Effect of electrospinning parameters on the morphology of polyurethane/polycaprolactone fibers

rial is bio-compatible in contact with blood cells and
tissue5. Also, polyurethane is highly favorable to the
proliferation of cells6. On the other hand, PCL -
which is biodegradable and biocompatible - possesses
eligible mechanical properties. Studies show that the
PU/PCL combination enhances themechanical prop-
erties of the composite as well as controls other fea-
tures like hydrophobicity and pore size distribution7.
As advantageous as it is, the versatility of electro-
spinning comes with inconsistency. The procedure is
prone to different ambient factors such as humidity
and temperature, as well as variations in equipment
and facilities. Moreover, recently we have created
a useful, low-cost electrospinning system8. Due to
these differences and the effect of electrospinning pa-
rameters on PU/PCL electrospun membrane was not
yet thoroughly investigated, reported electrospinning
conditions were unable to produce satisfied scaffold
with our equipment. Thus, this study aims to inves-
tigate how the electrospinning parameters affect the
Cite this article : Nguyen T B, Tran N M, Dang N N, Truong L P, Nguyen H T. Effect of electrospinning
parameterson themorphologyofpolyurethane/polycaprolactonefibers. Sci. Tech. Dev. J.; 23(3):564-
568.
564
Science & Technology Development Journal, 23(3):564-568
morphology of PU/PCL membrane and optimize the
fabrication procedure of PU/PCL electrospun mem-
brane for further research.
MATERIALS ANDMETHODS
Materials
Polycaprolactone, poly[4,40-methylenebis(phenyl
isocyanate)-alt-1,4 butanediol/di(propylene
glycol)/polycaprolactone] (PU), N,N-
Dimethylformamide (DMF), and tetrahydrofuran
(THF) - used to fabricate the membrane – were
purchased from Sigma-Aldrich (USA).
Methods
Investigation of parameters of electrospinning 12%
w/w polymer solution was prepared by adding mixed
DMF: THF (1:1 v/v) solvent into 1.2 g PU/PCL pellets
(1:1 w/w). Then, the mixture was stirred overnight
at room temperature until the solution became trans-
parent and homogeneous. The solution was placed in
a syringe and attached to a peristaltic pump (Harvard
Apparatus, Infusion Syringe Pump 980638). A high
voltage between the syringe and the collector was sup-
plied by a high DC voltage power supply. For investi-
gation purposes, the following parameters have been
varied: the distance from the tip of the needle to the
collector was set at 10cm and 12cm, the flow rate was
changed from 0.5ml/h to 1.5 ml/h and voltage fixed at
15kV and 20kV.
Scanning electron microscopy. Electrospun mem-
brane (1 x 1 cm) were sputter-coated with gold for 60
s prior to scanning electronmicroscopy (SEM).Then,
SEM (JSM-IT100, JEOL, Japan) with an accelerating
voltage of 10 kV was used to acquire the SEM images
of the membranes. The fiber diameter of each mem-
brane was measured from 3 SEM images (10 fibers
per image) and analyzed using ImageJ software (NIH,
USA).
Statistical analysis. The fiber diameter was presented
as average  standard deviation and analyzed using
SPSS Statistics software (IBM). One-way ANOVA fol-
lowed by Tukey- Kramer posthoc test was used to
compared comparison three or more groups. p-value
<0.05 was considered significant.
RESULTS
The solution of 12% w/w PU/PCL in DMF/THF were
electrospun with different parameters to investigate
their effect on the morphology of the membrane and
to achieve a suitable non-wovenmesh. Figure 1 shows
the SEM images of PU/PCL membranes electrospun
at 15 kV. When the tip was 10 cm away from the
drum collector, fibers at all conditions of flow rates
were all flattened. Most of the fibers fused at their
intersections, creating a woven matrix. As a result,
the meshes were dense with interconnected fibers. At
the tip-collector distance of 12 cm, this phenomenon
only happened at the 1.5 mL/h flow rate. The other
two flow rates yielded fibers with smaller diameters.
However, the fibers created with a flow rate of 1 mL/h
were still significantly larger than its counterpart with
several joints. Moreover, at 15 kV, the combination
of a flow rate of 0.5 mL/h and tip-to-collector dis-
tance of 12 cm yielded the best result, where their
small fiberswere distinctly separated and created non-
woven meshes. However, the fibers remained widely
varied in terms of cross-sectional diameter. This pa-
rameter also fluctuated between different sections of
every single fiber, indicated an unstable electrospin-
ning procedure.
The PU/PCL membranes are then electrospun at 20
kV with different flow rates. Overall, the fabrication
of PU/PCL at 20 kV displayed better fibers than a pre-
vious condition - porous with smaller and separated
fibers. No condition yielded largely, flatten fibers as
observed with the applied voltage of 15 kV. However,
the differences caused by flow rate and distance were
still observable when comparing the sample. At 10
cm tip-to-collector distance, membranes electrospun
at a higher flow rate (namely 1.5 mL/h) were denser
and less uniformwith several fused positions. This ef-
fect was also observed with a distance of 12 cm. Most
of the samples presented fiber morphology similar to
which of the 15 kV – 12 cm – 0.5 mL/h membrane,
where the cross-section of every single fiber was not
stable. Only the sample fabricated at a flow rate of 0.5
mL/h and a distance of 12 cm yield virtually uniform
fibers.
From SEM images, the fiber diameter of the mem-
branes was quantified using ImageJ software. As il-
lustrated in Figure 3, fibers fabricated at 15 kV have
a diameter ranging from 670 nm to 1900 nm with
high fluctuations, whereas the diameters of the 20 kV-
electrospun fiberswere all in the nanoscale (530 nm to
890 nm) with small variations.
The other trend regarding the flow rate observed from
the SEM results were also confirmed quantitatively.
Among each group with the same applied voltage and
distance, an increased flow rate generally leads to sig-
nificantly higher fiber diameter. For instance, in the
15kV – 12 cm group, fibers of the 0.5 mL/h mem-
brane averaged at 670 nm, whereas the flow rate of
1 mL/h and 1.5 mL/h produced 1611 nm fibers and
1940 fibers, respectively (p<0.05). Although the 20
kV – 10 cm and 20 kV – 12 cm groups exhibit lower
565
Science & Technology Development Journal, 23(3):564-568
Figure 1: The SEM images of PU/PCLmembranes electrospun at 15 kV. The images represent the sample elec-
trospun at the condition showed in the headings of their respective row and column. The images were acquired
at 2000x magnification, the scale represented a length of 10 mm.
Figure 2: The SEM images of PU/PCLmembranes electrospun at 20 kV. The images represent the sample elec-
trospun at the condition showed in the headings of their respective row and column. The images were acquired
at 2000x magnification, and the scale represented a length of 10 mm.
fluctuations, the difference in flow rate still induced a
significant difference between the samples, as noted
in Figure 3.
In contrast, the tip-to-collector distance showed a
negligible effect on these parameters. Except for the
disparity between 15 kV – 10 cm – 0.5 mL/h and 15
kV – 12 cm – 0.5 mL/h (p<0.05), the remaining five
pairs of conditions produced similar fibers.
DISCUSSION
The effect of the parameters can be seen in the trend
exhibited by the data. Slower flow rate, longer tip-
to-collector distance, and higher voltage all resulted
in smaller, less sticky, and more uniform fibers. As
stated by Akduman et al.9, sticky and blended fibers
generally occurred because the solvent did not have
sufficient time to evaporate completely before hitting
the collector. When the solvent remained on the
polymer matrix, the fibers were prone to be flattened
on impact and fused with the previously deposited
566
Science & Technology Development Journal, 23(3):564-568
Figure 3: Fiber diameter of PU/PCL membranes electrospun in different conditions. For each sample, the
diameter was quantified from 3 SEM images (10 fibers/image).*: p <0.05.
layers. The solution jets also tend to split into the
smaller stream the further they travel from the nee-
dle tip. Thus, reduce the flow rate and increase the
tip-to-collector distance both prolong this duration,
allowing the fibers to become completely dried. How-
ever, as showed by quantification, the distance had
the weakest effect on the morphology of the electro-
spun membrane. The tip-to-collector distance was
also limited due to the machine setting and applied
voltage. If the tip is excessively far, the voltage could
be insufficiently strong to pull the fibers so the solu-
tion jet could be pulled to the surrounding instead of
gather on the collector.
Besides these two factors, the results suggested that
the voltage affected the fibers greatly as it determines
the charges of the solution. As in this study, it can
be seen that the higher voltage led to more uniform
and smaller fibers. This result was in accordance with
other studies, as higher voltage leads to larger pulling
force and greater stretching applied on the polymer
jets10,11. For a solution with low viscosity, a higher
voltage can also induce the formation of secondary
jets, which typically result in smaller fibers. How-
ever, this conclusion is contradicted by other reports,
whichmight suggest that there is an interplay between
the factors, and there could be a critical range of volt-
age.
Wu et al. found that the fiber diameters decreased
with increasing voltage to a critical point where the
trend reversed with voltage continued to go higher12.
While higher voltage can produce smaller fibers as
discussed, it could also lead to other phenomenons in-
creasing the fiber size. With larger pulling force, it also
induces faster acceleration of the solution jets towards
the collector. Thus, for each particular polymer solu-
tion, a variety of electrospinning parameters and their
interaction should be investigated to fully understand
their effects.
In this study, the factors were varied to understand
their effect and yield a resultingmembrane resembled
the nano-topography of vascular extracellular matrix
with high surface area, interconnected pores, and de-
cent porosity for transportation of gas and nutrients.
Therefore, the condition set of voltage: 20 kV – tip-
to-collector distance: 12 cm – flow rate: 0.5 mL/h
was a PU/PCL electrospinning condition to produce
nanofibers for application in tissue engineering.
CONCLUSION
Thestudy has determined the effect of electrospinning
parameters on PU/PCLmorphology. The varying pa-
rameters, including voltage, tip-to-collector distance,
and flow rate, directly affected the amount of sol-
vent remained on the fibers when contacted with the
collector. If the pulled fibers still had residual sol-
vents, they were not sufficiently separated and fused
together, resulting in larger and woven fibers. With
the voltage of 20 kV, tip-to-collector distance of 12
cm, and the flow rate of 0.5 ml/h, the electrospun
fibers were uniform, and themorphology of themem-
brane was suitable for further application.
567
Science & Technology Development Journal, 23(3):564-568
LIST OF ABBREVIATIONS
DMF: N,N-Dimethylformamide
PCL: Polycaprolactone
PU: Polyurethane
SEM: Scanning electron microscopy
THF: Tetrahydrofuran
CONFLICT OF INTEREST
The authors declare that they have no competing in-
terest.
AUTHORS’ CONTRIBUTION
T.B.N and N.M.T performed experiments under the
supervision of L.P.T and H.T.N. All authors designed
experiments, analyzed data. T.B.N and N.M.T wrote
the paper.
ACKNOWLEDGEMENT
This research was funded by National Foundation for
Science and Technology Development (NAFOSTED,
Vietnam) under grant number 108.06-2018.18
REFERENCES
1. Pham QP, Sharma U, Mikos AG. Electrospinning of polymeric
nanofibers for tissue engineering applications: a review. Tis-
sue engineering. 2006;12(5):1197–1211. PMID: 16771634.
Available from: https://doi.org/10.1089/ten.2006.12.1197.
2. Huang ZM, Zhang YZ, Kotaki M, Ramakrishna S. A review
on polymer nanofibers by electrospinning and their applica-
tions in nanocomposites. Composites science and technol-
ogy. 2003;63(15):2223–2253. Available from: https://doi.org/
10.1016/S0266-3538(03)00178-7.
3. Braghirolli DI, Steffens D, Pranke P. Electrospinning for regen-
erative medicine: a review of the main topics. Drug discovery
today. 2014;19(6):743–753. PMID: 24704459. Available from:
https://doi.org/10.1016/j.drudis.2014.03.024.
4. Doshi J, Reneker DH. Electrospinning process and ap-
plications of electrospun fibers. Journal of electrostatics.
1995;35(2-3):151–160. Available from: https://doi.org/10.
1016/0304-3886(95)00041-8.
5. Guo HF, Dai WW, Qian DH, Qin ZX, Lei Y, Hou XY, et al. A simply
prepared small-diameter artificial blood vessel that promotes
in situ endothelialization. Acta Biomaterialia;(Supplement C).
2017;54:107–116. PMID: 28238915. Available from: https://
doi.org/10.1016/j.actbio.2017.02.038.
6. Punnakitikashem P, Truong D, Menon JU, Nguyen KT, Hong
Y. Electrospun biodegradable elastic polyurethane scaffolds
with dipyridamole release for small diameter vascular grafts.
Acta Biomaterialia. 2014;10(11):4618–4628. PMID: 25110284.
Available from: https://doi.org/10.1016/j.actbio.2014.07.031.
7. Nguyen TH, Padalhin AR, Seo HS, Lee BT. A hybrid electro-
spun PU/PCL scaffold satisfied the requirements of blood ves-
sel prosthesis in termsofmechanical properties, pore size, and
biocompatibility. Journal of Biomaterials Science, Polymer
Edition. 2013;;24(14):1692–1706. PMID: 23627704. Available
from: https://doi.org/10.1080/09205063.2013.792642.
8. Do TM, Ho MH, Do TB, Nguyen NP, Toi TV. A Low Cost High
Voltage Power Supply to Use in ElectrospinningMachines. In-
ternational Conference on the Development of Biomedical
Engineering in Vietnam: Springer. 2018;Available from: https:
//doi.org/10.1007/978-981-13-5859-3_16.
9. Akduman C, Kumbasar EPA. Electrospun Polyurethane
Nanofibers. Aspects of Polyurethanes. 2017;17. Available
from: https://doi.org/10.5772/intechopen.69937.
10. Buchko CJ, Chen LC, Shen Y, Martin DC. Processing and mi-
crostructural characterization of porous biocompatible pro-
tein polymer thin films. Polymer. 1999;40(26):7397–7407.
Available from: https://doi.org/10.1016/S0032-3861(98)00866-
0.
11. Lee IS, Kwon OH, Meng W, Kang IK, Ito Y. Nanofabrication of
microbial polyester by electrospinning promotes cell attach-
ment. Macromolecular Research. 2004;12(4):374–378. Avail-
able from: https://doi.org/10.1007/BF03218414.
12. Wu CM, Chiou HG, Lin SL, Lin JM. Effects of electro-
static polarity and the types of electrical charging on elec-
trospinning behavior. Journal of Applied Polymer Science.
2012;126(S2):E89–E97. Available from: https://doi.org/10.
1002/app.36680.
568