- Email: [email protected]
Gelatin nanofibers prepared by spiral-electrospinning and cross-linked by vapor and liquid-phase glutaraldehyde
Author's Accepted Manuscript
Gelatin nanofibers prepared by spiralelectrospinning and cross-linked by vapor & liquid-phase glutaraldehyde Weipeng Lu, Ming Ma, Haitao Xu, Bing Zhang, Xiaofeng Cao, Yanchuan Guo
www.elsevier.com/locate/matlet
PII: DOI: Reference:
S0167-577X(14)01946-6 http://dx.doi.org/10.1016/j.matlet.2014.10.146 MLBLUE17965
To appear in:
Materials Letters
Received date: 15 August 2014 Revised date: 22 October 2014 Accepted date: 27 October 2014 Cite this article as: Weipeng Lu, Ming Ma, Haitao Xu, Bing Zhang, Xiaofeng Cao, Yanchuan Guo, Gelatin nanofibers prepared by spiral-electrospinning and cross-linked by vapor & liquid-phase glutaraldehyde, Materials Letters, http://dx. doi.org/10.1016/j.matlet.2014.10.146 This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting galley proof before it is published in its final citable form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
Gelatin nanofibers prepared by spiral-electrospinning and cross-linked by vapor & liquid-phase glutaraldehyde Weipeng Lua, Ming Maa, Haitao Xua, Bing Zhanga, Xiaofeng Caoa, Yanchuan Guoa,* a
Key Laboratory of Photochemical conversion and Optoelectronic Material, Technical
Institute of Physics and Chemistry, Chinese Academy of Sciences, Beijing 100190, China Abstract The aim of this study was to mass-produce gelatin nanofibers by spiral-electrospinning and investigate the performance of different cross-linking methods such as glutaraldehyde vapor and liquid phase cross-linking. Compared with conventional single-needle electrospinning, nanofibers produced by spiral-electrospinning were finer and an enhancement of more than 1000 times over the traditionally obtained nanofibers productivity was obtained. The mechanical testing showed the tensile strength of nanofiber membranes increased from 1.33 to 2.60MPa after glutaraldehyde vapor cross-linking and from 1.33 to 5.08 MPa after liquid phase cross-linking. Moreover, SEM and FTIR analysis indicated the nanofiber membrane obtained by liquid phase cross-linking had better properties and was an ideal material for wound dressing applications. Keywords: fibre technology, nanofibers, spiral-electrospinning, FTIR, polymers ∗ Corresponding author Tel.: +86-10-82543583; Fax: +86-10-62554670 E-mail address: [email protected]
1. Introduction Electrospinning was a versatile technique to fabricate continuous nanofibers with many outstanding characteristics such as high porosity, high ratio of surface area to mass and superior mechanical properties[1]. So, electrospun nanofibrous had many important applications in various fields, such as wound dressing and tissue engineering[2]. Conventional single-needle electrospinning was widely used to produce nanofibers, but the system was inefficient for industrial production of nanofibers due to low production rate. Although multi-needle nozzle configuration may improve the productivity, a complicated 1
interaction between nozzles weakened the electric field at the nozzle tip and led to non-uniform nanofibers[3]. Needleless electrospinning setups had attracted much attention over the past decades as an effective approach to enhance the productivity of electrospinning. However, those needleless electrospinning systems still needed to improve the fiber uniformity, while increased the production rate. Gelatin was commercially made from skins and skeletons of bovine and porcine. Due to its biodegradability, biocompatibility and non-toxicity, it has been used extensively in the medical, food and other industries[4]. As a principal structural element of the native extracellular matrix (ECM) in many native tissues, gelatin had emerged as an important polymer to electrospin for diverse bioclinical applications[5]. However, the gelatin nanofibers had as a drawback a poor structural consistency in wet conditions[6]. So cross-linking of gelatin nanofibers was necessary to increase their stability in aqueous environments. The process could be achieved by either physical methods, such as heat and radiation, or chemical methods by vapor or liquid phase cross-linking which exploited many chemical agents to modify gelatin functional side groups[7]. In this study, the spiral-electrospinning technique was used for massive production of gelation nanofibers, and water was chosen as the solvent to examine the electospinnability of gelatin aqueous solution. The productivity was about 100g/h, which was thousands of times higher than that of conventional single needle electrospinning. Moreover, a comparative study between glutaraldehyde vapor phase cross-linking and liquid cross-linking was carried out. The SEM, FT-IR and texture analyzer were used to analyze the changes of the morphology, functional groups and mechanical properties of GE nanofibers. 2. Experimental 2.1. Material Gelatin powder (GE) was obtained from Baotou Dongbao Bio-Tech Co., Ltd., China. Glutaraldehyde (GA, AR) was purchased from sinopharm chemical Reagent Beijing Co.,
O
Ltd.
O
H
H glutaraldehyde 2
Electrospinning setup: the scheme of the novel needleless electrospinning system was shown in Fig.1, which contained five major components:, a teflon solution reservoir, a helix-slice spinneret, a grounded collector, a high-voltage direct-current power supply and an air heater. As the helix slice was rotated, every edge of the spinneret was coated by polymer solution. Once the electric filed exceeded the critical value needed to overcome the surface tension, multi-fluid jets ejected from the edge of helix slice. 2.2. Electrospinning Process and Cross-linking Reaction 2.2.1 Method A Ten percent GE solution was prepared by dissolving GE in deionized water with vigorous stirring for 6 h at 40
℃. Then, the solution was poured in the teflon reservoir and
electrospun for one hour, an air heater was used to controlled the solution temperature
℃
(40 ). The distance between the helix slice and the collector was 170mm, voltage was 80KV and the rotating speed of spinneret was 10rpm. Five different concentrations (0.1, 0.5, 1.0, 3.0, 5.0M) of GA solution were prepared and the GE nanofibers were exposed to the GA vapor for one hour at each concentration. The total cross-linking procedure was carried out in a sealed vessel. 2.2.2 Method B As GE nanofibers can be dissolved instantly in water, so cross-linking by liquid phase must be performed in the electrospinning process. GE solutions were prepared by dissolving a measured amount of GE in deionized water
℃
and stirred for 6 h at 40 . Then, GA was added to prepare five different concentrations (0.0, 0.1, 0.5, 1.0, 3.0, 5.0M) of GA solution, and the final GE concentration was 10wt%. The mixed solution was evenly stirred, poured in the teflon reservoir, and electrospun for one hour. An air heater controlled the solution temperature; the processing parameters were the same as those in the method A. The product with a large surface area-to-volume ratio and a small pore size was stored in a desiccator under vacuum for several days to remove any residual solvent. 2.3 Charaterization Morphological investigations of the precipitated samples were carried out with an S-4800 scanning electron microscope (SEM, Hitachi, Japan). The functional groups in the GE 3
membrane were characterized by FT-IR. The mechanical properties were measured by a texture analyzer, the GE nanofiber membranes were cut into rectangular mats of approximate length 50mm, width 10mm, and thickness 1mm with load speed of 0.5mm/s. 3. Results and discussion 3.1 Cross-linking Reaction of GA Fig. 2a showed an SEM image of gelatin nanofibers electrospun from GE aqueous solution, the randomly collected nanofibers with average fiber diameter of 292nm were free of bead defects. However, the non-cross-linked nanofiber membrane was found instantly dissolving in water as it swelled considerably and nanofibers started to fuse with each other and destroy porous openings of the membrane (Fig.2a`). Maintaining the peculiar biomimetic nanofibrous morphology and interfiber pores of nanofiber membrane was important for medical applications where high surface areas and high porosity were considered advantageous[8]. To investigate the effect of GA cross-linking, vapor phase and liquid cross-linking was applied. As a result of the cross-linking process, electrospun nanofibers became strongly interconnected, forming an apparently robust and stiffer network. Method A: the vapor phase cross-linking was made by employing a sealed vessel with different concentrations of GA (0.1, 0.3, 0.5, 1.0, 3.0M) and the vessel was tightly closed with the GE nanofiber membrane attached onto the inside of the lid exposed to the GA vapor for 1h at ambient temperature. As the GA concentration increased, not more than 1.0M, the nanofibers, which were originally straight, became merged among each other and formed interfiber bonding/fused mostly at the intersection point of nanofibers (Fig. 2b-2f). When the GA concentration was above 1.0M, The nanofiber membrane (Fig. 2f) became visibly shrank; the nanofibers became strongly entangled and interconnected. Fig.2b`-2f` showed the SEM images of nanofibers after rinsing in water. The junction zones appeared fused together and the nanofibers became swell. However, as the GA concentration increased, the changes of nanofiber morphology decreased in aqueous environments. Method B: the liquid phase cross-linking was performed by adding GA to GE solution. Fig.2g-2k showed SEM images of GE nanofiber membranes cross-linked by different 4
concentrations (0.1, 0.3, 0.5, 1.0, 3.0M) of GA. As the GA concentration increased, the formed interfiber bonding/fusing at the intersection points of nanofibers rose. When the GA concentration was above 1.0M, the GE nanofibers fused and formed a plane because of excessive cross-linking. In the images recorded after nanofibers immersion in water (Fig. 2g`-2k`), the fibers showed a morphology change and many junction zones merged together. However, the liquid cross-linked nanofibers with GA concentrations of 1.0 M were found to be stable and their morphology remained intact as it was electrospun. The nanofibers after excessive cross-linking also did not change too much in wet conditions, as the membrane have become a plane. Compared the vapor phase and liquid cross-linking, the nanofiber membranes by liquid phase were evenly cross-linked and tightly packed, but the cross-linking degree of membranes by vapor phase had the feature of hierarchy, the middle layers of membrane were poorly cross-linked, so excessive cross-linking by vapor phase led to the membranes shrinking. Immersing the cross-linked GE nanofibers in water, the membranes morphology by liquid phase had fewer changes. 3.2 mechanical properties Fig.3. showed typical tensile stress-strain curves before (neat GE) and after (GA vapor or liquid phase) cross-linking. The ultimate tensile strength of the GE nanofiber membrane was measured to be 1.33MPa and its ultimate strain was 41.78%, whereas after GA vapor cross-linking, the ultimate tensile strength of the GE nanofiber membrane increased about 1.95 fold to be 2.60 MPa and its ultimate strain decreased to 28.23%. Moreover, after GA liquid cross-linking, the ultimate tensile strength of the GE nanofiber membrane increased about 3.82 fold to be 5.08MPa and its ultimate strain decreased to 22.9%. The enhanced ultimate tensile strength indicated that GA cross-linking made GE nanofiber membrane became mechanically more strong and stable. In addition, liquid phase cross-linking ensured that nanofibers had a rigid web of interfiber bonding and membrane was tightly packed, so the liquid phase cross-linking was a better choice. 3.3 FTIR of GE nanofibers Representative IR spectra (Fig.4) of GE nanofibers and GE nanofibers cross-linked by GA were analyzed. Compared the neat GE nanofibers and the cross-linked samp1es, the 5
large band observed at 3429.5cm-1were associated with the stretching vibration of N-H group, the band observed at 1648.5cm-1represented the bending vibration of N-H group, and their intensity were observed relatively decreasing and the peaks moved to low wavenumber after cross-linking, the phenomena was more obvious after liquid phase cross-linking. For cross-linked GE nanofiber membranes, the intensity of bands between 1250 and 1160cm-1decreased, which indicated the amount of C-N-C groups reduced. 4. Conclusion In this paper, the spiral-electrospinning technique was used for massive production of gelation nanofibers, this novel needleless electrospinning produced finer nanofibers with the productivity of about 100g/h. The GE nanofiber membrane by GA liquid phase cross-linking presented more evenly cross-linked, close-packed and higher tensile strength, compared with vapor cross-linking, so the effect of liquid phase cross-linking was better. Acknowledgment The authors sincerely acknowledge the financial support by Baotou Dongbao Bio-Tech Co., Ltd., China (Grant No LHS-DBSW 2013-02) Reference [1] Bhardwaj N, Kundu SC. Electrospinning: A fascinating fiber fabrication technique. Biotechnology Advances. 2010;28:325-47. [2] Forward KM, Flores A, Rutledge GC. Production of core/shell fibers by electrospinning from a free surface. Chemical Engineering Science. 2013;104:250-9. [3] Wang X, Hu X, Qiu X, Huang X, Wu D, Sun D. An improved tip-less electrospinning with strip-distributed solution delivery for massive production of uniform polymer nanofibers. Materials Letters. 2013;99:21-3. [4] Aewsiri T, Benjakul S, Visessanguan W, Eun J-B, Wierenga PA, Gruppen H. Antioxidative activity and emulsifying properties of cuttlefish skin gelatin modified by oxidised phenolic compounds. Food Chemistry. 2009;117:160-8. [5] Choi MO, Kim Y-J. Fabrication of gelatin/calcium phosphate composite nanofibrous membranes
by
biomimetic
mineralization.
International
Journal
of
Biological
Macromolecules. 2012;50:1188-94. [6] Panzavolta S, Gioffrè M, Focarete ML, Gualandi C, Foroni L, Bigi A. Electrospun 6
gelatin nanofibers: Optimization of genipin cross-linking to preserve fiber morphology after exposure to water. Acta Biomaterialia. 2011;7:1702-9. [7] Torres-Giner S, Gimeno-Alcañiz JV, Ocio MJ, Lagaron JM. Comparative Performance of Electrospun Collagen Nanofibers Cross-linked by Means of Different Methods. ACS Applied Materials & Interfaces. 2008;1:218-23. [8] Destaye AG, Lin C-K, Lee C-K. Glutaraldehyde Vapor Cross-linked Nanofibrous PVA Mat with in Situ Formed Silver Nanoparticles. ACS Applied Materials & Interfaces. 2013;5:4745-52.
Fig.1. the diagram of spiral electrospinning
Fig.3. stress-strain curves of nanofiber membrane
7
Fig.2. SEM images of GE nanofibers (a), GE nanofibers by liqiuid phase cross-linking ing (b-f, 0.1-3M), 3M), GE nanofibers by vapor phase (g-k, 0.1-3.0M) 3.0M) and after rinsing in water (a`-k`) (a`
Fig.4. FT-IR IR of GE nanofibers and cross-linked cross GE nanofibers 8
Highlights • • • •
The spiral-electrospinning technique was used for massive production of gelation nanofibers. The productivity was about 100g/h. A comparative study between glutaraldehyde vapor phase cross-linking and liquid cross-linking was carried out. The analysis showed the nanofiber membrane obtained by glutaraldehyde liquid phase cross-linking had better properties.
10
Gelatin nanofibers prepared by spiralelectrospinning and cross-linked by vapor & liquid-phase glutaraldehyde Weipeng Lu, Ming Ma, Haitao Xu, Bing Zhang, Xiaofeng Cao, Yanchuan Guo
www.elsevier.com/locate/matlet
PII: DOI: Reference:
S0167-577X(14)01946-6 http://dx.doi.org/10.1016/j.matlet.2014.10.146 MLBLUE17965
To appear in:
Materials Letters
Received date: 15 August 2014 Revised date: 22 October 2014 Accepted date: 27 October 2014 Cite this article as: Weipeng Lu, Ming Ma, Haitao Xu, Bing Zhang, Xiaofeng Cao, Yanchuan Guo, Gelatin nanofibers prepared by spiral-electrospinning and cross-linked by vapor & liquid-phase glutaraldehyde, Materials Letters, http://dx. doi.org/10.1016/j.matlet.2014.10.146 This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting galley proof before it is published in its final citable form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
Gelatin nanofibers prepared by spiral-electrospinning and cross-linked by vapor & liquid-phase glutaraldehyde Weipeng Lua, Ming Maa, Haitao Xua, Bing Zhanga, Xiaofeng Caoa, Yanchuan Guoa,* a
Key Laboratory of Photochemical conversion and Optoelectronic Material, Technical
Institute of Physics and Chemistry, Chinese Academy of Sciences, Beijing 100190, China Abstract The aim of this study was to mass-produce gelatin nanofibers by spiral-electrospinning and investigate the performance of different cross-linking methods such as glutaraldehyde vapor and liquid phase cross-linking. Compared with conventional single-needle electrospinning, nanofibers produced by spiral-electrospinning were finer and an enhancement of more than 1000 times over the traditionally obtained nanofibers productivity was obtained. The mechanical testing showed the tensile strength of nanofiber membranes increased from 1.33 to 2.60MPa after glutaraldehyde vapor cross-linking and from 1.33 to 5.08 MPa after liquid phase cross-linking. Moreover, SEM and FTIR analysis indicated the nanofiber membrane obtained by liquid phase cross-linking had better properties and was an ideal material for wound dressing applications. Keywords: fibre technology, nanofibers, spiral-electrospinning, FTIR, polymers ∗ Corresponding author Tel.: +86-10-82543583; Fax: +86-10-62554670 E-mail address: [email protected]
1. Introduction Electrospinning was a versatile technique to fabricate continuous nanofibers with many outstanding characteristics such as high porosity, high ratio of surface area to mass and superior mechanical properties[1]. So, electrospun nanofibrous had many important applications in various fields, such as wound dressing and tissue engineering[2]. Conventional single-needle electrospinning was widely used to produce nanofibers, but the system was inefficient for industrial production of nanofibers due to low production rate. Although multi-needle nozzle configuration may improve the productivity, a complicated 1
interaction between nozzles weakened the electric field at the nozzle tip and led to non-uniform nanofibers[3]. Needleless electrospinning setups had attracted much attention over the past decades as an effective approach to enhance the productivity of electrospinning. However, those needleless electrospinning systems still needed to improve the fiber uniformity, while increased the production rate. Gelatin was commercially made from skins and skeletons of bovine and porcine. Due to its biodegradability, biocompatibility and non-toxicity, it has been used extensively in the medical, food and other industries[4]. As a principal structural element of the native extracellular matrix (ECM) in many native tissues, gelatin had emerged as an important polymer to electrospin for diverse bioclinical applications[5]. However, the gelatin nanofibers had as a drawback a poor structural consistency in wet conditions[6]. So cross-linking of gelatin nanofibers was necessary to increase their stability in aqueous environments. The process could be achieved by either physical methods, such as heat and radiation, or chemical methods by vapor or liquid phase cross-linking which exploited many chemical agents to modify gelatin functional side groups[7]. In this study, the spiral-electrospinning technique was used for massive production of gelation nanofibers, and water was chosen as the solvent to examine the electospinnability of gelatin aqueous solution. The productivity was about 100g/h, which was thousands of times higher than that of conventional single needle electrospinning. Moreover, a comparative study between glutaraldehyde vapor phase cross-linking and liquid cross-linking was carried out. The SEM, FT-IR and texture analyzer were used to analyze the changes of the morphology, functional groups and mechanical properties of GE nanofibers. 2. Experimental 2.1. Material Gelatin powder (GE) was obtained from Baotou Dongbao Bio-Tech Co., Ltd., China. Glutaraldehyde (GA, AR) was purchased from sinopharm chemical Reagent Beijing Co.,
O
Ltd.
O
H
H glutaraldehyde 2
Electrospinning setup: the scheme of the novel needleless electrospinning system was shown in Fig.1, which contained five major components:, a teflon solution reservoir, a helix-slice spinneret, a grounded collector, a high-voltage direct-current power supply and an air heater. As the helix slice was rotated, every edge of the spinneret was coated by polymer solution. Once the electric filed exceeded the critical value needed to overcome the surface tension, multi-fluid jets ejected from the edge of helix slice. 2.2. Electrospinning Process and Cross-linking Reaction 2.2.1 Method A Ten percent GE solution was prepared by dissolving GE in deionized water with vigorous stirring for 6 h at 40
℃. Then, the solution was poured in the teflon reservoir and
electrospun for one hour, an air heater was used to controlled the solution temperature
℃
(40 ). The distance between the helix slice and the collector was 170mm, voltage was 80KV and the rotating speed of spinneret was 10rpm. Five different concentrations (0.1, 0.5, 1.0, 3.0, 5.0M) of GA solution were prepared and the GE nanofibers were exposed to the GA vapor for one hour at each concentration. The total cross-linking procedure was carried out in a sealed vessel. 2.2.2 Method B As GE nanofibers can be dissolved instantly in water, so cross-linking by liquid phase must be performed in the electrospinning process. GE solutions were prepared by dissolving a measured amount of GE in deionized water
℃
and stirred for 6 h at 40 . Then, GA was added to prepare five different concentrations (0.0, 0.1, 0.5, 1.0, 3.0, 5.0M) of GA solution, and the final GE concentration was 10wt%. The mixed solution was evenly stirred, poured in the teflon reservoir, and electrospun for one hour. An air heater controlled the solution temperature; the processing parameters were the same as those in the method A. The product with a large surface area-to-volume ratio and a small pore size was stored in a desiccator under vacuum for several days to remove any residual solvent. 2.3 Charaterization Morphological investigations of the precipitated samples were carried out with an S-4800 scanning electron microscope (SEM, Hitachi, Japan). The functional groups in the GE 3
membrane were characterized by FT-IR. The mechanical properties were measured by a texture analyzer, the GE nanofiber membranes were cut into rectangular mats of approximate length 50mm, width 10mm, and thickness 1mm with load speed of 0.5mm/s. 3. Results and discussion 3.1 Cross-linking Reaction of GA Fig. 2a showed an SEM image of gelatin nanofibers electrospun from GE aqueous solution, the randomly collected nanofibers with average fiber diameter of 292nm were free of bead defects. However, the non-cross-linked nanofiber membrane was found instantly dissolving in water as it swelled considerably and nanofibers started to fuse with each other and destroy porous openings of the membrane (Fig.2a`). Maintaining the peculiar biomimetic nanofibrous morphology and interfiber pores of nanofiber membrane was important for medical applications where high surface areas and high porosity were considered advantageous[8]. To investigate the effect of GA cross-linking, vapor phase and liquid cross-linking was applied. As a result of the cross-linking process, electrospun nanofibers became strongly interconnected, forming an apparently robust and stiffer network. Method A: the vapor phase cross-linking was made by employing a sealed vessel with different concentrations of GA (0.1, 0.3, 0.5, 1.0, 3.0M) and the vessel was tightly closed with the GE nanofiber membrane attached onto the inside of the lid exposed to the GA vapor for 1h at ambient temperature. As the GA concentration increased, not more than 1.0M, the nanofibers, which were originally straight, became merged among each other and formed interfiber bonding/fused mostly at the intersection point of nanofibers (Fig. 2b-2f). When the GA concentration was above 1.0M, The nanofiber membrane (Fig. 2f) became visibly shrank; the nanofibers became strongly entangled and interconnected. Fig.2b`-2f` showed the SEM images of nanofibers after rinsing in water. The junction zones appeared fused together and the nanofibers became swell. However, as the GA concentration increased, the changes of nanofiber morphology decreased in aqueous environments. Method B: the liquid phase cross-linking was performed by adding GA to GE solution. Fig.2g-2k showed SEM images of GE nanofiber membranes cross-linked by different 4
concentrations (0.1, 0.3, 0.5, 1.0, 3.0M) of GA. As the GA concentration increased, the formed interfiber bonding/fusing at the intersection points of nanofibers rose. When the GA concentration was above 1.0M, the GE nanofibers fused and formed a plane because of excessive cross-linking. In the images recorded after nanofibers immersion in water (Fig. 2g`-2k`), the fibers showed a morphology change and many junction zones merged together. However, the liquid cross-linked nanofibers with GA concentrations of 1.0 M were found to be stable and their morphology remained intact as it was electrospun. The nanofibers after excessive cross-linking also did not change too much in wet conditions, as the membrane have become a plane. Compared the vapor phase and liquid cross-linking, the nanofiber membranes by liquid phase were evenly cross-linked and tightly packed, but the cross-linking degree of membranes by vapor phase had the feature of hierarchy, the middle layers of membrane were poorly cross-linked, so excessive cross-linking by vapor phase led to the membranes shrinking. Immersing the cross-linked GE nanofibers in water, the membranes morphology by liquid phase had fewer changes. 3.2 mechanical properties Fig.3. showed typical tensile stress-strain curves before (neat GE) and after (GA vapor or liquid phase) cross-linking. The ultimate tensile strength of the GE nanofiber membrane was measured to be 1.33MPa and its ultimate strain was 41.78%, whereas after GA vapor cross-linking, the ultimate tensile strength of the GE nanofiber membrane increased about 1.95 fold to be 2.60 MPa and its ultimate strain decreased to 28.23%. Moreover, after GA liquid cross-linking, the ultimate tensile strength of the GE nanofiber membrane increased about 3.82 fold to be 5.08MPa and its ultimate strain decreased to 22.9%. The enhanced ultimate tensile strength indicated that GA cross-linking made GE nanofiber membrane became mechanically more strong and stable. In addition, liquid phase cross-linking ensured that nanofibers had a rigid web of interfiber bonding and membrane was tightly packed, so the liquid phase cross-linking was a better choice. 3.3 FTIR of GE nanofibers Representative IR spectra (Fig.4) of GE nanofibers and GE nanofibers cross-linked by GA were analyzed. Compared the neat GE nanofibers and the cross-linked samp1es, the 5
large band observed at 3429.5cm-1were associated with the stretching vibration of N-H group, the band observed at 1648.5cm-1represented the bending vibration of N-H group, and their intensity were observed relatively decreasing and the peaks moved to low wavenumber after cross-linking, the phenomena was more obvious after liquid phase cross-linking. For cross-linked GE nanofiber membranes, the intensity of bands between 1250 and 1160cm-1decreased, which indicated the amount of C-N-C groups reduced. 4. Conclusion In this paper, the spiral-electrospinning technique was used for massive production of gelation nanofibers, this novel needleless electrospinning produced finer nanofibers with the productivity of about 100g/h. The GE nanofiber membrane by GA liquid phase cross-linking presented more evenly cross-linked, close-packed and higher tensile strength, compared with vapor cross-linking, so the effect of liquid phase cross-linking was better. Acknowledgment The authors sincerely acknowledge the financial support by Baotou Dongbao Bio-Tech Co., Ltd., China (Grant No LHS-DBSW 2013-02) Reference [1] Bhardwaj N, Kundu SC. Electrospinning: A fascinating fiber fabrication technique. Biotechnology Advances. 2010;28:325-47. [2] Forward KM, Flores A, Rutledge GC. Production of core/shell fibers by electrospinning from a free surface. Chemical Engineering Science. 2013;104:250-9. [3] Wang X, Hu X, Qiu X, Huang X, Wu D, Sun D. An improved tip-less electrospinning with strip-distributed solution delivery for massive production of uniform polymer nanofibers. Materials Letters. 2013;99:21-3. [4] Aewsiri T, Benjakul S, Visessanguan W, Eun J-B, Wierenga PA, Gruppen H. Antioxidative activity and emulsifying properties of cuttlefish skin gelatin modified by oxidised phenolic compounds. Food Chemistry. 2009;117:160-8. [5] Choi MO, Kim Y-J. Fabrication of gelatin/calcium phosphate composite nanofibrous membranes
by
biomimetic
mineralization.
International
Journal
of
Biological
Macromolecules. 2012;50:1188-94. [6] Panzavolta S, Gioffrè M, Focarete ML, Gualandi C, Foroni L, Bigi A. Electrospun 6
gelatin nanofibers: Optimization of genipin cross-linking to preserve fiber morphology after exposure to water. Acta Biomaterialia. 2011;7:1702-9. [7] Torres-Giner S, Gimeno-Alcañiz JV, Ocio MJ, Lagaron JM. Comparative Performance of Electrospun Collagen Nanofibers Cross-linked by Means of Different Methods. ACS Applied Materials & Interfaces. 2008;1:218-23. [8] Destaye AG, Lin C-K, Lee C-K. Glutaraldehyde Vapor Cross-linked Nanofibrous PVA Mat with in Situ Formed Silver Nanoparticles. ACS Applied Materials & Interfaces. 2013;5:4745-52.
Fig.1. the diagram of spiral electrospinning
Fig.3. stress-strain curves of nanofiber membrane
7
Fig.2. SEM images of GE nanofibers (a), GE nanofibers by liqiuid phase cross-linking ing (b-f, 0.1-3M), 3M), GE nanofibers by vapor phase (g-k, 0.1-3.0M) 3.0M) and after rinsing in water (a`-k`) (a`
Fig.4. FT-IR IR of GE nanofibers and cross-linked cross GE nanofibers 8
Highlights • • • •
The spiral-electrospinning technique was used for massive production of gelation nanofibers. The productivity was about 100g/h. A comparative study between glutaraldehyde vapor phase cross-linking and liquid cross-linking was carried out. The analysis showed the nanofiber membrane obtained by glutaraldehyde liquid phase cross-linking had better properties.
10