Self-Assembly of Biopolymers on Colloidal Particles via Hydrogen

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Self-Assembly of Biopolymers on Colloidal Particles via Hydrogen Bonding Uttam Manna and Satish Patil* Solid State and Structural Chemistry Unit, Indian Institute of Science, Bangalore-560012, India

ABSTRACT Fabrication of multilayer microcapsules via layer-by-layer approach through hydrogen bonding has attracted enormous interest due to its strong response to pH. In this communication, we have prepared hydrogen-bonded multilayer microcapsule without using any cross-linking agent by using DNA base pair (adenine and thymine) modified biocompatible polymers. The growth of the self-assembly on colloidal (melamine formaldehyde; MF) particles has been monitored with zeta potential measurement. The capsules were obtained on dissolution of MF particles at 0.1N HCl. The capsules were characterized with scanning electron microscopy. Moreover, we have observed the salt induced microscopic change in self-assembly of this system on the surface of colloidal particles. SECTION Nanoparticles and Nanostructures

ayer-by-layer (LbL) approach is currently attracting widespread scientific and technological interest as a simple method for the self-assembly of variety of materials.1,2 It has been successfully applied to fabricate multilayer thin film and hollow micro- and nanocapsules for drug delivery, gene delivery, fabrication of composite materials, encapsulation of enzymes, and dual drug delivery applications.3-10 The unique control over nanoscale assembly of thin film has been utilized extensively in a plethora of drug carrier material, electronic and photonic applications. In the past decade, the sequential adsorption of two complementary polyelectolytes through electrostatic attraction has been exploited for a variety of applications.11 In the recent past, efforts were made to build a multilayer self-assembly through hydrogen and covalent bonding that allows one to manipulate the membrane to respond to different stimuli (pH, solvent, temperature, etc.), and these materials are very significant in the context of drug and gene delivery.12-15 Caruso et al. reported the H-bonded self-assembly of poly(N-isopropylacrylamide) (PNIPAAm)/ poly(acrylic acid) (PAA) to deliver the encapsulated content at elevated temperature.16 Hammond and co-workers showed that H-bonded poly(acrylic acid)/poly(ethylene oxide)-block-poly(ε-caprolactone) (PAA/ PEO-b-PCL)17 undergoes disassociation on exposing this multilayer assembly to physiological conditions and attributed this to the weak nature of the H-bonding in the self-assembly. These approaches usually require a two-step formulation process to achieve stable microcapsules: (i) development of polymeric materials with H-bonding responsive functional group (ii) cross-linking of self-assembly.18 Introduction of a cross-linker results in poor control over the self-assembly as well as physicochemical properties.19 Recently, we reported the self-assembly of adenine-modified chitosan and thyminemodified hyaluronic acid (ACHI/THUA) through H-bonding

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r 2010 American Chemical Society

Figure 1. LbL assembly of ACHI (neutral) and THUA (negatively charged) polymers on an MF particle. The 0th layer is the MF particle, all odd layers (1, 3, 5, and 7) are THUA, and all even layers (2, 4, 6, and 8) are ACHI. The inset shows the chemical structures of ACHI and THUA.

on a planar substrate without any cross-linking agent.20 In this communication, we have accounted for the self-assembly of ACHI/THUA (Scheme 1) on colloidal particles to obtain stable microcapsules. The chemical structures of ACHI/THUA are shown as an inset in Figure 1. During this process, we observed interesting morphological changes in the presence of salt. These polymers were synthesized by following our earlier reported protocol.20 The degree of adenine substitution in Received Date: January 22, 2010 Accepted Date: February 16, 2010 Published on Web Date: February 22, 2010

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DOI: 10.1021/jz100089f |J. Phys. Chem. Lett. 2010, 1, 907–911

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Figure 2. (a) TEM image of an LbL-coated MF particle. The inset shows higher magnification of one of the spheres with a scale bar of 100 nm. (b) CLSM image of a coated MF particle after encapsulation of Rhodamine-B in a multilayer membrane. Scheme 1. Fabrication of H-Bonded Microcapsule Using the Watson-Crick Base Pairing Principle

chitosan and thymine substitution in hyaluronic acid is ∼53% and ∼75%, respectively. In the present system, one of the polymers (THUA) is a negatively charged polyelectrolyte. A flexible backbone of THUA rapidly responds to the salt and undergoes conformational rearrangement and results in a porous structure on colloidal particles. Here, we report the LbL self-assembly of biopolymers through hydrogen bonding on a colloidal particle and the salt-induced porous structure. In this self-assembly, one of the coating materials (THUA) is negatively charged, and the complementary polymer (ACHI) is neutral, we have employed zeta-potential measurement to


monitor the growth of thin film on melamine formaldehyde (MF) particles. Figure 1 shows the representative zeta potential of polyelectrolyte deposited on MF particles. As bare MF particles have positive charge on the surface, it shows a positive (þ53.5 mV) zeta potential (considered as the zeroth layer), whereas all the odd layers show negative potential values (25 ( 3 mV), and in the case of all the even layers, the surface potential is almost zero. These results suggest the alternate deposition of THUA and ACHI via hydrogen bonding. Subsequently, the formation of multilayer membrane on MF particle was observed under a transmission electron

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Figure 3. (a) FESEM image of an H-bonded multilayer (five bilayers) hollow microcapsules of ACHI/THUA. The inset shows the magnified image of more microcapsules with a scale bar of 2 μm. (b) CLSM image of Rhodamine-B encapsulated microcapsules in water.

Figure 4. Morphological change of this H-bonded self-assembly in the presence of salt. (a,b,c) Morphology of the assembly on an MF particle after treatment of salt (0.1 N) NaCl solutions for 5 min, 15 min, and 6 h, respectively.

microscope (TEM) as shown in Figure 2a. These results indicate that a uniform coating of THUA and ACHI was obtained. This can be more clearly seen in the higher magnification


image as shown in the inset image in Figure 2a. The thickness of this membrane is 40 ( 5 nm for five bilayers. So, the average thickness of each bilayer is 8 ( 1 nm, which is very

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conformational rearrangement of the ACHI backbone as shown in Scheme 2.24 The prolonged treatment of salt solution did not show any definite influence, suggesting that the hydrogen bonding network of THUA and ACHI did not disassemble completely, but it remained intact with the substrate, resulting in a porous structure on colloidal particles. In conclusion, this work has examined the role of a functional group on a polymer backbone for the fabrication of stable multilayer H-bonded polymer microcapsules. The morphological changes of a multilayer membrane by addition of electrolyte provide porous thin films on colloidal particles. These new features of H-bonded LbL self-assembly on colloidal particles are of potential interest for applications in materials science.

Scheme 2. Conformational Rearrangement of Polymer Segment within Multilayer Assembly in the Presence of Salt (0.1N NaCl Solution)

similar to that of regular membranes formed from polyelectrolyte polymers through electrostatic attraction. Furthermore, these coated MF particles were incubated with Rhodamine-B overnight. The subsequent confocal laser scanning microscope (CLSM) image shows that these particles are efficient to load functional dyes by diffusion, as shown as in Figure 2b. The hollow microcapsules were obtained by following the standard protocol of MF particle dissolution in 0.1 N HCl solution as shown in Figure 3a.21,22 The field emission scanning electron microscope (FESEM) image clearly shows that the spherical shape of MF particles is not retained. This can be attributed to several factors, such as drying effect while recording FESEM and variation of the interaction involved between the two polymers. In the present system, we believe that the drying effect is playing important role because these microcapsules encapsulated with Rhodamine-B shows spherical shape in water as shown in CLSM (Figure 3b). This clearly indicates that the stable hollow microcapsules can be obtained by following this method. The additional functional groups of adenine and thymine on polymer backbone play a significant role in obtaining stable hollow microcapsules. The morphological changes of self-assembly in the presence of salt were followed by FESEM as shown in Figure 4a-c. The THUA- and ACHIcoated MF particles were incubated with salt solution, and the resulting change in morphology was followed as a function of time. The self-assembly of THUA and ACHI rapidly responds to the salt solution, resulting in porous structure on colloidal particles. The porosity of this assembly increases with incubation time in salt (0.1N NaCl) solution as shown in Figure 4a,b. But we found that this membrane is stable enough and remains intact on the substrate (colloidal) even after 6 h of treatment of salt solution, as shown in Figure 4c. These intriguing changes in the self-assembly appear to be due to conformational rearrangement of polymers within a confined region as shown in Scheme 2. The system studied in this work is stabilized by hydrogen bonds, but one of the biopolymers (THUA) is an anionic polyelectrolyte. It is wellknown that the electrostatic rigidity of hyaluronic acid (HA) is affected by the salt solution due to Coulomb repulsion.23 The structure of THUA bears resemblance to that of HA, consisting of a repeating disaccharide unit. The addition of salt solution to the present self-assembly may cause a coil-globule transition of THUA molecules and consequently force the


SUPPORTING INFORMATION AVAILABLE Materials, experimental methods, and sample characterization details. This material is available free of charge via the Internet at http://pubs. acs.org.

AUTHOR INFORMATION Corresponding Author: *To whom correspondence should be addressed. Tel: þ91-8022932651. Fax: þ91-80-23601310. E-mail:[email protected].

ACKNOWLEDGMENT The authors thank the Nano Centre for assistance with SEM and TEM measurements.

REFERENCES (1)

(2)

(3)

(4)

(5)

(6)

(7)

(8)

(9)

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Decher, G.; Hong, J. D. Buildup of Ultrathin Multilayer Films by a Self-Assembly Process: Consecutive Adsorption of Anionic and Cationic Bipolar Amphilifiles on Charged Surfaces. Makromol. Chem. Macromol. Symp. 1991, 46, 321–327. Qiu, X.; Leporatti, S.; Donath, E.; Mohwald, H. Studies on the Drug Release Properties of Polysaccharide Multilayers Encapsulated Ibuprofen Microparticles. Langmuir 2001, 17, 5375–5380. Kim, B. S.; Lee, H.; Min, Y.; Poon, Z.; Hammond, P. T. Hydrogen-Bonded Multilayer of pH-Responsive Polymeric Micelles with Tannic Acid for Surface Drug Delivery. Chem. Commun. 2009, 28, 4194–4196. Johnston, A. P. R.; Caruso, F. Exploiting the Directionality of DNA: Controlled Shrinkage of Engineered Oligonucleotide Capsules. Angew. Chem., Int. Ed. 2007, 46, 2677–2680. Caruso, F.; Trau, D.; Mohwald, H.; Renneberg, R. Enzyme Encapsulation in Layer-by-Layer Engineered Polymer Multilayer Capsules. Langmuir 2000, 16, 1485–1488. Manna, U.; Patil, S. Encapsulation of Uncharged WaterInsoluble Organic Substance in Polymeric Membrane Capsules via Layer-by-Layer Approach. J. Phys. Chem. B 2008, 112, 13258–13262. Su, X.; Kim, B. S.; Kim, S. R.; Hammond, P. T.; Irvine, D. J. Layer-by-Layer Assembled Multilayer Films for Transcutaneous Drug and Vaccine Delivery. ACS Nano 2009, 3, 3719–3729. Manna, U.; Patil, S. Dual Drug Delivery Microcapsules via Layer-by-Layer Self-Assembly. Langmuir 2009, 25, 10515– 10522. Kim, B. S.; Smith, R. C.; Poon, Z; Hammond, P. T. MAD (Multiagent Delivery) Nanolayer: Delivering Multiple


pubs.acs.org/JPCL

(10)

(11) (12)

(13)

(14)

(15)

(16)

(17)

(18)

(19)

(20)

(21)

(22)

(23)

(24)

Therapeutics from Hierarchically Assembled Surface Coatings. Langmuir 2009, 25, 14086–14092. Manna, U.; Patil, S. Borax Mediated Layer-by-Layer SelfAssembly of Neutral Poly(vinyl alcohol) and Chitosan. J. Phys. Chem. B 2009, 113, 9137–9142. Decher, G. Fussy Nanoassemblies: Toward Layered Polymeric Multi-composites. Science 1997, 277, 1232–1237. Kozlovskaya, V.; Kharlampieva, E.; Mansfield, M. L.; Sukhishvili, S. A. Poly(methacrylic acid) Hydrogel Films and Capsules: Response to pH and Ionic Strength and Encapsulation of Macromolecules. Chem. Mater. 2006, 18, 328-–336. Lutkenhaus, J. L.; Hrabak, K. D.; McEnnis, K.; Hammond, P. T. Elastomeric Flexible Free-Standing Hydrogen-Bonded Nanoscale Assemblies. J. Am. Chem. Soc. 2005, 127, 17228– 17234. Kozlovskaya, V.; Sukhishvili, S. A. Amphoteric Hydrogel Capsules: Multiple Encapsulation and Release Routes. Macromolecules 2006, 39, 6191–6199. Cavalieri, F.; Postma, A.; Lee, L.; Caruso, F. Assembly and Functionalization Of DNA-Polymer Microcapsules. ACS Nano 2009, 3, 234–240. Quinn, J. F.; Caruso, F. Facile Tailoring of Film Morphology and Release Properties Using Layer-by-Layer Assembly of Thermoresponsive Materials. Langmuir 2004, 20, 20–22. Kim, B. -S.; Park, S. W.; Hammond, P. T. Hydrogen-Bonding Layer-by-Layer- Assembled Biodegradable Polymeric Micelles as Drug Delivery Vehicles from Surfaces. ACS Nano 2008, 2, 386–392. Feng, Z.; Wang, Z.; Gao, C.; Shen, J. Template Polymerization to Fabricate Hydrogen-Bonded poly(acrylic acid)/poly(vinylpyrrolidone) Hollow Microcapsules with a pH-Mediated Swelling-Deswelling Property. Chem. Mater. 2007, 19, 4648– 4657. Guan, Y.; Zhang, Y.; Zhou, T.; Zhou, S. Stability of HydrogenBonded Hydroxypropylcellulose/poly(acrylic acid) Microcapsules in Aqueous Solutions. Soft Mater 2009, 5, 842–849. Manna, U.; Bharani, S.; Patil, S. Layer-by-Layer Self-Assembly of Modified Hyaluronic Acid/Chitosan Based on Hydrogen Bonding. Biomacromolecules 2009, 10, 2632–2639. Peyratout, C. S.; Dahne, L. Tailor-Made Polyelectrolyte Microcapsules: From Multilayers to Smart Containers. Angew. Chem., Int. Ed. 2004, 43, 3762–3783. Manna, U.; Dhar, J.; Nayak, R.; Patil, S. Multilayer SingleComponent Thin Films and Microcapsules via Covalent Bonded Layer-by-Layer Self-Assembly. Chem. Commun. [Online early access]. DOI: 10.1039/b924240f. Cleland, R. L. Ionic Polysaccharides. II. Comparison of Polyelectrolyte Behavior of Hyaluronate with That of Carboxymethyl Cellulose. Biopolymers 1968, 6, 1519–1529. Lapcik, L., Jr; Lapcik, L.; Smedt, S. D.; Demeester, J.; Chabrecek, P. Hyaluronan: Preparation, Structure, Properties, and Applications. Chem. Rev. 1998, 98, 2663–2684.


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Self-Assembly of Biopolymers on Colloidal Particles via Hydrogen

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