Article pubs.acs.org/Langmuir
Highly Stable, Protein-Resistant Surfaces via the Layer-by-Layer Assembly of Poly(sulfobetaine methacrylate) and Tannic Acid Peng-Fei Ren,† Hao-Cheng Yang,† Hong-Qing Liang,† Xiao-Ling Xu,‡ Ling-Shu Wan,*,† and Zhi-Kang Xu*,† †
Ministry of Education (MOE) Key Laboratory of Macromolecular Synthesis and Functionalization, Joint Laboratory for Adsorption and Separation Materials, Department of Polymer Science and Engineering, and ‡Department of Chemistry, Zhejiang University, Hangzhou, Zhejiang 310027, People’s Republic of China S Supporting Information *
ABSTRACT: Zwitterionic materials have received great attention because of the non-fouling property. As a result of the electric neutrality of zwitterionic polymers, their layer-by-layer (LBL) assembly is generally conducted under specific conditions, such as very low pH values or ionic strength. The formed multilayers are unstable at high pH or in a high ionic strength environment. Therefore, the formation of highly stable multilayers of zwitterionic polymers via the LBL assembly process is still challenging. Here, we report the LBL assembly of poly(sulfobetaine methacrylate) (PSBMA) with a polyphenol, tannic acid (TA), for protein-resistant surfaces. The assembly process was monitored by a quartz crystal microbalance (QCM) and variable-angle spectroscopic ellipsometry (VASE), which confirms the formation of thin multilayer films. We found that the (TA/PSBMA)n multilayers are stable over a wide pH range of 4−10 and in saline, such as 1 M NaCl or urea solution. The surface morphology and chemical composition were characterized by specular reflectance Fourier transform infrared spectroscopy (FTIR/SR), X-ray photoelectron spectroscopy (XPS), and atomic force microscopy (AFM). Furthermore, (TA/PSBMA)n multilayers show high hydrophilicity, with a water contact angle lower than 15°. A QCM was used to record the dynamic protein adsorption process. Adsorption amounts of bovine serum albumin (BSA), lysozyme (Lys), and hemoglobin (Hgb) on (TA/PSBMA)20 multilayers decreased to 0.42, 52.9, and 37.9 ng/cm2 from 328, 357, and 509 ng/cm2 on a bare gold chip surface, respectively. In addition, the protein-resistance property depends upon the outmost layer. This work provides new insights into the LBL assembly of zwitterionic polymers.
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INTRODUCTION
polymers also makes them difficult to be introduced onto material surfaces, which has become a major challenge for their practical applications. To address this issue, great efforts have been devoted to developing methods for the immobilization of zwitterionic betaine polymers. Jiang and co-workers prepared poly(sulfobetaine methacrylate) (PSBMA) brushes on gold and glass surfaces through the adsorption of PSBMA-block-poly(propylene oxide)15 or the surface-initiated atom transfer radical polymerization (ATRP) of sulfobetaine methacrylate (SBMA),16,17 respectively. After that, a series of zwitterionic
Zwitterionic betaine-containing polymers, such as polycarboxybetaine and polysulfobetaine, have received increasing attention in the construction of antifouling surfaces for biomedical materials and separation membranes.1−3 These polymers possess strong ionic hydration capability because they have both cationic and anionic groups on the same monomer unit.4,5 Therefore, they exhibit excellent antifouling property compared to traditional materials, such as polyethylene glycol (PEG),6−8 peptides,9,10 and multi-hydroxyl polymers.11−13 For example, Holmlin et al. reported that self-assembled sulfobetaine monolayers can substantially resist the adsorption of bovine serum albumin (BSA), fibrinogen, and lysozyme (Lys).14 However, the excellent hydratability of zwitterionic © XXXX American Chemical Society
Received: March 12, 2015 Revised: May 3, 2015
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DOI: 10.1021/acs.langmuir.5b00920 Langmuir XXXX, XXX, XXX−XXX
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Langmuir antifouling surfaces has been designed via “grafting from” or “grafting to” methods.18−21 In addition, we co-deposited polydopamine and PSBMA onto a porous polypropylene membrane, which shows enhanced antifouling performance.22 Layer-by-layer (LBL) assembly has been demonstrated to be a versatile and facile approach to the fabrication of multilayer films with target properties on various material surfaces.23 This technique has been widely explored and applied in electrical, optical, biomedical, and environmental devices.24−26 A variety of polyelectrolytes, including synthetic polymers, dendrimers, polysaccharides, DNA, and proteins, have been used to construct LBL multilayers via electrostatic interaction or hydrogen bonding on surfaces of substrates with different shapes.27−30 Zwitterionic polymers are difficult to assemble under common conditions because of their electric neutrality. However, the zwitterionic groups can form charge asymmetries by protonation under very low pH values31−34 or by selective interactions between their opposite ions in low-salt solutions.35,36 Thus, under some specific conditions, a LBL process can be used to construct multilayers of zwitterionic polymers via electrostatic interaction with common polyelectrolytes. Gui et al. used poly(acrylic acid) (PAA) and PSBMA to construct temperature-responsive multilayer films in a low-pH solution (pH 1.0),37 in which PSBMA carries weak cationic charges because of the partial protonation of its sulfonate groups that can be completely protonated at pH < 0.8. de Grooth et al. built ionic-strength responsive membranes through LBL assembly of PSBMA and poly(diallyldimethylammoium chloride) in NaCl solutions.38 The adsorption amount of PSBMA on silica is strongly dependent upon ionic strength and significantly decreases with the ionic strength of solutions. Besides, the protonated zwitterionic group, which is a hydrogen-bond donor, is able to assemble with a hydrogen bond acceptor.39 However, the LBL process must be conducted under specific conditions of very low pH values or ionic strength. As a result, the formed multilayers are unstable at high pH or in a high ionic strength environment. For example, (PAA/PSBMA)n multilayers disintegrated when pH increased to 3.7 at room temperature.37 It is because the deprotonation of sulfonate groups can impair the electrostatic interactions between the zwitterionic polymer and the polyanion.34 Therefore, there is a critical demand for new assembling partners to fabricate highly stable LBL multilayers of zwitterionic polymers. In this work, we found that a natural polyphenol, tannic acid (TA), is able to assemble with PSBMA (Scheme 1), forming stable and antifouling multilayers. A quartz crystal microbalance
(QCM) was used to monitor the LBL growth process of PSBMA/TA multilayers, the stability of the multilayers at different pH values and ionic environments, and the dynamic protein adsorption behaviors of the surfaces. This work provides some insights into the interactions between PSBMA and TA and a simple and convenient method to construct zwitterionic antifouling surfaces.
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EXPERIMENTAL SECTION
Materials. N-(3-Sulfopropyl)-N-(methacryloxyethyl)-N,N-dimethylammonium betaine (SBMA, 97%), TA (1.7 kDa), and branched polyethylenimine (BPEI, 25 kDa) were purchased from Sigma-Aldrich (St. Louis, MO) and used without further purification. BSA (pI = 4.8, 67 kDa), hemoglobin (Hgb) (pI = 7.0, 65 kDa), and Lys (pI = 10.8, 14.4 kDa) were acquired from Sinopharm Chemical Reagent Co., Ltd. (China). Phosphate-buffered saline (PBS, pH 5.0 or 7.4, ionic strength of 10 mM) was prepared from analytical-grade chemicals and ultrapure water (18.2 MΩ, produced from an ELGA Lab Water system, France). Other reagents were used as received. PSBMA was synthesized by free radical polymerization following the procedure described in a previous work,39 and characterized by 1H nuclear magnetic resonance (NMR) [see Figure S1 of the Supporting Information; 400 MHz, D2O, ppm in δ): 4.55 (2H), 3.86 (2H), 3.64 (2H), 3.28 (6H), 3.03 (2H), 2.32 (2H), 2.04 (2H), 1.05−1.36 (3H)] and gel permeation chromatography (GPC) (Mw = 3.6 kDa; see Table S1 of the Supporting Information). LBL Assembly of PSBMA and TA. The LBL assembly of PSBMA and TA was performed using a typical alternate dipping process. Prior to assembly, gold chips were cleaned with piranha solution [7:3 (vol/ vol) H2SO4/H2O2] and then rinsed in ultrapure water. The chips were pretreated in BPEI solution with a concentration of 1 mg/mL for 1 h and blown dried with N2 for further use. (TA/PSBMA)n multilayers, where n represents the number of bilayers, were deposited by alternate dipping of the substrates into solutions of TA and PSBMA for 5 min, followed by two intermediate washings with ultrapure water. Each solution is 0.5 mg/mL in PBS (pH 5.0, 10 mM). QCM Analysis. The growth process and stability of the multilayer films as well as the dynamic protein adsorption were monitored by a Q-SENSE E1 system (Q-SENSE, Sweden). The sensor crystals are 5 MHz, AT-cut, and polished quartz discs (chips), with gold deposited on both sides (Q-SENSE). The resonance frequency change (Δf) was measured simultaneously at different overtones during QCM measurements. Growth Process. The chip pretreated with BPEI was placed in a flow cell and allowed to equilibrate in PBS (pH 5.0, 10 mM) for 1 h to obtain a flat baseline at 25 °C. TA solution (0.5 mg/mL) was then flowed over the surface at a rate of 15 μL/min for 5 min. After that, a buffer solution was flowed through the system to wash away the residual and reversibly adsorbed TA. The washing step lasted 10 min. Then, the buffer solution was changed into 0.5 mg/mL PSBMA solution. The total flow time was also 5 min for the PSBMA solution. When the assembly and washing steps were repeated, multilayer films with five bilayers were obtained. Multilayer Stability. A QCM chip deposited with (TA/PSBMA)20 multilayers was placed in the flow cell and allowed to equilibrate in ultrapure water at 25 °C for 1 h until a flat baseline was obtained. NaCl, urea, or acid/base solution was then introduced for ∼10 min at a rate of 15 μL/min, followed by rinsing with ultrapure water until equilibration. Dynamic Protein Adsorption. The measurement procedure was similar to that for the stability test. After equilibration of baseline PBS (pH 7.4, 20 mM) at 25 °C for 1 h, the solution of BSA, Lys, or Hgb (1 mg/mL) was flowed in the cell for ∼20 min at a rate of 15 μL/min, followed by a rinse with PBS for 20 min. In the QCM measurements, Δf was used to calculate the adsorption amount by the Sauerbrey equation40
Scheme 1. Chemical Structures of TA and PSBMA
Δm = − B
C Δf n DOI: 10.1021/acs.langmuir.5b00920 Langmuir XXXX, XXX, XXX−XXX
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Langmuir where n is the overtone number (n = 1, 3, 5, ...) and C denotes a constant characteristic of the sensitivity of the resonator to changes in mass (17.7 ng Hz−1 cm−2 for the used 5 MHz quartz crystals). Curves from the third overtone (n = 3) are used as representative curves for all of the graphs. Characterizations. The thickness of multilayer films was measured using variable-angle spectroscopic ellipsometry (VASE) spectra by a MD-2000I spectroscopic ellipsometer (J.A. Woollam, Lincoln, NE) at the incident angles of 60°, 65°, and 70° with a wavelength range of 800−1000 nm. Surface morphology of the multilayer films was observed by atomic force microscopy (AFM, MultiMode 8, Bruker Corporation, Billerica, MA). Surface chemistry was characterized by specular reflectance Fourier transform infrared spectroscopy (FTIR/ SR, Nicolet FT-IR/Nexus470, Thermo Fisher Scientific, Waltham, MA) with a SR accessory. X-ray photoelectron spectroscopy (XPS) analysis was performed on the RBD upgraded PHI-5000C ESCA system (PerkinElmer, Waltham, MA) with Al Kα radiation (hν = 1486.6 eV). Water contact angles (WCAs) on the multilayer surfaces were determined using a CTS-200 system (Mighty Technology Pvt. Ltd., China) fitted with a drop shape analyzer.
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RESULTS AND DISCUSSION LBL Assembly of TA and PSBMA. TA is a natural polyphenol that has a definite molecular structure compared to humic or fulvic acid. TA has been widely used as a building block for assemblies with positively charged polyelectrolytes or hydrogen bond acceptors.41−46 To the best of our knowledge, it is still not clear whether TA can participate in the LBL
Figure 2. Stability of (TA/PSBMA)20 multilayers in (a) NaCl and urea solutions (1 M) and (b) acidic/alkaline solution at different pH values. The inset in panel b represents QCM curves measured in the acidic/ alkaline solutions.
assembly with zwitterionic polymers. In this work, a QCM was used to investigate the interaction between PSBMA and TA. Multilayers of (TA/PSBMA)5 were assembled on QCM chip surfaces. The frequency change Δf was recorded for each assembly step at a third overtone (see Figure S2 of the Supporting Information). The decrease in frequency represents a mass increase induced by LBL deposition of TA and PSBMA. Moreover, if we observe the curve carefully, a slight increase in the frequency can be found during each rinsing step, which indicates the desorption of loosely bound substances. Figure 1a summaries the relationship between the mass gain and the bilayer number. The total mass gain is nearly the same for each bilayer of TA/PSBMA, whereas the mass gain of the TA layer (∼118 ng/cm2) is always smaller than that of the PSBMA layer (∼472 ng/cm2). We further analyzed (TA/PSBMA)n multilayers with different bilayer numbers and thicknesses. Figure 1b plots the total thickness and average bilayer thickness versus the bilayer numbers for (TA/PSBMA)n multilayers with n = 5, 10, 15, and 20. It can be seen that the total thickness increases gradually from 6.5 ± 0.68 to 14.1 ± 1.47 nm. Meanwhile, the average bilayer thickness decreases from 1.3 ± 0.14 to 0.7 ± 0.07 nm with the increase of the bilayer number from 5 to 20. These results indicate that the assembly behavior of TA and PSBMA is
Figure 1. LBL assembly behavior of TA with PSBMA: (a) mass growth of (TA/PSBMA)n multilayer films with bilayer number and (b) total film thickness and average bilayer thickness. C
DOI: 10.1021/acs.langmuir.5b00920 Langmuir XXXX, XXX, XXX−XXX
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Langmuir
Figure 3. AFM images of (TA/PSBMA)n multilayers on silicon substrates (1.5 × 1.5 μm; zmax = 9.66, 14.5, 22.2, and 26.1 nm, and roughness Rq = 3.48, 3.67, 4.77, and 4.29 nm for n = 5, 10, 15, and 20, respectively).
Figure 5. Water contact angles on (TA/PSBMA)n multilayer films with different bilayer numbers.
Multilayer Stability and the Driving Force for LBL Assembly. We explored the stability of (TA/PSBMA)20 multilayers under various conditions, such as in acidic/alkaline and saline solutions, and studied the interaction between TA and PSBMA. These multilayers are not affected by saline solutions, including NaCl and urea solutions, with concentrations ranging from 0.05 to 1.0 M (Figure S3 of the Supporting Information). As we know, the swelling degree and solubility of PSBMA in aqueous solutions are strongly dependent upon the ionic strength.38 Figure 2a indicates that the multilayers are stable even when the concentration of NaCl solution reaches 1.0 M. It is worth noting that (TA/PSBMA)20 multilayers also keep stable in 1.0 M urea solution, which is commonly considered as a hydrogen-bond breaker.52 The results demonstrate that hydrogen bonding contributes little to the formation of the multilayers. Figure 2b shows the pH-dependent stability of (TA/ PSBMA)20 multilayers. The multilayers are rather stable under pH ranging from 4 to 10. When the pH value decreases to 3, the multilayers start to disassemble, which is convinced by the mass loss. The disassembly process accelerates when the pH value declines to 2. It is known that the phenol groups of TA have a pKa of 5−8.553,54 and the sulfonate groups are totally protonated at pH < 0.8.37 In the PBS solution with high pH value, such as 10, the phenol groups of TA are totally deprotonated and the sulfonate groups of PSBMA are also deprotonated. Under this high pH value condition, the multilayers are highly stable, which indicates that the sulfonate groups show a minor impact to the multilayers. When the pH decreases to 3, the phenol groups of TA begin protonating and disassembly of the multilayers occurs. It can be concluded that the stability of the multilayers is closely related to the deprotonation of TA phenol groups. In general, TA can
Figure 4. (a) FTIR/SR and (b) XPS spectra of the (TA/PSBMA)20 multilayer film.
different from those of traditional polyelectrolytes. In general, LBL multilayers show two growth behaviors: linear or exponential growth.47−50 In the former case, the thickness of multilayer films increases linearly with the bilayer number, in which the polyelectrolytes from the solution mainly interact with the outer layer of multilayers with little diffusing into the inner architecture. In the latter case, as the polyelectrolytes diffuse into the multilayer films, the thickness increases exponentially with the bilayer number. In our case, TA, a small molecule, can diffuse into the underlying layer, which leads to a quite different growth behavior. Our result is similar to the growth behavior of LBL multilayers of TA and thrombin reported by Shukla et al.51 D
DOI: 10.1021/acs.langmuir.5b00920 Langmuir XXXX, XXX, XXX−XXX
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Langmuir
Figure 6. Protein adsorption behaviors measured by QCM: (a) BSA, (b) Lys, (c) Hgb, and (d) protein adsorption amount calculated with the Sauerbrey equation.
(Figure 1b). Overall, the (PSBMA/TA)n multilayer films have relatively smooth surfaces, which is beneficial for protein resistance, as discussed in the following text. In addition, the surface morphology of the thin multilayer films changes little after they were immersed into acidic/alkaline and saline solutions (see Figure S4 of the Supporting Information). The chemistry of (TA/PSBMA)n multilayers is confirmed by FTIR/SR and XPS spectra. As shown in Figure 4a, the peak at 1608 cm−1 is assigned to the overlap of CC resonance vibration in the aromatic ring of TA. On the other hand, peaks from PSBMA appear at 1725 cm−1 (O−CO stretching vibration), 1483 cm−1 (N−C stretching vibration), 1160 cm−1 (SO asymmetric stretching vibration), and 1031 cm−1 (S O asymmetric stretching vibration). XPS analyses also reveal the assembly of TA with PSBMA on the Au surface. A typical spectrum is shown in Figure 4b. The major peaks are at 284.6 and 541.2 eV, which are ascribed to the binding energy of C1s and O1s, respectively. The peaks from S2p3 and N1s, which indicate the existence of PSBMA, can also be found. Moreover, the ratio of S/N is close to 1.0 (see Table S2 of the Supporting Information), indicating that the sulfobetaine structure remained in the multilayers. Protein Resistance. It is generally accepted that hydrophilic surfaces can form a hydrated layer and, thus, repel biomacromolecule (such as protein) adsorption via repulsive hydration forces. A static water contact angle was used to evaluate the surface hydrophilicity of (TA/PSBMA)n multilayers with different bilayer numbers (Figure 5). The first TA
interact with other molecules via hydrogen bond or electrostatic force. In the former case, the phenol groups of TA are protonated, which is regarded as a hydrogen-bond donor; in the latter case, TA becomes negatively charged as the phenol groups begin deprotonating. In this work, the stability of (TA/ PSBMA)n multilayer films maintains with the deprotonation of TA, which is similar to other works.41 Therefore, the driving force for the TA/PSBMA LBL assembly is attributed to local electrostatic interactions between deprotonated phenol groups of TA (anionic groups) and the quaternary ammoniums of PSBMA (cationic groups). Moreover, It can be seen that the stability of (TA/PSBMA)n multilayers is higher than that of (PAA/PSBMA)n.37 It may be attributed to phenol groups and the dendritic structure of TA, which is different from the carboxylic acid groups and linear structure of PAA. Here, pKa of phenol groups of TA might also play an important role for the stability of the TA/PSBMA films. Surface Morphology and Chemistry. Figure 3 depicts the surface morphologies of (TA/PSBMA)n multilayers with n = 5, 10, 15, and 20. Small nanoparticles can be found on all of the surfaces, which are believed to be TA/PSBMA aggregates. When n = 5, the aggregates distribute unevenly. These aggregates distribute much uniformly with the increase of the bilayer number. The root-mean-squared roughness (Rq) increases from 3.48 to 4.77 nm with increasing the bilayer number from 5 to 15. When n is further increased from 15 to 20, Rq decreases slightly to 4.29 nm, leading to a smoother surface, and meanwhile, the average bilayer thickness decreases E
DOI: 10.1021/acs.langmuir.5b00920 Langmuir XXXX, XXX, XXX−XXX
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Langmuir layer has a water contact angle of ∼47°. It decreases to 30−35° with the increase of the bilayer number (n = 1.5, 2.5, 3.5, and 4.5). However, the water contact angle is below 15° for multilayers with PSBMA as the outmost layer. This result is consistent with the fact that zwitterionic polymers, such as PSBMA, are superhydrophilic materials. As mentioned above, the PSBMA layer has excellent hydrophilicity, which may inhibit the adsorption of proteins from solutions. BSA, Lys, and Hgb were used to systematically evaluate the protein resistance properties of (TA/PSBMA)n multilayers. Figure 6 shows the adsorption behaviors of BSA, Lys, and Hgb on a bare gold surface and (TA/PSBMA)n with different bilayer numbers (n = 5, 10, 15, and 20) and (TA/ PSBMA)20TA (n = 20.5) multilayers films. Panels a−c of Figure 6 illustrate the adsorption process of the three proteins, and Figure 6d summaries the amounts of adsorbed proteins. The amounts of proteins adsorbed onto the surface were calculated from the frequency change according to the Sauerbrey relationship. On the bare gold chips, which were used as control samples, the three model proteins adsorb a lot (328, 357, and 509 ng/cm2 for BSA, Lys, and Hgb, respectively). In contrast, surfaces assembled with (TA/PSBMA)n multilayers show significantly lower protein adsorption. The adsorption amounts obviously decrease to 0.42, 52.9, and 37.9 ng/cm2 with increasing the bilayer number to 20 for BSA, Lys, and Hgb, respectively. The PSBMA layer has an excellent protein resistance property, which is similar to previously reported results.55−57 However, when TA is the outmost layer, for example, (TA/PSBMA)20TA multilayer films, the adsorption is very serious and even higher than that of the bare gold chip (Figure 6d). Therefore, the results indicate that the hydrated PSBMA surface layer on the (TA/PSBMA)n multilayers is necessary, which improves the hydrophilicity of the multilayer film and endows the surface with excellent protein-resistant property.
free of charge on the ACS Publications website at DOI: 10.1021/acs.langmuir.5b00920.
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Corresponding Authors
*Fax: +86-571-8795-1773. E-mail:
[email protected]. *Fax: +86-571-8795-1773. E-mail:
[email protected]. Notes
The authors declare no competing financial interest.
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ACKNOWLEDGMENTS This work was supported by the National Natural Science Foundation of China (Grants 21374100 and 50933006).
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REFERENCES
(1) Jiang, S. Y.; Cao, Z. Q. Ultralow-fouling, functionalizable, and hydrolyzable zwitterionic materials and their derivatives for biological applications. Adv. Mater. 2010, 22, 920−932. (2) Mi, L.; Jiang, S. Integrated antimicrobial and nonfouling zwitterionic polymers. Angew. Chem., Int. Ed. 2014, 53, 1746−1754. (3) Chen, S.; Jiang, S. An new avenue to nonfouling materials. Adv. Mater. 2008, 20, 335−338. (4) Chen, S.; Zheng, J.; Li, L.; Jiang, S. Strong resistance of phosphorylcholine self-assembled monolayers to protein adsorption: Insights into nonfouling properties of zwitterionic materials. J. Am. Chem. Soc. 2005, 127, 14473−14478. (5) Wu, J.; Zhao, C.; Hu, R.; Lin, W.; Wang, Q.; Zhao, J.; Bilinovich, S. M.; Leeper, T. C.; Li, L.; Cheung, H. M.; Chen, S.; Zheng, J. Probing the weak interaction of proteins with neutral and zwitterionic antifouling polymers. Acta Biomater. 2014, 10, 751−760. (6) Li, D.; Chen, H.; McClung, W. G.; Brash, J. L. Lysine-PEGmodified polyurethane as a fibrinolytic surface: Effect of PEG chain length on protein interactions, platelet interactions and clot lysis. Acta Biomater. 2009, 5, 1864−1871. (7) Hucknall, A.; Rangarajan, S.; Chilkoti, A. In pursuit of zero: Polymer brushes that resist the adsorption of proteins. Adv. Mater. 2009, 21, 2441−2446. (8) Ma, H.; Hyun, J.; Stiller, P.; Chilkoti, A. “Non-fouling” oligo(ethylene glycol)-functionalized polymer brushes synthesized by surface-initiated atom transfer radical polymerization. Adv. Mater. 2004, 16, 338−341. (9) Lau, K. H. A.; Ren, C. L.; Sileika, T. S.; Park, S. H.; Szleifer, I.; Messersmith, P. B. Surface-grafted polysarcosine as a peptoid antifouling polymer brush. Langmuir 2012, 28, 16099−16107. (10) Alswieleh, A. M.; Cheng, N.; Canton, I.; Ustbas, B.; Xue, X.; Ladmiral, V.; Xia, S. J.; Ducker, R. E.; El Zubir, O.; Cartron, M. L.; Hunter, C. N.; Leggett, G. J.; Armes, S. P. Zwitterionic poly(amino acid methacrylate) brushes. J. Am. Chem. Soc. 2014, 136, 9404−9413. (11) Luk, Y.-Y.; Kato, M.; Mrksich, M. Self-assembled monolayers of alkanethiolates presenting mannitol groups are inert to protein adsorption and cell attachment. Langmuir 2000, 16, 9604−9608. (12) Wei, Q.; Becherer, T.; Noeske, P.-L. M.; Grunwald, I.; Haag, R. A universal approach to crosslinked hierarchical polymer multilayers as stable and highly effective antifouling coatings. Adv. Mater. 2014, 26, 2688−2693. (13) Ham, H. O.; Park, S. H.; Kurutz, J. W.; Szleifer, I. G.; Messersmith, P. B. Antifouling glycocalyx-mimetic peptoids. J. Am. Chem. Soc. 2013, 135, 13015−13022. (14) Holmlin, R. E.; Chen, X.; Chapman, R. G.; Takayama, S.; Whitesides, G. M. Zwitterionic SAMs that resist nonspecific adsorption of protein from aqueous buffer. Langmuir 2001, 17, 2841−2850. (15) Chang, Y.; Chen, S.; Zhang, Z.; Jiang, S. Highly protein-resistant coatings from well-defined diblock copolymers containing sulfobetaines. Langmuir 2006, 22, 2222−2226.
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CONCLUSION A facile LBL assembly process of a zwitterionic polymer, PSBMA, with a natural polyphenol, TA, was proposed to fabricate stable protein-resistant multilayers. We demonstrated that the main driving force in this LBL assembly process is the local electrostatic interaction between PSBMA and TA. The presence of TA has significantly improved the multilayer stability against pH and ionic strength. The multilayers are stable in 1.0 M NaCl and urea solutions and do not disassemble when pH changes between 4 and 10. The (TA/PSBMA)20 multilayers exhibit good hydrophilicity and excellent resistance to proteins, such as BSA, Hgb, and Lys. The adsorption amounts of BSA, Lys, and Hgb on (TA/PSBMA)20 multilayers decreased to 0.42, 52.9, and 37.9 ng/cm2 from 328, 357, and 509 ng/cm2 on a bare gold chip surface, respectively. In addition, the protein-resistance property depends upon the outmost layer. This work demonstrates a novel system for the LBL assembly of zwitterionic polymers to form highly stable multilayer films and provides new insights into the interaction of zwitterionic polymers with polyphenols, which may be of great promise in antifouling biomaterials and separation membranes.
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AUTHOR INFORMATION
ASSOCIATED CONTENT
S Supporting Information *
1
H NMR spectrum of PSBMA, QCM curves, and surface chemical composition. The Supporting Information is available F
DOI: 10.1021/acs.langmuir.5b00920 Langmuir XXXX, XXX, XXX−XXX
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DOI: 10.1021/acs.langmuir.5b00920 Langmuir XXXX, XXX, XXX−XXX
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DOI: 10.1021/acs.langmuir.5b00920 Langmuir XXXX, XXX, XXX−XXX
