The formation of a noncovalent triblock copolymer based on a coiled-coil peptide motif is demonstrated in solution. A specific peptide pair (E and K) able to assemble into heterocoiled coils was chosen as the middle block of the polymer and conjugated to poly(ethylene glycol) (PEG) and polystyrene (PS) as the outer blocks. Mixing equimolar amounts of the polymer-peptide block copolymers PS-E and K-PEG resulted in the formation of coiled-coil complexes between the peptides and subsequently in the formation of the amphiphilic triblock copolymer PS-E/K-PEG. Aqueous self-assembly of the separate peptides (E and K), the block copolymers (PS-E and K-PEG), and equimolar mixtures thereof was studied by circular dichroism, dynamic light scattering, and cryogenic transmission electron microscopy. It was found that the noncovalent PS-E/K-PEG copolymer assembled into rodlike micelles, while in all other cases, spherical micelles were observed. Temperature-dependent studies revealed the reversible nature of the coiled-coil complex and the influence of this on the morphology of the aggregate. A possible mechanism for these transitions based on the interfacial free energy and the free energy of the hydrophobic blocks is discussed. The self-assembly of the polymer-peptide conjugates is compared to that of polystyrene-b-poly(ethylene glycol), emphasizing the importance of the coiled-coil peptide block in determining micellar structure and dynamic behavior.

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In this paper the thermal conductivity of epoxy-based composite materials is analysed. Twoand three-phase Lewis-Nielsen models are proposed for fitting the experimental values of the thermal conductivity of epoxy-based polymer composites. Various inorganic nano-and microparticles were used, namely aluminium oxide, aluminium nitride, magnesium oxide and silicon dioxide with average particle size between 20 nm and 20 µm. It is shown that the filler-matrix interface plays a dominant role in the thermal conduction process of the nanocomposites. The two-phase model was proposed as an initial step for describing systems containing 2 constituents, i.e. an epoxy matrix and an inorganic filler. The three-phase model was introduced to specifically address the properties of the interfacial zone between the host polymer and the surface modified nanoparticles.

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We report the design and structural characterization of cationic diblock copolymer vesicles loaded with plasmid DNA based on a single emulsion technique. For this purpose, a DNA solution was emulsified in an organic solvent and stabilized by an amphiphilic diblock copolymer. The neutral block forms an interfacial brush, whereas the cationic attachment complexes with DNA. A subsequent change of the quality of the organic solvent results in the collapse of the brush and the formation of a capsule. The capsules are subsequently dispersed in aqueous medium to form vesicles and stabilized with an osmotic agent in the external phase. Inside the vesicles, the plasmid is compacted in a liquid-crystalline fashion as shown by the appearance of birefringent textures under crossed polarizers and the increase in fluorescence intensity of labeled DNA. The compaction efficiency and the size distribution of the vesicles were determined by light and electron microscopy, and the integrity of the DNA after encapsulation and subsequent release was confirmed by gel electrophoresis. We demonstrate reverse transfection of in vitro cultured HeLa cancer cells growing on plasmid-copolymer vesicles deposited on a glass substrate.

The structure of spherical micelles of the diblock poly(styrene-block-acrylic acid) [PS-b-PA] copolymer in water was investigated up to concentrations where the polyelectrolyte coronal layers have to shrink and/or interpenetrate in order to accommodate the micelles in the increasingly crowded volume. We obtained the partial structure factors pertaining to the core and corona density correlations with small angle neutron scattering (SANS) and contrast matching in the water. The counterion structure factor was obtained with small angle X-ray scattering (SAXS) with a synchrotron radiation source. Furthermore, we have measured the flow curves and dynamic visco-elastic moduli. The functionality of the micelles is fixed with a 9 nm diameter PS core and a corona formed by around 100 PA arms. As shown by the SAXS intensities, the counterions are distributed in the coronal layer with the same density profile as the corona forming segments. Irrespective ionic strength and micelle charge, the corona shrinks with increasing packing fraction. At high charge and minimal screening conditions, the polyelectrolyte chains remain almost fully stretched and they interdigitate once the volume fraction exceeds the critical value 0.53±0.02. Interpenetration of the polyelectrolyte brushes also controls the fluid rheology: the viscosity increases by 3 orders of magnitude and the parallel frequency scaling behavior of the dynamic moduli suggests the formation of a physical gel. In excess salt, the coronal layers are less extended and they do not interpenetrate in the present concentration range.

Encapsulation of DNA 2Encapsulation of dsDNA fragments (contour length 54 nm) by the cationic diblock copolymer poly (butadiene-b-N-methyl 4-vinyl pyridinium) has been studied with phase contrast, polarized light, and fluorescence microscopy, as well as scanning electron microscopy. Encapsulation was achieved with a single emulsion technique. For this purpose, an aqueous DNA solution is emulsified in an organic solvent (toluene) and stabilized by the amphiphilic diblock copolymer. The PBd block forms an interfacial brush, whereas the cationic P4VPQ block complexes with DNA. A subsequent change of the quality of the organic solvent results in a collapse of the PBd brush and the formation of a capsule. Inside the capsules, the DNA is compacted as shown by the appearance of birefringent textures under crossed polarizers and the increase in fluorescence intensity of labeled DNA. The capsules can also be dispersed in aqueous medium to form vesicles, provided they are stabilized with an osmotic agent (polyethylene glycol) in the external phase. It is shown that the DNA is released from the vesicles once the osmotic pressure drops below 10 5 N/m 2 or if the ionic strength of the supporting medium exceeds 0.1 M. The method has also proven to be efficient to encapsulate pUC18 plasmid in sub-micron sized vesicles and the general applicability of the method has been demonstrated by the preparation of the charge inverse system: cationic poly(ethylene imine) encapsulated by the anionic diblock poly(styrene-b-acrylic acid). IntroductionSelf-assembly is clearly a necessary tool to realize practical nanoscale structures. These nanostructures will probably involve membrane vesicles either as the nanostructures themselves, or as templates for more complex structures. Micron and nano-size polymeric vesicles and capsules have considerable potential in industrial, medical, and pharmaceutical applications, because of their ability to take up and carry a reagent through an otherwise hostile medium. The usual preparation procedure involves the adsorption of alternating layers of oppositely charged polyelectrolytes on a colloidal particle. 7,8 In the next step, the colloidal core is destroyed either by UV irradiation or immersion in a strong acid or base. The resulting empty capsule can subsequently be loaded with a drug. A drawback of this method is that the molecular weight of the reagent is restricted by the pore size in the capsule membrane, because the reagent is usually introduced after the preparation of the capsule. This restriction makes it difficult to encapsulate rather large macromolecules such as clone vector DNA, although recently progress has been made by precipitation of spermidine condensed DNA onto the surface of template micro-particles. 9 There is a clear need for high enough compaction of DNA, efficiency of encapsulation, and control of the structure and properties of the protective shell.Our encapsulation experiments are inspired by DNA-polycation complexes (polyplexes). 10 DNA forms complexes with cationic poly...