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- Bakardzhiev, Pavel, et al.
(author)
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Novel polyglycidol-lipid conjugates create a stabilizing hydrogen-bonded layer around cholesterol-containing dipalmitoyl phosphatidylcholine liposomes
- 2015
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In: Journal of Drug Delivery Science and Technology. - : Elsevier. - 1773-2247. ; 29, s. 90-98
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Journal article (peer-reviewed)abstract
- Hybrid liposomes resulting from co-assembly of dipalmitoylphosphatidylcholine and polyglycidol-derivatized lipids were prepared. The latter were composed of a lipid-mimetic residue to which a linear polyglycidol chain (degree of polymerization, DP, in the 23–110 range) was conjugated. Formulations with varying copolymer type and content were prepared by film hydration technique followed by extrusion. The hybrid structures were studied by means of dynamic and electrophoretic light scattering, cryogenic transmission electron microscopy, and fluorescence spectroscopy. Cytotoxicity towards OPM-2 (multiple myeloma) and EJ (human urinary bladder carcinoma) cell lines was assessed as well. Predominantly unilamellar liposomes with mean hydrodynamic diameters in the 113–134 nm range and neutral to slightly negative surface potential were prepared. The integrity of liposomes containing copolymers with DP of the polyglycidol chain 23 and 30 was preserved at copolymer contents up to 10 mol%. Bilayer disks were observed at somewhat lower contents of the copolymers of the highest DP of the polyglycidol chain. The hybrid structures were less leaky than the plain liposomes, which was attributed to formation of a strongly hydrogen-bonded polyglycidol layer around the bilayer membrane. They exhibited low toxicological potential, favorable physicochemical characteristics, and ability to act as containers for sustained release.
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- Momekova, Denitsa, et al.
(author)
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Effects of Amphiphilic Copolymers Bearing Short Blocks of Lipid-Mimetic Units on the Membrane Properties and Morphology of DSPC Liposomes
- 2008
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In: Journal of Dispersion Science and Technology. - : Informa UK Limited. - 0193-2691 .- 1532-2351. ; 29:8, s. 1106-1113
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Journal article (peer-reviewed)abstract
- Amphiphilic, nonionic diblock copolymers based on poly(ethylene glycol) (PEG 2000-5000), comprising short blocks of lipid-mimetic units, where tested for their ability to afford steric stabilization of distearoylphosphathydilcholine:cholesterol liposomes. The copolymers bear 1-4 lipid-mimetic anchors per copolymer chain. Effects on liposomes size depend on copolymer type and content. Cryo-TEM reveals well-sepd., intact, predominantly spherical liposomes at copolymer contents up to 5 mol%. A "flat" liposomes fraction occurs upon incorporation of above 7.5 mol% of copolymers bearing 2 or 4 lipid anchors. 5,6-carboxyfluorescein assay indicates lower leakage of stabilized vs. plain liposomes up to concn. 7.5 mol%. Leakage from liposomes with higher copolymer concn. is insignificantly greater.
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- Rangelov, Stanislav, et al.
(author)
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Polyglycidol-Based Analogues of Pluronic Block Copolymers. Light Scattering and Cryogenic Transmission Electron Microscopy Studies
- 2007
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In: The Journal of Physical Chemistry C. - : American Chemical Society (ACS). - 1932-7447 .- 1932-7455. ; 111:35, s. 13185-13191
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Journal article (peer-reviewed)abstract
- In this paper we parametrize nanostructures formed in water by a series of macromol. surfactants based on polyglycidol (PG). They are considered analogs of Pluronic, that is poly(ethylene oxide)-poly(propylene oxide)-poly(ethylene oxide) (PEO-PPO-PEO) block copolymers, in which the blocks of PEO are substituted by PG. PG is structurally similar to PEO and differs in that each monomer unit bears a hydroxyl group. The investigated PG-PPO-PG copolymers are of a const. d.p. of the middle PPO block of 34; they cover a mol. wt. range from 2900 to 12400 and PG content from 30 to 84 wt %. The major techniques used to examine the behavior at the dil. (but invariably above the crit. aggregation concn.) concn. limit were static and dynamic light scattering; the aggregates were visualized by cryogenic transmission electron microscopy. The wt.-av. mol. wts., radii of gyration, second virial coeffs., diffusion coeffs., and hydrodynamic radii were detd. at different temps. The light scattering results revealed that the particles were considerably larger in size and aggregation no. than the micelles of the Pluronic copolymers. Hydrophobic interactions and interactions via hydrogen bonding are equally involved in formation of well-sepd. spherical particles with discontinuous hydrophobic PPO domains randomly distributed in a strongly hydrogen-bonded continuous medium consisting of PG and water.
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- Rangelov, Stanislav, et al.
(author)
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Structural Characterization of Lipid-based Colloidal Dispersions using Cryogenetic Transmission Microscopy
- 2010
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In: Microscopy. - : Formatex. - 9788461461912 ; , s. 1724-1734
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Book chapter (peer-reviewed)abstract
- Cryogenic transmission electron microscopy is an important technique for investigation of nano-structures formed by amphiphilic molecules in dilute aqueous solution. The basic principle and applicability of the method as well as sample preparation, interpretation of images and some artefacts are briefly outlined. The introductory section is followed by structural characterization of aqueous dispersions prepared from lipids with lamellar and non-lamellar propensities that form, respectively, liposomes and nano-size particles with a dense, frequently regular, internal structure. Eggphosphatidylcholine, soybean phosphatidylcholine, distearoyl phosphatidylcholine, dipalmitoyl phosphatidylcholine, and dioleoyl phosphatidylethanolamine are amongst the lipids with lamellar propensity, whereas glycerylmonooleate represents those of non-lamellar propensity. Steric stabilization of the nano-structures is achieved by using non-ionic block copolymers based on poly(ethylene glycol) that bear short blocks of lipid-mimetic units. Other physicochemical and biopharmaceutical techniques are employed to complement the structural investigations.
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| 10. |
- Rangelov, Stanislav, et al.
(author)
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Structural Polymorphism Exhibited by Polyglycidol-Based Analogues to Pluronic Copolymers in Aqueous Solution
- 2008
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In: Macromolecules. - : American Chemical Society (ACS). - 0024-9297 .- 1520-5835. ; 41:22, s. 8885-8894
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Journal article (peer-reviewed)abstract
- In this paper, nanostructures formed in water by a novel series of (G)n(PO)68(G)n triblock copolymers, where n = 18−135, and G and PO stand for glycidol and propylene oxide, respectively, are parametrized. The copolymers are considered analogues of Pluronic copolymers in which the flanking poly(ethylene oxide) (PEO) blocks are substituted by polyglycidol (PG). PG is structurally similar to PEO and differs in that each monomer unit bears a hydroxymethylene group. In composition, the copolymers are closest to the Pluronic series L121−F127. Dilute (but invariably above the critical aggregation concentration) aqueous solutions in the temperature interval 25−70 °C were investigated by means of dynamic and static light scattering, cryogenic transmission electron microscopy, and small-angle neutron scattering (SANS). In the temperature-composition continuum studied the novel copolymers exhibit rich structural polymorphism. Large compound particles as those observed earlier for related copolymers, small core-corona micelles, rods, and vesicles were detected and parametrized by combining light scattering and SANS. Upon heating, the simultaneous increase in both hydrophobicity of poly(propylene oxide) and hydrophilicity of PG cause counteracting effects that are reflected in appearance of maxima in the temperature dependence of aggregation numbers of the particles, variations in the density of the latter, and anomalous thermotropic transitions for some of the copolymers.
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