Hydrophilic Polymer Chains Research Articles

Development of Core-Corona Type Polymeric Nanoparticles as an Anti-HIV-1 Vaccine

We developed a novel technology for core-corona polymeric nanoparticles having hydrophilic polymer chains with functional groups. Polystyrene nanoparticles immobilized with the mannose-specific lectin concanavalin A could efficiently capture human immunodeficiency virus type 1 (HIV-1) particles and gp120 antigens on their surface. Since the antigen-capturing nanoparticles were capable of inducing humoral and cellular immune responses to HIV-1, they could be developed as a mucosal vaccine against HIV-1 infection.

Comparison of two approaches to grafting hydrophilic polymer chains onto polysulfone films

AbstractTo reduce the surface protein adsorption of polysulfone (PSf) film, we improved the hydrophilicity of this film by photochemical grafting of methoxypoly (ethylene glycol) (MPEG) derivatives on its surface. Grafting was achieved with both the simultaneous method and the sequential method. Surface analysis of the grafted film by X‐ray photoelectron spectroscopy (XPS) revealed that the PEG chains had successfully grafted onto the surface of the film. The grafting efficiencies by simultaneous and sequential methods were 20.8% and 10.2%, respectively. With an atomic force microscope (AFM), the surface topography of PEG‐grafted films by these two methods was compared. Static water contact angle measurement indicated that the surface hydrophilicity of the film had been improved. Protein adsorption measurement showed that the surface protein adsorption of the modified film was significantly reduced compared with that of the unmodified PSf film. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 103: 3818–3826, 2007

Rapid surface functionalization of iron-filled multi-walled carbon nanotubes

Iron-filled multi-walled carbon nanotubes (Fe@MWCNTs) were surface functionalized with various functionalities via a rapid, single-step process involving ultrasonication assisted and microwave-induced radical polymerization reactions. Both hydrophobic (e.g., polystyrenes and polymethyl methacrylate) and hydrophilic (e.g., polyacrylamide, polyacrylic acids, and polyallyl alcohols) polymer chains can be chemically grafted onto the surface of MWCNTs by the same process within ∼10 min. The surface grafted polymers were identified by FTIR, TGA, TEM, EELS and Raman spectra. The solubilities of the surface derivatized MWCNTs are in the range of 1200–2800 mg/l in solutions. The polyacrylic acids modified iron filled MWCNTs have a saturated magnetic dipole moment of ∼40 emu/g at room temperature with a coerceive field of nearly zero gauss.

Preparation, characterization and enzyme inhibition of methylmethacrylate copolymer nanoparticles with different hydrophilic polymeric chains

Methylmethacrylate copolymer nanoparticles with different hydrophilic chains were prepared by the free radical polymerization of methylmethacrylate with N-isopropylacrylamide (NIPAAm), N-methacrylic acid (MAA), N-trimethylaminoethylmethacrylate chloride (TMAEMC) or N-dimethylaminoethylmethacrylate hydrochloride (DMAEMC). These particles were characterized by particle size and zeta potential. The polymerization conditions were shown to influence the particle size and surface charge. Particle sizes of MMA–NIPAAm nanoparticles after 3 h of reaction reached constant level at 180 nm. An increasing amount of total monomer (0.5–5%) would result in the nanoparticles of particle size of 115–204 nm for 30% NIPAAm of the total monomer. In the same range of 5–40% NIPAAm of the total monomer, the particle size decreased from 280 to 170 nm. The concentration of the initiator APS up to a concentration of 0.2% for MMA–TMAEMC and 0.1% for MMA–NIPAAm showed no effect on the particle size of the final nanoparticle suspensions, while higher concentration would lead to aggregation in the polymerization process. MMA–NIPAAm nanoparticles were pH-dependent in zeta potential at pH 1–12 values reducing from 12.2 mV to −16.8 mV, respectively. Nanoparticles were incubated with pepsin and trypsin at 37 °C for 20 min and their enzyme inhibition was determined. The activity of pepsin decreased to 27% in the presence of MMA–NIPAAm nanoparticles, and MMA–MAA nanoparticles reduced the activity of trypsin to 39%, respectively.

Swelling of N-isopropyl acrylamide hydrogels in aqueous solutions of sodium chloride

Hydrogels are three-dimensional networks of hydrophilic polymer chains. Hydrogels can absorb/desorb water and hydrophilic solutes. This behavior is called swelling/shrinking, as it is accompanied by a volume change. The amounts of absorbed substances depend on the structure of the hydrogel and the composition of the coexisting liquid phase. This paper deals with experimental investigations of the swelling behavior of nonionic, chemically crosslinked, synthetic hydrogels of N-isopropyl acrylamide. The swelling equilibrium of some hydrogels in aqueous solutions of sodium chloride was investigated at 298 K. The experimental results are presented, discussed and correlated/predicted with a thermodynamic model which combines an expression for the Gibbs energy of a liquid phase with an expression for the Helmholtz energy of an elastic network.

New Nanophase Separated Intelligent Amphiphilic Conetworks and Gels

AbstractAmphiphilic conetworks (APCN) are new materials composed of covalently bonded otherwise immiscible hydrophilic and hydrophobic polymer chains. The amphiphilic nature of these new crosslinked polymers is indicated by their swelling ability in both hydrophilic and hydrophobic solvents. Special synthetic techniques have been developed for the preparation of these new unique materials, such as poly(2‐hydroxyethyl methacrylate)‐l‐polyisobutylene (PHEMA‐l‐PIB), poly(methacrylic acid)‐l‐polyisobutylene (PMAA‐l‐PIB) and poly(N,N‐dimethylaminoethyl methacrylate)‐l‐polyisobutylene (PDMAEMA‐l‐PIB) (‐l‐ stands for linked by). Due to their unique architecture, macrophase separation of the immiscible components is prevented by the chemical bonding in the conetworks. As a results, phase separation leads to nanodomains with usually 2‐20 nm domain sizes as shown by AFM measurements. The nanophase separated morphology may also lead to smart temperature responsive gels with high mechanical stability, such as in the case of poly(N,N‐dimethylaminoethyl methacrylate)‐l‐polyisobutylene APCNs as discovered during these studies. In another approach, poly(2‐hydroxyethyl methacrylate)‐l‐polyisobutylene and poly(methacrylic acid)‐l‐polyisobutylene APCNs were prepared by a special two‐step process. The new PMAA‐l‐PIB polyelectrolyte APCNs possess smart (intelligent) reversible pH‐responsive properties in aqueous media. These unique conetwork structures and properties of these new emerging materials may lead to numerous new potential applications, such as smart materialk products, sustained drug release matrices, biomaterials, nanohybrids, nanotemplates etc.

Swelling of N-isopropyl acrylamide hydrogels in aqueous solutions of poly(ethylene glycol)

Hydrogels are three-dimensional networks of hydrophilic polymer chains with properties between liquids and solids. One of the most interesting features is their capability to absorb liquids. This feature is called swelling. The amount of absorbed substances depends on the structure of the gel and the composition of the coexisting liquid phase. This paper reports experimental investigations of the swelling behavior of non-ionic, synthetic hydrogels of N-isopropyl acrylamide. The swelling equilibrium of two hydrogels in aqueous solutions of poly(ethylene glycol) with different average molecular weights was investigated at 298 K. The equilibrium properties and the compositions of the coexisting phases (gel phase and surrounding liquid solution) are correlated/predicted with a thermodynamic model which combines an expression for the Gibbs energy of a liquid with an expression for the Helmholtz energy of an elastic network.

Swelling of n-isopropyl acrylamide hydrogels in water and aqueous solutions of ethanol and acetone

Hydrogels are three-dimensional networks of hydrophilic polymer chains with properties in between liquids and solids. One of the most interesting features is their capability to swell as well as to shrink depending on their surroundings. This paper deals with experimental investigations of the swelling behavior of nonionic synthetic hydrogels of n-isopropyl acrylamide. The swelling of some hydrogels differing in, e.g. the cross-linking density and the length of the polymer chains, in aqueous solutions of ethanol as well as of acetone was investigated at 298 K. The experimental results are presented and discussed also with respect to the phenomenon of “multiple phase transitions”. Typically, the amount of absorbed material depends on the composition of the solvent showing a considerable decrease at around 20–40 mass% of the organic solvent component. In aqueous solutions of ethanol, some hydrogels reveal a phase transition from a swollen into a shrunken state at a certain ethanol concentration. “Multiple phase transitions” (i.e. several transitions at different ethanol concentrations) were also observed, but they proved to be caused by the kinetics of the swelling/shrinking process which can result in heterogeneous gel structures. The equilibrium properties are correlated with a thermodynamic model which combines an expression for the Gibbs energy of a liquid with an expression for the Helmholtz energy of an elastic network. The compositions of the coexisting phases (gel phase and surrounding liquid solution) were also determined. As long as the gel absorbs a large amount of solvent, there are only small differences between the solvent concentrations in the gel and in the surrounding liquid. When the gel is in a shrunken state, there are (small) differences in the composition which are reliably predicted.

Association behavior of poly(methyl methacrylate-b-methacrylic acid-b-methyl methacrylate) in aqueous medium

Abstract ABA type triblock amphiphilic polyelectrolyte consisting of poly(methyl methacrylate- block -methacrylic acid- block -methyl methacrylate) (P(MMA- b -MAA- b -MMA)) was synthesized by atom transfer radical polymerization technique and the self-assembly behavior of the polymers in aqueous solution was studied over the course of neutralization. Combination of potentiometric and conductometric titrations along with dynamic light scattering techniques were used to investigate the size and shape of aggregates at various degrees of neutralization. The effect of hydrophobic–hydrophilic (MMA–MAA) ratio and polymer chain length on the aggregation behavior during neutralization was studied. P(MMA- b -MAA- b -MMA) with longer MMA segment self-assembles via the closed association mechanism through stronger self-entanglement of MMA chains, whereas P(MMA- b -MAA- b -MMA) with shorter MMA chain self-assembles via the open association mechanism, as confirmed by transmission electron microscopy. Conductometric titration was used to determine the counterion condensation during the course of neutralization. When the charge density of micelle approaches a critical value as neutralization progresses, counterion condensation of Na + ions on the polymer chains occurs. The effect of counterion condensation on the aggregation behavior during neutralization was elucidated.

Toward the development of biomimetic polymers by protein immobilization: PEGylation of insulin as a model reaction.

Many current tissue-engineering investigations aim at the rational control of cell adhesion and tailored composition of biomaterial surfaces by immobilizing various protein and peptide components, such as growth factors. As a step on the way to develop polymers that allow for such surface modifications, water-soluble polymers were used as model substances to examine reactions with proteins containing amine groups. Consequently, the uncommon PEGylation of insulin in aqueous buffers was used to characterize reaction products and simulate the intended immobilization step for surface modification. Amine reactive poly(ethylene glycol)s were synthesized and characterized by (1)H nuclear magnetic resonance and gel-permeation chromatography. Furthermore, the model protein insulin was characterized concerning its accessible amino groups, using a fluorescent dye (TAMRA-SE). The resulting reaction products were identified by reversed-phase high-performance liquid chromatography and electrospray mass spectrometry. After PEGylation with hydrolytically stable poly(ethylene glycol) succinimidyl ester, the obtained PEGylated insulin was investigated by gel filtration chromatography, indicating successful attachment of the hydrophilic polymer chains. Application of an aqueous PEGylation scheme opens the door to the immediate investigation of various growth factors in cell culture, allowing for direct assessment of biological activity after forming the polymer-protein constructs with regard to later immobilization on surfaces.

Mild Synthesis of Amino‐Poly(ethylene glycol)s. Application to Steric Stabilization of Clays

AbstractThe hydroxyl end groups of poly(ethylene glycol) (PEG) have been transformed easily and quantitatively into amino groups via the Mitsunobu reaction. Phthalimide was alkylated with PEGs and the hydrazinolysis of the resulting phthalimido‐PEGs gave the amino compounds in high yields. Quaternization of the amino groups leads to hydrophilic polymer chains bearing a positive charge on one or two ends, depending on the chosen PEG. Such products can be used to protect sterically, negatively charged particles such as clays.magnified image

Optimized chemical structure of nanoparticles as carriers for oral delivery of salmon calcitonin

Nanoparticles having two kinds of surface hydrophilic polymeric chains were prepared by the free radical copolymerization between styrene and hydrophilic macromonomers terminating in vinylbenzyl groups. Their potential as carriers for oral peptide delivery was investigated using salmon calcitonin (sCT) in rats. After oral administration of mixtures of sCT and nanoparticles, the ionized calcium concentration in blood was measured. The absorption of sCT was significantly enhanced by nanoparticles having poly- N-isopropylacrylamide (PNIPAAm) chains on their surfaces. This enhancement effect was considerably increased by introducing cationic poly-vinylamine (PVAm) groups to the surface of PNIPAAm nanoparticles. The absorption enhancement depended on the ratio of NIPAAm and VAm macromonomers to styrene in the nanoparticle preparation. In contrast, the introduction of nonionic poly-vinylacetamide (PNVA) groups eliminated completely the absorption-enhancing function of PNIPAAm nanoparticles. It was suggested that this disappearance was due to the shielding of PNIPAAm groups by PNVA groups. The enhancement effect of sCT absorption by nanoparticles was greatly dominated by their chemical structure that was closely related to surface characteristics. Optimization of the chemical structure on the basis of the mechanism of the absorption enhancement resulted in the further improvement of sCT absorption.

Behavior of mucoadhesive nanoparticles having hydrophilic polymeric chains in the intestine

The behavior of nanoparticles having surface hydrophilic poly( N-isopropylacrylamide), poly( N-vinylacetamide), poly(vinylamine) or poly(methacrylic acid) chains in the intestine was examined. The permeability of salmon calcitonin (sCT) from the mucosal to serosal side of the everted jejunum was enhanced in the presence of nanoparticles. This enhancement, which correlated with the amount of sCT incorporated in nanoparticles, disappeared completely after removal of the mucous layer. When fluorescein isothiocyanate–dextran (FD-4) was used instead of sCT, its permeability through the everted jejunum with and without mucous layer was not enhanced by any nanoparticles, because FD-4 was not incorporated in nanoparticles at all. These findings indicated that the accumulation of nanoparticles incorporating sCT in the mucous layer resulted in the enhancement of sCT permeability. Nanoparticles with poly( N-isopropylacrylamide) or poly(vinylamine) on their surfaces did not cause any damage to the intestinal mucosa. Also, none of the nanoparticles opened the tight junction of the intestinal membrane. It was concluded that mucoadhesion of nanoparticles incorporating sCT to the gastrointestinal mucosa contributed to the absorption enhancement of sCT.

Polymer of Controlled Chain Length Carrying Hydrophilic Galactose Moieties for Immobilization of DNA Probes

The synthesis and the living cationic polymerization of a new saccharidic monomer namely the 1,2:3,4-di-O-isopropylidene-6-O-(2-vinyloxy ethyl)-D- galactopyranose have been investigated. The monomer structure has been characterized by 1 H and 13 C NMR, elemental analysis and mass spectrometry. It has been polymerized with acetaldehyde diethyl acetal/trimethylsilyl iodide as initiating system in presence of ZnCl 2 as coinitiator. Macromolecules of controlled chain length (from 2 500 g.mol -1 to 7 500 g.mol -1 ) were obtained, bearing protected saccharidic moieties as side-groups, and aldehyde as ω-end-groups which could be turned into amine ω-end-groups. Finally, the saccharidic residues were deprotected in order to perform the binding of DNA probes (oligonucleotides) onto the hydrophilic polymer chains through the anomeric site of the galactose moieties.

Amine-reactive biodegradable diblock copolymers.

A new class of diblock copolymers was synthesized from biodegradable poly(lactic acid) and poly(ethylene glycol)minus signmonoamine. These polymers were activated by covalently attaching linkers such as disuccinimidyl tartrate or disuccinimidyl succinate to the hydrophilic polymer chain. The polymers were characterized by (1)H NMR spectroscopy, (13)C NMR spectroscopy and gel permeation chromatography (GPC). These investigations indicated that the polymers were obtained with the correct composition, in high purities, and the expected molecular weight. By using dyes containing primary amine groups such as 5-aminoeosin as model substrates, it was possible to show that the polymers are able to bind such compounds covalently. The diblock copolymers were developed to suppress unspecific protein adsorption and allow the binding of bioactive molecules by instant surface modification. The polymers are intended to be used for tissue engineering applications where surface immobilized cell adhesion peptides or growth factors are needed to control cell behavior.

Conformation of Polymer Brushes at Aqueous Surfaces Determined with X-ray and Neutron Reflectometry. 2. High-Density Phase Transition of Lipopolyoxazolines

We have investigated the molecular conformations of a lipopolymer with a polyoxazoline headgroup at air/water interfaces as a function of lateral area per molecule with X-ray and neutron reflectometry. The polymer 1,2-dioctadecanyl-sn-glycero-3-poly(2-methyl-2-oxazoline), PMO−(C18)2, forms stable surface monolayers. Pressure/area isotherms around room temperature show a plateau region, indicative of a phase transition whose origin was examined. For data evaluation, a novel approach was used that acts on explicit quasi-molecular ensemble conformations of the polymer [Politsch et al., preceding paper in this issue]. At lower surface pressure, the polymer density distribution exhibits a maximum near the interface, indicative of attractive interaction between the predominantly hydrophilic polymer chains and the hydrophobic surface. Across the plateau region of the isotherm, a change in the volume density distribution of the alkyl chains was observed which is indicative of a partial immersion of the lipid moie...

Kinetics of swelling and shrinking of poly ( N-isopropylacrylamide) hydrogels at different temperatures

The swelling ratio of dried poly( N-isopropylacrylamide) hydrogels in distilled water was kinetically studied at different temperatures. The water content in the gel little increases after 30 min at higher temperatures than 33°C (LCST), while it increases for the initial 30 min with time. Between 25 and 33°C, the water content continues to increase for 8 hours, keeping the higher increase ratio at lower temperature. On the other hand, the hydrogel swollen in distilled water at 4°C starts to shrink after the hydrogel being moved into the distilled water kept at different temperatures between 25 and 40°C. There observed two types of shrinking behavior above and below LCST. In the initial 30 min of the shrinking process of the hydrogel, the water content decreases more obviously at higher temperatures. Over 3 h later, however, the water content kept in the hydrogel little decreases at 40°C, and the decreasing ratio during a unit time is highest at 35°C. At 37°C, the decreasing ratio of the water amount during a unit time gradually decreases with time after 1 h. Therefore, the water content kept in the hydrogel after the shrinking process of the swollen hydrogel for 24 h is lowest at 35°C, while that after the swelling process of dried hydrogel for 24 h is lowest at 37 and 40°C. From these findings, it is considered that there are at least three types of water molecules in the hydrogels, as follows: (i) water molecules adsorbed on the hydrophobic polymer chains in the tight skin phase formed by the shrinkage of the hydrogel at 37 and 40°C; (ii) water molecules movable in the looser polymer network in the skin phase formed around LCST and those adsorbed on the polymer chains; (iii) water molecules connected to each other with hydrogen bonds, adsorbed on the hydrophilic polymer chains, and movable in the polymer matrices.

A highly effective water-soluble polymer-supported catalyst for the two-phase asymmetric hydrogenation: preparation and use of a PEG-bound BINAP ligand

A new type of amphiphilic PEG-bound BINAP ligand was synthesized through polycondensation of 5,5′-diamino BINAP ( 1), polyethylene glycol and terephthalyol chloride in the presence of pyridine. It was proven that ruthenium complex based on the new polymeric ligand was an effective catalyst for the asymmetric hydrogenation of prochiral α,β-unsaturated carboxylic acids in both ethyl acetate/water two-phase and in methanolic solvent systems. The activity and/or enantioselectivity in two-phase systems were observed to be higher than that in ethyl acetate or methanol–water homogeneous systems. The replacement of water with ethylene glycol increased the activity and enantioselectivity. The activity of the new catalyst was shown to be about 30 times higher in the two-phase hydrogenation of 2-(6′-methoxy-2′-naphthyl)-acrylic acid than the Ru(BINAP-4SO 3Na) catalyst without the long hydrophilic polymer chain, which illustrated the importance of the amphiphilic structure of the polymeric ligand.

Investigation of polyacrylamide hydrogels using 1-anilinonaphthalene-8-sulfonate as fluorescent probe

The fluorescent intensity of 1-anilinonaphthalene-8-sulfonate (ANS) has been studied in dioxane–water solutions and in polyacrylamide hydrogels. In dioxane–water solutions both static and dynamic quenching of ANS fluorescence by water molecules occurs. In polyacrylamide hydrogels, whether ionic or not, the fluorescence intensity of ANS is always larger than in dioxane–water solutions for the same water content. This does not result from heterogeneities in hydrogels but from a decrease of the efficiency of both static and dynamic quenching. On the one hand, static quenching is reduced because water molecules close to the hydrophilic polymer chains in the gel are in some way bound to the polymer. On the other hand, dynamic quenching is less efficient because the path length for diffusive transport of water molecules is increased in hydrogels as compared to dioxane–water solutions.

Polycation comb-type copolymer reduces counterion condensation effect to stabilize DNA duplex and triplex formation

We have previously demonstrated that the polycation comb-type copolymer having abundant grafts of hydrophilic polymer chains significantly stabilizes DNA duplexes and triplexes [Maruyama et al., Bioconjugate Chem., 8 (1997) 3, Ferdous et al., Nucleic Acids Res., 26 (1998) 39]. This study was designed to estimate the mechanisms involved in the copolymer-mediated stabilization of DNA duplexes and triplexes. The melting temperatures, T m, of DNA duplex and triplex increased with increasing salt concentration, as well documented by the Poisson–Boltzmann and counterion condensation theories that were originally proposed by Manning [J. Chem. Phys., 51 (1969) 924] and further elaborated by Manning [Biopolymers 11 (1972) 937, Biopolymers. 15 (1976) 2385] and Record [Biopolymers, 14 (1975) 2137–2158, Biopolymers, 15 (1976) 893]. In the presence of the copolymer, however, the T m values of DNA duplexes and triplexes did not show significant change with salt concentration. It was concluded that the copolymer is capable of reducing the counterion condensation effects to stabilize DNA duplexes and triplexes. Strong but exchangeable interaction between the copolymer and DNA is seemingly involved in the stabilization behavior.