Encapsulation of pristine fullerene C60 within block copolymer micelles through interfacial instabilities of emulsion droplets
Graphical abstract
Instability of oil/water interfaces leads to kinetically trapping of pristine fullerene and/or conducting polymer into block copolymer micelles.
Introduction
Well-ordered polymer/fullerene (C60) hybrid micelles are of interest for their ability to combine the advantages of hybrid nano-objects [1], [2] and the unique properties of fullerenes [3], [4], [5]. Recently, a growing interest has developed in the potential use of fullerenes in biomedicine, therapy, photovoltaics and nano-electronics [6]. However, the low dispersibility of fullerenes in water hampers further studies and biomedical applications, including enzyme inhibition, DNA cleavage, radical quenching activity, and photodynamic therapy (PDT) [7], [8]. To improve the aqueous dispersibility of fullerene, one acknowledged procedure is based on the modification of C60 with hydrophilic polymers or small molecules via chemical bonds. This strategy can generate more order and stable structures which are important for the practical applications, but this technique leads to disruption of its symmetry and pseudo-aromaticity and likely disrupts the physical and chemical properties of C60 [6], [9], [10]. An alternative approach is the transfer of C60 into water through the formation of supramolecular complexes by means of non-covalent interactions, which can keep the properties of C60 and provide the possibility to be further functionalized. Amphiphilic block copolymers possess the ability to spontaneously self-assemble into nanosized micelles with a typical core, interface, and corona structure, thus have attracted much attention as promising carriers for poorly water soluble agent and drugs as well as genes. Selective localization of different constituent materials is of interest in biomedical, catalysis, sensing, and others [11], [12]. For example, anti-cancer drugs and quantum dots (QDs) can be loaded into the hydrophobic core of the micelles. Simultaneous localization of the C60 at the interface of the micelles demonstrates more advantages in photosensitization [13]. In this case, the drug, the PDT reagent C60 and QDs, were trapped in one delivery system where drug can be maintained for a long period in the micelles, with photoluminescence (PL) from the QDs being preserved. The resulting hybrid micelles were also able to generate a large amount of reactive oxygen species to kill cancer cells upon irradiation of the encapsulated C60 with UV or visible light [14].
Nowadays, various synthetic techniques have been developed for the preparation of polymer/C60 hybrid micelles. For instance, simultaneous desolvation of both the C60 and amphiphilic block polymer in mixed solvents leads to the formation of micelles with encapsulated C60 in the micellar cores [13]. Supramolecular polymer assisted self-assembly of C60 has also been reported to generate C60 loaded hybrid micelles [15], [16]. Recently, encouraged by the broad applications of C60, newly developed approaches of co-assembly of C60 with polymer into hybrid micelles, including sequential self-assembly [17], [18], film rehydration method [19], co-precipitation [20], and others, have been emerged. Yet, it is still a challenge to generate C60 loaded micelles with high loading density and tunable micellar morphologies in a simple manner.
The aim of this work is to explore a facile and effective approach to encapsulate C60 into amphiphilic block copolymer micelles. We recently reported a simple yet robust approach to drive assembly of amphiphilic copolymers through interfacial instability [21]. Hydrophobic inorganic nanoparticles were effectively encapsulated in both wormlike and spherical block copolymer micelles through this process [22]. Inspired by this motif of assembly, we anticipated that this process would allow the encapsulation of C60 into micelles, providing the possibility to explore multifunctional photodynamic therapy reagent. Herein, we show that this method can be expanded to load C60 within both spherical and cylindrical block copolymer micelles (Fig. 1). Interestingly, fullerene addition will induce transition of micellar morphological from cylindrical micelles to string-of-vesicles and then to spherical micelles with the increase in fullerene content. Additionally, poly(3-hexylthiophene) (P3HT), a conducting polymer, can be co-encapsulated with C60 into the micellar core through similar procedure. In the hybrid micelles, fluorescence of P3HT can be quenched due to photoinduced energy transfer from electron-donating P3HT to electron-accepting C60 molecules.
Section snippets
Materials
Sodium dodecylsulfate (SDS) (purity > 98%) and Nile Red (purity > 98%) were purchased from Sigma–Aldrich. Polystyrene-b-poly(ethylene oxide) PS38k-b-PEO11k (PDI = 1.06) was purchased from Polymer Source, Inc., Canada. Pristine fullerene C60 (purity > 99.9%) was purchased from Puyang Yongxin Science and Technology Co., China. All other chemicals were used after receiving without further purification.
Synthesis of poly(3-hexylthiophene) (P3HT)
In a three-neck round bottom flask, 2,5-dibromo-3-hexylthiophene (1.41 g, 4.33 mmol) was dissolved in THF
Strategy for encapsulating C60 into micellar cores
In a typical experiment, amphiphilic diblock copolymer PS38k-b-PEO11k (PEO content: 22 wt%) and C60 were separately dissolved in chloroform and carbon disulfide. Then, the solutions were mixed together at the desired ratio, and the resulting solution was emulsified with aqueous SDS solution. Emulsions were left in an open glass container and the resulting solution was kept gently stirring overnight. The increasing concentration of the PS-b-PEO within each shrinking droplet eventually triggered
Conclusions
In summary, we demonstrate the loading of pristine fullerene in water soluble, structurally defined PS-b-PEO micelles through self-assembly of fullerene and PS-b-PEO during a solvent evaporation process of emulsion droplets. Compared to the available literature strategies [13], [17], [20], this interfacial instability processing presents a facile and efficient route to encapsulate C60, which does not require chemical modification of pristine fullerene and achieves a high C60 loading efficiency.
Acknowledgments
We gratefully acknowledge funding for this work provided by the National Basic Research Program of China (973 Program, 2012CB932500), National Natural Science Foundation of China (21004025), Excellent Youth Foundation of Hubei Scientific Committee (2012FFA008), and Fundamental Research Funds for the Central Universities (HUST: 2013ZZGH016). We also thank the HUST Analytical and Testing Center for allowing us to use its facilities.
References (42)
- et al.
Chem. Phys. Lett.
(1995) - et al.
J. Colloid Interface Sci.
(2012) Nat. Mater.
(2008)- et al.
J. Chem. Soc. Chem. Commun.
(1994) - et al.
Chem. Soc. Rev.
(2010) - et al.
Adv. Mater.
(2010) - et al.
Proc. Natl. Acad. Sci. USA
(2002) - et al.
Chem. Commun.
(2012) - et al.
J. Polym. Sci. Polym. Chem.
(2011) - et al.
Science
(2012)
Chem. Rev.
Acc. Chem. Res.
Angew. Chem. Int. Ed.
Nanotechnology
Polym. Chem.
Science
Angew. Chem. Int. Ed.
Angew. Chem. Int. Ed.
Langmuir
J. Phys. Chem. B
J. Phys. Chem. C
Cited by (14)
Light-adjusted supramolecular host–guest interfacial recognition for reconfiguring soft colloidal aggregates
2023, Journal of Colloid and Interface ScienceSelf-assembly of green tea catechin derivatives in nanoparticles for oral lycopene delivery
2017, Journal of Controlled ReleaseCitation Excerpt :With the increase in the loading of lycopene, more lycopene may adsorb at the NP interface, such that the NP cannot maintain small interfacial tension, and then the aggregation would happen; this is consistent with recently reported results [31]. The highest loading of lycopene in PLGA is 7.0%, and the reason might be the lower affinity between lycopene and PLGA [32,33]. During the storage of the lycopene solution, the lycopene can easily rearrange into different geometric isomers and oxidize.
New hybrid macromolecular structures of C<inf>60</inf> fullerene-amphiphilic copolymers of N-vinylpyrrolidone and triethylene glycol dimethacrylate
2015, Materials Today CommunicationsCitation Excerpt :They are based on the processes of spontaneous aggregation of polymer colloids (micelles, emulsions, etc.) and the fullerene in various solvents. For this purpose, amphiphilic block copolymers forming polymer micelles in appropriate solvents are typically used [13–22]. It allows to convert C60 into water-soluble colloids for biomedical applications, e.g. as photosensitizer to photodynamic cancer therapy.
Surfactant: An ancient but young member in chemical world
2023, Kexue Tongbao/Chinese Science BulletinCo-Assembly of Diblock Copolymers and Molecular Bottlebrushes
2022, MacromoleculesSelf-Stabilized Giant Aggregates in Water from Room-Temperature Ionic Liquids with an Asymmetric Polar-Apolar-Polar Architecture
2020, Journal of Physical Chemistry B