Article pubs.acs.org/Macromolecules
Surface Click Reactions on Polymeric Nanocapsules for Versatile Functionalization Grit Baier, Joerg Max Siebert, Katharina Landfester, and Anna Musyanovych* Max Planck Institute for Polymer Research, Ackermannweg 10, 55128 Mainz, Germany ABSTRACT: One-step synthesis of poly(butyl cyanoacrylate-co-propargyl cyanoacrylate) (P(BCA/PCA)) and polyurethane (PUR) azide nanocapsules for direct covalent and variable functionalization is reported. The capsules in the size range between 230 and 350 nm were synthesized in an inverse (water-in-oil) miniemulsion system through either interfacial anionic polymerization (in the case of P(BCA/PCA)) or interfacial polyaddition reaction with 2,4-toluene diisocyanate (PUR azide). Surface functionalization of nanocapsules was achieved by different copper-catalyzed azide−alkyne cycloaddition (CuAAC) reactions, which were carried out under mild and ambient conditions. Click reactions of rhodamine azide and anthracene azide to P(BCA-co-PCA) nanocapsules were performed for quantitative determination of the surface alkyne bonds. PUR-azide nanocapsules were functionalized with propiolic acid and fluorescent alkyne dye. The reaction kinetics between propiolic acid and the azide monomer was studied by 1 H NMR spectroscopy. Furthermore, the functionalization of nanocapsules with propiolic acid was extended to copper-free azide−alkyne cycloaddition, thus making the system suitable for copper-sensitive materials.
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reaction conditions and results in high yields.20,21 To date, numerous click-chemistry-based strategies have been reported for the modification of surfaces. Over the past few years, several click reactions have been particularly elaborated for the modification of curved surfaces, i.e., micro- and nanoparticles. Ranjan and Brittain22 combined living radical polymerization with click chemistry to modify the surface of silica nanoparticles with polymers. The possibilities of postfunctionalization of poly(6-azidohexyl methacrylate)-grafted silica nanoparticles with various functional alkynes via click reactions were also demonstrated by Li and Benicewicz.23 Using Cu-catalyzed click reaction, the modification of polymeric particles with azide- or alkyne-functionalized dyes and macromolecules, i.e., poly(ethylene oxide), was successfully achieved in aqueous and nonaqueous environments.24−26 Ouadahi et al.27 reported the synthesis of azide-functionalized polystyrene nanoparticles, which were used as clickable polymeric scaffolds for the grafting of dansyl and fluorescein derivatives through copper(I)-catalyzed azide−alkyne cycloaddition. For localized cell delivery, self-assembled polymeric nanoparticles containing azide groups were modified with targeting alkyne-functionalized ligands by the aqueous Huisgen’s 1,3 dipolar cycloaddition reaction, catalyzed by copper sulfate and sodium ascorbate.28 Magnetic poly(N-propargylacrylamide) microspheres were used as the anchor to enable a “click” reaction with an azidoend-functionalized model peptide.29 The versatility of copper-
INTRODUCTION In the past decades there is a growing interest in the development of nanocarriers with well-defined structures and tailorable properties for drug delivery systems. The particle size, shape, and surface functionality are the most important factors that influence the distribution of the particles within the body, their interaction, and uptake by living cells.1−4 Colloidal carriers such as liposomes, micelles, dendritic polymers, and nanoparticles or nanocapsules are the most promising candidates with regards to the site-specific targeting and controlled drug release.5−8 The main advantages to use nanocapsules for drug delivery are the efficient protection of a drug against degradation caused by the influence of the environment, and preventing desorption of a drug, as it could be the case with physically adsorbed drug molecules onto the particle surface. In recent years, the fabrication of polymer nanocapsules made from different materials and using various approaches was described by many research groups ranging from the layer-bylayer approach of preformed polymer(s) to the interfacial reactions of monomers at stable nanodroplets.9−13 For the drug delivery application it is of immense interest that the capsules are biocompatible and possess functional groups on the surface that enable covalent attachment of biomolecules for the sitespecific targeting. The covalent attachment can be achieved by numerous coupling reactions, such as amine/epoxide, amine/ glutaraldehyde, thiol/maleimide, carbodiimide, and so on.14−16 Click chemistry, which is based on the copper-catalyzed azide− alkyne cycloaddition, reported simultaneously in 2001/2002 by Sharpless et al.17,18 and Meldal et al.,19 is a very efficient strategy for the functionalization as it proceeds at the mild © 2012 American Chemical Society
Received: February 15, 2012 Revised: March 30, 2012 Published: April 11, 2012 3419
dx.doi.org/10.1021/ma300312n | Macromolecules 2012, 45, 3419−3427
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Scheme 1. Schematical Presentation of the Alkyne-Functionalized PBCA/P(BCA-co-PCA) and Azide-Functionalized Polyurethane Nanocapsules
either interfacial anionic polymerization (P(BCA/PCA)) or interfacial polyaddition reaction (PUR azide). The presence of propargyl and azide groups on the surface of P(BCA/PCA) and PUR nanocapsules, respectively, enables to achieve high yields of functionalization using the click chemistry. Different fluorescent markers were attached onto the surface of P(BCA/PCA) and PUR nanocapsules through Cu(I)-catalyzed azide−alkyne cycloaddition (CuAAC) reactions performed under mild and ambient conditions (Scheme 1). Furthermore, in order to avoid any cytotoxic and side effects related to the copper,39 the concept was extended to the copper-free azide alkyne cycloaddition. In this way, PUR capsules functionalized with any functional group can be obtained; as an example we show here the functionalization with carboxylic groups by using propiolic acid. We believe that the approach disclosed in this paper can be applied to prepare a wide range of hybrid polycyanoacrylate- and polyurethane-based capsules with advanced properties.
catalyzed alkyne−azide coupling (CuAAC) in functionalizing drug-loaded polymer nanoparticles was demonstrated via the modification of surface of acetylene-functionalized nanoprticles with folate, biotin, and gold nanoparticles30 Using click chemistry, the surface functionalization of poly(N-vinylpyrrolidone) capsules with antibodies that are specific to colorectal cancer cells was recently published by Caruso et al.31 Poly(alkyl cyanoacrylates) (PACAs) have gained an increased clinical interest mainly due to their biodegradability, low toxicity, and enhancement of the drug intracellular penetrations. In the mid-1960s, cyanoacrylates were widely employed as bioadhesives in surgery and later in the 1980s as the polymeric carriers for delivery of biomolecules.32−37 However, the attachment of specific target molecules onto the surface of PACAs nanocarriers still remains a big challenge. The most commonly used systems for preparing of the drugloaded (PACA) particles/capsules is the anionic polymerization initiated by a nucleophilic group. Depending on the used surfactant (or cosurfactant), a certain amount of functional groups might remain on the surface of nanocarriers after polymerization. Recently, Nicolas et al.38 described the preparation of functionalized PACA-based nanoparticles made from a preformed poly(hexadecyl cyanoacrylate)-co-azidopoly(ethylene glycol) cyanoacrylate copolymer. The obtained nanoparticles display azide functionalities at the extremity of the PEG chains, which were further reacted with the model alkynes by click chemistry. In this work we describe the one-step synthesis of poly(butyl cyanoacrylate-co-propargyl cyanoacrylate) (P(BCA/PCA)) and polyurethane (PUR) azide nanocapsules for direct covalent and variable functionalization. Both types of capsules were synthesized in inverse (water-in-oil) miniemulsion through
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EXPERIMENTAL SECTION
Materials. All chemicals were used as received without further purification. Demineralized water was used throughout the experiments. The monomers n-butyl cyanoacrylate and propargyl cyanoacrylate (1H NMR (CDCl3, 400 MHz, δ in ppm): 2.59 (t, J = 2.5 Hz, alkyne), 4.88 (t, J = 2.5 Hz, 2H, =CH2), 6.72 (s, 1H, vinyl), 7.13 (s, 1H, vinyl) were kindly donated by Henkel AG & KGaA, Duesseldorf, Germany. The oil Miglyol 812N (caprylic/capric triglycerides) was a donation from Sasol, Germany. 2,4-Toluene diisocyanate (TDI, 99%) and cyclohexane (>99.9%) were purchased from Sigma-Aldrich. The oil-soluble block copolymer surfactant poly[(ethylene-co-butylene)-b-(ethylene oxide)], P(E/B-b-EO), consisting of a poly(ethylene-co-butylene) block (Mw = 3700 g mol−1) and a poly(ethylene oxide) block (Mw = 3600 g mol−1) was synthesized 3420
dx.doi.org/10.1021/ma300312n | Macromolecules 2012, 45, 3419−3427
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starting from ω-hydroxypoly(ethylene-co-butylene), which was dissolved in toluene, by adding ethylene oxide under the typical conditions of an anionic polymerization. 40 P(E/B-b-EO) was vacuum-dried prior to use. The anionic surfactant sodium dodecyl sulfate (SDS, 99%) was purchased from Fluka. The nonionic block copolymer Lutensol AT50 (BASF), which is a poly(ethylene oxide) hexadecyl ether with an EO block length of about 50 units, was used as surfactant. The surfactants Span80 and Tween80 were supplied by Aldrich. Ethanol (Aldrich), dimethylformamide (Aldrich), ethyl acetate (VWR), methylene chloride (
