Electrospinning of Three-DimensionalNanofibrous Tubes with ControllableArchitecturesDaming Zhang and Jiang Chang*

Biomaterials and Tissue Engineering Research Center, Shanghai Institute of Ceramics, ChineseAcademy of Sciences, 1295 Dingxi Road, Shanghai 200050, People’s Republic of China

Received June 10, 2008; Revised Manuscript Received August 6, 2008

ABSTRACT

This paper reports a novel static method to fabricate three-dimensional (3D) fibrous tubes composed of ultrafine electrospun fibers. By usingthis unique technique, micro and macro single tubes with multiple micropatterns, multiple interconnected tubes, and many tubes with thesame or different sizes, shapes, structures, and patterns can be prepared synchronously. Parameters that could influence the order degreeof patterned architectures have also been investigated. It is expected that electrospun tubes with controllable patterned architectures and 3Dconfigurations may be attractive in many biomedical and industrial applications.

Electrospinning is currently the only technique that allowsfabrication of nanoscale continuous fibers. Electrospunultrafine fibers with extremely long length and high specificsurface area1,2 have found extensive applications in manybiomedical and industrial fields.3-6 For example, electrospunfibrous tubes have shown great potential in vascular, neural,and tendinous tissue engineering.7-10 However, electrospunfibers are generally collected as two-dimensional (2D)membranes with randomly arranged structures, which hasgreatly limited their applications. In order to fully realizethe potential of electrospun fibers, it is important to fabricatefibrous assemblies with controllable three-dimensional (3D)microstructures as the fiber arrangement will significantlyaffect the performance of devices.11 Considering specificrequirements of tubular scaffolds in tissue engineeringapplications, such as the variation in anatomic location andbiological environment,12 it is important to design and controlmicroscopic and macroscopic 3D structures of tubes to createdesired cellular responses.13,14 Intensive studies on assemblyof electrospun fibers have met with some success both inmicroscopic arrangements of fibers15-17 and macroscopic 3Dtubular structures.8,9 Li and co-workers have demonstratedthat nanofibers can be uniaxially aligned by introducinginsulating gaps into conductive collectors.15 Furthermore, ourgroup has successfully fabricated electrospun mats withcontrollable architectures and patterns.17 These specificarchitectures might promote favorable biological responsesin tissue regeneration, such as enhanced protein adsorptionas well as enhanced cell attachment and proliferation in tissue

regeneration.18,19 However, these electrospun mats withspecific fiber arrangements were usually collected as 2Dmembranes. Generally, rotating devices could be used tocollect 3D fibrous tubes. Nevertheless, there still remain somedisadvantages of this collecting method. For example, it isdifficult to control the arrangements of fibers and thearchitectures of electrospun tubes, except for the circumfer-ential well-aligned arrangement because of the rotationalmovements of the collectors. Meanwhile, failures in fabrica-tion of tiny tubes (less than 0.3 mm), tubes with one closedend, and tubes with multiple interconnected tubular struc-tures, may also limit the application of fibrous tubes, andthere still remains considerable difficulties in fabricatingfibrous tubes with controllable micropatterns and macro-scopic 3D tubular structures synchronously, and complextissue structure and fiber orientation still cannot be mimickedadequately.14 To overcome various limitations of the currentpreparation methods, a unique static collecting method withcombinatorial electric fields was designed and nanofibroustubes with different microscopic architectures and macro-scopic 3D tubular structures were fabricated in the presentstudy. The novel method using novel 3D collecting templatesis based on manipulation of electric field and electric forces,and micro and macro single tubes with multiple micropat-terns, multiple interconnected tubes and many tubes withsame or different sizes, shapes, structures and patterns canbe prepared synchronously using this unique technique. Inaddition, effects of parameters such as voltage, feeding rate,and solvents ratio on architectures of the tubes wereinvestigated, which demonstrated the possibility to adjust theorder degree of fiber deposition and arrangement.

* To whom correspondence should be addressed. E-mail: jchang@mail.sic.ac.cn.

NANOLETTERS

2008Vol. 8, No. 10

3283-3287

10.1021/nl801667s CCC: $40.75 2008 American Chemical SocietyPublished on Web 09/04/2008

Figure 1a shows a schematic illustration of electrospinningtechnique combined with a unique collecting method. Part1 shows designed 3D columnar collectors, and relevantfibrous tubes with similar configurations could be generatedafter electrospinning as schematically shown in part 2. It isfound that the macroscopic structures of the tubes arecontrollable by controlling the configurations of collectors.Tubular structures with different lengths, diameters, as wellas cross-section shapes could be fabricated. Meanwhile, byusing this unique method, tubes with multiple interconnectedtubular structures could also be fabricated.

Basically, the collector could be divided into two parts inthe collecting process, the working collector (“w” in Figure1a) with similar configuration of desired fibrous tubes andthe assistant collectors (“sa” and “pa” in Figure 1a). Witheffect of electric forces, fiber loops could deposit on bothworking and assistant collectors. When an individual co-lumnar template is used as the collector, fibers tend toconverge toward the top part of the collector because of theconcentration of electric field pointing to the top of thecollector,20 especially when the top part is in a sharp shape.It has been reported that fiber deposition could be influencedeven with a slight variation in electric field profile.12,21-23

Thus, a plane assistant collector (pa) is used to alter theelectric field and further extend the deposition areas of fibers,and as a result convergent deposition of fibers on the top ofthe collector could be avoided. Meanwhile, it has been foundthat fibers may suspend between the root of columnarcollectors and assistant collectors in some situations, whichcould cause inhomogeneous collections. Thus, another stickassistant collector (sa) is introduced.

Polycaprolactone (PCL) and D,L-poly(lactic acid) (PDLLA)were dissolved in dimethylformamide (DMF) and tetrahy-

drofuran (THF), and the solutions were used in a typicalelectrospinning process (Supporting Information, Materialsand Methods). Figure 1b shows optical photograph of a tinyfibrous tube fabricated using this method. The diameter ofthe tube is 0.50 mm, and the relevant cross section image isshown in the inset. It could be found from Figure 1c thatthe 3D fibrous tube is composed of randomly arrangedultrafine fibers. By using this method, 3D fibrous tubes withdifferent diameters, lengths, and various cross-section shapes,as well as tubes with one closed end, can be fabricated(Supporting Information, Figure S1).

Many applications require patterned architectures of thematerials. For example, materials with parallel orientationor specific patterned structure may have specific biologicaleffects on tissue regeneration.24,25 In the previous work, wedemonstrated that nanofibrous materials with patternedarchitectures could be fabricated using 2D flat collectors.17

In the present work, our study is focused on electrospinningusing 3D collectors with patterned structures. One of the mostimportant advantages of the unique technique is the fabrica-tion of tubes with controllable patterned architectures. Aschematic illustration of collecting process using a cylindricalcollector with equally spaced circular protrusions is shownin Figure 2a. Fibers tend to deposit randomly on theprotrusions and suspend in a parallel manner between theprotrusions with the effect of electric forces F. Figure 2bshows the generated fibrous tube with patterned architectures.

Figure 1. (a) Schematic illustration of fabrication of fibrous tubesby electrospinning technique using 3D columnar collectors. 1: 3Dcolumnar collectors. 2: relevant fibrous tubes. (w, working collector;pa, plane assistant collector; sa, stick assistant collector) (b) Fibroustube with diameter of 500 µm (inset is the cross-section image).(c) SEM image of fiber assemblies of tube shown in panel b.

Figure 2. (a) Schematic illustration of collecting process using acylindrical collector with equally spaced circular protrusions (es,electrospinning process; pc, patterned collector). (b) A fibrous tubewith patterned architectures (scale bar ) 5 mm). (c) Magnifiedimage of panel b (scale bar ) 200 µm). (d) Schematic illustrationof collectors with two different patterns and relevant fibrous tube(pc, patterned collector; ft, fibrous tube). (e) A fibrous tube withtwo different patterns (scale bar ) 5 mm). (f,g) Magnified imagesof two different patterns of panel e (scale bar ) 200 µm).

3284 Nano Lett., Vol. 8, No. 10, 2008

Partly magnified image of the tube is shown in Figure 2c.Fibers deposited on the protrusions are much denser thanthose aligned in parallel between the protrusions, and thesuspended fibers tend to adhere together to form fiberbundles; as a result, a specific patterned architecture isgenerated.

In many situations, different patterned structures orarchitectures may be required in one tube, and two or moredifferent patterns can be generated in one tube by the newtechnique presented in this study. Figure 2d shows aschematic illustration of fabrication of a tube with twodifferent patterned structures. A 3D collector with twodifferent patterns is illustrated in Part 1, while the generatedtube with two relevant patterned architectures is shown inpart 2. Figure 2e shows a fibrous tube with two differentpatterned architectures. It could be found that, besides thestructure aligned in parallel and shown in Figure 2f, a gridlikepatterned architecture was also generated in the same tube(Figure 2g). It is believed that fibrous tubes with variouscontrollable patterned architectures in one tube could begenerated by design of appropriate 3D collectors, and atypical example of one fibrous tube with four differentpatterns on four sides of the tube is presented in SupportingInformation (Figure S2).

The deposition and arrangement of fibers, as well as theformation of patterned architectures are determined byelectric forces.15,17 Fibers move toward the 3D collectors withthe effect of electrostatic forces resulting from the alteredelectric field. When fibers get close to a patterned collector,the deposition and arrangement of fibers are primarilyaffected by Coulomb interactions and deposit on the protru-sions by the stronger Coulomb interactions with the protru-sions as opposed to the bottom part of the collectors.17 Whena patterned plane template is used as a collector, fiber loopsmove vertically toward the 2D collector. The arrangementof fibers on the patterned collectors is primarily influencedby the patterned architecture, and generally if a symmetricalpatterned collector is used preferential symmetrical depositionof the fibers between protrusions will occur. In contrast, whena 3D patterned template is used as collector the collectingsides, which can be regarded as separated 2D plane collec-tors, are parallel along the moving direction of the fiber loopsat the beginning of the spinning process, and the fibers willbe attracted toward the patterned surface of the collectorsonly when they are getting close to the templates. Apparently,it is expected that the fiber deposition on a 3D patternedcollector might be different from that on a 2D collector, sincethe moving direction of fiber loops toward the collector isdifferent between the 3D and 2D collectors. However, noany obvious change of symmetry in the patterns formed on3D collectors was observed as compared to the patternsformed on 2D collectors. This may be explained by the muchsmaller distance between the protrusions of the patternedcollectors as compared to moving distance of the fiber loops;the formation of the patterned fibers is determined mainlyby the fiber fragments close to the protrusions, but not byfiber loops.

It is known that the structures with patterns of differentordering could affect the cell activities in tissue engineering.26

Thus, it is necessary to control the order degree of the fibrousarchitectures. In the previous study, we have shown thefabrication of patterned fibrous structures using flat patternedcollectors. 17 In the present study, a patterned collector withprotrusions was used to investigate the influences of elec-trospinning parameters on the order degree of the patterns.Figure 3 shows the influence of voltage, feeding rate, andvolume ratio of solvents on the patterned architectures. Itwas found that with proper parameters, a fully patternedstructure could be generated.17 However, with the increaseof voltage (7.5 kv), some fibers adhere together, and theordered orientation of suspended crossing fibers has beenchanged. When the voltage is as large as 10 kv, no obviousordered fiber arrangement could be found. Similar phenom-ena is found with increased feeding rate as shown in Figure3b. The volume ratio of the solvents also showed significantinfluence on the ordering of the patterned structures. WhenTHF volume ratio in solvents increased, both the orderedfiber arrangement and specific fiber deposition on protrusionschanged, and patterned architectures tended to disappear(Figure 3c).

There are two factors that directly determine the patterningof the fibers: velocity of fibers, and surface charge densityof fibers. When the velocity of fibers is relatively small,surface charge density of fibers is the key factor. Highercharge density induces stronger Coulomb interactions, whichwill result in the increase of the order degree of fiberarrangement. However, when the velocity of fibers isrelatively large, it turns to be more effective as compared tosurface charges. Many fibers will deposit on the substratesbefore they are drawn to the patterned positions. With theincrease of voltage, the fiber movement is affected byincreased electrical forces, so that the fibers arrive at thecollectors with high velocity,1 which leads to disorderedstructures on patterned collectors. It has been reported thatcharge density on the fibers decreases with increased feedingrate.27 Thus, fibers will experience smaller Coulomb interac-tions, and the order degree will be reduced. Meanwhile, asmore liquid jets are drawn out of the syringe, the vaporpressure of solvents around the fiber loops becomes ratherhigher, and the evaporation of solvents will be resisted.Therefore, many fibers adhere together as they are wet whendeposited on the collectors, which could also influence themotion of fibers because of adhesion. The permittivity ofTHF (7.4) is about one fifth of that of DMF (36.7), and withthe increase of THF/DMF volume ratio the permittivity ofsolvent is reduced obviously. As a result, the charge densityon the fibers is highly decreased, which leads to smallerCoulomb interactions and random fiber deposition. In sum-mary, by adjusting the process parameters of the electro-spinning, patterned architectures with different order degreecould be fabricated, and lower voltage, smaller feeding rate,and solvents with high permittivity could promote theformation of highly patterned architectures. However, it isworth indicating that the relationship between the parametersand order degree of the patterns identified in our system may

Nano Lett., Vol. 8, No. 10, 2008 3285

not be suitable for other systems, and optimization of theparameters needs to be carried out for each specific systemin engineering applications.

Besides simple tubes, this static collecting method can alsobe used to fabricate fibrous tubes with multi-interconnectedtubular structures, which seems to be difficult by usingrotating devices. Figure 4a shows a schematic illustrationof a typical collecting process, and the generated crossingtube with interconnected tubular structure is shown in Figure4b. The combinatorial collector 1 is composed of two parts,a removable part C1 and a basal part C2 with a circular holethat has the same diameter as C1. In the process 2, a tubewith crossing structure was formed on the surface of thecombinatorial collector during electrospinning. After elec-trospinning, C1 was then removed as shown in process 3,followed by the removal of the crossing tube from C2 asshown in process 4. Some similar complex tubes fabricatedusing this method are shown in Figure 4c. By designingcombinatorial collectors with complex tubular structures,interconnected tubes with many branches can be fabricated.This kind of interconnected tubes may find importantapplications in blood vessel reconstruction.28,29

Besides fabrication of fibrous tubes with controllablepatterned architectures and 3D configurations, another im-portant feature of the new technique is the batch fabricationof tubes with different size, shape, wall structure, and pattern.Figure 4d shows a schematic illustration of a typical batch

fabrication process. 3D collectors with the same or differentconfigurations and microscopic architectures could be fixedin one plane assistant collector, and various tubes could begenerated synchronously. Figure 4e shows an optical pho-tograph of nine tiny tubes fabricated in one combinatorialcollector. Distance between the individual 3D collectors isa key parameter in this process, and excessively smalldistance may cause fiber suspension between collectors.However, the exact value is influenced by lots of parameterssuch as materials used and applied electrospinning param-eters, and may vary in different experimental situations.

In summary, electrospinning with unique 3D collectingmethod is a versatile technique to fabricate fibrous tubes forvarious industrial and biomedical applications. By designing3D collectors, fibrous tubes with different macroscopicconfigurations (length, diameter, shape) can be fabricated,and multiple tubes with various interconnected tubularstructures could be fabricated using removable collectingtemplates. Furthermore, fabrication of tubes with patternedarchitectures is synchronously controllable in this process,and two or more different patterns could be generated inone tube. Voltage, feeding rate, and volume ratio of solventscould influence the order degree of patterned architectures.In addition, this method has been proven to be effective inbatch fabrication of tubes with the same or differentconfigurations and architectures at one time. Manipulationof electric field is the basic principle of this method, and

Figure 3. (a) Influence of voltage on patterned architectures (v, voltage). (b) Influence of feeding rate on patterned architectures (FD,feeding rate). (c) Influence of volume ratio of solvents (DMF/THF) on patterned architectures (VR, volume ratio; D, DMF; T, THF). (scalebar ) 100 µm).

3286 Nano Lett., Vol. 8, No. 10, 2008

many parameters including the distance between tip ofspinneret and the top part of 3D collector, as well as thespecific properties of materials and the enviromental condi-tions, may affect the tube structures. The influence of theseparameters might mutually be dependent, and further studiesare required to determine the role of all of these parameters.It is expected that electrospinning with the static collectingmethod using 3D collectors with specifically designedpatterns and configurations has great potential for fabricationof fibrous tubes with controllable architectures and 3Dconfigurations, and these kinds of fibrous tubes may be

attractive in many biomedical and industrial applications suchas tissue engineering and filtration applications.

Acknowledgment. This work is supported by the NationalBasic Science Research Program of China (973 Program)(Grant 2005CB522704) and the Natural Science Foundationof China (Grant 30730034).

Supporting Information Available: Materials and meth-ods and figures. This material is available free of charge viathe Internet at http://pubs.acs.org.

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NL801667S

Figure 4. (a) Schematic illustration of process for fabrication oftubes with multiple interconnected tubular structure (C1, removablecollector; C2, basal collector; T, tubes with interconnected tubularstructure). (b) A crossing tube (scale bar ) 5 mm). (c) Tubes withvarious interconnected tubular structures (scale bar ) 5 mm). (d)Schematic illustration of the batch fabrication of tubes with sameor different configurations and microscopic architectures. (e) Imageof batch fabrication of nine micro tubes.

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