Surface modification and antibacterial activity of electrospun ...

Journal of Membrane Science 320 (2008) 259–267
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Journal of Membrane Science
journal homepage: www.elsevier.com/locate/memsci
Surface modification and antibacterial activity of electrospun polyurethane
fibrous membranes with quaternary ammonium moieties
Chen Yao a,b , Xinsong Li a,∗ , K.G. Neoh b,∗ , Zhilong Shi b , E.T. Kang b
a School of Chemistry and Chemical Engineering, Southeast University, Sipailou 2, Nanjing 210018, PR China
b Department of Chemical and Biomolecular Engineering, National University of Singapore, Kent Ridge, 119260 Singapore, Singapore
article
info
abstract
Article history:
Received 26 February 2008
Received in revised form 3 April 2008
Accepted 5 April 2008
Available online 15 April 2008
Keywords:
Electrospinning
Antibacterial
Surface modification
Polyurethane
A novel antibacterial material was developed by surface modification of electrospun polyurethane (PU)
fibrous membranes, using a process which involved plasma pretreatment, UV-induced graft copolymerization
of 4-vinylpyridine (4VP), and quaternization of the grafted pyridine groups with hexylbromide.
The success of modification with poly(4-vinyl-N-hexyl pyridinium bromide) groups on these was ascertained
by X-ray photoelectron spectroscopy (XPS). The morphologies and mechanical properties were
investigated by scanning electron microscopy (SEM) and tensile test, respectively. The results showed
that the morphologies of PU fibrous membranes changed slightly during the modification process and
the fiber structures were maintained. The tensile strength of PU fibrous membranes decreased after surface
modification, with the smallest decrease (90%) [19]. Electrospun cellulose acetate fibers containing
silver nanoparticles showed strong antimicrobial activity against
both Gram-negative and Gram-positive bacteria [20,21]. Kenawy et
al. modified the poly(vinyl phenol) either by sulphonation or by formation
of lithium salt of the sulphonated species, and investigated
the antibacterial activities of the modified poly(vinyl phenol) electrospun
mats [22]. Polyurethane cationomers polymerized from
base PU with chain extenders having a quaternary ammonium
0376-7388/$ – see front matter © 2008 Elsevier B.V. All rights reserved.
doi:10.1016/j.memsci.2008.04.012

260 C. Yao et al. / Journal of Membrane Science 320 (2008) 259–267
group were electrospun into non-woven nanofiber mats for antimicrobial
nanofilter applications [23].
A more straightforward way is to modify the surface of polymer
nanofibers without affecting bulk properties of the treated
nanofibers. The methods used to impart surface modification usually
depend strongly on the nature of the fiber-forming polymer
and include, but are not limited to, covalent polymer grafting
[24], plasma treatment [25], physisorption (e.g., hydrogen-bonding
interactions) [26], chemisorption [27], and chemical derivatization
[28]. Among the various methods, plasma treatment provides a
clean and environmentally friendly way for surface modification
[29]. The free radicals and electrons created in the plasma treatment
could be used to modify the polymer nanofibers chemically. Covalent
attachment of functional compounds to polymer fiber surfaces
is the preferred approach to introduce functionalities permanently
and at reasonably high efficiency.
There are numerous antimicrobials suitable for immobilization
on polymer surfaces. Quaternary ammonium compounds seem
attractive because their target is primarily the microbial membrane
and they accumulate in the cell driven by the membrane potential
[30]. To maximize efficiency, quaternary ammonium compound
is used as monomeric link in the polymeric leash and poly(4-
vinylpyridine) (PVP) is usually selected as the carrying polymer.
Tiller et al. showed that the surfaces of commercial polymers
treated with N-alkylated PVP groups were lethal on contact to both
Gram-positive and Gram-negative bacteria, and it was also shown
that N-alkyl chain of six carbon units in length was the most effective
[31].
The purpose of this paper was to develop novel antibacterial
PU fibrous membranes by electrospinning the polymer followed
by plasma pretreatment, UV-induced graft copolymerization and
quaternization reaction. Electrospun PU fibrous membranes were
modified with poly(4-vinyl-N-hexyl pyridinium bromide) on the
surfaces to achieve antibacterial activities. The modified PU fibrous
membranes were subsequently characterized in terms of their
morphologies, surface chemical compositions and mechanical
properties. The antibacterial activities of the fibrous membranes
were assessed against both Gram-positive Staphylococcus aureus (S.
aureus) and Gram-negative Escherichia coli (E. coli).
2. Experimental
2.1. Materials
Polyurethane elastomer, Elastollan ® 1180A10, was received from
BASF. 4-Vinylpyridine (4VP) monomer was obtained from Aldrich
Chemical Co. and freshly distilled under reduced pressure before
use. Hexylbromide and solvents, such as tetrahydrofuran (THF),
N,N-dimethyl formamide (DMF), heptane, 2-propanol, were of
reagent grade and used as received from Aldrich Chemical Co. Peptone,
yeast extract, agar and beef extract were purchased from
Oxoid. S. aureus (ATCC 25923) and E. coli (ATCC DH5) were
obtained from American Type Culture Collection.
2.2. Electrospinning of PU
PU was dissolved in a mixed solvent of THF and DMF (1:1, v/v) to
produce various spinning solutions with PU concentrations ranging
from 5% to 11% (w/v, g/mL). Viscosity, conductivity and surface
tension of the prepared solutions were measured with a viscometer
(NDJ-9S, ShangPing), a conductivity meter (DDB-303A, Rex) and
a surface tension meter (BZY-1, HengPing) at 20 ◦ C, respectively. A
syringe pump was used to feed the polymer solution through a 20-
mL plastic syringe fitted with a needle of tip diameter of 0.6 mm
at a delivery rate of 6 mL/h. After high voltage ranging from 10
to 12 kV was applied to the needle, a positive charged jet of PU
solution formed from the Taylor cone and sprayed to a grounded
drum, approximately 10 cm from the needle tip. With the evaporation
of solvent, PU fibers were deposited on the drum to form
fibrous membrane. The as-spun fibrous membrane was then dried
under vacuum and annealed at 80 ◦ C for 6 h. All electrospinning
experiments were carried out at 20 ◦ C and relative humidity of 50%.
2.3. Surface modification of PU fibrous membranes
PU fibrous membranes were subjected to argon plasma pretreatment
in an Anatech SP100 plasma system, equipped with a
cylindrical quartz reactor chamber. The glow discharge was produced
at a plasma power of 35 W, an applied oscillator frequency
of 40 kHz and an argon pressure of approximately 80 Pa. After
subjected to glow discharge for 60 s on both surfaces, the fibrous
membrane was exposed to air for 5 min to facilitate formation of
surface oxide and peroxide groups.
The plasma pretreated fibrous membranes were immersed
in 2-propanol solution of 20 vol.% 4VP in a Pyrex glass tube.
Degassing of the solution was achieved by bubbling nitrogen vigorously
for 30 min and sealing the tube with silicon rubber stopper.
The tube was then exposed to UV irradiation in a Riko rotary
photochemical reactor (RH400-10W) for 60 min on each surface.
The graft-copolymerized fibrous membranes were subjected to
washing with copious amounts of 2-propanol to remove residual
monomer and physically adsorbed homopolymer.
The fibrous membranes with graft-copolymerized 4VP were
then placed in heptane solutions containing 20 vol.% hexylbromide
and the reaction mixture was stirred for 48 h at 60 ◦ C. The fibrous
membranes were then thoroughly rinsed with heptane and dried
under vacuum.
2.4. Surface characterization
The morphology of PU fibrous membranes was observed with a
scanning electron microscope (JEOL JSM 5600LV) after gold sputtercoating.
Diameters of the electrospun fibers were measured directly
from SEM images, with an average value being calculated from at
least 100 measurements.
Surface compositions of PU fibrous membranes were analyzed
by XPS on an AXIS HSi spectrometer (Kratos Analytical Ltd.) using
the monochromatized Al K X-ray source (1486.6 eV photons) at
a constant dwell time of 100 ms and a pass energy of 40 eV. The
anode voltage was 15 kV, and the anode current was 10 mA. The
core-level signals were obtained at a photoelectron takeoff angle
of 90 ◦ (with respect to the membrane surface). To compensate for
surface charging effect, all binding energies (BEs) were referenced
to the C 1s hydrocarbon peak at 284.6 eV. In the peak synthesis,
the line width (full width at half-maximum) of the Gaussian
peaks was maintained constant for all components in a particular
spectrum. The peak area ratios for the various elements were corrected
using experimentally determined instrumental sensitivity
factors.
2.5. Mechanical property
Tensile tests of PU fibrous membranes were performed using
an Instron universal materials testing machine (Model 5544) with
a 10 N load cell in a constant relative humidity (50%) room at
25 ◦ C. “Dog-bone” shaped samples were cut from the fibrous membranes
(5-mm wide at the narrowest point with a gage length of
15 mm). The thickness of these samples was measured with a digital
micrometer having a precision of 1 m. A cross-head speed of

C. Yao et al. / Journal of Membrane Science 320 (2008) 259–267 261
Fig. 1. Electrospinning solution parameters and average diameter of the as-spun fibers with different PU concentrations.
10 mm/min was used and at least five samples were tested for each
type of the fibrous membranes.
2.6. Determination of antibacterial activity
S. aureus was incubated in 10 mL of a 3.1% yeast–dextrose broth
(containing 10 g/L peptone, 8 g/L beef extract, 5 g/L sodium chloride,
5 g/L glucose, and 3 g/L yeast extract at a pH 6.8) for 6–8 h at 37 ◦ C
until the exponential growth phase was reached [32].
The bacteria-containing broth was centrifuged at 3000 rpm for
10 min, and after removal of supernatant, the cells were washed
twice with sterile phosphate-buffered solution (PBS). The bacteria
cells were resuspended to provide a final density of 10 6 cells/mL
in PBS (based on standard calibration with the assumption that
the optical density of 1.0 at 540 nm is equivalent to approximately
10 9 cells/mL) [33].
PU fibrous membranes electrospun from 10% (w/v) solutions in
THF and DMF (1:1, v/v) (either pristine or modified, 8 mm × 8 mm)
were sterilized with ultraviolet irradiation for 30 min, and then
immersed in 10 mL of the bacterial suspension in an Erlenmeyer
flask and shaken at 200 rpm at 37 ◦ C. The viable cell counts of
bacteria were measured by surface spread plate method. At the
predetermined time, 1 mL of bacteria culture was taken from the
flask and decimal serial dilutions with PBS were repeated with each
Fig. 2. XPS wide scans of (a) pristine PU fibrous membranes, (d) PU membranes grafted with PVP, and (g) PU membranes modified with poly(4-vinyl-N-hexylpyridinium
bromide); C 1s core-level spectra of (b) pristine PU fibrous membranes, (e) PU membranes grafted with PVP, and (h) PU membranes modified with poly(4-vinyl-Nhexylpyridinium
bromide); N 1s core-level spectra of (c) pristine PU fibrous membranes, (f) PU membranes grafted with PVP, and (i) PU membranes modified with
poly(4-vinyl-N-hexylpyridinium bromide). PU fibrous membranes were electrospun from 10% (w/v) PU solutions in THF and DMF (1:1, v/v).

262 C. Yao et al. / Journal of Membrane Science 320 (2008) 259–267
initial sample. A 0.1-mL drop of the diluted sample was then spread
onto solid growth agar plates. After incubation of the plates at 37 ◦ C
for 24 h, the number of viable cells (colonies) was counted manually,
and expressed as mean colony-forming units per milliliter
(CFU/mL) after multiplication with the dilution factor. After 4 h, the
PU fibrous membranes were removed from the bacterial suspension
with sterile forceps and gently washed with PBS. The bacteria
retained on membranes were dislodged by mild ultrasonication (for
10 min) in a 100 W ultrasonic bath. Serial 10-fold dilutions were performed
and viable counts estimated following the surface spread
plate method. The number of colony-forming units on each membrane
surface was computed and expressed relative to the apparent
surface area of the membrane (CFU/cm 2 ). All experiments were performed
in triplicate and the quantitative value was expressed as the
average ± standard deviation.
The extent of bacterial adhesion on PU fibrous membranes
(both pristine and modified) were also assessed by examining
these membranes after 4 h immersion in the PBS suspension of
Fig. 3. SEM images of (a), (c) and (e) pristine, (b), (d) and (f) modified PU fibrous membranes with poly(4-vinyl-N-hexylpyridinium bromide). PU fibrous membranes were
electrospun from (a) and (b) 6%, (c) and (d) 8%, (e) and (f) 10% (w/v) solutions in THF and DMF (1:1, v/v).

C. Yao et al. / Journal of Membrane Science 320 (2008) 259–267 263
10 7 cells/mL S. aureus. Control experiment was carried out with the
filter paper. The membranes were then examined under SEM (JEOL
JSM 5600LV) to assess the adhesion and viability of the bacteria.
The membrane fixation and preparation for SEM were as follows:
the membranes were first washed with PBS and 3 vol.% glutaraldehyde
in PBS was added for 5 h and stored at 4 ◦ C. The glutaraldehyde
solution was then removed and the membranes were washed with
PBS, followed by step dehydration with 25%, 50%, 70%, 95%, and
100% ethanol for 10 min each. The membranes were dried under
vacuum and gold sputter-coated before SEM observation.
For E. coli, the same assay procedures were used as those
described above for S. aureus.
3. Results and discussion
3.1. Electrospinning of PU
While electrospinning has proven to be a versatile and powerful
means of fabricating polymer micro/nanofibers, its applicability
to obtain smooth, uniform fibrous structure is not straightforward.
Among various parameters of electrospinning process, such
as applied voltage, needle tip-to-receiver distance and solution
delivery rate, concentration or corresponding viscosity of spinning
solution is one of the most effective variables for controlling fiber
morphology and diameter. Results obtained from our study showed
that solution concentration was found to be the major factor controlling
the morphology of the fibers in the electrospinning of PU.
Various PU solutions with concentration in the range of 5–11%
(w/v, g/mL) in THF and DMF (1:1, v/v) were electrospun. A beadon-string
morphology with several big beads was obtained at
PU concentration of 5% (w/v). The distribution density of beads
decreased when PU concentration increased to 6% (w/v). The shape
of the beads became spindle-like. Smooth and homogeneous fibers
without beads were produced when PU concentration reached 8%
(w/v). As PU concentration increased from 9% to 11% (w/v), the
electrospun fibers became thicker and more adhesive at various
bonding sites, which led to a film-like character and structural
integrity of the fibrous membranes.
The effects of electrospinning solution parameters on the average
diameter of PU nanofibers were investigated. As shown in
Fig. 1a, viscosity of PU solutions increased with increasing PU
concentration. However, both conductivity and surface tension of
PU solutions with different concentrations did not differ much
(Fig. 1b). The viscosity of a polymer solution reflects the intermolecular
interactions between polymer chains. Polymer solutions
with higher viscosity usually exhibit longer stress relaxation times,
which may facilitate the formation of fibers with large diameters
during electrospinning [34]. When the viscosity of PU solutions
increased greatly from 0.186 Pa s up to 0.459 Pa s with increasing
PU concentration from 9% to 11% (w/v), the average fiber diameter
increased dramatically from 820 nm to 1.95 m(Fig. 1a). Therefore,
Fig. 4. (a) Tensile strength, (b) elongation at break and (c) Young’s modulus of PU fibrous membranes electrospun from solutions with different concentrations (both pristine
membranes and those modified with poly(4-vinyl-N-hexylpyridinium bromide)).

264 C. Yao et al. / Journal of Membrane Science 320 (2008) 259–267
it was considered that the viscosity of solution was the major factor
affecting the average diameter of electrospun PU nanofibers.
3.2. Surface modification of PU fibrous membranes
The success of modification with poly(4-vinyl-N-hexyl pyridinium
bromide) on electrospun PU fibrous membranes can be
ascertained by comparing the XPS spectra of the pristine and modified
membranes as shown in Fig. 2.
The spectra of pristine PU fibrous membranes showed three
main signals corresponding to C 1s (284.6 eV), O 1s (532 eV) and
N 1s (400 eV) (Fig. 2a). The XPS C 1s core-level spectrum of pristine
PU fibrous membrane (Fig. 2b) was resolved into three component
peaks: a hydrocarbon environment (C–H, C–C, 284.6 eV), a carbon
singly bound to oxygen environment (C–O, 286.0 eV), and a carbon
in a carbamate environment (–CO–, 289.0 eV) [35]. The corresponding
N 1s spectrum (Fig. 2c) showed an intense peak at the binding
energy (BE) of 399.5 eV attributable to the nitrogen (–NH–) in carbamate
of PU.
After UV-induced graft copolymerization of PVP onto the PU
fibrous membranes, the C 1s core-level spectrum (Fig. 2e) showed
an additional peak at 285.5 eV attributable to C–N species. The
intensity of the peak assigned to C–O species became weaker and
that of –CO– species was barely discernible compared with Fig. 2b.
Similarly, the corresponding N 1s spectrum (Fig. 2f) showed an
additional peak at the BE of 398.5 eV attributable to imine moiety
(–N ) of the pyridine rings [36] and a decrease in the intensity of
–NH– peak component compared with Fig. 2c. The extent of surface
grafting of PVP can be estimated from the sensitivity factor corrected
ratio of the total N 1s peak over the total C 1s peak, expressed
as [N]/[C]. Previous work of surface graft copolymerization showed
that graft concentration of PVP was affected by the monomer concentration
[37]. In this experiment, 4VP concentration of 20% was
chosen for effective surface graft copolymerization. As determined
by XPS, the surface [N]/[C] ratio of the 4VP grafted onto PU fibrous
membrane was 0.12, close to the value of 0.14, expected for the 4VP
monomeric unit (C 7 H 7 N 1 ). It indicated that the surface was almost
completely covered by 4VP copolymers, which could provide abundant
reactive sites for the subsequent quaternization.
Fig. 2g–i shows the XPS spectra of the graft-copolymerized PU
fibrous membrane N-alkylated with hexylbromide. No significant
difference was observed in C 1s core-level spectrum before (Fig. 2e)
and after (Fig. 2h) N-alkylation. The corresponding N 1s core-level
spectrum in Fig. 2i showed an additional peak at BE above 400 eV,
attributable to the N + groups of the pyridinium ions [38], which
confirmed the derivatization of the –N groups by hexylbromide.
On the basis of the [N + ]/[N] ratio, the degree of alkylation of the
pyridine rings on the PU fibrous membrane was around 50–60%.
Fig. 3 shows the typical SEM images of PU fibrous membranes
before and after surface modification. The morphologies of the surface
modified PU fibrous membranes electrospun from 6%, 8% and
10% (w/v) solution changed slightly compared with those of pristine
PU fibrous membranes. The result indicated that the fiber structures
were maintained during the modification process, and no
significant change in fiber diameter was observed.
3.3. Mechanical property
PU fibrous membranes both pristine and modified with
poly(4-vinyl-N-hexylpyridinium bromide) were tested for their
mechanical integrity in terms of tensile strength, elongation at
break and Young’s modulus, as indicated in Fig. 4. It can be seen
that the pristine electrospun PU fibrous membranes had tensile
strength of 3.27–11.8 MPa, elongation at break of 159.2–349.7%,
and Young’s modulus of 1.78–3.73 MPa, depending on the concentration
of polymer solution used for electrospinning. PU fibrous
membranes electrospun from 7% (w/v) solution had the lowest tensile
strength of 3.27 MPa (Fig. 4a). As the concentration increased
to 8% (w/v), the tensile strength increased to 3.88 MPa. The Young’s
modulus and elongation at break showed an increasing trend with
concentration as well (Fig. 4b and c). This is mainly due to more
interstices between the fibers with smaller diameters, resulting in
a lower number of closely adjacent binding in the fibrous membranes.
Since strong “sticky” binding interactions make a major
contribution to the strength of the membranes, increasing the fiber
diameters can lead to increases of tensile strength [39]. When PU
concentration increased from 9% to 11% (w/v), the tensile strength
of the pristine as-spun fibrous membranes increased significantly
from 4.32 to 11.80 MPa, in agreement with the increase in fiber
diameters as shown in Fig. 1a.
On the other hand, the tensile strength and elongation at break
of PU fibrous membranes decreased after surface modification,
whereas the Young’s moduli did not show much change. As shown
in Fig. 4a, the tensile strength of PU fibrous membranes electrospun
from 7% (w/v) solution decreased from 3.27 to 1.99 MPa after
modification, losing almost 40% of tensile strength. As the solution
Fig. 5. Viable cell numbers of (a) Staphylococcus aureus, and (b) Escherichia coli as a function time in contact with: () control, () pristine and () modified PU fibrous
membranes. The cell number was determined by surface spread plate method.

C. Yao et al. / Journal of Membrane Science 320 (2008) 259–267 265
concentration increased, smaller decreases in the tensile strength
were observed. With a concentration of 11% (w/v) which resulted in
the largest diameter of fibers in PU fibrous membranes, the loss of
tensile strength was approximately 16%. The results indicated that
the surface modification may have less adverse effect on the tensile
strength of fibrous membranes with larger diameters. In view
of these results, the antibacterial assays were carried out with surface
modified PU fibrous membranes electrospun from 10% (w/v)
solutions in THF and DMF (1:1, v/v) in order to achieve a balance
between mechanical properties and fibrous structures.
3.4. Antibacterial activity
Antibacterial efficacy of surface modified PU fibrous membranes
with poly(4-vinyl-N-hexylpyridinium bromide) was investigated
by estimating the number of viable bacteria cells in the S. aureus
and E. coli suspension after being in contact with membranes for
various periods of time, and the results were shown in Fig. 5. As
expected, no significant loss of viable bacteria was detected in the
control experiment (i.e. without the membranes). For pristine PU
fibrous membranes, the viable cell numbers in bacteria suspen-
Fig. 6. SEM images of (a) and (d) filter paper (control), (b) and (e) pristine, and (c) and (f) modified PU fibrous membranes after immersed in PBS suspension of (a)–(c) S.
aureus, or (d)–(f) E. coli at 10 7 cells/mL for 4 h. PU fibrous membranes were electrospun from 10% (w/v) solutions in THF and DMF (1:1, v/v).

266 C. Yao et al. / Journal of Membrane Science 320 (2008) 259–267
sions were similar to the control (Fig. 5a). The surface modified PU
fibrous membranes had a high antibacterial efficacy for S. aureus,
reaching 99.9% and 99.999% after 1 and 4 h contact, respectively.
In comparison, the antibacterial efficacy for E. coli was 99.9% after
4 h contact (Fig. 5b), lower than that for S. aureus. Although the
mechanism of the antibacterial activity of immobilized quaternary
ammonium groups is not entirely clear. It has been hypothesized
that these immobilized moieties disrupt the integrity of the cytoplasmic
membrane to cause cell death, similar to the mechanism
of free biocides [40]. The difference in antibacterial efficacy is postulated
to be the result of the different cell membrane structures
between S. aureus and E. coli bacteria. The multilayered cell envelope
structure of Gram-negative bacteria may be more resistant to
access by the bactericidal moieties to the inner membrane of the
organism [15].
Fig. 6 shows the SEM images of different substrates after immersion
in bacteria suspensions. Numerous distinguishable S. aureus
cells can be observed on the filter paper as shown in Fig. 6a. The
number of S. aureus cells on the pristine PU fibrous membranes was
significantly less (Fig. 6b). The S. aureus was distributed not only on
the pristine PU fibrous membrane upper surface but also entrapped
in the space between the thin fibers. In contrast, very few sparsely
distributed bacteria cells could be spotted over the entire surface
of the modified PU fibrous membrane (Fig. 6c). Similar results were
observed for E. coli on the surface of fibrous membranes as shown
in Fig. 6d–f. The results indicated that both filter paper and pristine
PU fibrous membranes are good templates for the proliferation of
bacteria and biofilm formation may occur readily on such surfaces
in contact with bacteria. The presence of quaternary ammonium
groups attached to the surface of PU fibrous membranes was thus
demonstrated to be very effective in preventing biofilm formation.
Since the interstitial spaces of the pristine PU fibrous membranes
are large enough, it can be expected that some bacteria
would have penetrated into the fibrous membranes during immersion
in the bacteria suspension. Therefore, the bacteria retained
in fibrous membranes were dislodged by mild ultrasonication and
the number of viable cells was counted by surface spread plate
method. For the pristine PU fibrous membranes, the mean number
of S. aureus and E. coli cells relative to the surface area was
(9.03 ± 0.63) × 10 4 and (1.65 ± 0.24) × 10 5 CFU/cm 2 , respectively.
For the modified PU fibrous membranes, the corresponding numbers
were 735 ± 35 of S. aureus and 2555 ± 315 CFU/cm 2 of E. coli
cells. Since very few bacteria cells could be observed on the surface
of the modified PU fibrous membrane (Fig. 6c), the bacteria
may be entrapped deep in the membrane either on fibers which
have lower concentration of the antibacterial N-alkyl pyridinium
units or on dead bacteria deposited on the fibers which provided a
shielding effect from the N-alkyl pyridinium groups.
4. Conclusions
The surface of electrospun PU fibrous membranes was successfully
modified with poly(4-vinyl-N-hexyl pyridinium bromide)
using a method involving plasma pretreatment, UV-induced
surface graft copolymerization and N-alkylation reaction. The morphologies
of PU fibrous membranes changed slightly and the fiber
structures were maintained after the modification process. The
tensile strength and elongation at break of modified PU fibrous
membranes decreased, whereas the Young’s moduli showed no significant
change. Antibacterial assays showed that the modified PU
fibrous membranes possessed highly effective antibacterial activities
against both Gram-positive S. aureus and Gram-negative E. coli.
The novel antibacterial PU fibrous membranes may have a wide
variety of potential applications in high-performance filters, protective
textiles, and biomedical devices.
Acknowledgements
Project 50573011 and 50673019 supported by the National Natural
Science Foundation of China. Grant no.: R 279000202112 from
the National University of Singapore, Ministry of Education, Singapore.
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