Towards Anti-biofouling PVDF Membranes - Langmuir (ACS

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Biological and Environmental Phenomena at the Interface

Towards Anti-biofouling PVDF Membranes Chen-Hua Hsu, Antoine Venault, Yu-Tzu Huang, Bo-Wei Wu, Chung-Jung Chou, Kazuhiko Ishihara, and Yung Chang Langmuir, Just Accepted Manuscript • DOI: 10.1021/acs.langmuir.9b00703 • Publication Date (Web): 01 May 2019 Downloaded from http://pubs.acs.org on May 2, 2019

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Towards Anti-biofouling PVDF Membranes Chen-Hua Hsu,a Antoine Venault,*a Yu-Tzu Huang,b Bo-Wei Wu,b Chung-Jung Chou,a Kazuhiko Ishihara,c and Yung Chang**

aR&D

Center for Membrane Technology and Department of Chemical Engineering,

Chung Yuan Christian University, 200 Chung Pei Rd, Chungli, Taoyuan 320, Taiwan. E.mail:

bResearch

Center for Analysis and Identification and Department of Environmental

Engineering, Chung Yuan Christian University, Chung-Li 32023, Taiwan

cDepartment

of Bioengineering, The University of Tokyo, Tokyo, Japan

KEYWORDS. zwitterionic, membrane, bioinert, biofouling

ACS Paragon Plus Environment

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ABSTRACT

Membranes for biological- and biomedical-related applications must be bioinert, that is, resist biofouling by proteins, human cells, bacteria, algae, etc. Hydrophobic materials such as polysulfone, polypropylene or poly(vinylidene fluoride) (PVDF) are often chosen as matrix materials but their hydrophobicity make them prone to biofouling, which in turn limits their application in biological/biomedical fields. Here, we designed PVDF-based membranes by precipitation from the vapor phase and zwitterionized them in-situ to reduce their propensity to biofouling. To achieve this goal, we used a copolymer containing phosphorylcholine groups. An in-depth physicochemical characterization not only revealed the controlled presence of the copolymer in the membrane, but also that bicontinuous membranes could be formed. Membrane hydrophilicity was greatly improved, resulting in the mitigation of a variety of biofoulants: the attachment of Stenotrophomonas maltophilia, Streptococcus mutans and platelets were reduced by 99.9%, 99.9% and 98.9%, respectively. Besides and despite incubation in a plasma-poor-platelet medium, rich in plasma proteins, a flux recovery ratio of 75% could be measured while it was only


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40% with a hydrophilic commercial membrane of similar structure and physical properties. Similarly, the zwitterionic membrane severely mitigated biofouling by Microalgae during their harvesting. All in all, the material/process combination presented in this work leads to anti-biofouling porous membranes with a large span of potential biomedical and biological-related applications.

INTRODUCTION

Antifouling membranes have attracted considerable attention of chemical engineers and materials scientists over the past 20 years as reducing fouling is critical in view of improving the efficiency of a large number of filtration operations such as sea desalination (mineral fouling or scaling),1 blood separation (biofouling by blood cells and plasma proteins),2 oil/water separation and vegetable oil processing (oil fouling),3 or more generally wastewater treatment (biofouling by proteins and bacteria).4 The commitment of scientific teams worldwide has led to significant improvements of membranes


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resistance to fouling, in particular to biofouling. Effort of Whitesides et al. permitted to clearly define the properties of antifouling materials,5-7 which also narrowed down their search. Currently, two major classes of materials are considered to efficiently endow interfaces with improved biofouling resistance: PEGylated materials and zwitterionic materials. The latter ones are considered as being more effective, which is partly due to their propensity to trap more water molecules per antifouling moiety, and eventually provide the interface with a tighter protective hydration layer.8, 9 However, PEG-based materials remain extensively used for (i) their ease of synthesis, (ii) the multiple possibilities of copolymerization with hydrophobic moieties and (iii) their solubility in numerous solvent systems. Membrane experts have made use of these findings and presented various designs in which PEGylated copolymers or zwitterionic copolymers were coated10-12, or grafted13-15 at the surface of membranes. Nonetheless, these two types of surface-modification processes cannot be as easily implemented as blending processes (or in-situ modification processes) which consist in preparing and modifying the membrane in one single unit operation.16-18 These processes require the antifouling copolymer to be soluble with the matrix copolymer, easily achievable with PEGylated


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copolymers.16, 18-20 With zwitterionic copolymers, it is much more troublesome because of major polarity differences between zwitterionic polymers and common membrane materials, often highly hydrophobic.

A copolymer of interest for the design of biomedical membranes was synthesized by Professor Ishihara almost 25 years ago.21 It is made of 2-methacryloyloxyethyl phosphorylcholine (MPC) units and methacryloyloxyethyl butylurethane groups. The high efficiency of MPC to improve the biocompatibility of interfaces has been thoroughly investigated and demonstrated and does not need to be discussed in details.22,

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Nonetheless, the introduction of urethane groups is particularly interesting with the view to blend the copolymer with hydrophobic materials because it provides flexibility to the copolymer backbone, which is thought of being where the miscibility of this copolymer with hydrophobic polymers originates. This copolymer has later on been used in the biomedical field to fabricate non-thrombogenic tissue engineering scaffolds, that is, bioinert biomaterials.24 However, little is known on its potential use as a membrane modifier or on its actual efficiency in miscellaneous biological applications of membranes.


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There are multiple types of biofouling components able to jeopardize the efficiency of a membrane material such that an in-depth investigations should be performed before declaring it perfectly anti-biofouling. Bacteria are a first typical example which can be commonly categorized in two major classes: gram positive and gram negative according to the composition of their cell wall. Distinct compositions affect their deformability, which in turn plays a role on segregation and membrane fouling,25 in particular when the membrane material is hydrophobic as it is the case of most base materials making filtration devices for biological applications (polysulfone, polypropylene, etc.).26-28 Besides, the analysis of bacterial resistance of membrane materials using pathogenic bacterial species is essential. Stenotrophomonas maltophilia bacteria (gram-negative) are commonly found in a number of habitats including agricultural soils and water sources. A study demonstrated that S. maltophilia is a global opportunistic pathogen, able to infect a wide range of organs.29 Membrane materials applied to water treatment should typically resist this kind of pathogenic bacterial species. In general, gram-negative bacteria should not adhere to a membrane material because their cell wall is very deformable. Consequently, bacteria can pass through pores smaller than their size.25


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Countless pathogenic microorganisms exist likely to be in contact with fluid filters in biological applications of membrane technology. Another example is Streptococcus

mutans, a well-known pathogen of dental caries also involved in cardiovascular diseases.30 Microfiltration membranes can be applied to the evaluation of microleakage in endodontics and as in any application of microfiltration membranes, biofouling resistance is highly desired.31-33 Besides, unlike S. maltophilia above-mentioned, it is a gram-positive bacteria. A recent investigation stressed on the effect of the nature/composition of the microbial species on biofilm formation on poly(vinylidene fluoride) (PVDF) membranes34 as well as Carretier et al. reported earlier distinct bacterial attachment behaviors on membranes.35 Hence, it is important to extend the range of bacterial adhesion tests to multiple pathogenic bacterial strains, i.e gram negative or positive, in the search for biofouling-resistant membranes and interfaces.

Another major class of biofouling components that needs to be considered is blood and more specifically, platelet-rich and platelet-poor-plasma fractions. These fractions, containing plasma proteins and/or platelets, are on the front line in the design of


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hemocompatible biomaterials for blood filtration materials or more generally bloodcontacting devices. The underlying explanation for it is related to the critical role of these blood components on the coagulation pathways: while plasma proteins adhere to the material first, then leading to the formation of fibrin, platelet activation or thrombosis follows.36 It is therefore essential to carry out dedicated tests involving plasma proteins and/or platelets in the search for bioinert membranes.

Finally, anti-biofouling membranes resisting Microalgae are of great interest as well. Microalgae are microscopic unicellular species with the ability to turn carbon dioxide into biofuels and other high value products. Their harvesting is usually done by centrifugation,37 fast but also highly energy-demanding. Membrane technology is more cost-effective but biofouling concerns have limited its application to Microalgae harvesting because irreversible biofouling prevents efficient concentration of the biological medium. So anti-biofouling membranes with improved resistance to micro-biofouling, i.e. biofouling by cells (bacteria, algae, et…) are needed. In-situ modified zwitterionic PVDF membranes may fulfil this goal.


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The major purpose of this study presented in Scheme 1 is to assess the anti-biofouling properties of zwitterionic membranes prepared by blending PVDF with a derivative copolymer of MPC, using a wide variety of biofoulants from multiple biological sources (pathogen bacteria, platelet-rich and poor fractions of whole blood, Microalgae), which has, to our knowledge, never been done. After an overview of the essential physicochemical properties of the porous materials, essential to the understanding of structure/property relationships, the emphasis of this paper is put on anti-biofouling properties of the membrane materials. The diversity of biofoulants tested to challenge our zwitterionic membranes and demonstrate their efficiency in an extensive range of biological environments suggests multiple potential applications.

H

F

C

C

H

F

Chamber with controlled T/RH n

O+

CH2CH2OPOCH2CH2N(CH3)3 O

Material selection

T: 30℃

RH: 70%

Membrane structure control

General biofouling resistance


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Scheme 1. Presentation of the objectives of the study: (1) to blend a phosphobetaine copolymer with PVDF, in order to (2) in-situ modify bi-continuous membranes formed by precipitation from the vapor phase, and (3) make the membrane materials resistant to a large variety of biofoulants commonly found in biomedicalrelated or bioenvironmental engineering related applications of porous membranes.

EXPERIMENTAL SECTION

Materials. PVDF with an approximate molecular weight of 150 kDa was supplied by Kynar®. It was washed alternatively with methanol and DI-water. The phosphobetainebased copolymer, which full name is poly(2-methacryloyloxyethyl phosphorylcholine-coethacryloyloxyethyl butylurethane), was synthesized by Prof. Ishihara. Details regarding the synthesis and characterization of this copolymer have been provided elsewhere.21 In this work, the copolymer had an approximate average molecular weight of 40 kDa. Nmethyl-2-pyrrolidone (NMP) was purchased from Tedia. Deionized water (DI water) was directly produced in our laboratory. Commercial hydrophilic PVDF membrane (pore size: 0.1 µm) was bought from Millipore.

Preparation of Casting Solutions. Casting solutions were prepared by dissolving first PVDF in NMP solvent at 35°C. Then, the zwitterionic copolymer was added to the


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solution. The PVDF content in the polymeric system was maintained to 20 wt%, while the copolymer content was 1, 3 or 5 wt%. Once the solution homogeneous (after 7 to 10 days in the case of the most concentrated solution), they were left to rest for 2h and immediately cast.

Preparation of Membranes. Membranes were prepared by vapor-induced phase separation. Solutions were cast on glass supports in a chamber inside which the temperature and relative humidity were maintained constant (T = 30°C and RH = 70%) with a metallic casting knife (Scheme 1). The initial thickness of the cast polymeric system was 300µm. After 20 min exposure to water vapours, the glass support was immersed in a DI water bath. Membranes were kept in the bath for 24h, period during which water was changed once. Finally, membranes were dried at ambient T for 24h, and stored at 4°C until use. From now on, membranes will be referred to as Pn with n = 0, 1, 3 or 5. The number corresponds to the initial copolymer content in the casting solution from which were formed the membranes. Hence P0 is the virgin membrane.


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Physicochemical Characterization of Zwitterionic PVDF Membranes. The structure of membranes was characterized by SEM and AFM (liquid state, tapping mode), using a Hitachi S3000 instrument and a JPK instrument, respectively. In the case of SEM observations, samples were first sputter-coated with gold for about 150s. Observations were carried out at an accelerating voltage of 10 kV. In the case of AFM tests, the commercial Si cantilever used was from TEST tip. Further details regarding the AFM protocol are provided elsewhere.35 Membrane pore size was measured with a capillary flow porometer (PMI). Membrane porosity was evaluated by gravimetric measurements. Membranes (1-cm diameter) were dried and weighed, and then immersed in ethanol for 24h. Next, membranes were weighed again. The porosity could then be determined from the knowledge of the membrane dry weight, the membrane wet weight, the polymer density and the wetting agent (alcohol). The surface chemistry of membranes was analysed by mapping FT-IR and XPS, using a Jasco FT/IR 6700 instrument and a PHI Quantera SXM/Auger spectrometer, respectively. The detailed method for mapping analysis in described in the work of Dizon.38 The procedure related to the XPS analysis is as follows. The instrument was equipped with a monochromated Al Kα X-ray source


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(photon energy: 1486.6 eV), while a hemispherical energy analyser was employed to measure the energy of emitted electrons. The photoelectron take off angle at which data were collected was 45°, which was measured with respect to the membrane surface. A Service Physics Inc. software was used to fit the spectra. In this work, wide spectra, as well as C1s, O1s, N1s and P2p spectra were recorded.

The surface hydrophilicity measurements were performed with an automatic contact angle meter (Kyowa Interface Science Co.) at ambient temperature, using 4 µL-water droplets. The water contact angles (WCA) reported for each membrane correspond to the average of 10 independent tests. The bulk hydrophilicity measurements (hydration capacity, mg/cm3) were determined by immersing membrane samples (1 cm) in DI water for 24h. Membranes were weighed before and after immersion. The difference in weight per unit volume corresponds to the hydration capacity of the membrane (that is, the amount of water trapped in the bulk of the membrane). 5 independent tests were performed for each membrane.


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Biofouling Tests Involving Bacteria. Membranes were incubated with Stenotrophomonas

maltophilia (gram-negative) or Streptococcus mutans (gram-positive) bacteria. First, membranes were washed with PBS and membrane samples (1.3-cm diameter) positioned in a multiwell plate. Then, they were incubated with 1 mL of either one of the bacterial solution, prepared according to a similar protocol as reported by Hsiao et al.39 Note that incubation was performed at 37°C for 24h, and that the bacterial solution was changed at t = 6, 12 and 18 h. At the end of the incubation, the samples were washed with PBS and stained with 0.2 mL of BacLightTM Green (ThermoFisher Scientific) for 10 min. Then, the membranes were observed with a Nikon confocal laser scanning microscope (CLSM A1R instrument). The emission and excitation wavelengths set for the observations were 488 nm and 520 nm, respectively. 3 independent bacterial attachment tests were conducted. For each test, at least 3 images were recorded. All images were analyzed using ImageJ® software, for quantitative assessment of bacterial densities on the membranes.


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Biofouling Tests Involving Platelets. Fresh human blood was obtained from the Taipei blood center in Beitou district, from a pool of healthy volunteers. It was fractionated following the protocol detailed by Jhong et al.40 Then, 1.3 cm-membranes were placed in a multiwell plate and equilibrated overnight with 1 mL of PBS, at 37°C. PBS was then changed to 0.8 mL of platelets concentrate. After a 1h-incubation at 37°C, membranes were washed with PBS (5 times). Then, 0.8 mL of a glutaraldehyde solution was used to fix the cells to the membranes, for 4h in a chamber which temperature was set to 4°C. The same confocal microscope and settings as mentioned in the section on “Biofouling tests involving bacteria” were used to observe the extent of platelet adhesion. Besides, images were analysed using ImageJ® software to obtain quantitative information on platelet density on the membranes (5 independent images for each membrane).

Biofouling Tests Involving Microalgae. Details on how Microalgae (Chlorella sp.) were cultured are provided in the work of Feng et al.41 Filtration of Chlorella sp. solution was performed in dead-end mode. Membranes (2.5-cm diameter) were first pre-wetted with ethanol for about 0.5h, and then positioned in the filtration cell, before being compacted


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with DI-water at a transmembrane pressure (TMP) of 1.5 atm. Flux was recorded and once steady, the TMP was decreased to 1 atm. Water flux was recorded for 0.5h. The tank containing DI-water was then disconnected from the filtration cell and replaced by the tank containing the Microalgae solution (1.3 ± 1 g/L) and flux recorded for 0.5h. After this operation, membranes was thoroughly washed by first flushing DI water and then immersing it in a DI water bath for 0.5h. Then, the entire operation (DI water filtration, Microalgae solution filtration, washing) was repeated, before ending with a final DI water filtration run. Flux recovery ratio (FRR), total flux decline ratio (DRt), irreversible flux decline ratio (DRir) and reversible flux decline ratio (DRr) were determined as follows: 𝑱 𝒘,𝒇

𝑭𝑹𝑹(%) =

𝑫𝑹 𝒕 (%) =

𝑱 𝒘,𝒊

𝑱 𝒘,𝒊 ― 𝑱 𝑴𝑨,𝒇 𝑱 𝒘,𝒊

𝑫𝑹 𝒊𝒓 (%) =

𝑫𝑹 𝒓 (%) =

(1)

× 𝟏𝟎𝟎

𝑱 𝒘,𝒊 ― 𝑱 𝒘,𝒇 𝑱 𝒘,𝒊

𝑱 𝒘,𝒇 ― 𝑱 𝑴𝑨,𝒇 𝑱 𝒘,𝒊

× 𝟏𝟎𝟎

(2)

× 𝟏𝟎𝟎

(3)

× 𝟏𝟎𝟎

(4)

Where Jw,i, Jw,f and JMA,f correspond to the initial water flux, the final water flux, and the final MicroAlgae solution flux, respectively.


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Biofouling Tests Involving Plasma Proteins. Filtration tests involving the use of a plateletpoor-plasma solution were also run as follows. Membranes (2.5-cm diameter) were first pre-wetted with ethanol for about 0.5h, and then positioned in the filtration cell, before being compacted with DI-water at a transmembrane pressure (TMP) of 1.5 atm. Membrane conditioning was the same as for the filtration of Microalgae (immersion in alcohol, DI water overpressure cycle). TMP was reduced to 1 atm and water permeability recorded for 0.5h. Then, membranes were immersed in a PBS solution for 2 h before being incubated with PPP (platelet-poor-plasma obtained after centrifugation of whole blood) for 2 h. PPP contains a number of plasma proteins including fibrinogen, albumin and globulin, likely to interact with the membrane material. After this adsorption step, DI water permeability was recorded again. Thereafter, a washing procedure consisting in flushing the membranes with DI water and then immersing the membranes in a DI water bath was repeated twice. Finally, DI water permeability was recorded on last time.

Flux recovery ratio (FRR), total flux decline ratio (DRt), irreversible flux decline ratio (DRir) and reversible flux decline ratio (DRr) were determined as follows:


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𝐽 𝑤,𝑓

𝐹𝑅𝑅(%) =

𝐷𝑅 𝑡 (%) =

𝐽 𝑤,𝑖

𝐷𝑅 𝑖𝑟 (%) =

𝐷𝑅 𝑟 (%) =

(1)

× 100

𝐽 𝑤,𝑖 ― 𝐽 𝑃𝑃𝑃 𝐽 𝑤,𝑖

𝐽 𝑤,𝑖 ― 𝐽 𝑤,𝑓 𝐽 𝑤,𝑖

𝐽 𝑤,𝑓 ― 𝐽 𝑃𝑃𝑃 𝐽 𝑤,𝑖

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× 100

(2)

× 100

(3)

× 100

(4)

Where Jw,i, Jw,f and JPPP correspond to the initial water flux, the final water flux, and the flux, after PPP incubation, respectively. Flux analysis indicators were also determined according to equations (1) to (4). However, in equations (2) and (4), JMA,f was changed to JPPP, the permeability recorded after incubation of the membranes with the PPP solution. Biofouling Tests Involving Microalgae. Details on how Microalgae (Chlorella sp.) were cultured are provided in the work of Feng et al.41 Filtration of Chlorella sp. solution was performed in dead-end mode. Membranes (2.5-cm diameter) were first pre-wetted with ethanol for about 0.5h, and then positioned in the filtration cell, before being compacted with DI-water at a transmembrane pressure (TMP) of 1.5 atm. Membrane conditioning was the same as described in previous section (immersion in alcohol, DI water


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overpressure cycle). Flux was recorded and once steady, the TMP was decreased to 1 atm. Water flux was recorded for 0.5h. The tank containing DI-water was then disconnected from the filtration cell and replaced by the tank containing the Microalgae solution (1.3 ± 1 g/L) and flux recorded for 0.5h. After this operation, membranes was thoroughly washed by first flushing DI water and then immersing it in a DI water bath for 0.5h. Then, the entire operation (DI water filtration, Microalgae solution filtration, washing) was repeated, before ending with a final DI water filtration run. Flux analysis indicators were also determined according to equations (1) to (4). However, in equations (2) and (4), JPPP was changed to JMA,f, the permeability recorded during last filtration run using the Microalgae solution.

Flux recovery ratio (FRR), total flux decline ratio (DRt), irreversible flux decline ratio (DRir) and reversible flux decline ratio (DRr) were determined as follows: 𝐽 𝑤,𝑓

𝐹𝑅𝑅(%) =

𝐷𝑅 𝑡 (%) =

𝐽 𝑤,𝑖

× 100

𝐽 𝑤,𝑖 ― 𝐽 𝑀𝐴,𝑓

𝐷𝑅 𝑖𝑟 (%) =

𝐽 𝑤,𝑖

𝐽 𝑤,𝑖 ― 𝐽 𝑤,𝑓 𝐽 𝑤,𝑖

(1)

× 100 (2)

× 100

(3)


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𝐷𝑅 𝑟 (%) =

𝐽 𝑤,𝑓 ― 𝐽 𝑀𝐴,𝑓 𝐽 𝑤,𝑖

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× 100 (4)

Where Jw,i, Jw,f and JMA,f correspond to the initial water flux, the final water flux, and the final MicroAlgae solution flux, respectively.

RESULTS AND DISCUSSION

Surface Chemical and Physical Properties of PVDF and Zwitterionic PVDF membranes. At first, we conducted an in-depth analysis of the surface chemistry of the membranes, using mapping FT-IR on the one hand, and XPS on the other hand. The related results are displayed in Figures 1 and 2. The FT-IR analysis of P1, P3 and P5 membrane revealed the presence of a peak at about 1730 cm-1, attributed to C=O stretch,42,

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logically not found in the spectrum of P0 membrane. This band ascertains the presence of the zwitterionic copolymer. In addition, Figure 2 1b presents the wide XPS scans but also a more detailed analysis obtained after peak deconvolution. Logically, the analysis of PVDF membrane reveals the presence of two peaks only corresponding to carbon and


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fluorine. However, oxygen peak (centered at 532 eV), nitrogen (centered at 399.7 eV) as well as a small phosphor peak (centered at 133 eV) could be detected on P1. P3 and P5 membranes, proving the presence of the copolymer. In addition, the C1s core-level spectra indicated the presence of [C=O] species44 found in both main segments of the zwitterionic copolymers (see its chemical composition in Figure 1). In addition, the presence of a main peak (BE = 399.5 eV) and a light shoulder (BE = 402.1 eV) on the N1s core level spectra of P1, P3 and P5 membranes as well as the peak centered at BE = 133 eV on the P2p spectra confirm the presence of phosphorylcholine.


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CH3 CH2

CH3

C

CH2

C

m C O

n

O

C O-

O +

CH2CH2OPOCH2CH2N(CH3)3

4000

O

O

CH2CH2NHCO(CH2)3CH3

3500

3000

2500

2000

3500

3000

2500

2000

O

1500

1000

1500

1000

P5

P3

P1

P0 4000

-1

Wavenumber (cm )


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Figure 1. Chemical characterization of membranes’ surfaces (a) Chemical structure of poly(2-methacryloyloxyethyl phosphorylcholine-

co-ethacryloyloxyethyl butylurethane) and FT-IR characterization of virgin PVDF (P0) and zwitterionic (P1 to P5) PVDF membranes. The characteristic band of C=O is highlighted at 1730 cm-1. (b) and (c) XPS characterization of virgin PVDF (P0) and zwitterionic (P1 to P5) PVDF membranes. (b) wide scan spectra; (c) O1s, N1s, C1s and P2p spectra.


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(a)

(b)

1200

1000

800

600

400

200

0

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O1s

N1s

C1s

F1s

P0

P2p CH2

C-F

C1s 540 538 536 534 532 530 528 526

P1

F1s

408 406 404 402 400 398 396 394

O-C

294 292 290 288 286 284 282

C-F

O1s

N1s

N(IV)

C1s

F1s C1s N1s

800

600

128

C=O

294 292 290 288 286 284 282

CH2, CH

N(IV)

C1s

138

136

134

132

130

128

PO4C=O

408 406 404 402 400 398 396 394

400

294 292 290 288 286 284 282

138

136

134

132

130

128

CH2

N(III) C-F

N(IV)

PO4-

CH C=O

P2p 540 538 536 534 532 530 528 526

1000

130

PO4-

CH

N(III)

O-C

N1s

1200

132

P2p 540 538 536 534 532 530 528 526

O1s

134

C-F

F1s

P5

408 406 404 402 400 398 396 394

O-C

O1s

136

P2p 540 538 536 534 532 530 528 526

P3

138

CH2

N(III)

200

408 406 404 402 400 398 396 394

294 292 290 288 286 284 282 138

136

134

132

130

128

0

Binding energy (eV)

Binding energy (eV)

Figure 2. XPS characterization of virgin PVDF (P0) and zwitterionic (P1 to P5) PVDF membranes. (a) wide scan spectra; (b) O1s, N1s, C1s and P2p spectra.

Bi-continuous structures are ideal to ensure both sustainable mechanical properties and high

permeability,

as

both

polymer-rich

and

polymer-poor

domains

are

all

interconnected.44 To reach this structure, we set the dissolution temperature of the casting solution to 35°C, in order to minimize growth of crystalline nuclei in the casting solution and crystallization-gelling during membrane formation.45,46 Besides, the other process parameters were set based on our experience of membrane structure control.18, 38


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Results of SEM and AFM analyses (Figure 32) both evidence the formation of highly porous membranes. As the concentration of copolymer increased (P1 to P5), nodules forming P0 tended to disappear and the membrane structure became bi-continuous, that is, with polymeric domains interconnected. The increase in the casting solution viscosity logically associated to an increase in total polymer content hinders nodule formation and their growth.18 Besides, the addition of the zwitterionic copolymer results in facilitated water transfer from the vapor phase to the casting solution, which accelerates phase separation, hence decreasing the chances for crystallization to occur. The change of structure (from nodular to bi-continuous) with the addition of copolymer also explains the decrease in membrane roughness, as clearly seen from the results of both 3D and phase AFM imaging. Moreover, the membranes remained highly porous (porosity ranging between 66% and 76%) with a pore size in the ultrafiltration domain (Table 1), even though it slightly decreased from P0 to P5 membrane, consistent with the addition of 1, 3 or 5 wt% of copolymer to the initial polymeric system containing a fixed amount of PVDF (20 wt%).


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Figure 2. Characterization of membrane surface by SEM and AFM. The scale indicated on the SEM images of P0 are valid for SEM images of other membranes. Only the z-scale varied on 3D AFM and phase AFM images.

Table 1. Some physical and hydration characteristics of the as-prepared membranes. ND: non-determined Membrane ID P0 P1 P3 P5

Pore size (µm) 0.03 0.03 0.02 0.02

Porosity (%) 72 ± 2 66 ± 2 75 ± 1 76 ± 1

Water contact angle (°) 137 ± 1 125 ± 1 120 ± 2 114 ± 2

Hydration capacity (mg/cm3) 75 ± 31 218 ± 35 266 ± 18 263 ± 42


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Commercial

0.1

70 ± 2

0

ND

The Effect of Zwitterionization on Membranes Hydrophilic Properties. One of the major criteria defined almost 20 years ago for nonfouling is the surface hdyrophilicity.6, 7 When it comes to in-situ modified porous membranes, one should not only look at the surface hydrophilicity (measured by the WCA) but more importantly, at the bulk hydration (measured by the hydration capacity). Indeed, large pore sizes and porosities contribute to increase the surface apparent hydrophobicity, according to the Cassie-Baxter equation,47 which means that slight reductions only in the WCA of the PVDF-based porous and rough membrane is often measured despite the use of antifouling polymers.18, 37

But when the membranes are immersed in an aqueous medium for a period of time

long enough (as during actual filtration), hydrophilic interactions (hydrogen bonds) are eventually established between the hydrophilic segments of the antifouling polymer and water, leading to permanent water trapping which protects the membrane from biofouling. Here, we did observe a slight reduction only in the WCA of the membrane as the WCA of P5 was 114° while it was 137° for the unmodified membrane (Table 1). Yet, overall


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hydration of the membranes increased a lot as it changed from 75 ± 31 mg/cm3 for P0 to 263 ± 42 mg/cm3 for P5 membrane. The increase in hydration capacity is associated to the increase in phopshobetaine-derivatives functional groups. Leng et al. reminded that water molecules generally form strong hydrogen bonding with zwitterionic polymers, which is induced by electrostatic interactions, and that a tight hydration layer is then critical to generate an anti-biofouling interface.48 Although other parameters strongly influence the extent of hydration of zwitterionic molecules (pH, nature of the brush, ionic strength, etc.), the sharp increase in hydration capacity observed here clearly results from water trapping by the MPC units of the copolymer. Besides, mapping analysis of the hydroxyl functional groups at 3300-3500 cm-1 corresponding to water molecules was conducted after freeze-drying the membranes (Figure 43). The color-coded maps of P0 membrane is dark blue, consistent with the absence of water. Then, lighter blue regions, green, yellow and even red regions are seen on the map of P1, indicating the presence of water and indirectly, the presence of the copolymer, but also its heterogeneous distribution. There are no blue spots detected on the maps of P3 and P5, which suggests the large presence water and of the copolymer


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over the entire surface scanned. Besides, P5 is the most homogeneous membrane, with two dominating colors composing the maps. Clearly and despite a drying step, P5 has trapped a lot of water molecules. These results suggest that a tight hydration layer can be formed surrounding the polymer skeleton, which should protect the membranes from biofouling.8

Figure 3. Results of FT-IR mapping performed at 3300~3500 cm-1 after membrane drying (OH functional groups) highlighting surface hydration. Dark blue colour indicates no hydration while red colour indicates high level of hydration.

The Effect of Zwitterionization on Resistance to Bacteria. An important characteristic of membrane to be used in biomedical-related applications or more generally, in medium containing biofoulants, is their ability to resist the attachment of bacteria. The as-prepared membranes were incubated with S. maltophilia (gram-negative) and S. mutans (gram-positive) bacteria for 24h,


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duration from which biofilm can be formed. The control sample is a hydrogel of sulfobetaine methacrylate as this material is known to resist bacteria,49 blood cells and plasma proteins50-52 but also fibroblasts.52 The related confocal observations and quantitative analyses are provided in Figures 5 4a and 64b. It is first (and logically) seen that PVDF porous membranes provide an ideal environment for biofoulants. The intrinsic hydrophobicity of PVDF arising from its chemical nature is enhanced by the highly porous nature of the membrane. In other words, another membrane preparation process (such as dry casting) would have led to significantly less hydrophobic membranes, as we showed it earlier for totally different types of PVDF-based membranes/applications.5349 Thus the highly hydrophobic nature of these membranes due to both the chemical nature of PVDF and the physical structure of the membranes leads to high bacterial attachment. Although the modified membranes remained highly porous, the results suggest that the addition of the copolymer drastically decreased biofouling. From a copolymer concentration in the casting solution as low as 1 wt%, a major improvement in biofouling resistance was already observed. Membranes prepared from a casting solution containing 5 wt% copolymer almost competed with reference control sample PSBMA hydrogels in terms of biofouling resistance. This is quite remarkable noting again the different physical nature of the systems, and confirms with different bacterial species, that the phosphobetaine-based copolymer is highly efficient to protect membranes from biofouling by bacteria. Finally, it is difficult to draw accurate comparisons with other published works because there is almost no study, to our knowledge, mentioning the preparation of zwitterionic antifouling membranes by a similar process. Yet, we noted that the improvement measured, compared to the virgin membrane (over 99.9% decrease), is even better than using a PVDF/PS-r-PEGMA-r-PSBMA membrane prepared in similar conditions (although different bacteria were used).38 We shall remind the reader at this particular point that both bacterial


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species tested are pathogenic to humans.30, 31 Although found in different habitats, they are both likely to be in contact with biomaterials, or materials used for membranes as pointed in the introduction section of this manuscript. Adding to the fact that some bacterial species can be deformable, depending on the composition of their cell-wall,25 it is necessary that membrane materials do not just act as a physical barrier to separate by the virtue of size differences, but resist biofouling and the approach/adsorption of bacteria towards the surface, through the formation of a protective hydration layer.


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Figure 4. The effect of the zwitterionic copolymer concentration on the resistance of membrane to the attachment of (a) Stenotrophomonas maltophilia bacteria after a 24h-incubation period, (b) Streptococcus mutans bacteria after a 24h-incubation period and (c) platelets.

Figure 6. The effect of the zwitterionic copolymer concentration on the resistance of membrane to the attachment of Streptococcus mutans bacteria after a 24h-incubation period.


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The Effect of Zwitterionization on Resistance to Platelets. A strong evidence of the bioinert property of materials for biomedical-related applications is their ability to resist platelet adhesion. Adhesion/activation of these sensitive cells is strongly correlated to the early adhesion of some particular plasma proteins. While Xu et al. reminded that albumin is considered inert and does not mediate thrombosis,540 fibrinogen plays a key role.551 Therefore, if a material resists platelet adhesion, it implies that interactions with plasma proteins are also limited. So, we conducted platelet adhesion tests, which results are presented in Figure 74c. While a high density of platelets was observed by confocal microscope and later on quantified, it is also undeniable that the adhesion of platelets was drastically reduced with the copolymer concentration in the membranes. These results clearly indicate that the bioinert property of the membrane material has been enhanced. Besides, the adsorption level measured for P5 membrane is almost comparable to that obtain with the model zwitterionic hydrogel (SBMA). It is again quite remarkable because the membranes are extremely porous, unlike the SBMA controls which are hydrogels filled with water. As above-mentioned, the porosity, regardless of the chemical nature of the substrate, facilitates cell entrapment. Hence, no platelet or very low density signifies that the copolymer is well distributed at the surface of the membrane, and at a concentration large enough to minimize structure contribution to cell adhesion.


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Figure 7. The effect of the zwitterionic copolymer concentration on the resistance of membrane to platelet adhesion.

The Effect of Zwitterionization on Resistance to PPP During Filtration Operation: Resistance to Plasma Proteins. Platelet adhesion tests tended to evidence the bioinert property of the modified membranes. To support these results, we performed filtration tests that involved incubation

with

platelet-poor-plasma,

a

medium

rich

in

plasma

proteins.

The

adsorption/incubation time of 2h was chosen taking into account that plasma protein adsorption is the first event that is involved in blood coagulation and in the biofouling of membranes in contact with blood, and occurs in a shorter time frame. A dedicated study highlighted that adsorption of proteins on surfaces reaches a plateau within hundreds of seconds at the longest.526 In addition, we observed that hydrophilic commercial membranes (supposedly able to resist better biofouling) exhibited severe biofouling after a similar treatment.573 So we chose a longer adsorption/incubation time then actually needed in order to maximize biofouling by plasma protein and remaining platelets. In Figure 85, we compared the performance of our best membrane P5 with those of a


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commercial hydrophilic PVDF membrane. Note that the changes of permeability over time were represented using the original dimensions (L/m2.h) and a dimensionless representation obtained by divided the permeability at each time step by the initial water permeability. The dimensionless form is useful to evaluate at a first glance the flux recovery, and so, the extent of biofouling. First, it is seen that the permeability of the two membranes can be considered as almost identical (taking into account experimental errors), around 1000 L/m2.h at 1 bar of transmembrane pressure, which will make further performance comparisons relevant. Despite the fact that our as-prepared membrane has a lower pore size than the commercial membrane, both water permeabilities were similar, which highlights the positive effect of the zwitterionic copolymer on membrane hydrophilization, and which is consistent with results of hydration (Table 1). After plasma protein adsorption, a more significant drop in permeability was measured using the commercial membrane, despite its inherent hydrophilicity. The exact composition of the commercial membrane is unknown, for sound business reasons, but the zwitterionic copolymer used to fabricate P5 seems to clearly outperform the hydrophilic agent used to make the commercial membrane. Resistance to biofouling by plasma proteins logically led to a quite high water permeability, and after complete washing of the membranes, a flux recovery ratio of about 75% was obtained with P5 (Figure 8c5c), while it was only 40% for the commercial hydrophilic membrane, due to a much larger proportion of irreversible fouling. These results clearly support those of Figure 6 4c and confirm the improved bioinert property of P5 membrane. Finally, one may also have noticed that the permeability of the commercial hydrophilic PVDF membrane slightly increased during the last filtration cycle, which is uncommon. Possible explanations for this trend are an uncontrolled increase in transmembrane pressure (human error during the test) or


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partial supplementary release of biofouling. However, it did not affect the conclusions regarding the superior antifouling property of P5 membrane.

Figure 5. Comparison of the performances of P5 membrane and of a commercial hydrophilic PVDF membranes during filtration after incubation with plasma-poor-platelet. (a) flux vs. time; (b) dimensionless representation of the filtration fluxes; (c) analysis of filtration through the determination of ratio indicators.

The Effect of Zwitterionization on Resistance to Microalgae. Microalgae are bio-organisms able to produce renewable energy from atmospheric CO2 and using light. They can be concentrated by a number of processes including membrane processes,584 but their high biofouling ability tends to limit the usage of membranes for this purpose. In order to further prove the superior general


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anti-biofouling properties of our materials as well as their applicability in processes during which the membrane comes in contact with miscellaneous bio-organisms, we conducted cyclic water/Microalgae filtration tests, and used again a hydrophilic commercial PVDF membrane as control. From the results of Figure 96, it is confirmed that both membranes have a very similar initial water permeability (although a 10% variability was obtained, compared to Figure 85, which may be attributed to a slight change in transmembrane pressure). In both cases, the flux dramatically drops once water is changed to microalgae solution, consistent with the large characteristic size of microphytes (typically larger than 1 µm) compared to membrane pore size. It results in a fast accumulation of the eukaryotic organisms on the membrane surface. It was noted that the flux obtained with P5 membrane is more than twice that of the commercial hydrophilic PVDF membrane, a first indication of the superior biofouling resistance of our zwitterionic membrane. Then, after a first washing, and switching back to water, it was observed that the water permeability dropped to 600 L/m2.h and less than 400 L/m2.h for P5 and the commercial membranes, respectively, indicating severe irreversible biofouling on both membranes but also better biofouling resistance of P5. Eventually, in the conditions of the tests, we measured a flux recovery ratio of 38% for P5 while it was as low as 17% for the commercial membrane. All in all, the zwitterionic copolymer and our design permit to decrease membranes biofouling by a 2 fold factor, and it is clearly seen that the surface of P5 membrane was significantly cleaner at the end of the test than that of the commercial hydrophilic membrane (Figure 107). Although FRR was significantly lower after Microalgae filtration tests than after incubation with PPP, consistent with the much larger size of Microalgae, results indicate that our zwitterionic membranes outperform commercial hydrophilic PVDF membranes in versatile situations. Though not totally bioinert, P5


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membrane offers an interesting substitute to existing commercial hydrophilic PVDF-based membranes.

Figure 6. Comparison of the performances of P5 membrane and of a commercial hydrophilic PVDF membranes during cyclic water/Microalgae filtration; (a) flux vs. time; (b) dimensionless representation of the filtration fluxes; (c) analysis of filtration through the determination of ratio indicators.


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Commercial hydrophilic PVDF

5 µm

Page 41 of 51

P5

5 µm

Figure 7. SEM images of commercial hydrophilic PVDF membrane and P5 membrane after cyclic water/Microalgae filtration.

CONCLUSIONS The results of this study demonstrated that copolymers composed of phosphorylcholine and urethane groups can be a viable solution to efficient biofouling mitigation of porous PVDF membranes in multiple scenarios involving biological compounds. In-situ modification can lead to controlled formation of effective anti-biofouling porous membranes, potentially suitable for a large span of biomedical and biological-related applications (blood filtration, Microalgae harvesting, etc.). As a proof of their efficiency, the modified membranes prepared in the frame of this study eliminated over 99.9% and 98.9% of biofouling caused in static conditions by bacteria and platelets, respectively. Besides, our results also suggest that a long incubation of membranes with a platelet-


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poor-plasma medium, rich in plasma proteins, does not lead to biofouling during filtration as severe as in the case of that measured with a commercial hydrophilic membrane (FRR = 75% vs. FRR = 40%). Finally, the use of the zwitterionic copolymer in the membranes enabled to significantly reduce irreversible biofouling during filtration of media containing Microalgae (DRir = 62% for P5 vs. 83% for a commercial membrane). In short, the designed zwitterionic membranes are applicable in a large variety of membrane processes during which the membrane is likely to contact miscellaneous biological compounds (proteins, bacteria, human cell or Microalgae).

AUTHOR INFORMATION

Corresponding Author * Antoine Venault: [email protected] tel: +886-(0)3 265 4194

** Yung Chang: [email protected] tel: +886-(0)3 265 4190

Author Contributions


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The manuscript was written through contributions of all authors. All authors have given approval to the final version of the manuscript.

ACKNOWLEDGMENT The Ministry of Science and Technology of Taiwan (MOST) is greatly acknowledged for funding this project through the grant MOST 107-2221-E-033-019-MY3.

REFERENCES (1)

Yang, H.L.; Huang, C.; Lin, J.C.-T. Seasonal Fouling on Seawater Desalination RO Membrane. Desalination, 2010, 250, 548-552, DOI:10.1016/j.desal.2009.09.021.

(2)

Yamamoto, K.; Hiwatari, M.; Kohori, F.; Sakai, K.; Fukuda, M.; Hiyoshi, T. Membrane Fouling and Dialysate Flow Pattern in an Internal Filtration-Enhancing Dialyzer. J. Artif. Organs, 2005, 8, 198-205, DOI:10.1007/s10047-005-0303-2.

(3)

Zhang, G.; Li, L.; Huang, Y.; Hozumi, A.; Sonoda, T.; Su, Z. Fouling-Resistant Membranes for Separation of Oil-in-Water Emulsions. RSC Adv., 2018, 8, 5306-5311, DOI:10.1039/C7RA13605F.

(4)

Nguyen, T.; Roddick, F.A.; Fan, L. Biofouling of Water Treatment Membranes: A Review of the Underlying Causes, Monitoring Techniques and Control Measures. Membranes, 2012, 2, 804-840, DOI:10.3390/membranes2040804.

(5)

Prime, K.L.; Whitesides, G.M. Self-Assembled Organic Monolayers: Model Systems for Studying Adsorption of Proteins at Surfaces. Science, 1991, 252, 1164-1167, DOI: 10.1126/science.252.5009.1164.


42

Page 44 of 51 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Langmuir

(6)

Chapman, R.G.; Ostuni, E.; Takayama, S.; Holmlin, R.E.; Yan, L.; Whitesides, G.M. Surveying for Surfaces That Resist the Adsorption of Proteins. J. Am. Chem. Soc., 2000, 122, 8303-8304, DOI:10.1021/ja000774f.

(7)

Ostuni, E.; Chapman, R.G.; Holmlin, R.E.; Takayama, S.; Whitesides, G.M. A Survey of Structure-Property Relationships of Surfaces That Resist the Adsorption of Protein. Langmuir, 2001, 17, 5605-5620, DOI:10.1021/la010384m.

(8)

Chen, S.; Li, L.; Zhao, C.; Zheng, J. Surface Hydration: Principles and Applications Toward Low-fouling/Nonfouling Biomaterials. Polymer, 2010, 51, 5283-5293, DOI:10.1016/j.polymer.2010.08.022.

(9)

Wu, J.; Lin, W.; Wang, Z.; Chen, S.; Chang, Y. Investigation of the Hydration of Nonfouling Material Poly(sulfobetaine methacrylate) by Low-Field Nuclear Magnetic Resonance. Langmuir, 2012, 28, 7436-7441, DOI:10.1021/la300394c.

(10)

Zhou, R.; Ren, P.-F.; Yang, H.-C.; Zhu, Z.-K. Fabrication of Antifouling Membrane Surface by Poly(sulfobetaine methacrylate)/Polydopamine co-Deposition. J. Membr. Sci., 2014, 466, 18-25, DOI:10.1016/j.memsci.2014.04.032.

(11)

Ma, W.; Rajabzadeh, S.; Matsuyama, H. Preparation of Antifouling Poly(vinylidene fluoride) Membranes via Different Coating Methods Using a Zwitterionic Copolymer. Appl. Sur. Sci., 2015, 357, 1388-1395, DOI: 10.1016/j.apsusc.2015.10.007

(12)

Wang, S.-Y.; Fang, L.-F.; Cheng, L.; Jeon, S.; Kato, N.; Matsuyama, H. Improved Antifouling Properties of Membranes by Simple Introduction of Zwitterionic Copolymers via Electrostatic Adsorption. J. Membr. Sci., 2018, 564, 672-681, DOI: 10.1016/j.memsci.2018.07.076

(13)

Hua, H.; Li, N.; Wu, L.; Zhong, H.; Wu, G.; Yuan, Z.; Lin, X.; Tang, L. Anti-fouling Ultrafiltration

Membrane

Prepared

from

Polysulfone-graft-methyl

Acrylate

Copolymers by UV-Induced Grafting Method. J. Environ. Sci., 2008, 20, 565-570, DOI:10.1016/S1001-0742(08)62095-1. (14)

Yu, H.; Cao, Y.; Kang, G.; Liu, J.; Li, M.; Yuan, Q. Enhancing Antifouling Property of Polysulfone Ultrafiltration Membrane by Grafting Zwitterionic Copolymer via UVInitiated

Polymerization.

J.

Membr.

Sci.,

2009,

342,

6-13,

DOI:10.1016/j.memsci.2009.05.041.


43

Langmuir 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

(15)

Page 45 of 51

Yang, Y.-F.; Li, Y.; Li, Q.-L.; Wan, L.-S.; Xu, Z.-K. Surface Hydrophilization of Microporous Polypropylene Membrane by Grafting Zwitterionic Polymer for AntiBiofouling. J. Membr. Sci., 2010, 362, 255-264, DOI:10.1016/j.memsci.2010.06.048

(16)

Hester, J.F.; Banerjee, P.; Mayes, A.M. Preparation of Protein-Resistant Surfaces on Poly(vinylidene fluoride) Membranes via Surface Segregation. Macromolecules, 1999, 32, 1643-1650, DOI:10.1021/ma980707u.

(17)

Fan, X.; Su, Y.; Zhao, X.; Li, Y.; Zhang, R.; Zhao, J.; Jiang, Z.; Zhu, J.; Ma, Y.; Liu, Y. Fabrication of Polyvinyl Chloride Ultrafiltration Membranes with Stable Antifouling Property by Exploring the Pore Formation and Surface Modification Capabilities of Polyvinyl Formal. J. Membr. Sci., 2014, 464, 100-109, DOI: 10.1016/j.memsci.2014.04.005.

(18)

Venault, A.; Wu, J.R.; Chang, Y.; Aimar, P. Fabricating Hemocompatible Bicontinuous PEGylated PVDF Membranes via Vapor-induced Phase Inversion. J. Membr. Sci., 2014, 470, 18-29, DOI:10.1016/j.memsci.2014.07.014.

(19)

Zhou, Z.; Rajabzadeh, S.; Shaikh, A.R.; Kakihana, Y.; Ma, W.; Matsuyama, H. Effect of Surface Properties on Antifouling Performance of Poly(vinyl chloride-copoly(ethylene glycol)methyl ether methacrylate)/PVC Blend Membrane. J. Membr. Sci., 2016, 514, 537-546, DOI:10.1016/j.memsci.2016.05.008.

(20)

Ma, W.; Rajabzadeh, S.; Shaikh, A.R.; Kakihana, Y.; Sun, Y.; Matsuyama, H. Effect of Type of Poly(ethylene glycol) (PEG) Based Amphiphilic Copolymer on Antifouling Properties of Copolymer/poly(vinylidene fluoride) (PVDF) Blend Membranes. J. Membr. Sci., 2016, 514, 429-439, DOI: 10.1016/j.memsci.2016.05.021.

(21)

Ishihara, K.; Hanyuda, H.; Nakabayashi, N. Synthesis of Phospholipid Polymers Having a Urethane Bond in the Side Chain as Coating Material on Segmented Polyurethane and Their Platelet Adhesion-Resistant Properties. Biomaterials, 1995, 16, 873-879, DOI: 10.1016/0142-9612(95)94150-J.

(22)

Ishihara, K.; Iwasaki, Y.; Ebihara, S.; Shindo, Y.; Nakabayashi, N. Photoinduced Graft Polymerization of 2-Methacryloyloxyethyl Phosphorylcholine on Polyethylene Membrane Surface for Obtaining Blood Cell Adhesion Resistance. Colloids Surf. B, 2000, 18, 325-335, DOI:10.1016/S0927-7765(99)00158-7.


44

Page 46 of 51 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Langmuir

(23)

Morimoto, N.; Iwasaki, Y.; Nakabayashi, N.; Ishihara, K. Physical Properties and Blood Compatibility of Surface-modified Segmented Polyurethane by SemiInterpenetrating Polymer Networks with a Phospholipid Polymer. Biomaterials, 2002, 23, 4881-4887, DOI: 10.1016/S0142-9612(02)00246-6.

(24)

Hong, Y.; Ye, S.-H.; Nieponice, A.; Soletti, L.; Vorp, D.A.; Wagner, W.R. A Small Diameter, Fibrous Vascular Conduit Generated from a Poly(ester Urethane)urea and Phospholipid

Polymer

Blend.

Biomaterials,

2009,

30,

2457-2467,

DOI:

10.1016/j.biomaterials.2009.01.013. (25)

Lebleu, N.; Roques, C.G.; Aimar, P.; Causserand, C. Role of the Cell-wall Structure in the Retention of Bacteria by Microfiltration Membranes, J. Membr. Sci., 2009, 326, 178-185, DOI:10.1016/j.memsci.2008.09.049.

(26)

Gérard, E.; Bessy, E.; Salvagnini, C.; Rerat, V.; Momtaz, M.; Hénard, G.; Marmey, P.; Verpoort, T.; J. Marchand-Brynaert, J. Surface Modifications of Polypropylene Membranes Used for Blood Filtration. Polymer, 2011, 52, 1223-1233, DOI: 10.1016/j.polymer.2011.01.029.

(27)

Wenten, I.G.; Aryanti, P.T.P.; Khoiruddin, K.; Hakim, A.N.; Himma, N.F. Advances in Polysulfone-Based Membranes for Hemodialysis. J. Membr. Sci. Res., 2016, 2, 7889, DOI:10.22079/JMSR.2016.19155.

(28)

Zhu, L.; Song, H.; Wong, J.; Xue, L. Polysulfone Hemodiafiltration Membranes With Enhanced Anti-fouling and Hemocompatibility Modified by Poly(vinyl pyrrolidone) Via In situ Cross-linked Polymerization. Mater. Sci. Eng. C, 2017, 74, 159-166, DOI:10.1016/j.msec.2017.02.019.

(29)

Brooke, J.S. Stenotrophomonas maltophilia: an Emerging Global Opportunistic Pathogen. Clin. Microbiol. Rev., 2012, 25, 2-41, DOI: 10.1128/CMR.00019-11.

(30)

Nakano, K.; Nomura, R.; Ooshima, T. Streptococcus Mutans and Cardiovascular Diseases, Jpn. Dent. Sci. Rev., 2008, 44, 29-37, DOI:10.1016/j.jdsr.2007.09.001.

(31)

Pommel, L.; Camps, J. Effects of Pressure and Measurement Time on the Fluid Filtration

Method

in

Endodontics.

J.

Endod.,

2001,

27,

256-258,

DOI:10.1097/00004770-200104000-00003.


45

Langmuir 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

(32)

Page 47 of 51

Javidi, M.; Naghavi, N.; Roohani, E. Assembling of Fluid Filtration System for Quantitative Evaluation of Microleakage in Dental Materials. Iran Endod. J., 2008, 3, 68-72.

(33)

Moradi, S.; Lomee, M.; Gharechahi, M. Comparison of Fluid Filtration and Bacterial Leakage Techniques for Evaluation of Microleakage in Endodontics. Dent. Res. J., 2015, 12, 109-114.

(34)

Zhao, G.; Chen, W.N. Biofouling Formation and Structure on Original and Modified PVDF Membranes: Role of Microbial Species and Membrane Properties. RSC Adv., 2017, 7, 37990-38000, DOI:10.1039/c7ra04459c.

(35)

Carretier, S.; Chen, L.-A.; Venault, A.; Yang, Z.-R.; Aimar, P.; Chang, Y. Design of PVDF/PEGMA-b-PS-b-PEGMA Membranes by VIPS for Improved Biofouling Mitigation. J. Membr. Sci., 2016, 510, 355-369, DOI: 10.1016/j.memsci.2016.03.017.

(36)

Kattula, S.; Byrnes, J.-R.; Wolberg, A.S. Fibrinogen and Fibrin in Hemostasis and Thrombosis.

Arterioscler.

Thromb.

Vasc.

Biol.,

2017,

37,

13-21,

DOI:10.1161/ATVBAHA.117.308564. (37)

Barros, A.I.; Gonçalves, A.L.; Simões, M.; Pires, J.C.M. Harvesting Techniques Applied to Microalgae: A Review. Renew. Sustain. Energy Rev., 2015, 41, 1489-1500, DOI:10.1016/j.rser.2014.09.037.

(38)

Dizon, G.V.; Venault, A. Direct In-situ Modification of PVDF Membranes with a Zwitterionic Copolymer to Form Bi-continuous and Fouling Resistant Membranes. J. Membr. Sci., 2018, 550, 45-58, DOI:10.1016/j.memsci.2017.12.065.

(39)

Hsiao, S.-W.; Venault, A.; Yang, H.-S.; Chang, Y. Bacterial Resistance of SelfAssembled

Surfaces

Using

PPOm-b-PSBMAn

Zwitterionic

Copolymer

–

Concomitant Effects of Surface Topography and Surface Chemistry on Attachment of Live

Bacteria.

Colloids

Surf.

B,

2014,

118,

254-260,

DOI:10.1016/j.colsurfb.2014.03.051. (40)

Jhong, J.F.; Venault, A.; Liu, L.; Zheng, J.; Chen, S.-H.; Higuchi, A.; Huang, J.; Chang, Y. Introducing Mixed-Charge Copolymers As Wound Dressing Biomaterials ACS Appl. Mater. Interfaces, 2014, 6, 9858-9870, DOI:10.1021/am502382n.


46

Page 48 of 51 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Langmuir

(41)

Feng, Y.; Li, C.; Zhang, D. Lipid Production of Chlorella Vulgaris Cultured in Artificial

Wastewater

Medium.

Bioresour.Technol.,

2011,

102,

101-105,

DOI:10.1016/.j.biortech.2010.06.016. (42)

Zhu, L.P.; Xu, Y.Y.; Dong, H.B.; Yi, Z; Zhu, B.K. Amphiphilic PPESK-graftP(PEGMA) Copolymer for Surface Modification of PPESK Membranes. Mater. Chem. Phys., 2009, 115, 223-228, DOI:10.1016/j.matechemphys.2008.11.054.

(43)

Jin, J.; Jiang, W.; Shi, Q.; Zhao, J.; Yin, J.; Stagnaro, P. Fabrication of PP-g-PEGMAg-heaprin and its Hemocompatibility: From Protein Adsorption to Anticoagulant Tendency, Appl. Surf. Sci., 2012, 258, 5841-5849, DOI:101016/j.apsusc.2012.02.113

(44)

Liu, F.; Xu, Y.-Y.; Zhu, B.-K.; Zhang, F.; Zhu, L.-P. Preparation of Hydrophilic and Fouling Resistant Poly(vinylidene fluoride) Hollow Fiber Membranes. J. Membr. Sci., 2009, 345, 331-339, DOI:10.1016/j.memsci.2009.09.020.

(45)

Li, C.L.; Wang, D.M.; Deratani, A.; Quemener, D.; Bouyer, D.; Lai, J.Y. Insight Into the Preparation of Poly(vinylidene fluoride) Membranes by Vapor-induced Phase Separation, J. Membr. Sci., 2010, 361, 154-166, DOI:10.1016/j.memsci.2010.05.064.

(46)

Lin, D.J.; Beltsios, K.; Young, T.H.; Jeng, Y.S.; Cheng, L.P. Strong Effect of Precursor Preparation on the Morphology of Semicrystalline Phase Iinversion Poly(vinylidene fluoride)

Membranes.

J.

Membr.

Sci.,

2006,

274,

64-72,

DOI:

10.1016/j.memsci.2005.07.043 (47)

Cassie, A.B.D.; Baxter, S. Wettability of Porous Surfaces. Trans. Faraday Soc., 1944, 40, 546-551, DOI: 10.1039/TF9444000546.

(48)

Leng, C.; Han, X.; Shao, Q.; Zhu, Y.; Li, Y.; Jiang, S.; Chen, Z. In Situ Probing of the Surface Hydration of Zwitterionic Polymer Brushes: Structural and Environmental Effects. J. Phys. Chem. C, 2014, 118, 15840-15845, DOI: 10.1021/jp504293r.

(49)

Shen, J.; Du, M.; Wu, Z.; Song, Y.; Zheng, Q. Strategy to Construct

Polyzwitterionic Hydrogel Coating with Antifouling, Drag-reducing and Weak Swelling Performance, RSC Adv. 2019, 9, 2081-2091, DOI: 10.1039/C8RA09358J.


47

Langmuir 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

(50)

Page 49 of 51

Shih, Y.-J.; Chang Y., Tunable Blood Compatibility of Polysulfobetaine from

Controllable Molecular-Weight Dependence of Zwitterionic Nonfouling Nature in Aqueous Solution, Langmuir 2010, 26, 17286-17294, DOI: 10.1021/la103186y. (51)

Chang, Y.; Yandi, W.; Chen, W.-Y.; Shih, Y.-J.; Yang, C.-C.; Chang, Y.; Ling,

Q.-D.; Higuchi, A. Tunable Bioadhesive Copolymer Hydrogels of Thermoresponsive Poly(N-isopropyl

acrylamide)

Containing

Zwitterionic

Polysulfobetaine,

Biomacromolecules 2010, 11, 1101-1111, DOI: 10.1021/bm100093g. (48)(52)

Lee, S.Y.; Lee, Y.; Thi, P.L.; Oh, D.H.; Park, K.D. Sulfobetaine Methacrylate

Hydrogel-coated Anti-fouling Surfaces for Implantable Biomedical Devices, Biomater. Res. 2018, 22, 3, DOI: 10.1186/s40824-017-0113-7. (49)(53)

Venault, A.; Chiang, C.-H.; Chang, H.-Y.; Hung, W.-S.; Chang, Y. Graphene

Oxide/PVDF VIPS Membranes for Switchable, Versatile and Gravity-driven Separation

of

Oil

and

Water,

J.

Membr.

Sci.,

2018,

565,

131-144,

DOI:10.1016/j.memsci.2018.08.018. (50)(54) at

Xu, L.-C.; Bauer, J.; Siedlecki, C.A. Proteins, Platelets, and Blood coagulation Biomaterial

Interfaces.

Colloids

Surf.,

B,

2014,

124,

49-68,

DOI:

10.1016/j.colsurfb.2014.09.040. (51)(55)

Grunkemeier, J.M.; Tsai, W.B.; Alexander, M.R.; Castner, D.G.; Horbett, T.A.

Platelet Adhesion and Procoagulant Activity Induced by Contact with Radiofrequency Glow Discharge Polymers: Roles of Adsorbed Fibrinogen and vWF. J. Biomed. Mater. Res., 2000, 51, 669-679, DOI: 10.1002/1097-4636(20000915)51:43.0.CO;2-%23. (52)(56)

Fang, F.; Satulovsky, J.; Szleifer, I. Kinetics of Protein Adsorption and

Desorption on Surfaces with Grafted Polymers. Biophys. J., 2005, 89, 1516-1533, DOI: 10.1529/biophysj.104.055079. (53)(57)

Venault,

A.;

Ballad,

M.R.B.;

Liu,

Y.-H.;

Aimar,

P.;

Chang,

Y.

Hemocompatibility of PVDF/PS-b-PEGMA Membranes Prepared by LIPS process. J. Membr. Sci., 2015, 477, 101-114, DOI: 10.1016/j.memsci.2014.12.024.


48

Page 50 of 51 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Langmuir

(54)(58)

Chisti, Y. Biodiesel From Microalgae. Biotechnol. Adv., 2007, 25, 294-306,

DOI:10.1016/j.biotechadv.2007.02.001.


49

Langmuir 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

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Towards Anti-biofouling PVDF Membranes - Langmuir (ACS

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