. Figure 1 shows the dependence of the viscosity and conductivity of PQ-4/PVA blend solutions on the PQ-4 content, and the data are summarized in Table 1. The viscosity and conductivity for 7 wt % PVA and PQ-4 solutions are 5000
12 Viscosity (cP) Conductivity (ms/cm)
4000
10 8
3000 6 2000 4 1000
Conductivity (ms/cm)
Cationic cellulose derivatives are large-scale commercial products, which have many useful characteristics, such as hydrophilicity, biodegradability, and antibacterial properties.1–3 They have been found to have numerous applications in a variety of fields including paper and textile, food, cosmetics, chemical, and pharmaceutical industries.4–7 Recently, cationic cellulose ethers containing quaternary ammonium groups are mostly studied among the cationic cellulose derivatives. Apart from industrial applications, they could be used in biomedical fields, for example, as DNA carriers, in gene transfections, as protein carriers and in drug deliveries.3,8–12 Owing to the antibacterial property and hydrophilicity, they are promising candidates for wound-dressing application.13 Electrospinning is an effective and straightforward method of preparing continuous ultrafine fibers and fibrous materials.14,15 Electrospun mats have large surface area and small pore size, which are favorable for the wound-dressing application.15 However, cationic cellulose derivatives are hardly able to be electrospun for the poor flexibility of polyelectrolyte chains.16 Polyvinyl alcohol (PVA) is a nontoxic, hydrophilic, biocompatible, and flexible synthetic polymer; it has been used as an important electrospinning auxiliary for those water-soluble but hard-electrospun materials.17–19 For example, nano-fibrous mats were successfully obtained by electrospinning of quaternized chitosan and PVA blend solutions.17–22 Polyquaternium-4 cellulose (PQ-4) is the hydroxyethyl cellulose diallyl dimethyl ammonium chloride copolymer, and the chemical structure is shown as Scheme 1.1 Owing to its quaternary ammo-
Viscosity (cP)
a r t i c l e
2
0 0
20
40
60
80
0 100
PQ-4 (wt%)
⇑ Corresponding author. Tel.: +86 27 87219274; fax: +86 27 68754067. E-mail address: [email protected] (J. Zhou). 0008-6215/$ - see front matter Ó 2011 Elsevier Ltd. All rights reserved. doi:10.1016/j.carres.2011.04.040
Figure 1. Viscosity and conductivity of PQ-4/PVA blend solutions. The total polymer concentrations are 7 wt %.
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185.1 cP and 1.10 ms/cm, 4722.8 cP and 10.32 ms/cm, respectively. Both the viscosity and conductivity of the blending solutions increase with the increase of PQ-4 content. Because of the poor flexibility of polyelectrolyte chains and high viscosity and charges of the solutions, pure PQ-4 solutions of 2–8 wt % were not capable of being electrospun. Therefore, PVA was selected to mix with PQ-4 for the electrospinning of PQ-4/PVA blend nano-fibers. Figure 2 shows the FT-IR spectra of the electrospun mats of PVA, PQ-4/PVA blends (weight ratios of 1:3 and 1:1), and the PQ-4 powder. Both PVA and PQ-4 showed a broadband at 3400 cm 1, which belongs to stretching vibration modes of O–H groups. The spectra of PQ-4/PVA showed characteristic bands of hydroxyethyl cellulose and quaternary ammonium groups. The band at 1129 cm 1 in Figure 2d was assigned to the stretching vibration of C–O–C groups of the cellulose backbone, and the band at 893 cm 1 indicated the blinked glucose of cellulose. The bands at 1474 and 1416 cm 1 (Fig. 2d) corresponded to the methyl groups and methylene groups next to ammonium and C–N stretching vibration on the quaternary ammonium groups.17,24,25 In Figure 2b and c, the characteristic bands of both PVA and PQ-4 were observed in the spectra of PQ4/PVA blend mats. According to Table 1, electrospinning of the PQ-4/PVA blend solutions was carried out, and continuous cylindrical fibers were obtained in the experiments. The impact of blending ratio and applied voltage on the morphology of the electrospun fibers was investigated. The morphology of the electrospun fibers was observed by scanning electron microscopy (SEM). The average diameter and diameter distribution were calculated by counting 100 random fibers, and the data were summarized in Table 1. Figure 3 shows the SEM images and diameter statistics of the electrospun fibers for PQ-4/PVA blends with the weight ratio of 1:3, 1:2, and 1:1, respectively. The average diameters of the blend fibers were in the range of 150–250 nm. The impact of blending ratio on the average Table 1 Composition of PQ-4/PVA blends, shear viscosity, and conductivity of the solutions, applied voltage, average fiber diameter, and standard deviation PQ-4/PVA (w/w)
Viscosity (cP)
Conductivity (ms/cm)
Applied voltage (kV)
Average diameter (nm)
Standard deviation
15 18 20 15 18 20 15 18 20
217 206 202 246 208 157 211 249 230
54 38 49 56 46 66 60 79 71
1:3
383.1
3.06
1:2
525.3
3.56
1:1
1046.3
5.31
Spinning distance is 15 cm and total concentration is 7wt %.
O
(CH 2CH 2O) nH OH O
HO
HO
O
O O OH O N
(CH 2CH 2O) nH
3
N Scheme 1. Chemical structure of polyquaternium-4 cellulose (PQ-4).
a
b c d
1474 4000
3500
3000
2500
2000
1416 1500
1129 1000
500
Wavenumber (cm-1) Figure 2. FT-IR spectra of the electrospun fibers of (a) PVA, PQ-4/PVA blends with weight ratios of (b) 1:3 and (c) 1:1, and (d) the PQ-4 powders.
diameter of fibers was not clear, and this might be due to the influence of both viscosity and repulsive force of quaternary ammonium groups. Higher viscosity led to larger fiber diameter,26 while the repulsive force stretched the fiber. According to the standard deviations summarized in Table 1, with the content of PQ-4 increasing, the fiber diameter distributed more widely and thinner fibers could be found according to histogram of Figure 3d and e. It indicated that the spinning process became more instable as the content of PQ-4 increased. How the PQ-4 content affected the average diameter was obscure, which could be attributed to the competitive relation of the viscosity and ionization level of the solutions. The effect of applied voltage on the morphology is not so regular. Fennessey and Farris27 reported that the diameter of electrospun fibers decreased with increasing of the applied voltage, while Reneker and Chun28 found no significant relation between the change of applied voltage and diameter. To find out how applied voltage works in this situation, different voltages 15, 18, and 20 kV were applied. Figure 4 shows the SEM images and diameter distributions of the electrospun fibers of PQ-4/PVA (weight ratio of 1:2) blend solution under 15, 18, and 20 kV, respectively. It was found that the applied voltage played an important role in the fiber diameter and its distribution. At 15 and 18 kV, the diameter distribution was relatively centralized, but at 20 kV, the diameter distribution broadened. In the case of PQ-4/PVA = 1:1, this disturbance became more obvious. More widely scattered diameters were observed in SEM images (Fig. 3e). Though more fibers with the diameter less than 100 nm were observed, the comparatively thick fibers made the average value much higher. The increasing applied potential widened the diameter distribution. This could be explained by the instability and disturbance of the electrospinning process at high applied field strength. However, the fiber diameter did not decrease or increase regularly with the increasing applied voltage. Agar plate method was used to evaluate the antibacterial activity against Escherichia coli (E. coli) and Staphylococcus aureus (S. aureus) of PQ-4/PVA (weight ratio of 1:1) and PVA electrospun mats and the results are shown in Figure 5. It was found that the electronspun PQ-4/PVA blend mats showed effective antibacterial activities against E. coli (Fig. 5a) and S. aureus (Fig. 5c). However, the pure PVA electronspun mats did not possess the ability of antibacteria, and the bacterium spread onto the PVA mats (Fig. 5b and d). Quaternary ammonium groups on the PQ-4 strand took charge of antibacterial performance. The cationic groups damaged structural organization and integrity of the cytoplasmic membrane,
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a
b
30
Frequency
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500
Diameter (nm) 35
c
d
30
Frequency
25 20 15 10 5 0 0
100
200
300
400
500
Diameter (nm) 35
e
f
30
Frequency
25 20 15 10 5 0 0
100
200
300
400
500
Diameter (nm)
Figure 3. SEM images and diameter statistics of the electrospun fibers for PQ-4/PVA blends with the weight ratio of 1:3 (a and b), 1:2 (c and d) and 1:1 (e and f). Applied voltage is 20 kV, spinning distance is 15 cm and the total polymer concentration is 7 wt %.
which caused cell leakage of intracellular material and finally cellular death.29 The antibacterial activity of PQ-4 and the high hydrophilicity of PVA and PQ-4 make the electrospun PQ-4/PVA blend mats potential material for wound dressings. In summary, nano-fibrous mats of PQ-4/PVA blends with the fiber average diameter ranging from 100 to 250 nm were obtained by electrospinning. PQ-4/PVA blend solutions with the weight ratio of 1:3 and 1:2 could be electrospun steadily at low field strength and the obtained fibers were relatively uniform. The electrospinning process became more instable with increasing PQ-4 content. The high applied voltage (20 kV) widened the diameter distribution dramatically. The electrospun PQ-4/PVA nano-fiber mats showed effective antibacterial activities against E. coli and S. aureus. And this indicates that the electrospun PVA/QC mats are potential materials for biomedical applications.
(Guangzhou, China), and the nitrogen content is 1.5–2.3%. PVA (DP = 1750 ± 50, degree of deacetylation 98%) with purity of analytical grade was purchased from Sinopharm Chemical Reagent Co., Ltd. (Shanghai, China). All the reagents were used without further purification. 1.2. Preparation of the spinning solutions PQ-4 was dissolved in distilled water at room temperature, and the clear solutions with concentrations of 2, 4, 7, and 8 wt % were obtained. PVA dispersed in distilled water, and then stirred at 90 °C for an hour to obtain 7 wt % and 10 wt % aqueous solutions, respectively. PQ-4 and PVA powders with the weight ratio of 1:3, 1:2 and 1:1 were dispersed in distilled water, and then stirred at 90 °C for an hour to obtain blend solutions; the total polymer concentrations were adjusted to 7 wt %.
1. Experimental 1.3. Electrospinning of the solutions 1.1. Materials Polyquaternium-4 cellulose (PQ-4) with purity of cosmetic grade was provided by Tinci Materials Technology Co., Ltd.
A conventional electrospinning setup was used in this work. About 3 mL of solution was first put into a 5 mL syringe and a stainless steel needle was fixed onto the syringe. The inner diame-
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B. Jia et al. / Carbohydrate Research 346 (2011) 1337–1341 35
a
b
30
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25 20 15 10 5 0 0
100
200
300
400
500
Diameter (nm) 35
c
d
30
Frequency
25 20 15 10 5 0 0
100
200
300
400
500
Diameter (nm) 35
e
f
30
Frequency
25 20 15 10 5 0 0
100
200
300
400
500
Diameter (nm)
Figure 4. SEM images and diameter statistics of the electrospun fiber of PQ-4/PVA blends (weight ratio of 1:2) under 15 kV (a and b), 18 kV (c and d) and 20 kV (e and f). Spinning distance is 15 cm and the total polymer concentration is 7 wt %.
ter of the orifice is 0.9 mm. The positive electrode of a high-voltage supply (Dongwen High Voltage Power Supply, China) with a DC supply range of 0–30 kV was connected to the needle and the applied electrical potential was 15, 18, and 20 kV. An aluminium foil was fixed onto the surface of a square board and earthed with a wire. The gap distance between the needle tip and the aluminium foil was 15 cm. A precision pump (Longer Precision Pump Co., Ltd., China) was used to give exact volume of the solutions, and the output of the solutions was set in the range of 0.4–0.7 mL/h. The applied potential was 15, 18, and 20 kV, respectively. PVA solution (10 wt %) was electrospun under the voltage of 19 kV. The other process parameters were all the same with the above. The experiments were carried out at normal laboratory conditions. 1.4. Characterization FT-IR spectra of the samples were performed with a Nicolet 170SX Fourier-transform infrared spectrometer. The test specimens were prepared by the KBr disk techniques. Shear viscosities of the spinning fluids were tested by ARES RFSIII rheometer with couttee cups (TA Instruments, USA) at the shear rate of 0.125 s 1
at 20 °C. The conductivity of each solution was measured by electric conductivity meter (Rex Instrument Factory, China). SEM images of the electrospun fibers were performed on a Sirion 200 field emission scanning electron microscope (FEI Co., Eindhoven, The Netherlands) at an accelerating voltage of 15 kV. The surfaces of the fibers were sputtered with gold for SEM measurement. 1.5. Testing of antibacterial activity The antibacterial property against (E. coli) and (S. aureus) of electrospun PVA and PQ-4/PVA mats were tested by agar plate method. Samples were first punched into wafers and these wafers were treated with ultraviolet radiation for half an hour. Culture medium (1000 mL) was prepared by mixing 3 g beef extract, 10 g peptone, 5 g NaCl, 16 g agar, and distilled water. After the activation, bacteria were inoculated and cultured in nutrient agar plate at 37 °C. The bacterial suspensions were prepared with physiological saline at a concentration of 105 cm 1. 50 lL of each bacterial suspension was measured and evenly spread onto the solidified cultural medium plate by coating method. The PVA and PQ-4/ PVA wafers were placed onto the substrates. The plates were then
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Figure 5. Antibacterial action against E. coli (a and b) and S. aureus (c and d) of electrospun mats of PQ-4/PVA = 1:1 (a and c) and PVA (b and d).
incubated at 37 °C for 24 h. Pictures of the plates were taken to illustrate the antibacterial performance of the samples. Acknowledgments This work was financially supported by the National Basic Research Program of China (973 Program, 2010CB732203), the National Natural Science Foundation of China (50973085), and the Fundamental Research Funds for the Central Universities (2081005). References 1. Rodríguez, R.; Alvarez-Lorenzo, C.; Concheiro, A. Biomacromolecules 2001, 2, 886–893. 2. Zhou, S.; Xu, C.; Wang, J.; Golas, P.; Batteas, J. Langmuir 2004, 20, 8482–8489. 3. Fayazpour, F.; Lucas, B.; Alvarez-Lorenzo, C.; Sanders, N. N.; Demeester, J.; De Smedt, S. C. Biomacromolecules 2006, 7, 2856–2862. 4. Brode, G. L.; Goddard, E. D.; Harris, W. C.; Salensky, G. A. Cationic Polysaccharides For Cosmetics and Therapeutics. In Cosmetic and Pharmaceutical Applications of Polymers; Gebelein, C. G., Cheng, T. C., Yang, V. C., Eds.; Plenum Press: New York, 1991; pp 117–128. 5. Rodríguez, R.; Alvarez-Lorenzo, C.; Concheiro, A. J. Controlled Release 2003, 86, 253–265. 6. Rodríguez, R.; Alvarez-Lorenzo, C.; Concheiro, A. Eur. J. Pharm. Biopharm. 2003, 56, 133–142. 7. Rodríguez, R.; Alvarez-Lorenzo, C.; Concheiro, A. Eur. J. Pharm. Sci. 2003, 20, 429–438. 8. Song, Y.; Sun, Y.; Zhang, X.; Zhou, J.; Zhang, L. Biomacromolecules 2008, 9, 2259– 2264.
9. Song, Y.; Wang, H.; Zeng, X.; Sun, Y.; Zhang, X.; Zhou, J.; Zhang, L. Bioconjugate Chem. 2010, 21, 1271–1279. 10. Song, Y.; Zhou, J.; Li, Q.; Guo, Y.; Zhang, L. Macromol. Biosci. 2009, 9, 857–863. 11. Song, Y.; Zhang, L.; Gan, W.; Zhou, J. Colloids Surf., B 2011, 83, 313–320. 12. Mazoniene, E.; Joceviciute, S.; Kazlauske, J.; Niemeyer, B.; Liesiene, J. Colloids Surf., B 2011, 83, 160–164. 13. Zahedi, P.; Rezaeian, I.; Ranaei-Siadat, S.; Jafari, S.; Supaphol, P. Polym. Adv. Technol. 2009, 21, 77–95. 14. Dzenis, Y. Science 2004, 304, 1917–1919. 15. Huang, Z.; Zhang, Y.; Kotaki, M.; Ramakrishna, S. Compos. Sci. Technol. 2003, 63, 2223–2253. 16. Spasova, M.; Manolova, N.; Paneva, D.; Rashkov, I. E-Polymers 2004, 56, 1–12. 17. Ignatova, M.; Starbova, K.; Markova, N.; Manolova, N.; Rashkov, I. Carbohydr. Res. 2006, 341, 2098–2107. 18. Alipour, S. M.; Mokhtari, J.; Bahrami, S. H. Carbohydr. Res. 2009, 344, 2496– 2501. 19. Greiner, A.; Wendorff, J. H. Angew. Chem., Int. Ed. 2007, 46, 5670–5703. 20. Ignatova, M.; Manolova, N.; Markova, N.; Rashkov, I. Macromol. Biosci. 2009, 9, 102–111. 21. Ignatova, M.; Manolova, N.; Rashkov, I. Eur. Polym. J. 2007, 43, 1112–1122. 22. Ignatova, M.; Manolova, N.; Toshkova, R.; Rashkov, I.; Gardeva, E.; Yossifova, L.; Alexandrov, M. Biomacromolecules 2010, 11, 1633–1645. 23. Gruber, J.; Kreeger, R. In Cellulose Ethers, Cationic, Polymeric Materials Encyclopedia; CRC Press: New York, 1996; Vol. 2, pp 1113–1118. 24. Kacˇuráková, M.; Ebringerová, A.; Hirsch, J.; Hromádková, Z. J. Sci. Food Agric. 1994, 66, 423–427. 25. Pal, S.; Mal, D.; Singh, R. P. Carbohydr. Polym. 2005, 59, 417–423. 26. Baumgarten, P. K. J. Colloid Interface Sci. 1971, 36, 71–79. 27. Fennessey, S. F.; Farris, R. J. Polymer 2004, 45, 4217–4225. 28. Reneker, D. H.; Chun, I. Nanotechnology 1996, 7, 216–223. 29. Denyer, S. P. Int. Biodeterior. Biodegrad. 1995, 36, 227–245.
Contents lists available at ScienceDirect
Carbohydrate Research journal homepage: www.elsevier.com/locate/carres
Note
Electrospun nano-fiber mats containing cationic cellulose derivatives and poly (vinyl alcohol) with antibacterial activity Baoquan Jia, Jinping Zhou ⇑, Lina Zhang Department of Chemistry, Wuhan University, Wuhan 430072, China
i n f o
Article history: Received 5 March 2011 Received in revised form 24 April 2011 Accepted 27 April 2011 Available online 3 May 2011 Keywords: Electrospinning Cationic cellulose derivatives Polyvinyl alcohol Antibacterial activity
a b s t r a c t Nano-fibrous mats have been successfully prepared by electrospinning of the blend solutions of cationic cellulose derivatives (PQ-4) and polyvinyl alcohol (PVA). Effects of the blending ratio and applied voltage on the morphology and diameter of the electrospun nano-fibers were investigated. The average diameter of the PQ-4/PVA blend fibers was in the range of 150–250 nm. The electrospinning process became instable and the fiber diameter distribution broadened with increasing PQ-4 content and applied voltage. The antibacterial activity of electrospun PQ-4/PVA blend mats against Gram-negative bacteria Escherichia coli and Gram-positive bacteria Staphylococcus aureus indicated potential for biomedical use. Ó 2011 Elsevier Ltd. All rights reserved.
nium groups, PQ-4 shows a natural attraction for some components of the skin and the hair, and particularly has applications in cosmetics and topical drug delivery devices.4,23 In the present work, nano-fibrous mats were prepared by electrospinning of the blend solutions of PQ-4 and PVA, and the morphology and antibacterial activities of the electrospun mats were investigated. Different blending ratios play a major role in the solution properties such as viscosity and conductivity, which are very important in the process of electrospinning. Figure 1 shows the dependence of the viscosity and conductivity of PQ-4/PVA blend solutions on the PQ-4 content, and the data are summarized in Table 1. The viscosity and conductivity for 7 wt % PVA and PQ-4 solutions are 5000
12 Viscosity (cP) Conductivity (ms/cm)
4000
10 8
3000 6 2000 4 1000
Conductivity (ms/cm)
Cationic cellulose derivatives are large-scale commercial products, which have many useful characteristics, such as hydrophilicity, biodegradability, and antibacterial properties.1–3 They have been found to have numerous applications in a variety of fields including paper and textile, food, cosmetics, chemical, and pharmaceutical industries.4–7 Recently, cationic cellulose ethers containing quaternary ammonium groups are mostly studied among the cationic cellulose derivatives. Apart from industrial applications, they could be used in biomedical fields, for example, as DNA carriers, in gene transfections, as protein carriers and in drug deliveries.3,8–12 Owing to the antibacterial property and hydrophilicity, they are promising candidates for wound-dressing application.13 Electrospinning is an effective and straightforward method of preparing continuous ultrafine fibers and fibrous materials.14,15 Electrospun mats have large surface area and small pore size, which are favorable for the wound-dressing application.15 However, cationic cellulose derivatives are hardly able to be electrospun for the poor flexibility of polyelectrolyte chains.16 Polyvinyl alcohol (PVA) is a nontoxic, hydrophilic, biocompatible, and flexible synthetic polymer; it has been used as an important electrospinning auxiliary for those water-soluble but hard-electrospun materials.17–19 For example, nano-fibrous mats were successfully obtained by electrospinning of quaternized chitosan and PVA blend solutions.17–22 Polyquaternium-4 cellulose (PQ-4) is the hydroxyethyl cellulose diallyl dimethyl ammonium chloride copolymer, and the chemical structure is shown as Scheme 1.1 Owing to its quaternary ammo-
Viscosity (cP)
a r t i c l e
2
0 0
20
40
60
80
0 100
PQ-4 (wt%)
⇑ Corresponding author. Tel.: +86 27 87219274; fax: +86 27 68754067. E-mail address: [email protected] (J. Zhou). 0008-6215/$ - see front matter Ó 2011 Elsevier Ltd. All rights reserved. doi:10.1016/j.carres.2011.04.040
Figure 1. Viscosity and conductivity of PQ-4/PVA blend solutions. The total polymer concentrations are 7 wt %.
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185.1 cP and 1.10 ms/cm, 4722.8 cP and 10.32 ms/cm, respectively. Both the viscosity and conductivity of the blending solutions increase with the increase of PQ-4 content. Because of the poor flexibility of polyelectrolyte chains and high viscosity and charges of the solutions, pure PQ-4 solutions of 2–8 wt % were not capable of being electrospun. Therefore, PVA was selected to mix with PQ-4 for the electrospinning of PQ-4/PVA blend nano-fibers. Figure 2 shows the FT-IR spectra of the electrospun mats of PVA, PQ-4/PVA blends (weight ratios of 1:3 and 1:1), and the PQ-4 powder. Both PVA and PQ-4 showed a broadband at 3400 cm 1, which belongs to stretching vibration modes of O–H groups. The spectra of PQ-4/PVA showed characteristic bands of hydroxyethyl cellulose and quaternary ammonium groups. The band at 1129 cm 1 in Figure 2d was assigned to the stretching vibration of C–O–C groups of the cellulose backbone, and the band at 893 cm 1 indicated the blinked glucose of cellulose. The bands at 1474 and 1416 cm 1 (Fig. 2d) corresponded to the methyl groups and methylene groups next to ammonium and C–N stretching vibration on the quaternary ammonium groups.17,24,25 In Figure 2b and c, the characteristic bands of both PVA and PQ-4 were observed in the spectra of PQ4/PVA blend mats. According to Table 1, electrospinning of the PQ-4/PVA blend solutions was carried out, and continuous cylindrical fibers were obtained in the experiments. The impact of blending ratio and applied voltage on the morphology of the electrospun fibers was investigated. The morphology of the electrospun fibers was observed by scanning electron microscopy (SEM). The average diameter and diameter distribution were calculated by counting 100 random fibers, and the data were summarized in Table 1. Figure 3 shows the SEM images and diameter statistics of the electrospun fibers for PQ-4/PVA blends with the weight ratio of 1:3, 1:2, and 1:1, respectively. The average diameters of the blend fibers were in the range of 150–250 nm. The impact of blending ratio on the average Table 1 Composition of PQ-4/PVA blends, shear viscosity, and conductivity of the solutions, applied voltage, average fiber diameter, and standard deviation PQ-4/PVA (w/w)
Viscosity (cP)
Conductivity (ms/cm)
Applied voltage (kV)
Average diameter (nm)
Standard deviation
15 18 20 15 18 20 15 18 20
217 206 202 246 208 157 211 249 230
54 38 49 56 46 66 60 79 71
1:3
383.1
3.06
1:2
525.3
3.56
1:1
1046.3
5.31
Spinning distance is 15 cm and total concentration is 7wt %.
O
(CH 2CH 2O) nH OH O
HO
HO
O
O O OH O N
(CH 2CH 2O) nH
3
N Scheme 1. Chemical structure of polyquaternium-4 cellulose (PQ-4).
a
b c d
1474 4000
3500
3000
2500
2000
1416 1500
1129 1000
500
Wavenumber (cm-1) Figure 2. FT-IR spectra of the electrospun fibers of (a) PVA, PQ-4/PVA blends with weight ratios of (b) 1:3 and (c) 1:1, and (d) the PQ-4 powders.
diameter of fibers was not clear, and this might be due to the influence of both viscosity and repulsive force of quaternary ammonium groups. Higher viscosity led to larger fiber diameter,26 while the repulsive force stretched the fiber. According to the standard deviations summarized in Table 1, with the content of PQ-4 increasing, the fiber diameter distributed more widely and thinner fibers could be found according to histogram of Figure 3d and e. It indicated that the spinning process became more instable as the content of PQ-4 increased. How the PQ-4 content affected the average diameter was obscure, which could be attributed to the competitive relation of the viscosity and ionization level of the solutions. The effect of applied voltage on the morphology is not so regular. Fennessey and Farris27 reported that the diameter of electrospun fibers decreased with increasing of the applied voltage, while Reneker and Chun28 found no significant relation between the change of applied voltage and diameter. To find out how applied voltage works in this situation, different voltages 15, 18, and 20 kV were applied. Figure 4 shows the SEM images and diameter distributions of the electrospun fibers of PQ-4/PVA (weight ratio of 1:2) blend solution under 15, 18, and 20 kV, respectively. It was found that the applied voltage played an important role in the fiber diameter and its distribution. At 15 and 18 kV, the diameter distribution was relatively centralized, but at 20 kV, the diameter distribution broadened. In the case of PQ-4/PVA = 1:1, this disturbance became more obvious. More widely scattered diameters were observed in SEM images (Fig. 3e). Though more fibers with the diameter less than 100 nm were observed, the comparatively thick fibers made the average value much higher. The increasing applied potential widened the diameter distribution. This could be explained by the instability and disturbance of the electrospinning process at high applied field strength. However, the fiber diameter did not decrease or increase regularly with the increasing applied voltage. Agar plate method was used to evaluate the antibacterial activity against Escherichia coli (E. coli) and Staphylococcus aureus (S. aureus) of PQ-4/PVA (weight ratio of 1:1) and PVA electrospun mats and the results are shown in Figure 5. It was found that the electronspun PQ-4/PVA blend mats showed effective antibacterial activities against E. coli (Fig. 5a) and S. aureus (Fig. 5c). However, the pure PVA electronspun mats did not possess the ability of antibacteria, and the bacterium spread onto the PVA mats (Fig. 5b and d). Quaternary ammonium groups on the PQ-4 strand took charge of antibacterial performance. The cationic groups damaged structural organization and integrity of the cytoplasmic membrane,
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B. Jia et al. / Carbohydrate Research 346 (2011) 1337–1341 35
a
b
30
Frequency
25 20 15 10 5 0 0
100
200
300
400
500
Diameter (nm) 35
c
d
30
Frequency
25 20 15 10 5 0 0
100
200
300
400
500
Diameter (nm) 35
e
f
30
Frequency
25 20 15 10 5 0 0
100
200
300
400
500
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Figure 3. SEM images and diameter statistics of the electrospun fibers for PQ-4/PVA blends with the weight ratio of 1:3 (a and b), 1:2 (c and d) and 1:1 (e and f). Applied voltage is 20 kV, spinning distance is 15 cm and the total polymer concentration is 7 wt %.
which caused cell leakage of intracellular material and finally cellular death.29 The antibacterial activity of PQ-4 and the high hydrophilicity of PVA and PQ-4 make the electrospun PQ-4/PVA blend mats potential material for wound dressings. In summary, nano-fibrous mats of PQ-4/PVA blends with the fiber average diameter ranging from 100 to 250 nm were obtained by electrospinning. PQ-4/PVA blend solutions with the weight ratio of 1:3 and 1:2 could be electrospun steadily at low field strength and the obtained fibers were relatively uniform. The electrospinning process became more instable with increasing PQ-4 content. The high applied voltage (20 kV) widened the diameter distribution dramatically. The electrospun PQ-4/PVA nano-fiber mats showed effective antibacterial activities against E. coli and S. aureus. And this indicates that the electrospun PVA/QC mats are potential materials for biomedical applications.
(Guangzhou, China), and the nitrogen content is 1.5–2.3%. PVA (DP = 1750 ± 50, degree of deacetylation 98%) with purity of analytical grade was purchased from Sinopharm Chemical Reagent Co., Ltd. (Shanghai, China). All the reagents were used without further purification. 1.2. Preparation of the spinning solutions PQ-4 was dissolved in distilled water at room temperature, and the clear solutions with concentrations of 2, 4, 7, and 8 wt % were obtained. PVA dispersed in distilled water, and then stirred at 90 °C for an hour to obtain 7 wt % and 10 wt % aqueous solutions, respectively. PQ-4 and PVA powders with the weight ratio of 1:3, 1:2 and 1:1 were dispersed in distilled water, and then stirred at 90 °C for an hour to obtain blend solutions; the total polymer concentrations were adjusted to 7 wt %.
1. Experimental 1.3. Electrospinning of the solutions 1.1. Materials Polyquaternium-4 cellulose (PQ-4) with purity of cosmetic grade was provided by Tinci Materials Technology Co., Ltd.
A conventional electrospinning setup was used in this work. About 3 mL of solution was first put into a 5 mL syringe and a stainless steel needle was fixed onto the syringe. The inner diame-
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Figure 4. SEM images and diameter statistics of the electrospun fiber of PQ-4/PVA blends (weight ratio of 1:2) under 15 kV (a and b), 18 kV (c and d) and 20 kV (e and f). Spinning distance is 15 cm and the total polymer concentration is 7 wt %.
ter of the orifice is 0.9 mm. The positive electrode of a high-voltage supply (Dongwen High Voltage Power Supply, China) with a DC supply range of 0–30 kV was connected to the needle and the applied electrical potential was 15, 18, and 20 kV. An aluminium foil was fixed onto the surface of a square board and earthed with a wire. The gap distance between the needle tip and the aluminium foil was 15 cm. A precision pump (Longer Precision Pump Co., Ltd., China) was used to give exact volume of the solutions, and the output of the solutions was set in the range of 0.4–0.7 mL/h. The applied potential was 15, 18, and 20 kV, respectively. PVA solution (10 wt %) was electrospun under the voltage of 19 kV. The other process parameters were all the same with the above. The experiments were carried out at normal laboratory conditions. 1.4. Characterization FT-IR spectra of the samples were performed with a Nicolet 170SX Fourier-transform infrared spectrometer. The test specimens were prepared by the KBr disk techniques. Shear viscosities of the spinning fluids were tested by ARES RFSIII rheometer with couttee cups (TA Instruments, USA) at the shear rate of 0.125 s 1
at 20 °C. The conductivity of each solution was measured by electric conductivity meter (Rex Instrument Factory, China). SEM images of the electrospun fibers were performed on a Sirion 200 field emission scanning electron microscope (FEI Co., Eindhoven, The Netherlands) at an accelerating voltage of 15 kV. The surfaces of the fibers were sputtered with gold for SEM measurement. 1.5. Testing of antibacterial activity The antibacterial property against (E. coli) and (S. aureus) of electrospun PVA and PQ-4/PVA mats were tested by agar plate method. Samples were first punched into wafers and these wafers were treated with ultraviolet radiation for half an hour. Culture medium (1000 mL) was prepared by mixing 3 g beef extract, 10 g peptone, 5 g NaCl, 16 g agar, and distilled water. After the activation, bacteria were inoculated and cultured in nutrient agar plate at 37 °C. The bacterial suspensions were prepared with physiological saline at a concentration of 105 cm 1. 50 lL of each bacterial suspension was measured and evenly spread onto the solidified cultural medium plate by coating method. The PVA and PQ-4/ PVA wafers were placed onto the substrates. The plates were then
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Figure 5. Antibacterial action against E. coli (a and b) and S. aureus (c and d) of electrospun mats of PQ-4/PVA = 1:1 (a and c) and PVA (b and d).
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