Characterization of the pore-surface gel phase in functionalized macroporous polymeric materials

Covalently immobilized pore-surface gel phases were prepared in a functionalized macroporous ultra-high-molecular-weight polyethylene by covalent coupling of lightly cross-linked polymer colloid particles [50% styrene, 49.8% (chloromethyl)stryrene, 0.2% divinylbenzene] to the interstitial pore surfaces. Swelling the covalently coupled colloid particles in a good solvent followed by chemical derivitization resulted in an immobilized pore-surface gel phase rich in primary amine groups. The macromolecular reactivity and molecular size-exclusion characteristics of the aminated pore-surface gel phase were then determined using monofunctional, amine-reactive, poly (ethylene glycol)s (PEG). Pegylated pore-surface gel phases that ranged from 71% (10,000 molecular weight PEG) to 56% (40,000 molecular weight PEG) PEG by weight resulted from reaction of the aminated gel phase with the PEG probe molecules. The number of PEG molecules reacting with the aminated pore-surface gel phase depends only on the Flory radius (or radius of gyration) of the PEG molecule to the negative 2.49th power i.e., 1/R _f ^2.49, corresponding to a M^−1.48 dependence. The immobilized and pegylated polymer colloid particles swell by a factor of 16–25 times the diameter of the original polymer colloid particles in water, thereby demonstrating that pegylation occurred though a substantial fraction of the volume of the immobilized colloid particles. Received: 18 January 1999 Accepted in revised form: 8 June 1999     

Small-angle neutron scattering study on microstructure of poly(N-isopropylacrylamide)-block-poly(ethylene glycol) in water

By employing small-angle neutron scattering (SANS), we investigated the microstructures of, poly(N-isopropylacrylamide) (PNIPA)-block-poly(ethylene glycol) (PEG) (NE) in deuterated water D₂O, as related to macroscopic behaviors of fluidity, turbidity and synerisis. SANS revealed following results: (i) microphase separation occurs at around above 17 °C in a temperature range of transparent sol below 30 °C. In the microdomain appeared in the transparent sol state, both block chains of PNIPA and PEG are swollen by water; (ii) for the NE solution of polymer concentration W_p > 3.5% (w/v), corresponding to opaque gel above 30 °C, a percolated structure, i.e., network-like domain is formed by NE as a result of macrophase separation due to dehydration of the PNIPA chains. As the temperature increases toward 40 °C, the network domain is squeezed along a direction parallel to the NE interface, which leads to increase of the interfacial thickness given by swollen PEG chains and to the macroscopic synerisis behavior.     

Macroporous Morphology of the Titania Films Prepared by a Sol-Gel Dip-Coating Method from the System Containing Poly(ethylene glycol). IV. General Principle of Morphology Formation and Effect of Heat Treatment

The variation of macroscopic morphology of the titania (TiO₂) films has been studied at various dipping conditions for a sol-gel dip-coating system containing poly(ethylene glycol) (PEG). The variation of macroscopic morphology is understood consistently by considering both the volume fraction of solvent phase during the phase separation and the water to alkoxide ratio in the sol film. The gel film shrinks and the average pore diameter increases concurrently with the thermal decomposition of PEG while the morphology depends less on the crystallization of titania gel.     

An injectable and biomimetic multi‐phase nanocomposite for non‐invasive bone tissue engineering: fabrication and mechanistic evaluation

An injectable, non‐hardening nanocomposite bone graft has been developed using a combination of nanohydroxyapatite as bioactive and osseointegrative material; P‐15 peptide‐modified poly(lactic‐co‐glycolic acid) (PLGA) microspheres as biomimetic and osteoinductive agent; and PLGA–poly(ethylene glycol) (PEG)–PLGA as a carrier gel. Increase in lactic acid/glycolic acid ratio of PLGA–PEG–PLGA resulted in stronger gels with a wider gelation window. Addition of 2.5‐fold nanohydroxyapatite resulted in significant changes in injectability (3.5‐fold force of injection), swelling characteristics (2.5 times swelling index), rheological (shear viscosity from 2.1 × 10¹ Pa s for NC3_700 to 1.5 × 10⁶ Pa s for NC3_73.52 and from 3.9 × 10² Pa s for NC8_700 to 3.76 × 10⁶ Pa s for NC8_732; an increase in elasticity at the level of 1–1000 kPa), and thermal properties of the nanocomposites. A mechanistic study showed that nanohydroxyapatite exhibits a high degree of association with the gel and interferes with its gelation owing to changes in hydrogen bonding interactions between C=?O of polymer chains and P–OH groups of nanohydroxyapatite with water molecules of the gel. A schematic was developed demonstrating changes in bonding interactions among constituent phases with respect to nanohydroxyapatite content emphasizing the importance of material interactions while fabricating multi‐phase nanocomposites for various biomedical applications. Copyright © 2017 John Wiley & Sons, Ltd.     

TiO2 Thin Film with Varied Porous Structure Applied on the Degradation of Methylene Blue

In this study, porous TiO₂ thin films were prepared by the sol‐gel method employing polyethylene glycol 1000 (PEG 1000) as an organic template. Pore sizes were adjusted by varying the concentration of PEG 1000. The optimal PEG concentration range required to form TiO₂ films with a regular porous structure was investigated and was found to be 0.01–0.015 M. As the PEG 1000 concentration increased, the surface of these films became rougher because of larger pores. Degradation of methylene blue (MB) under UV irradiation was used to determine the photocatalytic activity of the films. In addition, the effect of the pH value of the MB solution on the films was evaluated by controlling its pH value at 5, 7, and 9. The results showed that the photocatalytic activity was correlated to the pore size and pore density of the thin films. TiO2 thin films possessing pore sizes in the diameter range of 35–85 nm exhibited the best conversion of 98% after 8 h of UV irradiation when the pH value was 7.     

Modelling of the pore structure variation with pH for pore-filled pH-sensitive poly(vinylidene fluoride)–poly(acrylic acid) membranes

Pore structure variation as a function of pH was investigated for the pore-filled pH-sensitive poly(acrylic acid)-poly(vinylidene fluoride) membranes. The pore radius reduced drastically as the poly(acrylic acid) gel incorporated inside the nascent substrate, which is from 113 nm of nascent substrate to as low as 7.0 nm of pore-filled membranes at pH acidic. For the membranes, the pore radii at pH neutral estimated by the extend Nernst–Planck equation (2.76–4.20 nm) and by the Spiegler–Kedem model with the steric-hindrance pore model (3.4–4.1 nm) are close to each other and comparable with that calculated from the poly(acrylic acid) gel correlation length (1.79–2.93 nm). The calculated pore density at pH neutral (49–258 × 10¹⁴ m⁻²) is much higher than that at pH acidic (2.8–39.8 × 10¹⁴ m⁻²). The results are interpreted in terms of the gel structure in the pore-filled membranes.     

'Laterally aggregated' polyacrylamide gels for electrophoresis.

A new method is described for producing highly porous polyacrylamide matrices: polymerization in presence of a preformed hydrophilic polymer. If a standard mixture of monomers (e.g., 5%T, 4%C) is polymerized in presence of, e.g., polyethylene glycol (PEG) 10 kDa, lateral chain aggregation occurs, with formation of large pore sizes. In PEG 10 kDa, the transition from a small- to a large-pore gel is clearly apparent at 0.5% PEG addition and reaches a plateau already at 2.5% PEG. Even with shorter PEG fragments (6.2 and 1 kDa) this transition occurs, but with progressively larger amounts of PEG in solution (up to 25% for the 1 kDa species). Other polymers such as hydroxymethyl cellulose (1000 kDa) and polyvinyl-pyrrolidone (360 kDa and 25 kDa) are also able to elicit this phenomenon. It appears that lateral chain aggregation (before the cross-linking event) is induced via intra-chain hydrogen bonding, since urea and temperature strongly inhibit it, whereas tetramethylurea (an agent quenching hydrophobic interactions) does not hamper it. By scanning electron microscope, it is found that the maximum pore size obtained in a 5%T, 4%C gel in presence of 2.5% PEG 10 kDA is of the order of 0.5 micron, whereas the same 5%T, 4%C control gel would have an average pore diameter of 5 nm. Thus, an increment of pore size of about 2 orders of magnitude is obtained: in these new matrices, a 21000 bp DNA fragment exhibits a much greater migration than in a control gel in which the sample is entrapped at the application site.     

Formation of Anatase Nanocrystals-Precipitated Silica Coatings on Plastic Substrates by the Sol-Gel Process with Hot Water Treatment

Anatase nanocrystals-precipitated silica coatings were formed on plastic substrates such as poly(ethylene terephtalate) (PET), acrylic resin (AC) and polycarbonate (PC) from silica-titania gel coatings with and without addition of poly(ethylene glycol) (PEG) by hot water treatment. The maximum thickness of the coatings which can be formed without cracking or peeling-off was 100 to 200 nm for PET and PC substrates, whereas it was less than 50 nm for AC substrates. After a hot water treatment at 90°C for 120 min, the size of the anatase nanocrystals increased to be 30 and 50 nm for the coatings obtained with and without PEG, respectively. Anatase nanocrystals were formed throughout the whole of the coatings obtained with PEG and were formed only on the surface of the coatings obtained without PEG. Both coatings obtained with and without PEG were highly transparent. The plastic substrates with coatings obtained without PEG showed good weathering resistance owing to the protective effects of the residual silica under-layer. The coatings obtained with PEG showed higher photocatalytic activities than those obtained without PEG due to smaller size and higher dispersion of anatase nanocrystals in the coatings.     

Control over wettability of polyethylene glycol surfaces using capillary lithography

We demonstrate that wettability of poly(ethylene glycol) (PEG) surfaces can be controlled using nanostructures with various geometrical features. Capillary lithography was used to fabricate PEG nanostructures using a new ultraviolet (UV) curable mold consisting of functionalized polyurethane with acrylate group (MINS101m, Minuta Tech.). Two distinct wetting states were observed depending of the height of nanostructures. At relatively lower heights (< 300 nm for 150 nm pillars with 500 nm spacing), the initial contact angle of water was less than 80 degrees and the water droplet easily invaded into the surface grooves, leading to a reduced contact angle at equilibrium (Wenzel state). At relatively higher heights (> 400 nm for 150 nm pillars with 500 nm spacing), on the other hand, the nanostructured PEG surface showed hydrophobic nature and no significant change in contact angle was observed with time (Cassie state). The presence of two wetting states was also confirmed by dynamic wetting properties and contact-angle hysteresis. The wetting transition from hydrophilic (bare PEG surface) to hydrophobic (PEG nanostructures) was described by the Cassie-Baxter equation assuming that enhanced hydrophobicity is due to the heterogeneous wetting mediated by an air pocket on the surface. The measured contact angles in the Cassie state were increased with increasing air fraction, in agreement with the theoretical prediction.     

Preparation of porous biodegradable PLLA with tunable pore size through simple variation of PEG/PLLA-blend crystallization conditions

In this study, porous poly(L-lactic acid) (PLLA) films are prepared via a facile and low-cost approach using poly(ethylene glycol) (PEG) and solution casting. In contrast to most studies, the PEG/PLLA samples are further processed under different crystallization conditions (i.e., different PLLA crystallization temperatures) before PEG removal. As the PEG is extracted via solvent at higher PLLA crystallization temperatures, the resultant PLLA samples have larger pores. Interconnected fibrillar-shaped pores are found in all systems, and the fibrillar-porous structure width is ~150 nm–1.2 μm, as observed via scanning electron microscopy. These pore sizes can be tuned by adjusting the blend composition and crystallization temperature. In addition, PEG/PLLA blends are subjected to hydrolytic degradation analysis according to their crystallization conditions. Higher PLLA crystallization temperature yields higher PLLA crystallinity and larger pores, as well as reduced surface interaction with water. Therefore, the PLLA degradation rate is decreased. The developed PLLA films have potential applications in drug delivery and tissue engineering.     

Streaming potential in cylindrical pores of poly(ethylene terephthalate) track-etched membranes: variation of apparent zeta potential with pore radius

Streaming potential variation with pressure measured through poly(ethylene terephthalate) track-etched membranes of different pore sizes led to the determination of an apparent interfacial potential zetaa in the presence of 10-2 M KCl. The variation of zetaa with the pore radius r0 is interpreted by (i) the electric double layer overlap effect and (ii) the presence of a conductive gel layer. We propose a method which integrates both effects by assuming a simple model for the conductive gel at the pore wall. We observed the following three domains of pore size: (i) r0 > 70 nm, where surface effects are negligible; (ii) approximately 17 nm < r0 < 70 nm, where the pore/solution interface could be described as a conductive gel of thickness around 1 nm; (iii) r0 < approximately 17 nm, which corresponds to the region strongly damaged by the ion beam and is not analyzed here. The first one (zeta = -36.2 mV) corresponds to the raw material when etching has completely removed the ion beam predamaged region, which corresponds to the second intermediate domain (zeta = -47.3 mV). There the conductance of the gel layer deduced from the treatment of streaming potential data was found to be compatible with the number of ionic sites independently determined by the electron spin resonance technique.     

Transport properties of thermo-responsive ion track membranes

The permeation of orange G (MW 452), methylene blue (MW 319), and bovine albumin (MW 68000), through thermo-responsive ion track membranes was studied. For this purpose, poly-N-isopropylacrylamide (poly-NIPAAm) hydro-gel was chemically grafted onto single/multi-pore ion track membranes of poly(ethylene terephthalate) (PET).The local transport properties were studied by measuring the electrical current through single pore membranes. It was found that the incorporation of the hydro-gel into the pores does not influence the phase transition temperature. The switching of the responsive membrane was reversible over 200 switching cycles applied during 30–50 days. The closed pores represent a physical barrier excluding organic molecules larger than 2±0.2 nm. This fact is based on the size exclusion method using mixtures of polyethylene glycol (PEG) of various molecular weights and 0.1 N potassium chloride.The global transport properties were studied using multi-pore membranes with 5×10⁵ to 5×10⁷ pores per cm² and pore diameters between 0.6 and 4.5 μm. For bovin insulin permeation in the open state was 35 times above the level of the closed state corresponding to the detection limit of the used permeation cell. In the open state the transport rates of the solvent and the solute were identical implying that the free space in the open pores was larger than the size of the permeating bovine albumin molecules (about 7.3 nm). The linear relation between pressure and mass current enabled to determine an effective open-pore diameter between 0.2 and 1 μm. In the open state, the membrane this is not molecular selective.     

PEGylation of an artificial O2 and CO receptor: synthesis, characterisation and pharmacokinetic study

A synthetic oxygen (O(2)) and carbon monoxide (CO) receptor (hemoCD) composed of 5,10,15,20-tetrakis(4-sulfonatophenyl)porphinatoiron(ii) and a per-O-methylated β-cyclodextrin dimer with a pyridine linker (Py3CD) was functionalised with poly(ethylene glycol) (PEG) to elongate the circulation time of the receptor in the bloodstream. α-PEG monocarboxylic acid (HOOC(CH(2))(3)(CO)O-PEG(mw)-OCH(3); mw = 750 or 5k) or α,ω-PEG dicarboxylic acid (HOOC(CH(2))(3)(CO)O-PEG(mw)-O(CO)(CH(2))(3)COOH; mw = 10k or 20k) was reacted with the amino group of 5-(4-aminophenyl)-10,15,20-tris(4-sulfonatophenyl)porphyrin to afford a porphyrin monomer having a PEG chain or a porphyrin dimer having a PEG linker, respectively. The ferrous complexes of these PEGylated porphyrins (PEG750-, PEG5k-, PEG10k- and PEG20k-hemoCDs) bound O(2) in aqueous solution, P(1/2) values being 6.5-8.1 Torr at pH 7.0 and 25 °C. Each PEG(mw)-hemoCD was infused into the femoral vein of a Wistar male rat. After 6 h of the infusions, 67, 82, 86 and 42% of PEG750-, PEG5k-, PEG10k- and PEG20k-hemoCD were excreted in the urine. PEG750-hemoCD with a hydrodynamic diameter (D(h)) of 3.4 nm seemed to partly leak from the blood vessels (pore size: 2-6 nm) before renal filtration (pore size: 4-14 nm). PEG5k- (D(h) = 6.2 nm) and PEG10k-hemoCDs (9.0 nm) hardly passed through the blood vessels but were fully filtered by the kidney, resulting in high excretion rates. A considerable amount of PEG20k-hemoCD (D(h) = 12.0 nm) was retained in the blood even at 6 h after administration. The present study demonstrates that the behaviour of hemoCD in blood after administration can be controlled by modification of hemoCD with PEG having an appropriate molecular weight.     

Synthesis of end‐functionalized AB copolymers. II. Synthesis and characterization of carboxyl‐terminated poly(ethylene glycol)–poly(amino acid) block copolymers

AB block copolymers composed of hydrophilic poly(ethylene glycol) (PEG) and hydrophobic poly(amino acid) with a carboxyl group at the end of PEG were synthesized with α‐carboxylic sodium‐ω‐amino‐PEG as a macroinitiator for the ring‐opening polymerization of N‐carboxy anhydride. Characterizations by ¹H NMR, IR, and gel permeation chromatography were carried out to confirm that the diblock copolymers were formed. In aqueous media this copolymer formed self‐associated polymer micelles that have a carboxyl group on the surface. The carboxyl groups located at the outer shell of the polymeric micelle were expected to combine with ligands to target specific cell populations. The diameter of the polymer micelles was in the range of 30–80 nm. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 3527–3536, 2004     

Thermal gelation or gel melting: (ethylene glycol)113‐(l‐alanine)12 and (ethylene glycol)113‐(l‐lactic acid)12

When PEG (M.W.～5000 Daltons) is conjugated to poly(l ‐alanine), the polymer aqueous solutions (<10.0 wt.%) undergo sol‐to‐gel (thermal gelation), whereas it is conjugated to poly(l ‐lactic acid), the polymer aqueous solutions (>30.0 wt.%) undergo gel‐to‐sol (gel melting) as the temperature increases. In the search for molecular origins of such a quite different phase behavior, poly(ethylene glycol)‐poly(l ‐alanine) (PEG‐PA; EG₁₁₃‐A₁₂) and poly(ethylene glycol)‐poly(l ‐lactic acid) (PEG‐PLA; EG₁₁₃‐LA₁₂) are synthesized and their aqueous solution behavior is investigated. PEG‐PAs with an α‐helical core assemble into micelles with a broad size distribution, and the dehydration of PEG drives the aggregation of the micelles, leading to thermal gelation, whereas increased molecular motion of the PLA core overwhelms the partial dehydration of PEG, thus gel melting of the PEG‐PLA aqueous solutions occurs. The core‐rigidity of micelles must be one of the key factors in determining whether a polymer aqueous solution undergoes sol‐to‐gel or gel‐to‐sol transition, as the temperature increases. © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2014 , 52, , 52, 2434–2441     

Permeability of anti-fouling PEGylated surfaces probed by fluorescence correlation spectroscopy

The present work reports on in situ observations of the interaction of organic dye probe molecules and dye-labeled protein with different poly(ethylene glycol) (PEG) architectures (linear, dendron, and bottle brush). Fluorescence correlation spectroscopy (FCS) and single molecule event analysis were used to examine the nature and extent of probe-PEG interactions. The data support a sieve-like model in which size-exclusion principles determine the extent of probe-PEG interactions. Small probes are trapped by more dense PEG architectures and large probes interact more with less dense PEG surfaces. These results, and the tunable pore structure of the PEG dendrons employed in this work, suggest the viability of electrochemically-active materials for tunable surfaces.     

醇/水介质对PEG大分子单体与BMA分散共聚反应的影响

通过端基反应法合成了苯乙烯单封端的聚乙二醇(St- PEG)大分子单体,使其与甲基丙烯酸丁酯(BMA)在乙醇 水混合介质中进行分散共聚,得到了聚乙二醇接枝的聚甲基丙烯酸丁酯(PBMA- g -PEG)高分子微球.PBMA- g -PEG共聚物的亲溶剂 疏溶剂平衡将影响微球的形成,反应结束时,体系随BMA浓度和介质中水含量的变化呈现出4种不同的状态,透明清液、乳液、伴有沉淀或凝胶的乳液和凝胶.用透射电子显微镜(TEM)和激光光散射(LLS)对乳液体系的粒径及其形态进行了表征,表明所得接枝高分子微球形态规整具有较好的单分散性.通过控制介质中水的含量和BMA的浓度可得粒径在4 0～5 0 0nm范围的PBMA -g -PEG微球.     

Poly(vinyl methyl ether) hydrogel formed by high energy irradiation

Poly(vinyl methyl ether) shows a lower critical solution temperature behavior in water. The dimension of the polymer molecules depends on the temperature. A thermo‐sensitive hydrogel was synthesized by irradiation of an aqueous solution of poly(vinyl methyl ether) with electron beam and γ‐rays. At high polymer concentration a bulk gel was formed. The structure of the gel in the dry, swollen and shrunken state was investigated by field emission scanning electron microscopy (FESEM). It could be shown, that the gel synthesized by electron beam has a sponge‐like structure consisting of cavities (≈1 μm) separated from each other by a polymer layer full of holes (≈10 nm). The macroscopic gel is characterized by several techniques, e.g. determination of the M_c‐value by NMR‐relaxation measurements.     

聚乙二醇、聚丙二醇和环氧乙烷-环氧丙烷嵌段共聚物在固液界面上的吸附——Ⅱ.硅胶/水界面

测定了25℃时硅胶自水溶液中吸附五种聚乙二醇(PEG)、一种聚丙二醇(PPG)和三种环氧乙烷(EO)-环氧丙烷(PO)嵌段共聚物的吸附等温线。除PPG的等温线为S型外,其余的均为Langmuir型的。计算结果表明,对于PEG系列和EO-PO嵌段共聚物系列都可得到极限吸附时的分子面积(A)与分子中所含EO数(n_(EO))的关系为不通过原点的曲线。当PEG分子量大到一定程度后,此A-n_(EO)关系即成近似于通过原点的直线。根据所得结果的分析,以及考虑了吸附水的影响,初步可得出分子是以平躺的方式被吸附的结论。文中还计算了吸附直由能,并对计算结果作了初步的解释。     

Interactions between hen egg-white lysozyme, PEG2,000, and PLA50 at the air-water interface

In this paper, we compared the efficiency of polymer films, made of a poly(ethylene glycol) (PEG2,000)/poly(d,l-lactide) (PLA50) mixture, or a PEG2,000-PLA50 copolymer, to prevent adsorption of a model protein, the hen egg-white lysozyme (HEWL), at the air-water interface. This was achieved by analyzing the surface pressure/surface area curves, and the X-ray reflectivity data of the polymer films spread on a Langmuir trough, obtained in absence or in presence of the protein. For both the mixture and the copolymer, the amount of protein adsorbed at the air-water interface decreases when the density of the polymer surface coverage increases. It was shown that even in a condensed state, the polymer film made by the mixture can not totally prevent HEWL molecules to adsorb and penetrate the polymer mixed film, but however, protein molecules would not be directly exposed to the more hydrophobic phase, i.e. the air phase. It was also shown that the configuration adopted by the copolymer at the interface in its condensed state would prevent adsorption of HEWL molecules for several hours; this would be due in particular to the presence of PEG segments in the interfacial film.