Qiangguo Du

The effect of a layer-by-layer chitosan-heparin coating on the endothelialization and coagulation properties of a coronary stent system

A biomacromolecular layer-by-layer coating process of chitosan/heparin onto a coronary stent is designed for the acceleration of the re-endothelialization and healing process after coronary stent deployment. The results of in vitro culturing of porcine iliac artery endothelial cells as well as the measurements of the APTT, PT and TT supported the rationale that the combination of chitosan and heparin could bring both endothelial cell compatibility and haemocompatibility to the stent surface. A porcine coronary injury model and arteriovenous shunt model were used for the further evaluation of the application of this kind of surface-modified stainless steel stent in vivo. The final results proved that this facile coating approach could significantly promote re-endothelialization and was safer compared with bare metal stents for its much improved anticoagulation property.

Macroporous Graphene Oxide–Polymer Composite Prepared through Pickering High Internal Phase Emulsions

Macroporous polymer-graphene oxide (GO) composites were successfully prepared using Pickering high internal phase emulsion (HIPE) templates. GO flakes were modified by the cationic surfactant cetyltrimethylammonium bromide (CTAB) and used as the stabilizer of water-in-oil (W/O) Pickering emulsions. CTAB-modified GO is effective at stabilizing W/O Pickering HIPEs, and the lowest GO content is only about 0.2 mg mL(-1) (relative to the volume of the oil phase). The close-cell morphology of the resulting poly-Pickering HIPEs is observed, and the void size of the porous polymers is tuned by varying the concentration of GO. Three-dimensional macroporous chemically modified graphene (CMG) monoliths with a high specific surface area of about 490 m(2) g(-1) were obtained after removing the cellular polymer substrates through calcination. The micropores were also found in CMGs, which may be caused by the decomposition of CTAB adsorbed on the surface of GO.

Preparation of graphene oxide coated polystyrene microspheres by Pickering emulsion polymerization.

Exfoliated graphene oxide (GO) nanosheets with hydrophilic oxygen-containing functional groups and hydrophobic residual conjugated structure are prepared by the oxidation of graphite powders. Polymerization of styrene stabilized by GO nanosheets is conducted at varied pH values. The morphology of the products is observed by field-emission scanning electron microscope (FE-SEM). It is found that GO coated polystyrene (PS) microspheres with narrow size distribution are obtained, although highly hydrophilic GO nanosheets cannot stabilize the monomer droplets in aqueous phase. Flocculation of polymer microspheres and GO nanosheets embedded in the PS matrix is induced by further decreasing the hydrophilicity of stabilizer. FT-IR, UV-vis spectra, XRD patterns and TGA results indicate the strong interaction between resulted PS chains and GO nanosheets during the initial stage of the polymerization. The amphiphilicity of GO nanosheets and the interaction between polymer and stabilizer are considered to be responsible for the fabrication of GO coated PS colloidal particles.

Encapsulated phase change materials stabilized by modified graphene oxide

The microencapsulation of phase change materials (n-hexadecane) with double-walled shells (polystyrene/graphene oxide) was realized from Pickering emulsion templating. Graphene oxide nanosheets were modified by the polycondensate of diethanolamine and adipic acid, which can well stabilize oil-in-water (O/W) Pickering emulsions. The morphology of the double-walled shell of polymer microspheres was observed by scanning electron microscopy (SEM). The thermal and barrier properties of microcapsules were studied using differential scanning calorimetry (DSC), thermal gravimetric analysis (TGA) and the flammability test. DSC results indicate that the encapsulation ratio of n-hexadecane is as high as 78%. The encapsulated phase change material has good thermal stability, owing to the existence of graphene oxide on the surface protecting the core material from leakage and evaporation. This double-walled microencapsulation of phase change materials may have potential applications in energy storage and energy saving.

Fabrication of Polymer Microspheres Using Titania as a Photocatalyst and Pickering Stabilizer

Facile photocatalytic emulsion polymerization was developed to fabricate polystyrene (PS) microspheres using a transparent anatase titania hydrosol both as a photocatalyst and stabilizer. Under the appropriate conditions, PS microspheres with a well-defined particle size distribution can be easily produced from 100 to 830 nm. The effects of cross-linking agent ethylene glycol dimethacrylate (EGDMA) and coupling agent acrylic acid (AA) on the particle size and the size distribution of PS microspheres were investigated by scanning electron microscopy (SEM), transmission electron microscopy (TEM), and other characterization means. It is proven that EGDMA and AA play importance roles in the morphology of microspheres. In addition, AA bonds a large number of titania nanoparticles on the surface of PS microspheres because its carboxyl group forms inorganic armored polymer microspheres. This interfacial interaction between titania nanoparticles and PS chains causes the elevated glass-transition temperature of microspheres.

The phase diagrams of mixtures of EVAL and PEG in relation to membrane formation

Abstract The phase diagrams of various ethylene–vinyl alcohol (EVAL) copolymer with different hydroxyl (OH) group contents and poly(ethylene glycol) (PEG) with different molecular weights (ranging from 200 to 600) are determined. It is found experimentally that both the liquid–liquid (L–L) phase boundaries and the crystallization curves are shifted to higher temperature when the OH group contents in EVAL increase. On the other hand, only the L–L phase boundaries shift to higher temperature when the molecular weights of PEG increase. These phenomena are interpreted by using solubility parameters ( δ d , δ p ) to estimate the Flory–Huggins interaction parameters, χ ∗ , of the mixtures. By extrapolating the L–L bi-phasic curves from cloud points of temperature ( T cloud ), the experimental interaction parameters χ are obtained, which are linearly correlated to the theoretically estimated interaction parameters, χ ∗ .

Dielectric Properties and Crystalline Morphology of Low Density Polyethylene Blended with Metallocene Catalyzed Polyethylene

Dielectric properties of low-density polyethylene (LDPE) blended with metallocene catalyzed polyethylene (MPE) to 1, 3, 5 wt% of the latter are reported. It was found that the 1 wt% MPE blend had the lowest volume resistivity, the highest direct current (DC) breakdown strength and the least accumulated space charge. The crystalline morphology of the blends was studied through differential scanning calorimetry (DSC), wide-angle X-ray diffraction (WAXD) and small-angle light scattering (SALS) measurements. It was found that blending increased the percentage crystallinity, decreased the spherulite size and caused the formation of imperfect spherulites, i.e. spherulites containing defects and impurities in their crystalline phases, and thus fewer impurities and defects on their boundaries. The improvement in dielectric properties of the blends, especially the 1 wt% MPE blend, is attributed to the increase in crystallinity and the formation of imperfect spherulites.

Interconnected Porous Polymers with Tunable Pore Throat Size Prepared via Pickering High Internal Phase Emulsions

Interconnected macroporous polymers were prepared by copolymerizing methyl acrylate (MA) via Pickering high internal phase emulsion (HIPE) templates with modified silica particles. The pore structure of the obtained polymer foams was observed by field-emission scanning electron microscopy (FE-SEM). Gas permeability was characterized to evaluate the interconnectivity of macroporous polymers. The polymerization shrinkage of continuous phase tends to form open pores while the solid particles surrounding the droplets act as barriers to produce closed pores. These two conflicting factors are crucial in determining the interconnectivity of macroporous polymers. Thus, poly-Pickering HIPEs with high permeability and well-defined pore structure can be achieved by tuning the MA content, the internal phase fraction, and the content of modified silica particles.

Preparation of pH-sensitive polyacrylic acid hollow microspheres and their release properties

The pH-sensitive polyacrylic acid (PAA) microspheres with a hollow structure are prepared via Pickering polymerization of acrylonitrile using diethanolamine–adipic acid modified silica nanoparticles as a stabilizer followed by hydrolysis in the presence of sodium hydroxide. The morphology and chemical structure of PAA hollow microspheres are investigated by scanning electron microscopy (SEM) and Fourier-transform infrared (FTIR) spectroscopy. The swelling of polymer hollow particles is observed by confocal microscopy. As a kind of functional material, the pH-sensitive PAA hollow microspheres can be used to load and release the substances. The release rates of the dye from PAA hollow microspheres are greatly dependent on pH value with sunset yellow (SSY) as a model molecule. It is proven that the release properties of PAA hollow microspheres can be well controlled via tuning the pH values.

Slightly surface-functionalized polystyrene microspheres prepared via Pickering emulsion polymerization using for electrophoretic displays

Slightly surface-functionalized polystyrene (PS) microspheres are prepared by photocatalytic Pickering emulsion polymerization using sodium styrene sulfonate (SSS)-modified titania hydrosol as a stabilizer. Aqueous electrophoresis measurements indicate the adsorption of bifunctional SSS anions on the surface of titania nanoparticles via electrostatic interaction. SSS molecules participate in the copolymerization with the monomers before the nucleation and thus have a great effect on the morphology and surface structure of the obtained PS microspheres. Appropriate SSS concentration leads to PS microspheres with small size, narrow distribution, and uniform surface chemistry. This kind of polymer particles can be used as a good candidate for the electrophoretic displays because of their high colloidal stability and electrophoretic mobility in the apolar solvent.