1
Prevention of bacterial adhesion on polyamide reverse
2
osmosis membranes via electrostatic interactions using a
3
cationic phosphorylcholine polymer coating
4
Daisuke Saeki, Tatsuya Tanimoto, Hideto Matsuyama*
5
Center for Membrane and Film Technology, Department of Chemical Science and Engineering, Kobe
6
University, 1-1 Rokkodai, Nada, Kobe 657-8501, Japan
7
* Corresponding author. E-mail:
[email protected]. Phone & FAX: +81-78-803-6180.
8 9
1
1
ABSTRACT
2
A simple and easy anti-adhesive coating method against bacteria via electrostatic interaction was
3
developed for polyamide reverse osmosis (RO) membranes using a cationic phosphorylcholine polymer.
4
A commercial polyamide RO membrane was immersed into an aqueous solution of phosphorylcholine
5
polymer containing cationic amino groups, poly[2-methacryloyloxyethyl phosphorylcholine (MPC)-co-
6
2-aminoethylmethacrylate (AEMA)] (p(MPC-co-AEMA)). From the results of contact angle and
7
surface potential measurements, the surface of the coated RO membrane became more hydrophilic than
8
that of raw membranes and had a neutral charge. Conversely, the surface of an RO membrane immersed
9
in an aqueous solution of MPC homopolymer without AEMA groups was not coated by the polymer.
10
Therefore, p(MPC-co-AEMA) was adsorbed via electrostatic interaction between the cationic amino
11
groups of AEMA and anionic carboxylic groups on the polyamide RO membrane. X-ray photoelectron
12
spectroscopy showed the existence of phosphorylcholine groups from p(MPC-co-AEMA) on the coated
13
membranes. The result of quartz crystal microbalance with dissipation monitoring measurements
14
showed that adsorbed p(MPC-co-AEMA) was hardly desorbed from the polyamide surface in a high
15
ionic strength solution at least for one day. The coated RO membrane had high resistance to bacterial
16
adhesion and retained its original rejection performance.
17
KEYWORDS: Reverse osmosis membrane; phosphorylcholine polymer; anti-biofouling; electrostatic
18
interaction
19
2
1
MANUSCRIPT TEXT
2
1. Introduction
3
Water treatment using reverse osmosis (RO) membranes saves energy and space compared with other
4
processes and has therefore been widely applied to various systems, such as desalination and waste
5
water recycle. Commercially available RO membranes are mainly polyamide composite membranes
6
composed of a polyamide rejection layer and polysulfone support membrane [1], which have advantages
7
of high water permeability and good rejection performance. The use of RO membranes enables
8
treatment of seawater and industrial waste water containing various organic matters, including bacteria
9
[2-4], proteins and polysaccharides [5-8]. Organic matters cause a decrease in membrane performance
10
by adhesion onto the membrane surface and blocking of membrane pores. In particular, bacteria grow
11
onto the membrane surface and form biofilms containing extracellular polymeric substances (EPS) such
12
as proteins and polysaccharides [3, 9]. This phenomenon is called “biofouling”. Adhered organic
13
matters are generally removed by chemical treatment, including chlorine [10]. However, amide bonds in
14
the polyamide membranes are cleaved by chlorine treatment, causing membrane performance to
15
decrease [11]. Prevention of bacterial adhesion is important for maintaining RO membranes and long-
16
term operation.
17 18
Various approaches for preventing bacterial adhesion onto membrane surfaces have been reported
19
[12]. Surface modification with polyethylene glycol (PEG) prevents the adhesion of biological materials
20
such as proteins [13, 14], cells [15], and bacteria [16] because of PEG’s high hydrophilicity and large
21
extruded volume [17]. PEG has already been applied as a surface modifier to prevent adhesion of
22
organic materials such as surfactants and proteins [18-20]. Recently, zwitterionic polymers such as
23
sulfobetaine polymers and phosphorylcholine polymers have also been reported to effectively prevent
24
adhesion of biological materials [21-24]. Zwitterionic polymers have a similar structure to biological
25
membranes and interact with water molecules via electrostatic interaction more strongly than PEG,
3
1
which interacts via hydrogen bond formation [25]. Modification with zwitterionic polymers is effective
2
for prevention of bacterial adhesion onto membrane surfaces [26, 27].
3 4
Surface modification with these polymers is generally carried out using a covalent grafting method
5
[13, 16, 18-20, 22, 23] or coating method [21, 24, 28, 29]. Although grafting methods have the
6
advantage of long-term stability, the modification process causes complexity in the overall membrane
7
fabrication process. On the other hand, coating methods, such as the dip coating method and spin
8
coating method, can immobilize target molecules much more simply. In addition, modification of a
9
target surface is not required. Ishigami et al. reported that RO membranes multilayer-coated using
10
oppositely charged polyelectrolytes via electrostatic interaction had resistance against adsorption of
11
proteins, although their water permeability was decreased [30]. For water treatment applications, surface
12
modification is required to retain the water permeability of the original membranes.
13 14
In this study, we developed a simple and easy modification method for coating phosphorylcholine
15
polymer onto a RO membrane via electrostatic interaction to prevent bacterial adhesion. We used
16
poly[2-methacryloyloxyethyl
17
(p(MPC-co-AEMA)), as a cationic phosphorylcholine polymer. Cationic phosphorylcholine polymer
18
has been reported as DNA careers for drug delivery [31-33]. A commercial polyamide RO membrane
19
was immersed into an aqueous solution of p(MPC-co-AEMA), and coated via electrostatic interaction
20
between the cationic amino groups of p(MPC-co-AEMA) and the anionic carboxyl groups on the RO
21
membrane. The surface properties of the coated RO membranes were evaluated by contact angle,
22
surface potential, and X-ray photoelectron spectroscopy (XPS). The coating behavior and coating
23
stability of p(MPC-co-AEMA) on the RO membrane was characterized by a quartz crystal microbalance
24
with dissipation (QCM-D) measurement. The water permeability, salt rejection, and anti-adhesive
25
properties against bacteria were evaluated for membrane performance.
phosphorylcholine
(MPC)-co-2-aminoethylmethacrylate
(AEMA)]
4
1 2
2. Methods
3
2.1. Materials
4
All chemicals, if not otherwise specified, were obtained from Wako Pure Chemical Industries (Osaka,
5
Japan) and were used without further purification. All aqueous solutions were prepared with Milli-Q
6
water. A commercial polyamide RO membrane, ES20, was obtained from Nitto Denko Corporation
7
(Osaka, Japan). MPC homopolymer and p(MPC-co-AEMA) (MPC : AEMA = 9 : 1, random copolymer;
8
Fig. 1), kindly provided by NOF Corporation (Tokyo, Japan), were used as phosphorylcholine polymers.
9
The weight-average molecular weight of each phosphorylcholine polymer was evaluated by gel
10
permeation chromatography (GPC) using a refractive index detector (RID-10A; Shimadzu Corporation,
11
Kyoto, Japan) and Shodex SB-805HQ column (Showa Denko, Tokyo, Japan) at 40°C. A mixed solvent
12
comprising 0.1 M NaNO3 aqueous solution and acetonitrile (8/2, v/v) was used as the eluent. The
13
weight-average molecular weights of MPC homopolymer and p(MPC-co-AEMA) were 4.6 × 105 and
14
9.7 × 105 , respectively.
15
16 17
Fig. 1
18 19
2.2. Membrane coating using cationic phosphorylcholine polymer
20
A polyamide RO membrane was coated by phosphorylcholine polymer via electrostatic interaction. A
21
commercial polyamide RO membrane was immersed into an aqueous solution of 0.1 wt%
22
phosphorylcholine polymer for 3 h in a refrigerator and washed by gentle shaking twice in an aqueous
5
1
solution of 3.5 wt% NaCl for 1 h to remove non-specifically adsorbed polymers.
2 3
2.3. Characterization of surface properties
4
We evaluated surface hydrophilicity, surface potential, and elemental composition of the membrane
5
surface. To evaluate surface hydrophilicity of the membranes, the water contact angle was measured
6
using a contact angle meter (DM-300; Kyowa Interface Science, Saitama, Japan). To evaluate the
7
surface potential of the membranes, the zeta-potential (-potential) was measured with an
8
electrophoretic light-scattering apparatus (ELS-4000K; Otsuka Electronics, Osaka, Japan) in 10 mmol/L
9
NaCl aqueous solution at pH 7.0. The chemical composition of the membrane surface was analyzed
10
using an XPS instrument (JPS-9010MC, JEOL, Tokyo, Japan). The membrane morphology was
11
observed using a field scanning electron microscope (FE-SEM; JSF-7500F; JEOL), the same as used in
12
our previous study [34].
13 14
2.4. Characterization of coating behavior and coating stability
15
The coating behavior and coating stability of p(MPC-co-AEMA) on the RO membrane were
16
characterized using a QCM-D instrument (Q-sense E1; BiolinScientific, Västra Frölunda, Sweden). A
17
polyamide-coated quartz sensor was prepared using an interfacial polymerization method with trimesoyl
18
chloride (TMC; Sigma-Aldrich Corp., St. Louis, MO) and m-phenylenediamine (MPD), commonly used
19
to fabricate polyamide RO membranes [11, 35]. Steiner et al. formed a polyamide layer on a gold
20
surface, producing a surface similar to of a polyamide RO membrane [36]. We modified their protocol
21
for a QCM-D sensor, as shown in Fig. 2. A gold-coated quartz sensor (QSX 301; BiolinScientific) was
22
immersed into an ethanol solution of 1 mmol/L 2-aminoethanethiol overnight to aminate the sensor
23
surface. The aminated sensor was washed with ethanol twice, dried, and washed with dichloromethane
24
(DCM) twice. The sensor was then immersed into a DCM solution containing 1 mmol/L TMC and 1.1
25
mmol/L triethylamine for 15 min, and washed twice with DCM, then twice with dimethylformamide
6
1
(DMF). To couple TMC and MPD, the sensor was immersed into a DMF solution of 10 mmol/L MPD,
2
and washed twice with DMF. These TMC and MPD coupling reactions were repeated six times. The
3
prepared sensor was analyzed by water contact angle and XPS measurements.
4 NH 2
Cl
Cl
O
Cl
CH 3
5
Gold-coated quartz sensor
HN CO
CO
NH
SH S
MPD
CO
NH 2
H2N
NH OC
O
TMC
2-aminoethanetiol
H 2N
NH
O
O
Cl
Cl
S CH 3
H 2N
NH2
S
TMC/MPD 6 cycles
CH 3
O
6
Fig. 2
7 8
The prepared sensor was placed into the QCM-D instrument. An aqueous solution of 0.1 wt%
9
p(MPC-co-AEMA) was supplied for 15 min at 50 L/min, and Milli-Q water was supplied for 1 h to
10
evaluate the adsorbed mass of p(MPC-co-AEMA). Consequently, an aqueous solution of 3.5 wt% NaCl,
11
which is roughly equal to the salt concentration of sea water, was supplied for 24 h, and Milli-Q water
12
was then supplied again for 1 h to evaluate the coating stability under high ionic strength conditions.
13
The mass adsorbed onto the quartz sensor was calculated using the Sauerbrey equation [37].
14 15
2.5. Evaluation of membrane performances
16
To evaluate membrane performance, the water permeability and NaCl rejection were evaluated using
17
a laboratory scale crossflow membrane test unit (Fig. S1, Supplementary data) [34]. An aqueous
18
solution of 0.05 wt% NaCl was used as feed water. The effective area of sample membranes was 8.0
19
cm2. The flow rate and applied pressure were 1.0 mL/min and 0.75 MPa, respectively. The feed water
20
side of the membrane cell was stirred at 300 rpm by a magnetic stirrer. The water permeability and
21
NaCl rejection were calculated from the accumulated mass and conductivity of permeate water, the
7
1
latter measured by a conductance meter (CM-30R; DKK-TOA Corporation, Tokyo, Japan).
2 3
2.6. Bacterial adhesion test
4
The anti-adhesive property of the membranes was evaluated by immersion into a bacteria suspension
5
using Sphingomonas paucimobilis NBRC 13935 as a model strain of Gram-negative bacteria. This
6
bacteria has been observed in biofilms on water treatment membranes [38]. Bacteria was cultured in
7
tryptic soy broth (Becton, Dickinson and Company, Franklin Lakes, Sparks, MD) medium for 18 h at
8
150 rpm at 30°C to reach the mid-exponential growth phase. The precultured bacterial suspension was
9
diluted 5 times with tryptic soy broth medium and cultured at 150 rpm at 30°C for 4.5 h. The
10
membranes were immersed in the prepared bacterial suspension (adjusted to approximately 108 cfu/mL)
11
at 150 rpm at 30°C for 2 h as an initial bacterial adhesion test and for 24 h as a bacterial growth test.
12
The living and dead bacteria on the membranes were stained by SYTO 9 and propidium iodide (Life
13
Technologies Corporation, Carlsbad, CA), respectively, and observed using a confocal laser scanning
14
microscope (CLSM; FV1000D; Olympus, Tokyo, Japan). The observed images were analyzed using
15
COMSTAT software [39].
16 17 18
3. Results and Discussion
19
3.1. Characterization of the surface of p(MPC-co-AEMA)-coated membranes
20
The membrane surface structures were observed by using FE-SEM (Fig. 3). The p(MPC-co-AEMA)-
21
coating did not change the morphology of the membrane surface and the coated membrane maintained
22
the rough structure of the polyamide layer.
23
8
A
B
1 2
Fig. 3
3 4
The water contact angles and surface potentials were measured as characteristic membrane physical
5
properties (Table 1). The water contact angle measurement showed that the RO membrane immersed
6
into the p(MPC-co-AEMA) solution was more hydrophilic than that of the raw RO membrane.
7
Conversely, the water contact angle of the RO membranes immersed into an MPC homopolymer
8
solution was similar to that of the raw membrane. The surface potential of the RO membrane immersed
9
into the p(MPC-co-AEMA) solution was also changed from a negative to a neutral value. These results
10
agree with a previous study in which zwitterionic polymers were immobilized by a covalent grafting
11
method [26]. It was considered that zwitterionic and hydrophilic p(MPC-co-AEMA) was immobilized
12
onto the polyamide RO membranes via electrostatic interaction between the cationic amide groups of
13
p(MPC-co-AEMA) and the anionic carboxyl groups on the RO membrane. The MPC groups of p(MPC-
14
co-AEMA) were oriented towards the outside of the RO membrane because the surface potential of the
15
RO membrane immersed into the p(MPC-co-AEMA) solution did not have the positive value of amino
16
groups but rather the neutral value of phosphorylcholine groups.
17
Figure 4 shows the XPS spectra for the RO membranes immersed into the p(MPC-co-AEMA)
18
solution. The spectrum of the p(MPC-co-AEMA)-coated membrane shows a strong peak of phosphorus
19
at 134 eV. This result also indicates the immobilization of p(MPC-co-AEMA) onto the RO membrane.
20
9
Intensity [a.u.]
P 2p
Coated membrane
Raw membrane 134
140
1 2
135 130 Binding Enery [eV]
125
Fig. 4
3 4
3.2. QCM-D measurement
5
At first, we characterized the prepared quartz sensors. The water contact angles of the bare quartz
6
sensor, aminated quartz sensor, and polyamide-coated quartz sensor were 69.8 (S.D. 1.4), 44.0 (1.3),
7
and 50.0 (1.7), respectively. The surface of the quartz sensor was hydrophilized by amination with
8
cysteamine, and the hydrophilic surface maintained through the polyamide coating. The XPS spectrum
9
of the polyamide-coated quartz sensor shows a peak shift for nitrogen from 400.1 to 399.8 eV (Fig. S2,
10
Supplementary data). This peak shift was also observed in a previous study [36]. These results show that
11
a polyamide layer was successfully formed on the quartz sensor.
12
The QCM-D experiments were carried out using the prepared polyamide-coated quartz sensor. Figure
13
5 shows the time course of the mass adsorbed on the polyamide-coated quartz sensor. The mass change
14
of the quartz sensor became stable immediately after the injection of the p(MPC-co-AEMA) aqueous
15
solution and remained constant for 15 min. This indicates that the cationic p(MPC-co-AEMA)
16
immediately adsorbed onto the anionic surface of the polyamide membrane via electrostatic interaction,
17
and non-specific adsorption or aggregation between p(MPC-co-AEMA) hardly occurred. The mass of
18
the adsorbed p(MPC-co-AEMA) was quantified as about 0.67 g/cm2 from the mass change after 1 h of
10
1
the Milli-Q water injection following the p(MPC-co-AEMA) injection. The immobilized polymer-chain
2
density of p(MPC-co-AEMA) was calculated as about 0.023 chains/nm2 from the quantified adsorbed
3
mass and the weight-average molecular weight measured by GPC. This value is considered reasonable
4
because it is comparable to previously reported values [40].
5
To evaluate coating stability under high ionic strength conditions, 3.5 wt% NaCl aqueous solution,
6
roughly equivalent to the salt concentration of sea water, was injected onto the p(MPC-co-AEMA)-
7
adsorbed sensor for 24 h. The mass adsorbed onto the quartz sensor hardly changed for 24 h, and the
8
mass of the adsorbed p(MPC-co-AEMA) was 0.50 g/cm2. A difference of 0.17 g/cm2 before and after
9
the introduction of salt solution was certainly physical adsorption. This result indicates that once
10
p(MPC-co-AEMA) had adsorbed onto the membrane surface via electrostatic interaction, it was not
11
easily desorbed, even under high ionic strength conditions. The amino groups of one molecule of
12
p(MPC-co-AEMA) were strongly adsorbed via multiple-point electrostatic interactions with the
13
carboxyl groups on the surface of the polyamide RO membrane. These results also show that the QCM-
14
D measurements presented in this study are potentially useful for investigating adsorption behaviors on
15
the surface of polyamide RO membranes for various research fields such as surface modification or
16
membrane fouling.
Adsorbed mass [g/cm2]
0.8 0.7 0.6 0.5
18
Detachment mass
0.4 0.3 0.2 3.5 wt% NaCl
0.1 0
17
Adsorbed mass
0
1
2
3
4
23 24 25 26 27 Time [h]
Fig. 5 11
1
3.3. Membrane performance of p(MPC-co-AEMA)-coated membranes
2
The effect of p(MPC-co-AEMA) coating on membrane performance was evaluated (Table 2). The
3
water permeability of the p(MPC-co-AEMA)-coated membranes decreased by about 20% compared
4
with bare RO membranes, although salt rejection was maintained at a high value of over 95%, which is
5
comparable with commercial membranes. The coated polymer was responsible for the resistance to
6
permeation of water molecules. The decrease in water permeability by zwitterionic polymer coating in
7
this study was lower than that observed after covalent grafting in previous studies [20, 41, 42]. The
8
present method could immobilize zwitterionic polymers while maintaining membrane performance.
9 10
3.4. Bacterial adhesion test
11
Figure 6 shows the results of the bacterial adhesion test. After 2 h immersion into the bacterial
12
suspension as an initial bacterial adhesion test, bacteria were clearly observed on the raw membrane
13
(Fig. 6A), but hardly observed on the p(MPC-co-AEMA)-coated membrane (Fig. 6D). After 24 h, the
14
surface of the raw membrane was significantly covered by bacteria (Fig. 6B and C), with a bacteria
15
coverage of 41.4% (Table 3). It was concluded that bacteria easily adhered to the surface of the raw
16
membrane, grew, and then formed biofilms. However, the surface of the p(MPC-co-AEMA)-coated
17
membrane remained clean (Fig. 6E and F), and the bacteria coverage was only 1.0% after 24 h
18
immersion. The mass of the adhered bacteria on the p(MPC-co-AEMA)-coated membrane was lower
19
than 2% of that on the raw membrane. In the both condition, dead bacteria were not observed (Fig. 6C
20
and F). The p(MPC-co-AEMA) immobilized by the coating method successfully prevented initial
21
bacterial adhesion and bacterial growth on the membrane surface, similar to a previously reported
22
grafting method [27]. This result also indicates that the MPC groups of p(MPC-co-AEMA) were
23
oriented towards the outside of the RO membrane, because if the cationic amino groups were oriented
24
towards the outside of the RO membrane, dead bacteria or bacterial adhesion would be observed due to
25
electrostatic interaction between the cationic groups of p(MPC-co-AEMA) and anionic bacterial
12
1
membranes [26]. The results of the QCM-D measurement and bacterial adhesion test showed the coated
2
p(MPC-co-AEMA) was stably adsorbed not only in high ionic strength condition but also bacterial
3
broth containing various organic substances and electrolytes.
4
5 6
Fig. 6
7 8
Conclusions
9
We developed a simple coating method for RO membranes using cationic phosphorylcholine
10
polymers via electrostatic interaction to prevent bacterial adhesion. By immersing RO membranes into
11
an aqueous solution of cationic phosphorylcholine polymer, p(MPC-co-AEMA), the surfaces were
12
readily coated by a phosphorylcholine polymer via electrostatic interaction between the cationic amino
13
groups of AEMA and the anionic carboxylic groups on the polyamide RO membrane. The surface of the
14
p(MPC-co-AEMA)-coated membrane was hydrophilic, and the surface potential was neutral, specific
15
for zwitterionic polymers. A QCM-D measurement showed that the mass of p(MPC-co-AEMA)
16
adsorbed onto the RO membrane was 0.67 g/cm2, and 0.50 g/cm2 of p(MPC-co-AEMA) was stably
17
adsorbed over 24 h under high ionic strength conditions equivalent to sea water. The p(MPC-co13
1
AEMA)-coated membrane showed a high anti-adhesive property against a model strain of Gram-
2
negative bacteria, Sphingomonas paucimobilis, while maintaining membrane performance. The methods
3
described herein are expected to be useful for long-term operation of RO membranes.
4 5 6
FIGURE CAPTIONS
7
Fig. 1. Chemical structure of p(MPC-co-AEMA). m : n = 9 : 1.
8 9
Fig. 2. Scheme for the preparation of the polyamide-coated quartz sensor for QCM-D measurement.
10 11
Fig. 3. FE-SEM images of the surface of a raw RO membrane (A) and p(MPC-co-AEMA)-coated RO
12
membranes (B). Bars indicate 1 m.
13 14
Fig. 4. XPS P 2p spectra for p(MPC-co-AEMA)-coated polyamide RO membranes.
15 16
Fig. 5. Time course for the mass adsorbed on the polyamide-coated quartz sensor by QCM-D
17
measurement. An aqueous solution of 0.1 wt% p(MPC-co-AEMA) was supplied for 15 min at 50
18
L/min, and Milli-Q water was supplied for 1 h. Consequently, an aqueous solution of 3.5 wt% NaCl
19
was supplied for 24 h, and Milli-Q water was again supplied for 1 h.
20 21
Fig. 6. Microscopic images of bacteria on the p(MPC-co-AEMA)-coated membranes after the bacterial
22
adhesion test, analyzed using COMSTAT software. In the CLSM images (C and F), the living and dead
23
bacteria were indicated by green and red color, respectively.
14
1 2 3 4
TABLES
5
Table 1. Surface properties of RO membranes immersed into various polymer solutions. Raw membrane
MPC homopolymer- p(MPC-co-AEMA)coated membrane coated membrane
Water contact angle [°]
36.0 (1.9)
30.0 (2.2)
18.6 (2.1)
Zeta potential* [mV]
-15.36 (0.94)
no data
-0.50 (1.72)
Numbers in parentheses indicate standard deviations. *Zeta potentials were measured in 10 mmol/L NaCl aqueous solution at pH 7.0. 6 7
Table 2. Performance of the RO membranes. Raw membrane
p(MPC-co-AEMA)-coated membrane
Water permeability [m3/m2 day]
0.997 (0.058)
0.755 (0.090)
NaCl rejection [%]
94.7 (0.7)
96.9 (0.4)
Numbers in parentheses indicate standard deviations. 8 9
Table 3. Quantification of biofilms on the membranes after the bacterial adhesion test. Raw membrane
p(MPC-co-AEMA)-coated membrane
Incubation time
2h
24 h
2h
24 h
Adhered bacteria [m3/m2]
0.58
3.78
0.05
0.05
Substratum coverage [%]
13.8
41.4
2.2
1.0
Maximum thickness (m)
10.60
17.10
6.49
8.26
10 11 12 15
1
REFERENCES
2
[1] R.J. Petersen, Composite reverse-osmosis and nanofiltration membranes, J. Membr. Sci., 83 (1993)
3
81-150.
4
[2] C.M. Pang, P.Y. Hong, H.L. Guo, W.T. Liu, Biofilm formation characteristics of bacterial isolates
5
retrieved from a reverse osmosis membrane, Environ. Sci. Technol., 39 (2005) 7541-7550.
6
[3] M. Herzberg, M. Elimelech, Biofouling of reverse osmosis membranes: Role of biofilm-enhanced
7
osmotic pressure, J. Membr. Sci., 295 (2007) 11-20.
8
[4] C. Leroy, C. Delbarre-Ladrat, F. Ghillebaert, C. Compere, D. Combes, Influence of subtilisin on the
9
adhesion of a marine bacterium which produces mainly proteins as extracellular polymers, J. Appl.
10
Microbiol., 105 (2008) 791-799.
11
[5] S. Lee, M. Elimelech, Relating organic fouling of reverse osmosis membranes to intermolecular
12
adhesion forces, Environ. Sci. Technol., 40 (2006) 980-987.
13
[6] Q.L. Li, Z.H. Xu, I. Pinnau, Fouling of reverse osmosis membranes by biopolymers in wastewater
14
secondary effluent: Role of membrane surface properties and initial permeate flux, J. Membr. Sci., 290
15
(2007) 173-181.
16
[7] Q.F. Yang, Y.Q. Liu, Y.J. Li, Control of protein (bsa) fouling in ro system by antiscalants, J. Membr.
17
Sci., 364 (2010) 372-379.
18
[8] W.S. Ang, A. Tiraferri, K.L. Chen, M. Elimelech, Fouling and cleaning of ro membranes fouled by
19
mixtures of organic foulants simulating wastewater effluent, J. Membr. Sci., 376 (2011) 196-206.
20
[9] M. Herzberg, T.Z. Rezene, C. Ziemba, O. Gillor, K. Mathee, Impact of higher alginate expression on
21
deposition of pseudomonas aeruginosa in radial stagnation point flow and reverse osmosis systems,
22
Environ. Sci. Technol., 43 (2009) 7376-7383.
23
[10] T. Kawaguchi, H. Tamura, Chlorine-resistant membrane for reverse-osmosis. I. Correlation
24
between chemical structures and chlorine resistance of polyamides, J. Appl. Polym. Sci., 29 (1984)
25
3359-3367.
16
1
[11] T. Shintani, H. Matsuyama, N. Kurata, Development of a chlorine-resistant polyamide reverse
2
osmosis membrane, Desalination, 207 (2007) 340-348.
3
[12] D. Rana, T. Matsuura, Surface modifications for antifouling membranes, Chem. Rev., 110 (2010)
4
2448-2471.
5
[13] K.L. Prime, G.M. Whitesides, Adsorption of proteins onto surfaces containing end-attached
6
oligo(ethylene oxide) - a model system using self-assembled monolayers, J. Am. Chem. Soc., 115
7
(1993) 10714-10721.
8
[14] E. Ostuni, R.G. Chapman, R.E. Holmlin, S. Takayama, G.M. Whitesides, A survey of structure-
9
property relationships of surfaces that resist the adsorption of protein, Langmuir, 17 (2001) 5605-5620.
10
[15] M. Zhang, T. Desai, M. Ferrari, Proteins and cells on peg immobilized silicon surfaces,
11
Biomaterials, 19 (1998) 953-960.
12
[16] K.D. Park, Y.S. Kim, D.K. Han, Y.H. Kim, E.H.B. Lee, H. Suh, K.S. Choi, Bacterial adhesion on
13
peg modified polyurethane surfaces, Biomaterials, 19 (1998) 851-859.
14
[17] F.Q. Nie, Z.K. Xu, X.J. Huang, P. Ye, J. Wu, Acrylonitrile-based copolymer membranes
15
containing reactive groups: Surface modification by the immobilization of poly(ethylene glycol) for
16
improving antifouling property and biocompatibility, Langmuir, 19 (2003) 9889-9895.
17
[18] G.D. Kang, M. Liu, B. Lin, Y.M. Cao, Q. Yuan, A novel method of surface modification on thin-
18
film composite reverse osmosis membrane by grafting poly(ethylene glycol), Polymer, 48 (2007) 1165-
19
1170.
20
[19] G.D. Kang, H.J. Yu, Z.N. Liu, Y.M. Cao, Surface modification of a commercial thin film
21
composite polyamide reverse osmosis membrane by carbodiimide-induced grafting with poly(ethylene
22
glycol) derivatives, Desalination, 275 (2011) 252-259.
23
[20] E.M. Van Wagner, A.C. Sagle, M.M. Sharma, Y.H. La, B.D. Freeman, Surface modification of
24
commercial polyamide desalination membranes using poly(ethylene glycol) diglycidyl ether to enhance
25
membrane fouling resistance, J. Membr. Sci., 367 (2011) 273-287.
17
1
[21] K. Ishihara, H. Nomura, T. Mihara, K. Kurita, Y. Iwasaki, N. Nakabayashi, Why do phospholipid
2
polymers reduce protein adsorption?, J. Biomed. Mater. Res., 39 (1998) 323-330.
3
[22] S.F. Chen, J. Zheng, L.Y. Li, S.Y. Jiang, Strong resistance of phosphorylcholine self-assembled
4
monolayers to protein adsorption: Insights into nonfouling properties of zwitterionic materials, J. Am.
5
Chem. Soc., 127 (2005) 14473-14478.
6
[23] G. Cheng, Z. Zhang, S. Chen, J.D. Bryers, S. Jiang, Inhibition of bacterial adhesion and biofilm
7
formation on zwitterionic surfaces, Biomaterials, 28 (2007) 4192-4199.
8
[24] K. Fujii, H.N. Matsumoto, Y. Koyama, Y. Iwasaki, K. Ishihara, K. Takakuda, Prevention of
9
biofilm formation with a coating of 2-methacryloyloxyethyl phosphorylcholine polymer, J. Vet. Med.
10
Sci., 70 (2008) 167-173.
11
[25] H. Kitano, T. Mori, Y. Takeuchi, S. Tada, M. Gemmei-Ide, Y. Yokoyama, M. Tanaka, Structure of
12
water incorporated in sulfobetaine polymer films as studied by atr-ftir, Macromolecular Bioscience, 5
13
(2005) 314-321.
14
[26] R. Bernstein, S. Belfer, V. Freger, Bacterial attachment to ro membranes surface-modified by
15
concentration-polarization-enhanced graft polymerization, Environ. Sci. Technol., 45 (2011) 5973-5980.
16
[27] F. Razi, I. Sawada, Y. Ohmukai, T. Maruyama, H. Matsuyama, The improvement of antibiofouling
17
efficiency of polyethersulfone membrane by functionalization with zwitterionic monomers, J. Membr.
18
Sci., 401 (2012) 292-299.
19
[28] K. Hirota, K. Murakami, K. Nemoto, Y. Miyake, Coating of a surface with 2-methacryloyloxyethyl
20
phosphorylcholine (mpc) co-polymer significantly reduces retention of human pathogenic
21
microorganisms, FEMS Microbiol. Lett., 248 (2005) 37-45.
22
[29] Y. Chang, S. Chen, Z. Zhang, S. Jiang, Highly protein-resistant coatings from well-defined diblock
23
copolymers containing sulfobetaines, Langmuir, 22 (2006) 2222-2226.
24
[30] T. Ishigami, K. Amano, A. Fujii, Y. Ohmukai, E. Kamio, T. Maruyama, H. Matsuyama, Fouling
25
reduction of reverse osmosis membrane by surface modification via layer-by-layer assembly, Sep. Purif.
18
1
Technol., 99 (2012) 1-7.
2
[31] S. Sakaki, M. Tsuchida, Y. Iwasaki, K. Ishihara, A water-soluble phospholipid polymer as a new
3
biocompatible synthetic DNA carrier, Bull. Chem. Soc. Jpn., 77 (2004) 2283-2288.
4
[32] A.L. Lewis, J. Berwick, M.C. Davies, C.J. Roberts, J.-H. Wang, S. Small, A. Dunn, V. O’Byrne,
5
R.P. Redman, S.A. Jones, Synthesis and characterisation of cationically modified phospholipid
6
polymers, Biomaterials, 25 (2004) 3099-3108.
7
[33] Z. Zhang, X. Cao, X. Zhao, S.B. Withers, C.M. Holt, A.L. Lewis, J.R. Lu, Controlled delivery of
8
antisense oligodeoxynucleotide from cationically modified phosphorylcholine polymer films,
9
Biomacromolecules, 7 (2006) 784-791.
10
[34] D. Saeki, S. Nagao, I. Sawada, Y. Ohmukai, T. Maruyama, H. Matsuyama, Development of
11
antibacterial polyamide reverse osmosis membrane modified with a covalently immobilized enzyme, J.
12
Membr. Sci., 428 (2013) 403-409.
13
[35] I.J. Roh, S.Y. Park, J.J. Kim, C.K. Kim, Effects of the polyamide molecular structure on the
14
performance of reverse osmosis membranes, Journal of Polymer Science Part B-Polymer Physics, 36
15
(1998) 1821-1830.
16
[36] Z. Steiner, J. Miao, R. Kasher, Development of an oligoamide coating as a surface mimetic for
17
aromatic polyamide films used in reverse osmosis membranes, Chem. Commun., 47 (2011) 2384-2386.
18
[37] G. Sauerbrey, Verwendung von schwingquarzen zur wagung dunner schichten und zur
19
mikrowagung, Zeitschrift Fur Physik, 155 (1959) 206-222.
20
[38] L.A. Bereschenko, G.H.J. Heilig, M.M. Nederlof, M.C.M. van Loosdrecht, A.J.M. Stams, G.J.W.
21
Euverink, Molecular characterization of the bacterial communities in the different compartments of a
22
full-scale reverse-osmosis water purification plant, Appllied and Environmental Microbiology, 74
23
(2008) 5297-5304.
24
[39] A. Heydorn, A.T. Nielsen, M. Hentzer, C. Sternberg, M. Givskov, B.K. Ersboll, S. Molin,
25
Quantification of biofilm structures by the novel computer program comstat, Microbiology-(UK), 146
19
1
(2000) 2395-2407.
2
[40] S. Yamamoto, M. Ejaz, Y. Tsujii, M. Matsumoto, T. Fukuda, Surface interaction forces of well-
3
defined, high-density polymer brushes studied by atomic force microscopy. 1. Effect of chain length,
4
Macromolecules, 33 (2000) 5602-5607.
5
[41] G.D. Kang, Y.M. Cao, H.Y. Zhao, Q. Yuan, Preparation and characterization of crosslinked
6
poly(ethylene glycol) diacrylate membranes with excellent antifouling and solvent-resistant properties, J.
7
Membr. Sci., 318 (2008) 227-232.
8
[42] I. Sawada, R. Fachrul, T. Ito, Y. Ohmukai, T. Maruyama, H. Matsuyama, Development of a
9
hydrophilic polymer membrane containing silver nanoparticles with both organic antifouling and
10
antibacterial properties, J. Membr. Sci., (2012) 1-6.
11 12
GRAPHICAL ABSTRACT
13 14
20