Cucurbit[8]uril Supramolecular Assembly for Positively Charged

Oct 22, 2013 - The design of positively charged ultrathin films for surface modification is of crucial importance for biomedical applications. Herein,...
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Cucurbit[8]uril Supramolecular Assembly for Positively Charged Ultrathin Films as Nanocontainers Dan-dan Li, Ke-feng Ren,* Hao Chang, Hai-bo Wang, Jin-lei Wang, Chao-jian Chen, and Jian Ji* MOE Key Laboratory of Macromolecular Synthesis and Functionalization, Department of Polymer Science and Engineering, Zhejiang University, Hangzhou, China S Supporting Information *

ABSTRACT: The design of positively charged ultrathin films for surface modification is of crucial importance for biomedical applications. Herein, we report the layer-by-layer assembly of pure positively charged ultrathin films based on the host−guest interaction of cucurbit[8]uril (CB[8]). Two positively charged poly(ethylenimine)s (PEI) functionalized with guest moieties methyl viologen (MV) and indole (ID) were alternately assembled with the formation of CB[8] ternary complex under basic conditions. The growth of the (PEI-MV@CB[8]/ PEI-ID) films was monitored by spectroscopic ellipsometry and quartz crystal microbalance. The morphology and structure of the films were characterized by scanning electron microscopy and UV−vis spectroscopy, respectively. These positively charged (PEI-MV@CB[8]/PEI-ID) films were very stable in the pH range from 4 to 9 but disassembled immediately when subjected to a competitive guest adamantylamine. Finally, the films were successfully employed as nanocontainers for DNA loading and subsequent directing the transfection of the adhered cells.

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INTRODUCTION The surface functionalization for biomaterials is crucially important for their applications and thus has attracted tremendous attention. In this area, designing positively charged ultrathin films on the surface of biomaterials is of particular interest, as these functional films provide the surface with special loading capacities for various negative functional molecules, such as DNA, proteins, and drugs.1,2 Several methods, including Langmuir−Blodgett (LB)3 and selfassembled monolayers (SAMs)4 techniques, have been employed to design nanostructured positively charged ultrathin films. However, films fabricated by these methods generally have disadvantages of instability and poor loading capacity for biological molecules.5 Therefore, the design of stable positively charged ultrathin films with high loading capacity is still a great challenge. Layer-by-layer (LbL) assembly is a versatile and simple technique for fabricating functional ultrathin films on solid substrates.5,6 However, the conventional electrostatic LbL method which is based on electrostatic interaction of oppositely charged polyelectrolytes cannot be used to fabricate uniformly charged ultrathin films. Therefore, other types of driving force such as strong covalent interactions and weak host−guest interactions have been exploited to construct uniformly charged LBL multilayer films. For instance, the covalently LbL assembly based on click chemistry is an effective way to build stable positively charged multilayer films.7 However, this method suffers from some shortcomings, including the lack of © 2013 American Chemical Society

responsiveness and the involving of cytotoxic copper catalyst in the assembly process,8 which limit its application in the field of biomedicine. As an alternative method, the host−guest chemistry has also been adopted to build positively charged ultrathin films in a supramolecular fashion. Employing the noncovalent nature of host−guest interactions provides the opportunity to build stimuli-responsive films for more complex functions. For example, Anzai and co-workers9 reported that βcyclodextrin (β-CD) dimer is a good binder for constructing thin films of positively charged ferrocene-appended poly(allylamine). After then, Auzély and co-workers10 reported the positively charged LbL film formation based on adamantaneand β-CD-grafted chitosans. Nevertheless, these supramolecular LbL assembly were not sustained (less than 2 bilayers), leading to poor loading ability which probably because the host−guest interactions of cyclodextrin/guests are not strong enough to overcome the electrostatic repulsion among polyelectrolytes. Cucurbit[8]uril (CB[8]), a member of the host family cucurbit[n]uril, can form a stable yet dynamic 1:1:1 ternary inclusion complex with an electron-deficient molecule [such as methyl viologen (MV)] and an electron-rich molecule [such as indole (ID)] via a host-stabilized charge-transfer interaction with very high association constant (Ka ca. 1 × 1012/M2).11−15 Received: March 11, 2013 Revised: October 21, 2013 Published: October 22, 2013 14101

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Figure 1. Schematic representation of PEI-MV and PEI-ID molecules and preparation of the (PEI-MV@CB[8]/PEI-ID) ultrathin film. MES buffer solution (pH = 5.5) in an ice bath for 0.5 h. PEI (1.2 g, 10 mmol of primary amine) was then added. The reaction mixture was stirred at room temperature for 24 h and then purified by dialyzing against distilled water for 3 days (MW cutoff 3500). The resulting solution was lyophilized, and the some yellow product was finally obtained. Synthesis of Indole-Functionalized Poly(ethylenimine) (PEIID). 3-Indolepropionic acid (0.8 g, 4.2 mmol) was activated by NHS (1.4 g, 12 mmol) and EDC (4 g, 21 mmol) in 70 mL of DMSO/water (v/v, 4/3) mixed solution at room temperature. The solution was then added to PEI (1.7 g, 14 mmol of primary amine) in 60 mL of DMSO/ water (v/v, 2/1). After stirring at room temperature for 24 h, the obtained mixture was purified by dialyzing against distilled water for 3 days (MW cutoff 3500). The solution was lyophilized, and the resulting yellow product was obtained. Preparation of (PEI-MV@CB[8]/PEI-ID) Films. PEI-MV@CB[8] was first prepared by dissolving PEI-MV (1 mg mL−1) and CB[8] (1.3 mg mL−1) in water with sonication (less than 2 min). PEI-ID was then dissolved in water with a concentration of 1 mg mL−1. The ultrathin film was built up by alternated adsorption of PEI-ID and PEI-MV@ CB[8] onto a substrate. Briefly, the substrate was immersed in polymer solution for 10 min and then 2 min rinsing with water between steps, followed by drying under a stream of dry N2. The process was repeated until desired number of layers had been deposited. Lap Shear Experiment. The lap shear test was performed using electromechanical testing systems (Instron 5540A) in air at ambient temperature. Multilayer films with different outermost layer were fabricated onto silicon substrates (5 × 5 mm). Two different types of samples were then adhered together with a load of 4.9 N for 60 min at ambient temperature in the presence of an aqueous drop (2 μL, with or without Ad). After the adhered sample was held at both ends with two mechanical chucks, it was loaded to failure at 50 μm min−1, and the failure strain was measured.22 HGF-pDNA Loading and Cell Transfection. The (PEI-MV@ CB[8]/PEI-ID)5.5 film was prepared for this experiment, and bare glass was selected as control group. For DNA loading, the films were incubated into HGF-pDNA solution (0.5 mg mL−1) for 10 min and rinsed with PBS. Human umbilical vein endothelial cells (HUVECs) adhesion was performed in 24-well plates for 4 h in fetal bovine serum supplemented medium. After that, the DNA loaded films were placed manually and gently on top of the cells as previous described method.23,24 The 100 μL culture medium was collected from each well for HGF measurement (ELISA), and 100 μL of fresh medium was

Based on this unique characteristic, CB[8] has been successfully utilized as a linker to prepare block copolymers,16 supramolecular polymers,17 micelles,18 vesicles,19 and hydrogels.20 Therefore, it is also possible and desirable to construct positively charged multilayer films through the special host− guest interaction of CB[8] and its guests. Herein, the CB[8] ternary complex was first designed and employed for the fabrication of positively charged multilayer films. Poly(ethylenimine) (PEI) was modified with two different guests of CB[8], and the assembly process is schematically shown in Figure 1. The highly stable CB[8] ternary complex is expected to offer the feasibility to realize more sustainable LbL assembly as compared to CD inclusion complex. Moreover, the use of CB[8] may also provide the stability and stimuli-responsiveness to the positively charged multilayer films. To test the possible loading ability of the functional multilayer films, plasmid DNA as a negatively charged biological compound was also loaded to the films, and the subsequent transfection was also investigated.

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EXPERIMENTAL SECTION

Materials. Poly(ethylenimine) (PEI, branched, Mw 25 000), cucurbit[8]uril, 1-ethyl-3-(3-(dimethylamino)propyl)carbodiimide (EDC), and N-hydrosulfosuccinimide (NHS) were purchased from Sigma-Aldrich. 4,4′-Bipyridine and 3-indolepropionic acid were purchased from Aladdin. 3-Bromopropionic acid was purchased from J&K Chemical Inc. Plasmid DNA encoding recombinant human hepatocyte growth factor (HGF-pDNA) was provided by Northland Biotech (Beijing, China). Recombinant human hepatocyte growth factor ELISA kit was purchased from Boster Bioengineering (Wuhan, China). Endothelial cell growth supplement (ECGS) was purchased from BD Biosciences (USA). Ultrapure water was produced by a Millipore water purification system (Milli-Q, >18 MΩ, Millipore). All other solvents and reagents were purchased from domestic suppliers and used as received. Synthesis of Methyl Viologen-Functionalized Poly(ethylenimine) (PEI-MV). 1-Carboxylpropyl-1′-methyl-[4,4′-bipyridine]-1,1′-diium bromide iodide (MV-COOH) was first prepared according to the literature with some improvements made.21 To synthesize PEI-MV, MV-COOH (4.5 g, 10 mmol) was first activated by EDC (10 g, 52 mmol) and NHS (3.6 g, 31 mmol) in 200 mL of 14102

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Figure 2. 1H NMR spectra of PEI-MV in D2O (a) and PEI-ID in CD3OD (b). replenished each day. The ELISA assay was carried out as described by given protocol. Instruments. 1H NMR spectra of the samples were obtained using a Bruker DMX500 spectrometer. Quartz crystal microbalance (QCM) measurements were taken with a Q-Sense (QCM-E4, Sweden) to follow the growth of the films. Spectroscopic ellipsometry was recorded using a M-2000 (J.A. Wollam Co. Inc.) to measure the film thickness on silicon wafers. A field emission scanning electron microscope (FESEM, SIRION-100, FEI, Holland) was used to characterize the morphology of the films. UV−vis spectra were carried out with a UV−vis spectrometer (Shimadzu UV-2505).

suggest formation of the ternary complex. We also observed the color of the mixture of PEI-MV@CB[8] and PEI-ID turned from colorless at pH 7 to light orange at pH 8 and became deeper at pH 9. In comparison, it was colorless at pH 9 when no CB[8] was added. Meanwhile, a new adsorption band at 420 nm was observed in the UV−vis spectra (Figure 4) when

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RESULTS AND DISCUSSION Poly(ethylenimine) modified with MV (PEI-MV) and ID (PEIID) were both synthesized via the EDC-mediated coupling method, and the grafting ratios determined by 1H NMR results in Figure 2 for the two polymers are 7.5% and 7.6%, respectively. The solubility of CB[8] in water is very limited, while it dissolved together with PEI-MV; the solubility was remarkably enhanced, and a clear solution was obtained, suggesting the formation of PEI-MV@CB[8] complex. The aqueous solution of PEI-ID (1 mg mL−1) and PEI-MV@CB[8] (2.3 mg mL−1, molar ratio of MV:CB[8] = 1:1) with pH ranging from 5 to 9 were then prepared for following experiments. Before LbL assembly, we monitored the host−guest interaction between PEI-MV@CB[8] and PEI-ID in solution by using 1H NMR and UV−vis spectroscopy. From the 1H NMR spectra in Figure 3, the extensive broadening and upfield shift of aromatic proton signals in the presence of CB[8]

Figure 4. UV−vis absorption spectra of equimolar mixture of PEI-MV and PEI-ID solutions at pH 9 (a), in the presence of equimolar of CB[8] at pH 7 (b) and pH 9 (c), each at 1 mM. At pH 9, a new enhanced charge transfer band appears at 420 nm for PEI-MV@ CB[8]/PEI-ID. The inset shows the mixture of PEI-MV@CB[8] and PEI-ID turns from colorless at pH 7 to orange at pH 9.

mixing PEI-MV@CB[8] with PEI-ID in a basic environment, exhibiting an enhanced charge-transfer adsorption, which is a solid evidence for the formation of CB[8] ternary complex.25 No charge-transfer adsorption was observed when mixing PEIMV@CB[8] with PEI-ID at pH 7. This phenomenon could be attributed to the difficulty of the inclusion between host and guest moieties. It is likely caused by the charge repulsion among the PEI molecules and structure of the polyelectrolytes. The pKa value of PEI is about 8,26 which means that the molecules of PEI-MV and PEI-ID are highly charged at pH 7, rendering strong charge repulsion. While in the case of pH 8 and 9, much more molecules are uncharged, leading to easier contact between MV@CB[8] and ID and formation of the ternary

Figure 3. 1H NMR spectra of PEI-MV and PEI-ID in D2O and the complex of PEI-MV, PEI-ID, and CB[8] in D2O at pH 9 tuned by NaOD, each at 1 mM. 14103

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Figure 5. Characterization of the (PEI-MV@CB[8]/PEI-ID) films. (a) Film growth at different pH conditions followed by spectroscopic ellipsometry. (b) The SEM image of 6 bilayers film assembled at pH 9 (the black arrow indicates the film and the white arrow indicates bare silicon).

Figure 6. (a) Frequency shifts of the (PEI-MV@CB[8]/PEI-ID) films as measured by QCM-D. The inset shows plot of multilayers’ thickness versus layer number. (b) UV−vis absorption spectra of a (PEI-MV@CB[8]/PEI-ID)10 film. The absorption band at 420 nm shows the presence of CB[8] ternary complex in the thin films.

Figure 7. Stability and mechanical properties of the (PEI-MV@CB[8]/PEI-ID)6 thin films. (a) Change of thickness of the films immersed in PBS at different pH or in the presence of Ad. (b) Lap shear strength of the films with or without Ad (*p < 0.05).

the (PEI-MV@CB[8]/PEI-ID) film was successfully fabricated at pH 9 with a thickness of 101 ± 25.8 nm for 6 bilayer numbers. The surface morphology of the film was very smooth as observed by SEM (Figure 5b). A control system of (PEIMV/PEI-ID) at same pH value without CB[8] showed no increase in thickness, indicating that CB[8] is essential for the

complex. These data suggest that pH value is a very important parameter in our system. The ultrathin films were then fabricated by sequentially dipping the substrates to PEI-MV@CB[8] and PEI-ID solutions. The assembly process was monitored by spectroscopic ellipsometry, as shown in Figure 5a. We can observe that 14104

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fabrication of the ultrathin films. However, growth of the film was obviously reduced at pH 8. The thickness was only 28.6 ± 3.3 nm for 6 bilayer numbers. When the pH continues down to 7 and 5, no film was achieved. These observations indicate that the interaction between MV@CB[8] and ID groups was significantly affected by pH values. The film buildup was further measured by quartz crystal microbalance with dissipation (QCM-D) as complementary characterization. As shown in Figure 6a, frequency shifts decrease gradually upon each alternate exposure to PEI-ID@CB[8] and PEI-ID solutions at pH 9, indicating a steady LbL deposition. The inset shows the thickness obtained for each adsorption by fitting the QCM-D curves according to viscoelastic model. The formation of CB[8] ternary complex in the ultrathin films was further confirmed by UV−vis spectroscopy. The adsorption band at 420 nm was similar to that observed in solution (Figures 4c and 6b). To measure the stability, the (PEI-MV@CB[8]/PEI-ID)6 film was incubated in phosphate buffer saline (PBS) at different pH values (9, 7.4, and 4) at 37 °C for 48 h. As shown in Figure 7a, the thickness of the films almost did not change in the three pH conditions, indicating the (PEI-MV@CB[8]/PEI-ID)6 film was very stable. It is interesting that the films were stable when the pH was as low as 4, under which the assembly of films cannot be conducted. This phenomenon suggests that the films cross-linked by the CB[8] ternary complex were stable enough to bear the charge repulsion in the films. Nevertheless, the (PEI-MV@CB[8]/PEI-ID) film disassembled immediately and completely when it was immerged in a PBS solution with 1 mg mL−1 Ad, which is a strong competitive guest against the CB[8] ternary complex.27 These data provide further evidence that the films were formed based on the host−guest interactions of CB[8] ternary complex. In light of the stability of the films, we wondered what the adhesion property would be. A lap-shear test of two substrates that coated with the ultrathin films to physically contact each other (Figure S1) was performed to examine the adhesion strength of the films.22 Considering a thickness of 100 × 2 nm, the (PEI-MV@CB[8]/PEI-ID) films showed high lap shear strength of 2.38 ± 0.72 MPa, as seen in Figure 7b. Such value is comparable to those of biomolecular adhesives inspired by mussels (∼4 MPa)28 and geckos (∼1 MPa).29 This strong adhesion strength of the films is obviously due to the formation of CB[8] ternary complex because a very low adhesion strength was obtained in the presence of Ad due to the disassembly of the CB[8] complexation (Figure 7b). The stable positively charged (PEI-MV@CB[8]/PEI-ID) films have, therefore, the great potential ability in loading negative functional molecules such as genes, drugs, and proteins. Herein, we chose plasmid DNA as an example to demonstrate the potential applications of our films. DNA encoding with hepatocyte growth factor (HGF-pDNA) was selected as a model DNA.24 After fabrication of 11 layers (PEIMV@CB[8]/PEI-ID) film, the films were then incubated into a HGF-pDNA solution for 10 min. The amount of DNA loaded in the films was measured by QCM-D. We can observe that there was a large decrease in frequencies when the films contacted with DNA solution, as shown in Figure 8a. The mass of HGF-pDNA loaded into the 11-layer films reached to approximately 3.2 μg/cm2 as calculated from frequencies shift according to Sauerbrey’s relation.30 Such an amount is similar to the adsorption ability of 16-layer (DNA/polymer) LbL films reported by Lynn and co-workers.23,31 In order to directly visualize the DNA loaded in the films, the films were then

Figure 8. Characterizations of the (PEI-MV@CB[8]/PEI-ID)5/PEIMV@CB[8]/HGF-pDNA films. (a) QCM frequency shift versus the number of deposition cycles. (b) Fluorescence image of the films with EtBr staining. (c) The secretion of HGF by cells after contacting with the films (*p < 0.05).

stained with ethidium bromide (EtBr) for 30 min. The fluorescence image was taken, showing relative homogeneous red color (Figure 8b), which provides a solid evidence for DNA loading, since EtBr can produce a strong fluorescence signal upon intercalation with DNA;32 otherwise, the image was black-colored without the incorporation of plasmid DNA (Figure S2). Furthermore, the cell experiment was carried out to evaluate the transfection ability of the HGF-pDNA loaded ultrathin films. After adhesion of endothelial cells for several hours, the glass slides coated with the (PEI-MV@CB[8]/PEIID)5.5/HGF-pDNA film were carefully covering the cells. The cells were then continuously cultured for 2 days. As what we expected, the cells that contacted with the HGF-pDNA loaded ultrathin films gave rise to a significant higher secretion of HGF as compared with the control glass group (Figure 7c). All these data suggest that the ultrathin positively charged (PEI-MV@ CB[8]/PEI-ID) films can highly load DNA molecules with keeping its biological activity. Therefore, our films could be served as nanocontainers for biomedical applications such as surface modification of implant biomedical devices. 14105

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(7) Ochs, C. J.; Such, G. K.; Städler, B.; Caruso, F. Low-fouling, biofunctionalized, and biodegradable click capsules. Biomacromolecules 2008, 9, 3389−3396. (8) Elchinger, P.-H.; Faugeras, P.-A.; Boëns, B.; Brouillette, F.; Montplaisir, D.; Zerrouki, R.; Lucas, R. Polysaccharides: the “click” chemistry impact. Polymers 2011, 3, 1607−1651. (9) Suzuki, I.; Egawa, Y.; Mizukawa, Y.; Hoshi, T.; Anzai, J. Construction of positively-charged layered assemblies assisted by cyclodextrin complexation. Chem. Commun. 2002, 2, 164−165. (10) Van der Heyden, A.; Wilczewski, M.; Labbe, P.; Auzely, R. Multilayer films based on host-guest interactions between biocompatible polymers. Chem. Commun. 2006, 30, 3220−3222. (11) Ko, Y. H.; Kim, E.; Hwang, I.; Kim, K. Supramolecular assemblies built with host-stabilized charge-transfer interactions. Chem. Commun. 2007, 13, 1305−1315. (12) Kim, H.-J.; Heo, J.; Jeon, W. S.; Lee, E.; Kim, J.; Sakamoto, S.; Yamaguchi, K.; Kim, K. Selective inclusion of a hetero-guest pair in a molecular host: formation of stable charge-transfer complexes in cucurbit[8]uril. Angew. Chem., Int. Ed. 2001, 40, 1526−1529. (13) Lagona, J.; Mukhopadhyay, P.; Chakrabarti, S.; Isaacs, L. The cucurbit[n]uril family. Angew. Chem., Int. Ed. 2005, 44, 4844−4870. (14) Masson, E.; Ling, X.; Joseph, R.; Kyeremeh-Mensah, L.; Lu, X. Cucurbituril chemistry: a tale of supramolecular success. RSC Adv. 2012, 2, 1213−1247. (15) Rauwald, U.; Biedermann, F.; Deroo, S. p.; Robinson, C. V.; Scherman, O. A. Correlating solution binding and ESI-MS stabilities by incorporating solvation effects in a confined cucurbit[8]uril system. J. Phys. Chem. B 2010, 114, 8606−8615. (16) Rauwald, U.; Scherman, O. A. Supramolecular block copolymers with cucurbit[8]uril in water. Angew. Chem., Int. Ed. 2008, 47, 3950− 3953. (17) Liu, Y.; Yu, Y.; Gao, J.; Wang, Z.; Zhang, X. Water-soluble supramolecular polymerization driven by multiple host-stabilized charge-transfer interactions. Angew. Chem., Int. Ed. 2010, 49, 6576− 6579. (18) Chen, C.-J.; Li, D.-D.; Wang, H.-B.; Zhao, J.; Ji, J. Fabrication of dual-responsive micelles based on the supramolecular interaction of cucurbit[8]uril. Polym. Chem. 2013, 4, 242−245. (19) Jeon, Y. J.; Bharadwaj, P. K.; Choi, S.; Lee, J. W.; Kim, K. Supramolecular amphiphiles: spontaneous formation of vesicles triggered by formation of a charge-transfer complex in a host. Angew. Chem., Int. Ed. 2002, 114, 4654−4656. (20) Appel, E. A.; Biedermann, F.; Rauwald, U.; Jones, S. T.; Zayed, J. M.; Scherman, O. A. Supramolecular cross-linked networks via hostguest complexation with cucurbit[8]uril. J. Am. Chem. Soc. 2010, 132, 14251−14260. (21) Yamaguchi, H.; Harada, A. Supramolecular formation of antibodies with viologen dimers: utilization for amplification of methyl viologen detection signals in surface plasmon resonance sensor. Biomacromolecules 2002, 3, 1163−1169. (22) Matsukuma, D.; Aoyagi, T.; Serizawa, T. Adhesion of two physically contacting planar substrates coated with layer-by-layer assembled films. Langmuir 2009, 25, 9824−9830. (23) Jewell, C. M.; Zhang, J.; Fredin, N. J.; Lynn, D. M. Multilayered polyelectrolyte films promote the direct and localized delivery of DNA to cells. J. Controlled Release 2005, 106, 214−223. (24) Chang, H.; Ren, K.-f.; Wang, J.-l.; Zhang, H.; Wang, B.-l.; Zheng, S.-m.; Zhou, Y.-y.; Ji, J. Surface-mediated functional gene delivery: an effective strategy for enhancing competitiveness of endothelial cells over smooth muscle cells. Biomaterials 2013, 34, 3345−3354. (25) Bush, M. E.; Bouley, N. D.; Urbach, A. R. Charge-mediated recognition of N-terminal tryptophan in aqueous solution by a synthetic host. J. Am. Chem. Soc. 2005, 127, 14511−14517. (26) Shepherd, E. J.; Kitchener, J. A. The ionization of ethyleneimine and polyethyleneimine. J. Chem. Soc. 1956, 2448−2452. (27) Loh, X. J.; del Barrio, J.; Toh, P. P. C.; Lee, T.-C.; Jiao, D.; Rauwald, U.; Appel, E. A.; Scherman, O. A. Triply triggered doxorubicin release from supramolecular nanocontainers. Biomacromolecules 2011, 13, 84−91.

CONCLUSIONS We have fabricated ultrathin positively charged (PEI-MV@ CB[8]/PEI-ID) films based on the host−guest interaction of the CB[8] ternary complex. The films could be successfully obtained under basic conditions such as pH 9, while decreasing of pH value significantly inhibited the buildup of the film. Because of the presence of CB[8] ternary complexes as crosslinkers, the films were very stable in the pH range from 4 to 9. The positively charged (PEI-MV@CB[8]/PEI-ID) films have proved to be effective nanocontainers for DNA. As for the possibility of adsorbing other negative molecules, these ultrathin films could also be expected for loading drugs and proteins, which will have various potential applications in fields of regenerative medicine and tissue engineering as well as biomedical devices.

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ASSOCIATED CONTENT

S Supporting Information *

The scheme of the lap shear test and fluorescence image of the control film with EtBr staining. This material is available free of charge via the Internet at http://pubs.acs.org.

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AUTHOR INFORMATION

Corresponding Authors

*E-mail [email protected] (K.R.). *E-mail [email protected] (J.J.). Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS Financial support from the National Natural Science Foundation of China (50830106, 21174126, 51103126, 51333005, 21374095), China National Funds for Distinguished Young Scientists (51025312), the National Basic Research Program of China (2011CB606203), Open Project of State Key Laboratory of Supramolecular Structure and Materials (SKLSSM201316), Research Fund for the Doctoral Program of Higher Education of China (20110101110037 and 20110101120049), and the Qianjiang Excellence Project of Zhejiang Province (2013R10035) is gratefully acknowledged.

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REFERENCES

(1) Ikonen, M.; Murtomäki, L.; Kontturi, K. Controlled complexation of plasmid DNA with cationic polymers: Effect of surfactant on the complexation and stability of the complexes. Colloids Surf., B 2008, 66, 77−83. (2) Sun, J.-k.; Ren, K.-f.; Zhu, L.-z.; Ji, J. Multilayers based on cationic nanocomplexes for co-delivery of doxorubicin and DNA. Colloids Surf., B 2013, 112, 67−73. (3) Kiss, É.; Heine, E. T.; Hill, K.; He, Y. C.; Keusgen, N.; Pénzes, C. B.; Schnöller, D.; Gyulai, G.; Mendrek, A.; Keul, H.; Moeller, M. Membrane affinity and antibacterial properties of cationic polyelectrolytes with different hydrophobicity. Macromol. Biosci. 2012, 12, 1181−1189. (4) Kao, W.-L.; Chang, H.-Y.; Yen, G.-J.; Kuo, D.-Y.; You, Y.-W.; Huang, C.-C.; Kuo, Y.-T.; Lin, J.-H.; Shyue, J.-J. Adsorption behavior of plasmid DNA on binary self-assembled monolayers modified gold substrates. J. Colloid Interface Sci. 2012, 382, 97−104. (5) Tang, Z. Y.; Wang, Y.; Podsiadlo, P.; Kotov, N. A. Biomedical applications of layer-by-layer assembly: From biomimetics to tissue engineering. Adv. Mater. 2006, 18, 3203−3224. (6) Thomas, B.; Thomas, C.; Kefeng, R.; Guillaume, B.; Catherine, P. Multiple functionalities of polyelectrolyte multilayer films: new biomedical applications. Adv. Mater. 2010, 22, 441−467. 14106

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(28) Yu, M.; Deming, T. J. Synthetic polypeptide mimics of marine adhesives. Macromolecules 1998, 31, 4739−4745. (29) Qu, L.; Dai, L.; Stone, M.; Xia, Z.; Wang, Z. L. Carbon nanotube arrays with strong shear binding-on and easy normal lifting-off. Science 2008, 322, 238−242. (30) Sauerbrey, G. Use of vibrating quartz for thin film weighing and microweighing. Z. Phys. 1959, 155, 206−222. (31) Saurer, E. M.; Yamanouchi, D.; Liu, B.; Lynn, D. M. Delivery of plasmid DNA to vascular tissue in vivo using catheter balloons coated with polyelectrolyte multilayers. Biomaterials 2011, 32, 610−618. (32) Dutton, M. D.; Varhol, R. J.; Dixon, D. G. Technical considerations for the use of ethidium-bromide in the quantitativeanalysis of nucleic-acids. Anal. Biochem. 1995, 230, 353−355.

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