Engineering Polyelectrolyte Capsules with Independently Controlled

Jun 26, 2015 - School of Chemical & Biomolecular Engineering, Georgia Institute of ... of Biomaterials and Engineering, 16 Xinsan Rd Hi-tech Industry ...
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Engineering Polyelectrolyte Capsules with Independently Controlled Size and Shape Xingjie Zan,*,†,‡,§ Anusha Garapaty,† and Julie A. Champion*,† †

School of Chemical & Biomolecular Engineering, Georgia Institute of Technology, Atlanta, Georgia 30332, United States Institute of Biomaterials and Engineering, Wenzhou Medical University, Chashan University Town, Wenzhou, Zhejiang Province 325035, PR China § Wenzhou Institute of Biomaterials and Engineering, 16 Xinsan Rd Hi-tech Industry Park, Wenzhou, Zhejiang Province 325011, PR China ‡

S Supporting Information *

ABSTRACT: Polyelectrolyte capsules (PECs) are a promising delivery system that has the ability to carry a large payload of a variety of cargoes. Controlling PEC properties is critical to understanding and tuning their cellular uptake efficiency, kinetics, and mechanism as well as their biodistribution in the body. The lack of a method to independently engineer PEC size, shape, and chemistry impedes both basic understanding of how physicochemical parameters affect PEC behavior in drug delivery and other applications, and the ability to optimize parameters for best function. Here, we report the successful fabrication of PECs having constant surface chemistry with independently controlled size and shape by combining soft organic templates created by the particle stretching method and a modified layer-by-layer (LBL) deposition process. Changing the template dispersion solution during LBL deposition from water to ethanol allowed us to overcome previous issues with organic templates, such as aggregation and template removal. These results will contribute not only to the basic study of the role of capsule shape and size on its function but also to the optimization of capsule properties for drug or imaging carriers, sensors, reactors, and other applications.

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INTRODUCTION Polyelectrolyte capsules (PECs) are considered to be a promising delivery system due to their ability to carry a large payload of a variety of cargoes (proteins, oligonucleotides, and small molecule drugs).1−9 As a vehicle for targeted delivery, the ability to avoid immune clearance is critical. It is well-known that a particle’s chemical and physical properties, such as size, shape, stiffness, and surface chemistry, have a significant impact on the particle’s cellular uptake efficiency, kinetics and mechanism, and biodistribution in the body.10−15 Endowing PECs with controllable properties is a sensible way to study and improve targeted delivery efficiency. Among these properties, the surface chemistry of PECs has been extensively studied.15−17 Researchers working with other types of particles have revealed a critical role for shape in immune avoidance, biodistribution, and delivery efficiency. Geng et al. reported that worm-shaped filomicelles increased the circulation half-life from several hours for spherical micelles to several days, resulting in an 8-fold increase of the accumulated drug in tumor tissue.18 Our previous work demonstrated that high-aspect-ratio wormshaped microparticles exhibited significantly reduced uptake by macrophages compared to spheres.19 However, varied results have been reported regarding the impact of shape on cellular interactions with particles of different sizes and types. Taking © XXXX American Chemical Society

the elongated shape as an example, gold nanospheres (14 nm) are internalized by HeLa cells to a greater extent than are gold nanorods (14 × 40 nm).20 In contrast, cationic poly(ethylene glycol)-based PRINT particles with an elongated aspect ratio (150 × 450 nm) are internalized by HeLa cells more quickly and to a greater extent than are spherical ones (200 nm).11 The different chemical composition of the particles used in these studies makes it hard to compare the results with each other. Also, the change in size associated with a change in shape is a critical factor when comparing results, even when the chemical composition of the particles being compared is the same.21 It is clear that the ability to independently control all PEC properties is very important to further increase their application. However, a method to engineer PECs systematically is not available. This impedes both basic understanding of how physicochemical parameters affect PEC behavior in drug delivery and other applications, and the ability to optimize those parameters to obtain the best functioning PEC. Traditionally, PECs can be made by sequentially adding oppositely charged polyelectrolyte layers onto a template and Received: May 3, 2015 Revised: June 15, 2015

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Piranha solution (70:30 vol % sulfuric acid/hydrogen peroxide). Caution! Piranha solution is dangerous! Particle Stretching and Recovery. The stretching and recovery of particles followed the reported method.41 In brief, 1 mL of 2.6 wt % PS spheres was mixed with 9 mL of PVA (1 mg mL−1) and cast and dried in air to form a film with a thickness of ∼75 μm. The film was stretched in a hot oil bath (120 °C) and then cooled to room temperature. The stretch ratio was defined as the ratio of the length of stretched film to the length of the original film. After removing oil by isopropyl alcohol (IPA), the film was cut into small pieces and dissolved in 70:30 vol % water/IPA. The particles were centrifuged for 15 min at 1000, 10 000, and 30 000 rcf for 3 μm, 500 nm, and 200 nm particles, respectively, and redispersed into the water/IPA mixture. The spin and redisperse cycle was repeated four times, and particles were ultimately dispersed into 80% ethanol. PAA−FITC Synthesis. FITC was dissolved in DMSO to 0.1 M. PAA was dissolved in 80% DMSO to 0.1 M. Twelve milligrams of EDC was added to 3 mL of PAA solution; then, 8 mg of NHS was added after 10 min, and 20 μL of FITC solution was added after another 5 min. After overnight reaction, the solution was dialyzed against 80% ethanol for 24 h. The whole reaction and dialysis process was protected from light. Assembly on Colloidal Particles and Capsule Fabrication. In a typical fabrication, 100 mL of a 2.6 wt % suspension of PS particles was dispersed in 4 mL of 80% ethanol. To this suspension was added 1 mL of the first adsorbing solution (bPEI), and adsorption was allowed to proceed for 10 min with sonication. Then, particles were pelleted by centrifugation for 10 min (1000, 5000, and 10 000 rcf for 3 μm, 500 nm, and 200 nm particles, respectively). The supernatant was removed and replaced with fresh 80% ethanol, and the particles were redispersed and pelleted again. Particles were then dispersed into 4 mL of 80% ethanol, and the adsorption of PAA, PAA−FITC, or PVPON was performed with the same washing protocol. The multilayers were formed via alternating adsorption of PVPON and PAA or PAA−FITC until the defined number of layers was obtained. To form capsules, the layered particles were dissolved in 4 mL of THF for 2 min and centrifuged for 25 min (1000, 5000, and 8000 rcf for 3 μm, 500 nm, and 200 nm particles, respectively). The supernatant was removed, and the pellet was rinsed with THF 2 times, using 200 μL of THF each time. Lastly, water (500 μL) was added to disperse the capsules. FTIR Sample Preparation. PAA and PVPON FTIR samples were prepared from the stock solutions, which were dialyzed against water (pH ∼ 3.0) overnight. Then, the solutions were freeze-dried before testing. The PVPON/PAA films were prepared under the same conditions as those used for capsule fabrication, except on a glass substrate, by the typical LBL process.50 The formed multilayers were scratched off by a razor and further dried under vacuum. PS particles, layered PS particles, and capsules were freeze-dried after fabrication. In order to prevent interference from water, all samples (particles or films) were kept in vacuum for at least 3 days before grinding with KBr for FTIR measurements. Measurements. Particle size distribution was measured by dynamic light scattering using a Zetasizer Nano ZS90 (Malvern Instruments Ltd.). The samples were measured in water at 25 °C with a scattering angle of 90°. Average particle size was calculated as the arithmetic mean of the distribution of at least three batches of particles. Zeta potential was determined by measuring the electrophoretic mobility of the nanoparticles in water using the same instrument. FTIR spectra were obtained on a Bruker Vertex 70 FTIR spectrometer equipped with a DTGS detector. Transmission electron microscopy (TEM) was carried out on a JEM-2010 microscope operating at 100.0 kV. A Zeiss Axio Observer inverted microscope Z1 was used for fluorescence microscopy images. A Millrock bench top freeze-dryer was used for freezing dry FTIR samples. Scanning electron microscopy (SEM) images were taken on a JEOL JSM 5600LV scanning electron microscope operating at 15 kV.

then dissolving the template. Further work has demonstrated that this phenomenon is not limited to electrostatic interactions, and hollow structures can be formed from layers with hydrogen bonding,22,23 host−guest interaction,24 metal− organic coordination interaction,25 and chemical reaction,26 including disulfide linkages,27 dopamine polymerization,28 and click chemistry.29,30 In most cases, the layers can be applied to templates of many sizes and shapes, regardless of the type of interaction between layers. Hollow PECs retain the size and shape of their template. The templates used for PEC fabrication can be divided into two categories: hard and soft. In most reports, hard templates are made from inorganic particles, including micro- and nanoparticles of a variety of shapes made from CaCO3,31−33 gold,34 silicon,35 and other inorganic materials.36−38 The CaCO3 template is the most commonly used for PEC fabrication due to the ease of trapping drugs into the pores formed during the particle preparation process and the simple removal of the template under mild conditions.39 However, synthesis of porous nanoscale CaCO3 templates with well-controlled, diverse shapes has not been reported. Compared to the synthesis of CaCO3, gold and silicon particles can be synthesized in various sizes and shapes. However, a toxic or dangerous solvent has to be used to remove the template: nitrohydrochloric acid for gold templates40 and hydrogen fluoride for silicon.21 In addition, independent control over the size and shape of gold or silicon particles has not been realized. On the other hand, soft templates, made of organic particles such as polystyrene (PS), polylactic-co-glycolic acid (PLGA), and PRINT particles, can be made in various sizes and shapes with independent control.41,42 These templates can be removed with less toxic organic solvents such as tetrahydrofuran (THF); however, they are used less frequently to make PECs due to issues such as aggregation of particles in the centrifugation process and final removal of the template, as reported by Caruso et al.43,44 Micron-sized spherical and collapsed spherical (discoid shaped) PS and PLGA templates have been used to fabricate poly(allylamine hydrochloride) (PAH) and bovine serum albumin or hemoglobin capsules that mimic platelet or red blood cell functions.45,46 Layer-by-layer (LBL) deposition has also been performed on cells, and PECs have been fabricated from red blood cells, Escherichia coli, and other cells.47−49 However, one is restricted to choosing from among the size and shape combinations available in nature, so control over these properties, particularly on the nanoscale, is not feasible. In this work, PECs with a constant surface chemistry and independently controlled size and shape were fabricated by applying a modified LBL deposition process on soft templates made by the particle stretching method. The aggregation and template removal issues related to organic templates were eliminated by using ethanol as the LBL solvent.

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EXPERIMENTAL SECTION

Materials. Polyacrylic acid (PAA, Mw ∼ 100 kDa), polyvinylpyrrolidone (PVPON Mw ∼ 55 kDa), branched polyethylenimine (bPEI, Mw ∼ 120 kDa) N-hydroxysuccinimide (NHS), tetrahydrofuran (THF), N-(3-(dimethylamino)propyl)-N-ethylcarbodiimide (EDC), fluorescein isothiocyanate (FITC), FITC−dextran (5 and 200 kDa), isopropyl alcohol (IPA), PVA (hydrolyzed degree 99+%, Mw 85−124 kDa), and ethanol were purchased from Sigma-Aldrich and used as received. Ultrapure water was obtained from a Millipore Synergy UV system (18.2 MΩ). Polystyrene (PS) carboxyl functionalized particles (3 μm, 500 nm, and 200 nm) were purchased from Polysciences. Stock solutions of bPEI (5 mg mL−1), PVPON (5 mg mL−1), and PAA (5 mg mL−1) were prepared in 80% ethanol. Glass was cleaned with B

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Figure 1. (a) Size distributions of layered particles (PS3μm‑r1/PEI/(PAA/PVPON)4.5, black line) and capsules after removal of the PS template (PEI/ (PAA/PVPON)4.5, red line). (b) Fluorescent image of the capsules, PEI/(PAA-F/PVPON)4.5. Scale bar is 5 μm. (c) FTIR spectra of pure PVPON (top, black), PAA (middle, red), and LBL PAA/PVPON films (bottom, blue) prepared in ethanol.

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RESULTS AND DISCUSSION Fabrication of Capsules. One of the obstacles to using soft templates to fabricate PECs is the aggregation of the particles during the LBL process. Due to the comparable densities of soft templates and water, high centrifugal force has to be applied to pellet particles dispersed in water. This leads to particle aggregation. After several layers, even higher centrifugal force is required to pellet particles due to the affinity of water to the deposited polyelectrolyte layers. Increased surface energy makes aggregation worse for nanosized particles. With the aim of avoiding aggregation, the dispersed solvent was changed from water to 80% ethanol. In ethanol, the required centrifugal force is reduced due to its lower density. More importantly, the decreased surface energy of the particles in ethanol, as compared to that in water, ensures redispersion of the particle pellet under slight sonication or shaking. Polyacrylic acid (PAA) and poly(vinylpyrrolidone) (PVPON) were chosen as building blocks for capsule fabrication because their good solubility in ethanol helps to disperse the particle pellet. In previous reports, the interaction between PAA and PVPON layers was shown to be mediated by hydrogen bonding between the proton donor of the COOH in PAA and the proton acceptor of CO in PVPON when the LBL process was executed in water or methanol.51−53 However, the polarity of ethanol is lower than that of water or methanol, which can weaken the strength of the hydrogen bonding between PAA and PVPON. In order to test whether hydrogen bonding in ethanol is strong enough to sustain LBL formation,

PAA and PVPON layers were applied to unstretched, carboxylated PS particles (diameter 3 μm and aspect ratio 1, PS3μm‑r1). Zeta potential was used to monitor the LBL process, beginning with PS particles at −69 eV, which rose to +45 eV after deposition of a base layer of polyethylenimine (PEI) (Supporting Information Figure S1a). PEI is used here for the purpose of creating an evenly distributed high charge density on the particle’s surface, which is critical for the subsequent buildup of layers.53 Then, with addition of PAA or PVPON layers, zeta potential values oscillated with dependence on the outmost layer, indicating successful sequential deposition of PAA and PVPON on the particles. The size of the PS3μm‑r1 particles with each additional layer was measured by dynamic light scattering (DLS) (Supporting Information Figure S1b). No size dependence on the number of the layers was observed, demonstrating good dispersion of the layered particles and no aggregation of particles during the LBL coating and washing processes. After incubating layered PS3μm‑r1 (PS3μm‑r1/PEI/ (PAA/PVPON)4.5) in THF to remove the PS core and form hollow capsules, the size of the capsules was measured, as shown in Figure 1a. Compared with the size of the layered particles, the size distribution profile of the capsules is similar but slightly larger, likely due to the swelling of the capsule wall. This has been observed for other PS templates upon removal of THF from solution.54 It also illustrates that the capsules are as well-dispersed as the layered particles. After producing capsules with FITC-modified PAA (PAA-F), capsules containing PAA-F layers were imaged with fluorescence microscopy. Figure 1b C

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Figure 2. (a) FTIR spectra of the original PS3μm‑r1 particles (top, black), coated particles (PS3μm‑r1/PEI/(PAA/PVPON)4.5, middle, red), and capsules obtained by incubating PS3μm‑r1/PEI/(PAA/PVPON)4.5 in THF for 2 min (bottom, blue). (b) TEM image of the capsules. Scale bar is 2 μm.

characteristic peaks of PS.56 After assembly of PEI/(PAA/ PVPON)4.5 layers on PS particles (middle spectrum), the peaks between 1550 and 1850 cm−1 widen, demonstrating the successful deposition of the layers without losing the characteristic PS signals. After incubation in THF to produce capsules (bottom spectrum), the characteristic PS peaks disappear, whereas the peaks at 1728 and 1652 cm−1 from the carbonyl vibration of PAA and PVPON remain. This indicates either the complete removal of the PS template or that the remaining PS is below the limit of detection. In detailed analysis, the spectrum of the capsules was comparable to the film spectrum (Supporting Information Figure S3), and no evidence of the third characteristic benzene peak at 3000− 3103 cm−1 was visible, further confirming that the PS template was not detected in capsules.54 An issue with organic solvent removal of template is that the capsules can be broken or damaged. In order to observe the capsule structure, transmission electron microscopy (TEM) was used to image capsules. Separate, intact capsules are clearly seen in Figure 2b. They are folded in some parts, indicating that the capsule walls are very thin but not damaged. Capsules incubated in 200 kDa FITC−dextran excluded the molecule from the capsule interior, further confirming that the capsules are intact (Supporting Information Figure S4). Compared with the TEM image of layered PS particles (Supporting Information Figure S5a), the TEM image of capsules further confirmed that the core was removed, as no impurities or black spots were seen inside the capsules. Quick template removal was attributed to the loosening of the hydrogen-bonded layer structure. Removal of organic templates begins with the swelling of the template and then dissolution and diffusion out of the capsule. The loose layer structure allowed space for these steps. Hydrogen bonding is a weaker interaction than electrostatic interaction or covalent bonding. Evidence of this weak interaction was the breaking of the capsules if the incubation time in THF was longer than 30 min (Supporting Information Figure S5b,c). Capsules formed by electrostatic interactions can endure at least several hours in THF without breaking.54 Overnight THF incubation has been shown to strengthen the interactions between ionic polyelectrolytes;57 however, it is not known if this effect would occur with only a short THF incubation of hydrogen-bonded polyelectrolytes. As a control, PAA in the layered particles

confirms that the capsules were well-dispersed and that no aggregation was observed. Conversely, serious aggregation was observed when the same particles were fabricated in water (Supporting Information Figure S2). We hypothesize that the good dispersion was mainly due to the lower surface energy and lower density of ethanol. The lower density reduced the centrifugal force required from 6000g in water to 1000g in ethanol. The lower surface energy led to easy redispersion in ethanol by only slight shaking and short sonication times; much longer sonication was required to redisperse in water. The repulsive forces indicated by the negative zeta potentials during the whole LBL process also contribute to the good dispersity and are a benefit of using hydrogen-bonding interactions between PAA and PVPON instead of electrostatic interactions. The formation of hydrogen bonds between PAA and PVPON in ethanol was confirmed by Fourier transform infrared (FTIR) spectroscopy spectra of LBL PAA/PVPON films prepared on glass with ethanol as the solvent, as was done for methanol LBL.52,53 As shown in Figure 1c, the peak centered at 1666 cm−1 in the top spectrum is assigned to the vibration of the carbonyl groups in PVPON, whereas the peak centered at 1714 cm−1 in the middle spectrum is attributed to the vibration of the carbonyl function of PAA carboxylic acid groups in the associated state. Compared to the spectra of pure polyelectrolytes, the carbonyl vibration of PAA in the film shifted to a higher wavelength number, 1728 cm−1, revealing that the carbonyl group is in a less-associated state than that in pure PAA. Meanwhile, the carbonyl vibration of PVPON in the film shifted lower, with the center at 1652 cm−1. These data demonstrate that hydrogen bonding between PAA and PVPON occurred and supported the film growth.52,53 Removal of Template. Removing the template is the final step to obtain capsules, and removing the template quickly and cleanly under mild conditions is ideal for capsule fabrication. In previous reports of PS templates, overnight, or at least several hours, was required for the template removal step.21,44,55 In our system, the PS template was removed with only a 2 min incubation in THF. Removal of the PS template was verified by FTIR in Figure 2a. The top spectrum was obtained from the original PS particles, where the peaks centered at 758 and 698 cm−1 are assigned to the out-of-plane hydrogen deformation of a monosubstituted phenyl group and the out-of-plane ring deformation for a monosubstituted phenyl group, denoted as D

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Langmuir was cross-linked by EDC/NHS in the presence of hexamethylenediamine.58 After cross-linking, the template could not be removed because of the limited space in the compacted network structure of the cross-linked layers (Supporting Information Figure S5d). Increasing the incubation time (2 days) or the incubation temperature (37 °C) in THF did not help to remove the core. As reported, PVPON can be removed by incubating it in basic solution due to the disruption of hydrogen bonding between carboxyl groups and PVPON under basic conditions.27 However, incubating the cross-linked layered particles in basic solution (incubation time ranged from hours to overnight; pH varied from 8 to 14) did not help to remove the PS core, demonstrating that the space left by the PVPON that was removed is not enough for PS core swelling or diffusion out of the particle to occur. Together, these results illustrate that the loose structure of the layers was critical for core removal. Different Shapes. To demonstrate independent control over capsule shape and size, capsules were fabricated by stretching the same PS template particles into different shapes. Because the starting PS particle is the same, the volume is conserved. As an example, we created elliptically shaped PS templates with an aspect ratio of 2 from 3 μm PS spheres (PS3μm‑r2). Particle stretching was accomplished by embedding the particles in a poly(vinyl alcohol) (PVA) film.41 Particle surface chemistry affects LBL deposition, so the removal of PVA was essential and was evaluated by zeta potential measurements of PS3μm‑r2. After four washing cycles, the zeta potential reached a plateau at a level that was slightly different than, but comparable to, that of spherical PS particles (Supporting Information Figure S6a). This illustrated that most PVA was removed and that the difference in the zeta potential may be a result of the increased particle surface area. The LBL process was monitored by zeta potential measurements, and the results were similar to those on spherical templates (Supporting Information Figure S6b), indicating the formation of layers. After the deposition of PEI/(PAA/ PVPON)4.5 layers, scanning electron microscopy (SEM) indicated that the particle’s shape was retained, as expected (Supporting Information Figure S6c). The template was removed by THF to form capsules, and with fluorescence microscopy, they appeared to retain the template shape and to be well-dispersed (Figure 3a). By TEM, the capsules were observed to be intact without broken or damaged walls (Figure 3b). To extend the limit of the capsule’s shape, we made capsules of the same shape and size but with a higher stretch ratio, 3, PS3 μm‑r3 particles. Due to the stretching and shape/ surface area change of the particles, the charge distribution might change, which is critical to LBL deposition. Another concern is the ability to maintain the shape of the capsules after the template is dissolved. After the deposition of PEI/(PAA/ PVPON)4.5 layers, SEM indicated that the shape was retained (Supporting Information Figure S6d). After removal of the template, fluorescent microscopy (Figure 3c) and TEM (Figure 3d) showed the shape of the particles was preserved and that they were well-dispersed, indicating that the capsule walls were stiff enough to support the shape of the particles without deformation. Size and Dispersity. Due to the higher surface energy of smaller particles, it can be difficult to disperse soft nanoscale templates, and significant aggregation during centrifugation can be a serious obstacle to nanocapsule fabrication with soft templates. To test the size range of this method, the size of the

Figure 3. Fluorescent images of PEI/(PAA-F/PVPON)4.5 capsules fabricated from (a) PS3μm‑r2 and (c) PS3μm‑r3 template particles. TEM images of PEI/(PAA-F/PVPON)4.5 capsules fabricated from (b) PS3μm‑r2 and (d) PS3μm‑r3 template particles. Scale bars are 5 μm for (a) and (c) and 2 μm for (b) and (d).

template was reduced to 500 nm with a stretch ratio of 3 (PS500nm‑r3) and 200 nm with a stretch ratio of 2 (PS200nm‑r2). After deposition of PEI/(PAA/PVPON)4.5 layers, SEM confirmed that the shapes of the particles were retained (Supporting Information Figure S7). The size distributions were assessed by DLS. As shown in Figure 4a,b, a single population of layered particles was observed, with size distributions centered at radii of 240 and 120 nm for PS500nm‑r3 and PS200nm‑r2, respectively. This is coincident with the size of original particles, although DLS cannot accurately measure the size of anisotropic particles. Small effective size increases are a good indication that there is no significant aggregation during the LBL process. After the templates were removed, the sizes of the capsules were measured. As shown in Figure 4a,b, the peak of the size distribution shifted larger, as with spherical templates, but remained a single population. These data illustrate the good dispersion of the shaped nanocapsules. As observed by TEM in Figure 4c,d, the shapes of the capsules were maintained, and the capsules were intact.

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CONCLUSIONS In summary, we developed a method for the fabrication of polyelectrolyte capsules (PECs) having a constant surface chemistry and independently controlled size and shape by combining particle stretching with soft template LBL. The capsule’s aspect ratio can be tuned by template stretching independent of its size (volume), and the size (volume) of the capsules can be tuned through the selection of the initial sphere size without altering the shape and aspect ratio of the capsule.41 This method is highly versatile for the production of isolated, monodisperse capsules with a wide range of possible sizes and shapes. Rod shapes were chosen as models, but this method could be easily used to fabricate capsules with any of the >20 various shapes stretched to a range of aspect ratios from spherical PS or PLGA particles.19,41,46 This method will enable not only the basic study of the role of capsule shape and size on its function but also the optimization of ideal physical parameters to identify those that function best for use as drug or imaging carriers, sensors, reactors, or other applications. E

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Figure 4. Size distributions of layered particles (black line) and capsules after removal of the PS template (red line) for PEI/(PAA/PVPON)4.5 fabricated with (a) PS500nm‑r3 and (b) PS200nm‑r2 template particles. TEM images of PEI/(PAA-F/PVPON)4.5 capsules fabricated with (c) PS500nm‑r3 and (d) PS200nm‑r2 template particles. Scale bars are 1 μm and 500 nm for (c) and (d), respectively.

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Notes

ASSOCIATED CONTENT

The authors declare no competing financial interest.

S Supporting Information *

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Additional methods: Capsule integrity test and capsule crosslinking test. Figure S1: Dependence of zeta potential of PS3μm‑r0/PEI/(PAA/PVPON)3.5 on the number of layers and particle size dependence on the number of polyelectrolyte layers. Figure S2: Optical image of the capsules, PEI/(PAA-F/ PVPON)4.5, fabricated with water as solvent. Figure S3: FTIR spectra of PAA/PVPON films prepared in 80% ethanol and capsules obtained by incubating PS 3μm‑r0 /PEI/(PAA/ PVPON) 4.5 in THF. Figure S4: PS 3μm‑r1 /PEI/(PAA/ PVPON)4.5 and PS3μm‑r1/PEI/(PAA-F/PVPON)4.5 capsules incubated with 200K FITC−dextran. Figure S5: TEM images of layered PS3μm‑r1/PEI/(PAA/PVPON)4.5 particles under various conditions. Figure S6: Dependence of the zeta potential of PS3μm‑r2 particles collected from the PVA film on the number of washing cycles and deposited layers. Figure S7: SEM images of layered particles of PS500nm‑r3 and PS200nm‑r2 after deposition of PEI/(PAA/PVPON)4.5 layers. The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acs.langmuir.5b01578.

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ACKNOWLEDGMENTS This work was supported by Georgia Institute of Technology and Air Products and Chemicals, Inc. The authors thank Prof. C. Jones and M. Sakwa Novak for assistance and use of FTIR.

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REFERENCES

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AUTHOR INFORMATION

Corresponding Authors

*(X.Z.) E-mail: [email protected]. *(J.A.C.) E-mail: [email protected]. F

DOI: 10.1021/acs.langmuir.5b01578 Langmuir XXXX, XXX, XXX−XXX

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DOI: 10.1021/acs.langmuir.5b01578 Langmuir XXXX, XXX, XXX−XXX