Fabrication of three-dimensional micro-nanofiber structures by a novel solution blow spinning device Feng Liang, Feiyu Fang, Jun Zeng, Zhifeng Wang, Weijun Ou, Xindu Chen, Peixuan Wu, Han Wang, and Lin Zhang Citation: AIP Advances 7, 025002 (2017); doi: 10.1063/1.4973719 View online: http://dx.doi.org/10.1063/1.4973719 View Table of Contents: http://aip.scitation.org/toc/adv/7/2 Published by the American Institute of Physics AIP ADVANCES 7, 025002 (2017) Fabrication of three-dimensional micro-nanofiber structures by a novel solution blow spinning device Feng Liang,1 Feiyu Fang,1 Jun Zeng,1 Zhifeng Wang,1 Weijun Ou,1 Xindu Chen,1 Peixuan Wu,1,a Han Wang,1,b and Lin Zhang2,c Guangdong Provincial Key Laboratory of Micro-nano Manufacturing Technology and Equipment, School of Electromechanical Engineering, Guangdong University of Technology, Guangzhou 510006, China Department of NanoEngineering, University of California, San Diego, La Jolla, California 92093-0448, USA (Received December 2016; accepted 22 December 2016; published online February 2017) The fabrication of three-dimensional scaffolds has attracted more attention in tissue engineering The purpose of this study is to explore a new method for the fabrication of three-dimensional micro-nanofiber structures by combining solution blow spinning and rotating collector In this study, we successfully fabricated fibers with a minimum diameter of 200 nm and a three-dimensional structure with a maximum porosity of 89.9% At the same time, the influence of various parameters such as the solvent volatility, the shape of the collector, the feed rate of the solution and the applied gas pressure were studied It is found that solvent volatility has large effect on the formation of the three-dimensional shape of the structure The shape of the collector affects the porosity and fiber distribution of the three-dimensional structure The fiber diameter and fiber uniformity can be controlled by adjusting the solution feed rate and the applied gas pressure It is feasible to fabricate high-quality three-dimensional micro-nanofiber structure by this new method, which has great potential in tissue engineering © 2017 Author(s) All article content, except where otherwise noted, is licensed under a Creative Commons Attribution (CC BY) license (http://creativecommons.org/licenses/by/4.0/) [http://dx.doi.org/10.1063/1.4973719] I INTRODUCTION Three-dimensional (3D) micro-nanofiber scaffolds are becoming more important in current tissue engineering research The 3D shape of the micro-nanofiber structure gives cells the opportunity to vertically proliferate compared to a two-dimensional (2D) membrane, and can grow into a 3D shaped tissue like bone1,2 or liver instead of 2D shape like skin.4,5 On the other hand, porosity is one of the most important properties of micro-nanofiber scaffolds High porosity ensures cell migration and nutrient transport.6 In general, ideal tissue-engineered scaffolds should have not only 3D shape but also high porosity to enhance cell attachment, cell-matrix interactions and proliferation.7 In the past few decades, researchers have developed several methods to fabricate 3D structures, including electrospinning,8,9 3D printing,10 light curing11 and so on Electrospinning, which has great promise in fabricating fibers, is suitable for a wide range of polymeric materials and also proud of its stability in producing homogeneous fibers However, the 3D shape structure is difficult to fabricate by using the conventional electrospinning device.12 In order to overcome this limitation, some special devices and novel methods have been developed For example, Zhu13 et al utilized “dumbbell” dynamic collector to fabricate multilayer 3D macro-structure Kim14 et al used modified wet-electrospinning supplemented with a femtosecond laser to produce 3D polycaprolactone (PCL) scaffolds Bryan15 et al obtained a cotton ball-like electrospun scaffold by designing a spherical dish a Author to whom correspondence should be addressed Electronic mail: peixuan@gdut.edu.cn; b Author to whom correspondence should be addressed Electronic mail: wanghangdut@126.com; c Author to whom correspondence should be addressed Electronic mail: zhanglin.materials@gmail.com 2158-3226/2017/7(2)/025002/7 7, 025002-1 © Author(s) 2017 025002-2 Liang et al AIP Advances 7, 025002 (2017) collector In the study of various collection methods, most methods have been successfully used in the fabrication of electrospinning 3D shape scaffold Solution blow spinning began to develop in the 21st century which was used to fabricate nonwoven webs The technology included advantages of electrospinning and melt blowing spinning In particular, the productivity of solution blow spinning was several times higher than the electrospinning Solution blow spinning apparatus equipped with a compressed gas source which provides high-speed gas flow and a concentric nozzles consisting of an inner nozzle and an outer nozzle The solution was pumped by the syringe pump through the inner nozzle and the high–speed gas flow passed through the outer nozzle By high-speed gas flow shearing, the solution was ejected into multiple fine streams towards a collector and the fibers came into being after the solvent component evaporating.16 In this work, a novel solution blow spinning device with a rotating collector which consisted several curving sticks in circular array was employed to fabricate high porosity 3D micro-nanofiber structures This study provided good guideline for fabricating 3D shape scaffolds by utilizing novel homemade device and method II MATERIALS AND METHODS A Materials Polyethyleneoxide (PEO, Mw = × 106 g · mol −1 , Aladdin, Shanghai, China) powder was dissolved in the mixture of water and ethanol in different volume ratio to prepare the PEO solution (5wt%) The PEO solution was stirred at room temperature for about hours and deaerated to remove bubbles before solution blow spinning process These materials were directly used without further purification B 3D micro-nanofiber structures statistical analysis The fibers diameter and the surface morphology of the 3D micro-nanofiber structures for all above experiments were observed by scanning electron microscopy (SEM) (3030, HITACHI Inc., Japan) The average diameter of the fibers was obtained for each sample by measuring the diameter of 50 different fibers randomly selected in four different fields per micrograph and averaging by ImagePro Plus 6.0 soft imaging system All measurements were calibrated with scale on the micrograph as reference Adsorption method was used to measure the porosity of the scaffolds by adsorbing acetone because PEO could not be dissolved in acetone in room temperature The measurement process was shown as followed: choose a cup-type pycnometer, pour acetone to 3/4 volume of pycnometer, mark the height of the liquid level, the weight is W , then get the weight of scaffold sample as W S , put the sample into the acetone and shake the pycnometer to make the acetone full fill into the pore of the scaffold, and then suck away the extra acetone and make the liquid level return to the initial height, get the weight as W , take away the scaffold and get the weight as W , ρ is 0.788 g/cm3 as the density of the acetone in room temperature The volume of the scaffold sample is V S : VS = (W1 + WS − W2 ) /ρ (1) The volume of the pore of the scaffold sample is V P : VP = (W2 + W3 − Ws ) /ρ (2) The porosity of the scaffold sample is ε: ε= VP = (W2 + W3 − Ws )/(W1 − W3 ) × 100% (VP + VS ) (3) C Solution blow spinning set-up A schematic diagram of the novel solution blow spinning device is shown in Fig An improved concentric nozzle consisted of an outer nozzle and an inner nozzle The inner nozzle diameter is 025002-3 Liang et al AIP Advances 7, 025002 (2017) FIG Schematic illustration of a novel solution blow spinning device 260 µm while the outer nozzle diameter is much larger than the inner nozzle A compressed air supplied device is connected to the outer nozzle and supplied the high-speed air flow The speed of the air flow can be adjusted by changing the valve of the gas pressure in the compressed air supplied device A syringe pump (Lange, Inc., China) is connected to the inner nozzle to deliver the PEO solution The collector consisted of several curving sticks in circular array fabricated by three-dimensional printer Its bottom was connected to a DC motor by a concentric coupling When the DC motor rotated, the sticks rotated simultaneously and resulted in a bowl-like collector The rotating speed of the DC motor ranged from to 3000 rpm and also could be adjusted by changing the duty ratio III RESULTS AND DISCUSSION A Solution blow spinning 3D micro-nanofiber structures characteristics In solution blow spinning process, the solution exited the inner nozzle into a droplet Then the high-speed air flow from the outer nozzle deformed the solution interface of droplet into a conical shape.16 When the surface tension was overcome by the forces of air flow, the solution droplet was ejected into multiple fine streams as shown in Fig 2(a) After the solvent evaporated, the streams became fine fibers and accumulated on the rotating collector along with the air flow as shown in Fig 2(b) The experiment parameters were chosen as followed: a square shape rotating collector with the circumscribed circle radius (opening radius) and the height of 60mm, a collector rotating speed of 1800 rpm, a solution feed rate of 0.5 µl/s, applied gas pressure of 75 Kpa, the nozzle-tip to collector distance of 500 mm, the volume ratio of water and ethanol in the solvent was : Through the solution slow spinning process, a 3D structure could be fabricated as shown in Fig 2(c)–(e) The fibers were intensively deposited in the center of the collector Fig 2(f) shows a SEM image of the sample in Fig 2(e) and the fibers diameter measuring by measuring in ImagePro Plus 6.0 soft imaging system ranged from µm to µm The porosity of this structure was 79.9% B The effect of solvent volatility In solution blow spinning, solvent volatility had a great influence on fabricating 3D structures To prove this result, solvent in different volume ratio of water and ethanol was prepared to investigate the 3D structures appearance As shown in Fig 3(a)–(c), the volume ratio of water and ethanol was : 1, : 1, : and the collector shape was square shape with the height and opening radius of 60 mm and other parameters were the same as Fig Through the solution blow spinning over two hours, it is found that the : and : volume ratio structures are significantly better than the : one The volatility of ethanol is much stronger than water PEO could not be dissolved in ethanol but in water Therefore in the solvent, water was used as a binder to mix the ethanol and PEO together As 025002-4 Liang et al AIP Advances 7, 025002 (2017) FIG (a)-(b) Optical photographs of solution blow spinning process (c)-(e) Photographs of fabrication of 3D micronanofiber structure in 0.5h (c), 1h (d), 2h (e) (f) SEM image of fiber morphology of 3D micro-nanofiber structure with magnification of 5,000x FIG Optical photographs of appearance of 3D micro-nanofiber structure fabricating in different volume ratios of water and ethanol the content of ethanol in the solution increased, the solvent evaporated more quickly so the structures would be more fluffy and thicker in the vertical direction As Fig 3(a) showed, the fibers deposited on the bottom of the collector as a membrane instead of a 3D shape structure shown in Fig 3(b)–(c) because of the incomplete evaporation of solvent C The effect of shape of collector Three kinds of shape of collector were used to investigate the effect and porosity of 3D scaffolds As shown in Fig 4, there were square shape, hemispherical shape and conical shape The opening radius and the height of these collectors was 60mm Through a simple calculation, the volume of these collectors was about 432 cm3 , 452.16 cm3 and 144 cm3 In this experiment, three kinds of collector were used in solution blow spinning to collect the fibers with collector rotating speed of 1800 rpm, solution feed rate of 0.5 µl/s, applied gas pressure of 75 Kpa, the nozzle-tip to collector distance of 500 mm, the volume ratio of water and ethanol in the solvent of : Through the solution slow spinning in two hours, as shown in Fig 4, the volume of the 3D structures would be slightly smaller than the volume of the collectors Most of the fibers were deposited in the center of the collector and formed a 3D shape fluffy structure while the other fibers wound around the collector and became fibrous layers It was easy to see it that the fibers distribution in conical collector was more concentrated than in other two collectors The porosity of the 3D structures in square collector, hemispherical collector and conical collector were 84.4%, 85%, 86.9%, respectively 025002-5 Liang et al AIP Advances 7, 025002 (2017) FIG Optical photographs of different shape of collectors and 3D micro-nanofiber structures in different view (a) Square shape collector, (b) hemispherical shape collector and (c) conical shape collector Red dotted line indicates the deformation of the top fibrous layer On the other hand, a very thick fibrous layer came into being on the top of the collector This thick layer would impede the passage of the air flow causing the newly born fibers to deposit on the layer rather than the center of the collector Eventually, this layer became much thicker and would be under the pressure of the air flow to a downward deformation which was not conducive to the fabrication of 3D structure As shown in Fig 5, a black conical shape collector whose height was twice as other collectors was used in solution blow spinning in four hours while the opening radius and other parameters were the same The 3D structure in this collector was much larger and the fibers distribution was more uniform and concentrated than in others, but the deformation of the top layer was much greater The porosity of this 3D structure was 89.9% D The effect of solution feed rate and applied gas pressure Figure 6(a) shows the relationship between average fiber diameter and the solution feed rate In these five successive experiments, the solution feed rate was 0.3 µl/s, 0.4 µl/s, 0.5 µl/s, 0.6 µl/s and 0.7 µl/s, the applied gas pressure was 75 Kpa, the collector rotating speed was 1800 rpm, the collector shape was hemispherical with the opening radius and height of 60 mm and other parameters were the same FIG Optical photographs of the larger conical shape collector and 3D micro-nanofiber structure in different view Red dotted line indicates the deformation of the top fibrous layer 025002-6 Liang et al AIP Advances 7, 025002 (2017) FIG (a) The average fiber diameter of 3D micro-nanofiber structure for various solution feed rate and (b) applied gas pressure (c) SEM image of fiber morphology of 3D micro-nanofiber structure of the solution feed rate of 0.3 µl/s and (d) 0.7 µl/s (e) SEM image of fiber morphology of 3D micro-nanofiber structure of applied gas pressure of 50 Kpa and (f) 100 Kpa Figure 6(b) shows the relationship between average fiber diameter and applied gas pressure In the five successive experiments, the applied gas pressure was 50 Kpa, 62.5 Kpa, 75 Kpa, 87.5 Kpa and 100 Kpa, the solution feed rate was 0.5 µl/s, the collector rotating speed was 1800 rpm, the collector shape was hemispherical with the opening radius and height of 60 mm and other parameters were the same Figure 6(c)–(d) shows the SEM images describing fiber morphology in 3D structures of the solution feed rate of 0.3 µl/s and 0.7 µl/s, respectively Fig 6(e)–(f) shows the SEM images describing fiber morphology in 3D structures of the applied gas pressure of 100 Kpa and 50 Kpa, respectively In Fig 6(c), the 3D structure contained a lot of nanofibers but the fiber diameter ranged from 200 nm to µm As the solution feed rate increased, the fiber diameter increased as well In Fig 6(d), there was no nanofiber but the fiber diameter increased to µm in a uniform morphology The result indicated that when the solution feed rate decreased, the high-speed air flow sheared at a smaller solution droplet on the inner nozzle which would have a stronger impact on the droplet and lead to finer fibers In Fig 6(f), the fiber morphology became extremely uneven There were both micron part and nano part in one fiber Compared with Fig 6(e), as the applied gas pressure increased, the fiber 025002-7 Liang et al AIP Advances 7, 025002 (2017) diameter decreased but the uniformity of the fiber became worse because of the unstable effect of the higher shear force of air flow on the droplet Based on this, uniform nanofibers could be fabricated by controlling the applied gas pressure and the solution feed rate That is to say the fiber morphology in the 3D structure could be controllable IV CONCLUSION In this study, a novel solution blow spinning device was used to fabricate a three-dimensional micro-nanofiber structure successfully with a minimum fiber diameter of 200 nm in the structure and a maximum porosity of 89.9% The shape of the collector affects the porosity and fiber distribution of the three-dimensional structure Both the applied gas pressure and the solution feed rate could also affect the fiber diameter and the fiber uniformity The formation of three-dimensional shape of the structure is influenced greatly by the solvent volatility This work provides a novel and effective method to fabricate controllable three-dimensional micro-nanofiber structures, indicating the great potential in tissue engineering SUPPLEMENTARY MATERIAL See supplementary material for the solution blow spinning process by using novel homemade device ACKNOWLEDGMENTS This work was financially supported by National Natural Science Foundation of China (No 51305084), Guangdong Innovative Research Team Program (No 201001G0104781202), Guangdong Innovative Research Team Program (No 2014ZT05G157), Project of Science and Technology of Guangdong Province, China (No.2013B011301005), Guangdong Provincial Key Laboratory of Micro-nano Manufacturing Technology and Equipment (GDMNML2013-1), Key Project of Science and Technology of Guangdong Province, China (No 2015B010124001), Guangdong Provincial Key Laboratory Construction Project of China (Grant No 2011A060901026), Key Joint Project of National Natural Science Foundation of China (Grant No U1134004), Project of Science and Technology of Guangdong Province(No 2015B010102014) V Mouri˜no and A R Boccaccini, Journal of the Royal Society Interface 7, 209 (2010) Duan, M Wang, W Y Zhou, W L Cheung, Z Y Li, and W W Lu, Acta Biomaterialia 6, 4495 (2010) Z Q Feng, X Chu, N P Huang, T Wang, Y Wang, X Shi, Y Ding, and Z Gu, Biomaterials 30, 2753 (2009) S G Kumbar, S P Nukavarapu, R James, L S Nair, and C T Laurencin, Biomaterials 29, 4100 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