A simple and environment-friendly approach for synthesizing macroporous polymers from aqueous foams.

We propose a facile and environment-friendly approach for the preparation of macroporous polyacrylamide (PAM) via thermal-initiated polymerization of aqueous foams that are stabilized by surface-modified silica nanoparticles. Cetyltrimethylammonium bromide (CTAB) is used to delicately adjust the surface amphiphilicity of silica to stabilize aqueous foams. The air bubble size and size distribution is affected by the wettability of silica particles, solid content and air volume fraction in the foams. The morphology of macroporous polymers is observed by a scanning electron microscope (SEM). The pore and pore throat size can be tailored effectively by varying the silica content and air volume fraction. A high porosity of 83% is achieved when the air volume fraction of the aqueous foam is 65%. PAM hydrogels obtained via polymerizing aqueous foams show pronounced advantage over the ones prepared from oil-in-water (O/W) emulsions in wastewater treatment because of their unique pore structure. This strategy would also be extended to prepare other macroporous polymers with well-defined pore structures.

Pore Structure of Macroporous Polymers Using Polystyrene/Silica Composite Particles as Pickering Stabilizers.

A novel approach for the preparation of interconnected macroporous polymers with a controllable pore structure was reported. The method was based on the polymerization of water-in-oil Pickering high internal phase emulsion (HIPE) stabilized by polystyrene (PS)/silica composite particles. The composite Pickering stabilizers were facilely obtained by mixing positively charged PS microspheres and negatively charged silica nanoparticles, and their amphiphilicity could be delicately tailored by varying the ratio of PS and silica. The droplet size of Pickering HIPEs was characterized using an optical microscope. The pore structure of polymer foams was observed using a scanning electron microscope. The interconnectivity of macroporous polymers was evaluated upon their gas permeability, which was greatly improved after etching PS microspheres included in the Pickering stabilizers with tetrahydrofuran. As a result, fine tailoring of the pore structure of polymer foams could be realized by simply tuning the ratio of PS to silica particles in the composite stabilizer.

Interconnectivity of Macroporous Hydrogels Prepared via Graphene Oxide-Stabilized Pickering High Internal Phase Emulsions.

Interconnected macroporous poly(acrylic acid) (PAA) hydrogels are prepared via oil-in-water (o/w) Pickering high internal phase emulsion (HIPE) templates stabilized by graphene oxide (GO). The amphiphilicity of GO is adjusted by slight modification with cetyltrimethylammonium bromide (CTAB). The morphology of macroporous PAA is observed by a field-emission scanning electron microscope (FE-SEM). The gas permeability is characterized to evaluate the interconnectivity of polymer foams. The pore and pore throat size can be tailored by varying the wettability and concentration of GO. The selective adsorption toward dyes of PAA hydrogels is proved. Macroporous PAA hydrogels with an open-cell structure show enhanced adsorption behavior of both methylene blue (MB) and copper(II) ions.

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.

Strings of polymer microspheres stabilized by oxidized carbon nanotubes.

Oxidized carbon nanotubes (CNTOs) with hydrophilic oxygen-containing functional groups and hydrophobic conjugated structure are prepared by the oxidation of carbon nanotubes (CNTs). After the polymerization of styrene with CNTOs dispersed in aqueous phase, polystyrene (PS) microspheres with string-like structure are obtained. Thermogravimetic analysis (TGA), differential scanning calorimeter (DSC) and Raman results indicate the strong interaction between the separated PS chains from the oil phase and CNTOs during the initial stage of the polymerization. These adsorbed PS chains on the surface of CNTOs are quickly swollen by the monomer and they grow in size during the further polymerization. The pH value and the ion strength of aqueous phase obviously affect the stability of PS microspheres. The particle size of microspheres is also determined by the pH. We demonstrate that the one-dimensional structure of CNTOs is responsible for the formation of polymer microspheres with special architecture.

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.

Tailoring surface structure of polymer nanospheres in Pickering emulsion polymerization.

A series of surface-functionalized polystyrene (PS) nanospheres with similar particles size of about 100 nm and adjusted content of sulfonate groups on the surface are prepared by Pickering emulsion polymerization using titania nanoparticles modified with a mixture of two surfactants as stabilizers. TEM and FE-SEM images indicate that the titania nanoparticles are firmly adsorbed on the surface of polymer nanospheres because of the electric attraction between negative charged surfactant molecules and positive charged titania particles. XPS and electrophoresis measurements confirm that the surfactant with a double bond has been successfully grafted on the surface of PS nanospheres, and the surfactant without a double bond is removed with titania nanoparticles. Polymer nanospheres with appropriate concentration of sulfonate groups on the surface have good colloidal stability in the nonpolar solvent and may be suitable for bistable electrophoretic display application.

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.

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.

Studies on a novel multi-sensitive hydrogel: influence of the biomimetic phosphorylcholine end-groups on the PEO-PPO-PEO tri-block co-polymers.

In the present study, a biomimetic phosphorylcholine group was employed in the end-capping modification of PEO-PPO-PEO tri-block co-polymers (Pluronic(®)). The structures of the resulting materials were characterized by (1)H-NMR and GPC. The effects of the additional phosphorylcholine end-groups to the thermo-sensitive sol-gel transition behaviors of the aqueous solutions of the resulting polymers were studied by rheology test in neutral (0.1 M NaCl) aqueous solutions and in acidic solutions (pH 3). It was found that the phosphorylcholine-end-capped Pluronic hydrogels still kept their thermo-sensitive mechanical properties with a slight change on the sol-gel transition behaviors. The phosphorylcholine-modified Pluronics exhibited a response to the change of the pH value, which made this kind of material a multi-sensitive hydrogel system. Also, the resulting polymers showed improved hemocompatibilities in the blood coagulation test using full human blood.

Synthesis of a zwitterionic silane and its application in the surface modification of silicon-based material surfaces for improved hemocompatibility.

A phosphorylcholine-like silane coupling agent bearing zwitterionic molecular structure was synthesized and studied. The chemical structure of this silane coupling agent was characterized by FTIR, 1H NMR and 31P NMR. The zwitterionic structure was successfully constructed onto the surface of silicon as a self-assembled layer (SAL). Static water contact angle, and atomic force microscopy (AFM) were used to investigate the wettability and surface topography of the modified silicon surfaces. Static water contact angle results indicated that the hydrophilicity of the surfaces could be effectively improved by the modification with this zwitterionic silane coupling agent. The changes of the topography and water contact angle of the modified surfaces with different incubation periods in PBS solution were also measured to evaluate the stability of the SALs. Blood compatibility of the modified surfaces were evaluated by testing the full-blood activated partial thromboplastin time (APTT), prothrombin time (PT), and thrombin time (TT), as well as by observing the adhered blood platelets onto the surface. The modified surfaces showed prolonged clotting time and fewer adherent platelets, revealing that the blood compatibility was evidently improved by the modification using this zwitterionic silane.

Novel drug-loaded gelatin films and their sustained-release performance.

A new particulate drug delivery system with gelatin matrix containing Ibuprofen as a model drug molecule was developed for an epidermis drug prolonged release. Gelatin films containing Ibuprofen-loaded poly-epsilon-caprolactone (PCL) microspheres have been developed on evaporation of organic solvent from an oil-in-water emulsion followed by cross-linking. The microspheres were characterized for particle size, encapsulation efficiency, and surface morphology. Water uptake, matrix erosion, and drug release profile of the microsphere-film system were investigated. The results indicated that drug-loaded microspheres introduced in this system successfully prolonged drug release time. This kind of microsphere-film system combined good adhesion, typical for gelatin films, with the sustained release performance of PCL microspheres.

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 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.

A simple method for AFM tip characterization by polystyrene spheres.

An AFM image would not be the true topography of a surface because of the limitation of a finite size of the tip. The true topography of the surface can be deduced if we can know the tip shape. In this paper a simple method has been established to determine the profile of an AFM tip. A geometrical model for the tip and a spherical object has been proposed to show the procedure for deducing the tip shape from AFM images. Isolated spheres and closely packed spheres with different diameters have been observed to confirm the tip shape by this method. It is a non-destructive method to determine the tip shape and the results can be used for future reconstruction of an AFM image.

Novel biodegradable blend matrices for controlled drug release.

Phosphorylcholine-functionalized poly-epsilon-caprolactone (PC-PCL) is a new biodegradable polymer with good biocompatibility. In this study modulation of the controlled release of Ibuprofen (IB), a model drug, from poly-epsilon-caprolactone (PCL) by direct blending with PC-PCL is investigated. The influence of several factors such as the content of PC-PCL in the blend, drug loading and the molecular weight of PCL matrix upon the IB release is recognized. The release mechanism is discussed in terms of degradation/erosion profiles and hydrophilicity of the blend matrices. The IB release rate increased with the PC-PCL content because PC-PCL increased the hydrophilicity and biodegradability of the blends. Simultaneously, that release rate decreased with increase in the molecular weight of PCL in the blend. The drug loading in the blend also affected the release property of the matrix. Analysis of the release profiles following the power law indicated that the IB release was governed mainly by diffusion kinetics.

Structure and release behavior of PMMA/silica composite drug delivery system.

The preparation, characterization, and in vitro release of aspirin from polymethylmethacrylate (PMMA)/silica composites prepared via a sol-gel route are reported. The in vitro drug release test revealed that the release rate of aspirin in PBS increased with the silica content in the composites; on the contrary, the increase of the content of 3-(trimethoxysilyl) propyl methacrylate (MSMA), a coupling agent, decreased the drug release rate. The drug release rate/composite structure relationship was studied using Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), and swelling ratio (SR) measurement. The results indicated that the interface between polymer matrix and inorganic fillers has significant influence on the drug release behavior of the composite materials. In addition, models of mass transfer based on Fickian diffusion law at constant temperature and pressure were employed to analyze the results of the in vitro drug release experiments. The drug release behaviors of the composite samples fitted well with the Fickian diffusion model. The values of k, which is in direct proportion to drug release rate, increased with the increasing content of silica while decreased with that of MSMA in the composite samples.