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Polymer and particle adsorption at the polydimethylsiloxane (PDMS) droplet-water interface has been investigated. Adsorption isotherms and adsorbed layer structure are reported for a range of PEO-PPO-PEO block copolymers, and hydrophilic and hydrophobic silica "nanoparticles". The influence of solution conditions on the adsorption behaviour has indicated the thermodynamics of polymer-droplet and particle-droplet interactions. The influence of droplet cross-linking (deformability) has indicated the role of interfacial penetration in controlling adsorption at the droplet-water interface. The plateau adsorbed amount (Gamma(max)) and adsorbed layer thickness (delta(max)) of PEO-PPO-PEO copolymers are dependent on the copolymer structure and the level of cross-linking within droplets. For a wide range of copolymer structures, Gamma(max) values are in the range 2 to 20 mg m(-2). For delta(max), values range from 2 to 20 nm and are directly proportional to the PEO block length. Droplet cross-linking significantly reduces Gamma and delta values; this is considered to be due to the influence of interfacial penetrability on the adsorbed copolymer conformation. Hydrophilic silica particles adsorb onto PDMS droplets with plateau surface coverages that correspond to their hard sphere radius+double layer thickness, i.e. lateral silica-silica interactions control particle packing. Free energies of adsorption (DeltaG(ads)) are concurrent with a physical adsorption mechanism. Surface coverages, DeltaG(ads) and particle packing at the interface are only weakly influenced by pH, but are significantly influenced by salt addition. Droplet cross-linking reduced particle adsorption only at higher salt concentrations; this was attributed to the increased likelihood of silica particles wetting PDMS. Freeze fracture SEM revealed that individual silica particles are adsorbed at the droplet interface with negligible interfacial aggregation. Densely packed adsorbed particle layers are only observed when the double layer thickness is a few nanometers. Adsorption of hydrophobic particles at the PDMS droplet-water interface is more pronounced (greater adsorbed amounts and DeltaG(ads) values) than for hydrophilic particles and displays a pH dependency in line with 'DLVO behaviour'. The surface coverage values correspond to multiple close packed layers and are significantly influenced by droplet cross-linking, conferring extensive interfacial penetration (confirmed by SEM). Densely packed adsorbed particle layers with interfacial aggregation are observed over a wide range of solution conditions. Interfacial particle saturation occurred at a salt concentration two orders of magnitude less than the critical coagulation concentration (ccc) for silica in water. This phenomenon was observed for both liquid and cross-linked PDMS droplets indicating that particle interaction through the water phase plays a decisive role in particle packing at the interface. SEM indicated the presence of a rigid interfacial crust layer at the salt concentration corresponding to interfacial saturation and a multi-layered interfacial particle wall at salt concentrations >/= ccc. The PDMS droplets under consideration, having inherent colloid stability in the absence of added stabilisers, are an excellent model system for characterising polymer and particle adsorption at the droplet-water interface. The insight gained concerning adsorption thermodynamics at the droplet-water interface is not available from more conventional emulsions.
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PMID:Polymer and particle adsorption at the PDMS droplet-water interface. 1507 33

Phase separation into controllable patterned microstructures was observed for Bombyx mori silkworm silk and poly(ethylene oxide) (PEO) (900000 g/mol) blends cast from solution. The evolution of the microstructures with increasing PEO volume fraction is strikingly similar to the progression of phases and microstructures observed with surfactants. The chemically patterned materials obtained provide engineerable biomaterial surfaces with predictable microscale features which can be used to create topographically patterned or chemically functionalized biomaterials. Solution blending was used to incorporate water-soluble PEO into silk to enhance elasticity and hydrophilicity. The sizes of the globule fibroin phase ranged from 2.1 +/- 0.5 to 18.2 +/- 2.1 microm depending on the ratio of silk/PEO. Optical microscopy and SEM analysis confirmed the micro-phase separation between PEO and silk. Surface properties were determined by XPS and contact angle. Methanol can be used to control the conformational transition of silk fibroin to the insoluble beta-sheet state. Subsequentially, the PEO can be easily extracted from the films with water to generate silk matrixes with definable porosity and enhanced surface roughness. These blend films formed from two biocompatible polymers provide potential new biomaterials for tissue engineering scaffolds.
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PMID:Biomaterial films of Bombyx mori silk fibroin with poly(ethylene oxide). 1513 51

The present work discusses the grafting by electron beam irradiation of poly(ethylene oxide) (PEO) star-shaped polymers onto porous expanded polytetrafluoroethylene (EXPTFE) surfaces. The resulting materials are intended to combine the good biocompatible properties of PEO with the outstanding mechanical properties of PTFE. The star-shaped PEOs were synthesized via anionic polymerization. 3 Mev electron beam irradiation was applied to graft these PEO stars onto porous EXPTFE surfaces. The hydrophobic EXPTFE surface had to be pre-modified with N-vinylpyrrolidone. ESCA was used to quantify the amount of grafted star-shaped PEO. Unmodified EXPTFE surfaces are well known, when implanted in a body, to be rapidly covered by a layer of cells and fibrin. The EXPTFE coated with PEO were implanted in the peritoneal cavity of rats (or under the back skin). This implantation did not induce any inflammation reactions and SEM analysis had attested the absence of adsorbed cells and fibrin. The glucose diffusion properties of these membranes were studied by a lag time analysis method and compared to those of pure PEO hydrogels. As expected, glucose diffuses through the hydrogel coated membrane and diffusion is not affected by the presence of the EXPTFE membrane.
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PMID:Hydrogel networks of poly(ethylene oxide) star-molecules supported by expanded polytetrafluoroethylene membranes: characterization, biocompatibility evaluation and glucose diffusion characteristics. 1546 57

Meshes of collagen and/or elastin were successfully prepared by means of electrospinning from aqueous solutions. Flow rate, applied electric field, collecting distance and composition of the starting solutions determined the morphology of the obtained fibres. Addition of PEO (M(w)=8 x 10(6)) and NaCl was always necessary to spin continuous and homogeneous fibres. Spinning a mixture of collagen and elastin resulted in fibres in which the single components could not be distinguished by SEM. Increasing the elastin content determined an increase in fibres diameters from 220 to 600 nm. The voltage necessary for a continuous production of fibres was dependent on the composition of the starting solution, but always between 10 and 25 kV. Under these conditions, non-woven meshes could be formed and a partial orientation of the fibres constituting the mesh was obtained by using a rotating tubular mandrel as collector. Collagen/elastin (1:1) meshes were stabilized by crosslinking with N-(3-dimethylaminopropyl)-N'-ethylcarbodiimide hydrochloride (EDC) and N-hydroxysuccinimide (NHS). This treatment afforded materials with a high thermal stability (T(d)=79 degrees C) without altering their original morphology. Upon crosslinking PEO and NaCl were fully leached out. Smooth muscle cells grew as a confluent layer on top of the crosslinked meshes after 14 d of culture.
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PMID:Electrospinning of collagen and elastin for tissue engineering applications. 1611 44

The aim of this study was to synthesize and characterize a novel biocompatible polymeric membrane system and demonstrate its potential use in various biomedical applications. Synthetic hydrogels based on poly(hydroxyethyl methacrylate), poly(HEMA), have been widely studied and used in biomedical fields. A novel copolymer hydrogel was prepared in the membrane form using 2-hydroxyethyl methacrylate monomer (HEMA) and a macromonomer p-vinylbenzyl-poly(ethylene oxide) (V-PEO) via photoinitiated polymerization. A series of poly(HEMA/V-PEO) copolymer membranes with different compositions was prepared. The membranes were characterized using infrared, thermal and SEM analysis. The thermal stabilities of the copolymer membranes were found to be lowered by an increase in the ratio of macromonomer (V-PEO) in the membrane structure. Because of the incorporation of PEO segments, the copolymers exhibited significantly higher hydrophilic surface properties than pure poly(HEMA), as demonstrated by contact angle measurements. Equilibrium swelling studies were conducted to investigate the swelling behavior of the membranes. The equilibrium water uptake was reached in about 4 h. Moreover, the blood protein adsorption and platelet adhesion were significantly reduced on the surface of the PEO containing copolymer membranes compared to control pure poly(HEMA). Drug release experiments were performed in a continuous release system using model drug (vancomycin) loaded copoly(HEMA/V-PEO) membranes. A specific poly(HEMA/V-PEO) membrane formulation possessing the highest PEO content (with a HEMA:V-PEO (mmol:mmol) feed ratio of 112:1 and loaded with 40 mg antibiotic/g polymer) released about 81% of the total loaded drug in 24 h at pH 7.4. This membrane composition provided the best results and can be considered as a potential candidate for a transdermal antibiotic carrier and various biomedical and biotechnological applications.
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PMID:Novel hydrogel membrane based on copoly(hydroxyethyl methacrylate/p-vinylbenzyl-poly(ethylene oxide)) for biomedical applications: properties and drug release characteristics. 1620 32

Ultrathin TiO2 films showing rich morphologies are prepared on Si(100) substrates using sol-gel chemistry coupled with an amphilic polystyrene-block-poly(ethylene oxide) (PS-b-PEO) diblock copolymer as a structure-directing agent. The block copolymer undergoes a good-poor solvent pair induced phase separation in a mixed solution of 1,4-dioxane, concentrated hydrochloric acid (HCl), and titanium tetraisopropoxide (TTIP). By adjusting the weight fractions of 1,4-dioxane, HCl, and TTIP, inorganic block copolymer composite films containing a variety of different morphologies are obtained. On the basis of the results a ternary phase diagram of the morphologies is mapped. By calcination, anatase TiO2 films are achieved. The morphologies and crystallographic phase of the films are studied with AFM, SEM, and XRD, respectively, and the formation mechanisms of the different morphologies are discussed.
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PMID:Morphology phase diagram of ultrathin anatase TiO2 films templated by a single PS-b-PEO block copolymer. 1659 3

New amorphous amphiphilic triblock copolymers of poly(3-hydroxybutyrate)-poly(ethylene glycol)-poly(3-hydroxybutyrate) (PHB-PEG-PHB) were synthesized using the ring-opening copolymerization of beta-butyrolactone monomer. They were characterized by fluorescence, SEM and (1)H NMR. These triblock copolymers can form biodegradable nanoparticles with core-shell structure in aqueous solution. Comparing to the poly(ethylene oxide)-PHB-poly(ethylene oxide) (PEO-PHB-PEO) copolymers, these nanoparticles exhibited much smaller critical micelle concentrations and better drug loading properties, which indicated that the nanoparticles were very suitable for delivery carriers of hydrophobic drugs. The drug release profile monitored by fluorescence showed that the release of pyrene from the PHB-PEG-PHB nanoparticles exhibited the second-order exponential decay behavior. The initial biodegradation rate of the PHB-PEG-PHB nanoparticles was related to the enzyme amount, the initial concentrations of nanoparticle dispersions and the PHB block length. The biodegraded products detected by (1)H NMR contained 3HB monomer, dimer and minor trimer, which were safe to the body.
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PMID:Biodegradable nanoparticles of amphiphilic triblock copolymers based on poly(3-hydroxybutyrate) and poly(ethylene glycol) as drug carriers. 1674 Mar 6

Homocentric ZnO nanobundles with pyramidlike and hexagonal prism shapes were synthesized in colloidal systems formed by PEO-PPO-PEO amphiphilic block copolymers. The prism- and pyramidlike ZnO crystals were produced by L64 and F68, respectively, which may be attributed to the different growth rates of various crystal facets. It was proposed that the two processes for crystallization, including nucleation and crystal growth, happened in the macromolecular micelles under hydrothermal conditions. The room-temperature photoluminescence spectra of the ZnO products showed sharp ultraviolet emission located around 390 nm originating from the radiative recombination of free excitons. The sharp emission, with a half-maximum of about 8 nm, gave a powerful attestation that the sample was of high crystal quality, which was consistent with the SEM and TEM observations. The single ultraviolet emission is important for the application of ZnO-based materials in the electronic and photonic realms.
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PMID:Hydrothermal synthesis of ZnO nanobundles controlled by PEO-PPO-PEO block copolymers. 1716 9

This paper is focused on the influence of polystyrene (PS)-poly(1,4-butadiene) (PB)-poly(ethylene oxide) (PEO) triblock terpolymers on the w/o microemulsion of the pseudo-ternary system water/sodium dodecylsulfate (SDS)/xylene-pentanol. Despite the insolubility of the copolymer in water as well as in the xylene-pentanol mixture, it can be incorporated into the w/o microemulsion and interactions between the triblock terpolymer molecules and the anionic surfactant headgroups can be detected by differential scanning calorimetry (DSC) measurements. Furthermore, dynamic light scattering measurements were used to determine the aggregate diameter of the modified microemulsions. For lower polymer concentrations large aggregates between 100 and 500 nm can be observed. Surprisingly, at a higher terpolymer concentration of 5 wt%, significant smaller aggregate diameters can be identified by dynamic light scattering and Cryo-SEM. One can conclude that the copolymers are incorporated in the inverse microemulsion droplets, where the PB blocks cover the water droplets. The thermally induced radical cross-linking of the butadiene units in the presence of azobisisobutyronitrile (AIBN) leads then to covalently closed nanocapsules with an average size of 10 nm.
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PMID:Covalently closed microemulsions in presence of triblock terpolymers. 1744 86

Solvent-free, composite electrolytes based on poly(ethylene oxide) (PEO) were prepared by using mesoporous silica SBA-15 with surface modification of (trimethylchlorosilane) as the filler. The samples were explored by emission FTIR spectroscopy at elevated temperatures. The results of emission FTIR spectra illustrated the dependence of crystalline PEO phase on temperature. On the basis of electrochemistry, SEM, and emission FTIR studies, the effect of inorganic filler on the ionic conductivity was analyzed, and a conclusion concerning the ion-conducting mechanism of composite polymer electrolyte was drawn. The exploratory experiments demonstrated that the emission FTIR spectroscopy is an important method to be applied in the study of lithium batteries.
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PMID:[Ion-conducting mechanism of composite polymer electrolyte: an emission FTIR spectroscopy study]. 1751 47


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