Perforated Block Copolymer Vesicles with a Highly Folded Membrane (original) (raw)
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Formation of Uni-Lamellar Vesicles in Mixtures of DPPC with PEO-b-PCL Amphiphilic Diblock Copolymers
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The ability of mixtures of 1.2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC) and the amphiphilic diblock copolymers poly (ethylene oxide)-block-poly(ε-caprolactone) (PEO-b-PCL) to stabilize uni-lamellar nano-vesicles is reported. Small angle neutron scattering (SANS) is used to define their size distribution and bilayer structure and resolve the copresence of aggregates and clusters in solution. The vesicles have a broad size distribution which is compatible with bilayer membranes of relatively low bending stiffness. Their mean diameter increases moderately with temperature and their number density and mass is higher in the case of the diblock copolymer with the larger hydrophobic block. Bayesian analysis is performed in order to justify the use of the particular SANS fitting model and confirm the reliability of the extracted parameters. This study shows that amphiphilic block copolymers can be effectively used to prepare mixed lipid-block copolymer vesicles with controlled lamella...
Journal of the American Chemical Society, 2015
Small angle X-ray scattering (SAXS), electrospray ionization charge detection mass spectrometry (CD-MS), dynamic light scattering (DLS), and transmission electron microscopy (TEM) are used to characterize poly(glycerol monomethacrylate)55-poly(2-hydroxypropyl methacrylate)x (G55-Hx) vesicles prepared by polymerization-induced self-assembly (PISA) using a reversible addition-fragmentation chain transfer (RAFT) aqueous dispersion polymerization formulation. A G55 chain transfer agent is utilized to prepare a series of G55-Hx diblock copolymers, where the mean degree of polymerization (DP) of the membrane-forming block (x) is varied from 200 to 2000. TEM confirms that vesicles with progressively thicker membranes are produced for x = 200-1000, while SAXS indicates a gradual reduction in mean aggregation number for higher x values, which is consistent with CD-MS studies. Both DLS and SAXS studies indicate minimal change in the overall vesicle diameter between x = 400 and 800. Fitting SA...
Pure and applied chemistry, 2004
Amphiphilic block copolymers have the ability to assemble into multiple morphologies in solution. Depending on the length of the hydrophilic block, the morphology can vary from spherical micelles, rods, and vesicles to large compound micelles (LCMs). Vesicle formation is favored upon an increase in total molecular weight of the block copolymer, that is, an increasing bending modulus (K). Owing to the polymeric character of this type of vesicle (also called polymersomes), they possess remarkable properties. The diffusion of (polymeric) amphiphiles in these vesicles is very low compared to liposomes and for high-molecular-weight chain entanglements even lead to reptation-type motions, which make it possible to trap near-equilibrium and metastable morphologies. Additionally, in contrast to liposomes, membrane thicknesses can exceed 200 nm. As a consequence, this increased membrane thickness, in combination with the conformational freedom of the polymer chains, leads to a much lower permeability for water of block copolymer vesicles compared to liposomes. The enhanced toughness and reduced permeability of polymersomes makes them, therefore, very suitable as stable nanocontainers, which can be used, for example, as reactors or drug delivery vehicles.
Spontaneous formation of vesicles of diblock copolymer EO6BO11 in water: A SANS study
The Journal of Physical …, 2006
Small angle neutron scattering (SANS) is used to study the structures formed in water by a diblock copolymer EO 6 BO 11 (having 6 ethylene oxide, EO, and 11 butylene oxide, BO, units). The data show that polymer solutions over a broad concentration range (0.05-20 wt %) contain vesicular structures at room temperature. Interestingly, these vesicles could be formed without any external energy input, such as extrusion, which is commonly required for the formation of other block copolymer or lipid vesicles. The EO 6 BO 11 vesicles are predominantly unilamellar at low polymer concentrations, whereas at higher polymer concentrations or temperatures there is a coexisting population of unilamellar and multilamellar vesicles. At a critical concentration and temperature, the vesicular structures fuse into lyotropic arrays of planar lamellar sheets. The findings from this study are in broad agreement with the work of Harris et al. (Langmuir, 2002, 18, 5337), who used electron microscopy to identify the vesicle phase in the same system.
Spontaneous Formation of Vesicles of Diblock Copolymer EO 6 BO 11 in Water:� A SAN
J Phys Chem B, 2006
Small angle neutron scattering (SANS) is used to study the structures formed in water by a diblock copolymer EO 6 BO 11 (having 6 ethylene oxide, EO, and 11 butylene oxide, BO, units). The data show that polymer solutions over a broad concentration range (0.05-20 wt %) contain vesicular structures at room temperature. Interestingly, these vesicles could be formed without any external energy input, such as extrusion, which is commonly required for the formation of other block copolymer or lipid vesicles. The EO 6 BO 11 vesicles are predominantly unilamellar at low polymer concentrations, whereas at higher polymer concentrations or temperatures there is a coexisting population of unilamellar and multilamellar vesicles. At a critical concentration and temperature, the vesicular structures fuse into lyotropic arrays of planar lamellar sheets. The findings from this study are in broad agreement with the work of Harris et al. (Langmuir, 2002, 18, 5337), who used electron microscopy to identify the vesicle phase in the same system.
ABCA Tetrablock Copolymer Vesicles
Macromolecules, 2004
Self-assembly of amphiphilic molecules provides a versatile mechanism for the creation of many forms of soft materials. Lipids, soaps, and surfactants spontaneously form bilayers, cylinders, and spheres when dispersed in water, depending on the size and shape of the hydrophilic and hydrophobic portions of the molecules. Perhaps the most important of these objects is the vesicle, comprised of a thin spherical hydrophobic shell that encapsulates an aqueous medium. Living cell membranes represent the most ubiquitous and significant type of vesicle. Various block copolymer architectures (e.g., AB diblocks 1-8 and ABA 9-11 and ABC 12-17 triblocks) have been shown to produce the same basic morphologies found with low molecular weight amphiphiles, and polymer vesicles, also referred to as "polymersomes", have been targeted at drug encapsulation and other biomimetic applications. Other methods to adjust micelle properties include using a triblock copolymer with a cross-linkable block, cross-linking that block in the melt, and dispersing the partially crosslinked block copolymer in a selective solvent to produce a "Janus-type" micelle with a cross-linked core and two different corona blocks. Control over the size and stability of polymer vesicles is of fundamental importance. Blending block copolymers containing different block sizes offers a promising solution to this problem. 29-32 Segregation of larger hydrophilic blocks to the outside surface breaks bilayer symmetry, potentially dictating spontaneous curvature and vesicle size. However, macroscopic segregation can result in multiple micelle morphologies. Alternatively, bilayer symmetry can be broken using architecturally asymmetric block copolymers. This communication describes our preliminary results obtained using this strategy. OSBO tetrablock copolymer vesicles were prepared with a microphase-segregated hydrophobic SB core, comprised of poly(styrene) (S) and poly-(butadiene) (B) and equal length hydrophilic poly-(ethylene oxide) (O) blocks. Dispersion of OSBO in water produced some degree of size control, and an unanticipated structural transition, as the fraction of O block was increased. These findings indicate that intramolecular symmetry breaking may provide a powerful tool for constructing polymersomes with prescribed dimensions and structural features.
Preparation of block copolymer vesicles in solution
Journal of Polymer Science Part B: Polymer Physics, 2004
Block copolymer vesicles can be prepared in solution from a variety of different amphiphilic systems. Polystyreneblock-poly(acrylic acid), polystyrene-block-poly(ethylene oxide), and many other block copolymer systems can produce vesicles of a wide range of sizes; those in the range of 100 -1000 nm have been explored extensively. Different factors, such as the absolute and relative block lengths, the presence of additives (ions, homopolymers, and surfactants), the water content in the solvent mixture, the nature and composition of the solvent, the temperature, and the polydispersity of the hydrophilic block, provide control over the types of vesicles produced. Their high stability, resistance to many external stimuli, and ability to package both hydrophilic and hydrophobic com-pounds make them excellent candidates for use in the medical, pharmaceutical, and environmental fields.
Polymerized ABA Triblock Copolymer Vesicles
Langmuir, 2000
The synthesis and the characterization of a poly(2-methyloxazoline)-block-poly(dimethylsiloxane)-blockpoly(2-methyloxazoline) (PMOXA-PDMS-PMOXA) triblock copolymer carrying polymerizable groups at both chain ends are described. This copolymer forms vesicular structures in dilute aqueous solution, the size of which can be controlled in the range from 50 nm up to about 500 nm. The methacrylate end groups of the triblock copolymer can be polymerized in the vesicular aggregates using an UV-induced free radical polymerization. Static and dynamic light scattering, scanning electron microscopy, and transmission electron microscopy on both the resulting nanocapsules and their nonpolymerized precursors clearly show that the cross-linking polymerization does not lead to morphological changes in the underlying vesicles. Moreover, due to their cross-linked structure, the nanocapsules are shape persistent, thus maintaining their integrity even after their isolation from the aqueous solution.