Higher-order assembly of crystalline cylindrical micelles into membrane-extendable colloidosomes

Nature Communications, Sep 2017

Crystallization-driven self-assembly of diblock copolymers into cylindrical micelles of controlled length has emerged as a promising approach to the fabrication of functional nanoscale objects with high shape anisotropy. Here we show the preparation of a series of crystallizable diblock copolymers with appropriate wettability and chemical reactivity, and demonstrate their self-assembly into size-specific cylindrical micelle building blocks for the hierarchical construction of mechanically robust colloidosomes with a range of membrane textures, surface chemistries and optical properties. The colloidosomes can be structurally elaborated post assembly by in situ epitaxial elongation of the membrane building blocks to produce microcapsules covered in a chemically distinct, dense network of hair-like outgrowths. Our approach provides a route to hierarchically ordered colloidosomes that retain the intrinsic growth activity of their constituent building blocks to permit biofunctionalization, and have potential applications in areas such as biomimetic encapsulation, drug delivery, catalysis and biosensing.

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Higher-order assembly of crystalline cylindrical micelles into membrane-extendable colloidosomes

Abstract Crystallization-driven self-assembly of diblock copolymers into cylindrical micelles of controlled length has emerged as a promising approach to the fabrication of functional nanoscale objects with high shape anisotropy. Here we show the preparation of a series of crystallizable diblock copolymers with appropriate wettability and chemical reactivity, and demonstrate their self-assembly into size-specific cylindrical micelle building blocks for the hierarchical construction of mechanically robust colloidosomes with a range of membrane textures, surface chemistries and optical properties. The colloidosomes can be structurally elaborated post assembly by in situ epitaxial elongation of the membrane building blocks to produce microcapsules covered in a chemically distinct, dense network of hair-like outgrowths. Our approach provides a route to hierarchically ordered colloidosomes that retain the intrinsic growth activity of their constituent building blocks to permit biofunctionalization, and have potential applications in areas such as biomimetic encapsulation, drug delivery, catalysis and biosensing. Introduction Self-assembly and stabilization of colloidal particles at oil/water droplet interfaces is an attractive bottom-up approach to the fabrication of functionally advanced polymer and inorganic microcapsules known as colloidosomes1,2,3,4,5,6. Colloidosomes have diverse applications in areas such as micro-encapsulation and controlled delivery7,8,9,10 and catalysis11,12,13,14, and have been exploited as synthetic protocells exhibiting membrane-gated enzyme reactivity15, artificial cytoskeletal assembly16, 17, growth and division18, and chemical signalling19. In each case, colloidal particles with appropriate wettability spontaneously assemble at the oil/water interface to produce Pickering emulsions that are subsequently stabilized by gelation or polymerization of the solvent-filled core, or alternatively, by thermal annealing or chemical crosslinking of the closely packed particulate shell, to produce mechanically robust colloidosomes1, 15,16,17,18,19. A wide range of inorganic and polymeric building blocks have been used for colloidosome fabrication. Typical examples include inorganic colloids consisting of hydrophobically modified silicas20, 21, titania22, a metal–organic coordination compound23, clay platelets19, 24, 25 and graphene oxide sheets26, as well as numerous modified polystyrene latexes1, 2, 27, 28, copolymers29, 30 and protein nanofibrils31. In many cases, the use of spherical particles or platelets leads to close packing in the colloidosome shell to produce a semipermeable membrane. Recently, highly anisotropic particles of cellulose32, 33 and epoxy polymers34 have been employed as relatively large and rigid micro-rods for the preparation of Pickering emulsions. In contrast, Armes and colleagues have introduced a new strategy for water-in-oil Pickering emulsion stabilization based on the self-assembly of block copolymer (BCP) nanostructures in the form of worm-shaped micelles with appropriate oil/water wettability35, 36. Herein, we develop a complementary approach using chemically transformed poly(ferrocenyldimethylsilane) (PFS)–poly(methylvinylsiloxane) (PMVS) diblock copolymers to prepare size-specific cylindrical micelles comprising a crystalline PFS core and disordered carboxylated PMVS corona by a seeded growth process known as living crystallization-driven self-assembly (CDSA)37,38,39,40,41. We exploit these specialized BCP building blocks for the hierarchical construction of mechanically robust polymer colloidosomes with a range of membrane textures, surface chemistries and optical properties. Significantly, regions of the PFS core exposed at the termini of the cylindrical micelles remain active to epitaxial elongation on addition of BCP unimers37, 38. As a consequence, the crosslinked colloidosome membrane can be structurally and chemically elaborated post assembly by a highly regulated in situ growth process. We use this strategy to generate colloidosomes with hair-like outgrowths consisting of elongated cylindrical micelles with contiguous fluorescent domains or arrays of biotinylated side chains capable of streptavidin binding. Overall, our results provide a step towards the interfacial assembly of colloidosomes that retain the intrinsic growth activity of their constituent building blocks. This approach could open up new routes to bespoke hierarchical structures for use in biomimetic encapsulation, drug delivery, catalysis and biosensing. Results Construction of hierarchical crystalline colloidosomes An integrated strategy involving polymer design, interfacial assembly and seeded growth was exploited for the fabrication of colloidosomes comprising a semipermeable membrane of closely packed cylindrical BCP micelles (Fig. 1a). Cylindrical micelles with appropriate levels of wettability were prepared by chemical modification of the diblock copolymer PFS25-b-PMVS (...truncated)


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Hongjing Dou, Mei Li, Yan Qiao, Robert Harniman, Xiaoyu Li, Charlotte E. Boott, Stephen Mann, Ian Manners. Higher-order assembly of crystalline cylindrical micelles into membrane-extendable colloidosomes, Nature Communications, 2017, Issue: 8, DOI: 10.1038/s41467-017-00465-z