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At least 1,207 records · Page 67Linked to original sources

PubMed2000

Effect of porosity and surface hydrophilicity on migration of epithelial tissue over synthetic polymer.

The relative effects of porosity and surface chemistry on the migration of epithelial tissue over the surface of a polymer were determined in vitro. These studies compared nonporous polymers with those having 0.1-microm diameter track-etched pores and were conducted on polycarbonate and polyester. Epithelial tissue migration over the polymer surface was stimulated by the presence of these pores. The surface chemistries of the polymers were modified by deposition of various polymer films using radio frequency gas deposition, giving a range of surfaces that varied in air:water sessile contact angle (SCA) of between 26 and 100 degrees. Tissue migration on the nonporous surfaces was affected by the surface chemistry, being generally linear as a function of the SCA and higher on hydrophilic than on hydrophobic surfaces but reduced if the hydrophilic surface had a mobile chemistry. The effects of the 0.1-microm diameter pores and the surface hydrophilicity were additive with the maximal level of epithelial tissue migration occurring on a porous, hydrophilic polymer surface.

Animals↗

PubMed2000

Characterization of mesogen-jacketed liquid crystalline polymers by matrix-assisted laser desorption/ionization time-of-flight mass spectrometry

For synthetic polymers, a proper sample preparation method is essential for successful characterization by matrix-assisted laser desorption/ionization time-of-flight (MALDI-TOF) mass spectrometry. In this work, six synthetic mesogen-jacketed liquid crystalline polymers (MJLCPs) with different main-chain, spacer and mesogenic units were investigated by MALDI-TOF mass spectrometry. Several factors that affect the analysis of these polymers were examined. These factors include matrices used, cationization salts used, the concentration of polymers, and the ratio of sample to matrix. After testing different conditions, we found a suitable sample preparation method for these six polymers. The number average molecular weight (M(n)), weight average molecular weight (M(w)) and polydispersity (PD) were calculated using data obtained in the linear mode. The end groups of the polymers were proposed using data obtained in reflectron mode. Copyright 2000 John Wiley & Sons, Ltd.

Journal Article↗

PubMed2001

The role of ruthenium and rhenium diimine complexes in conjugated polymers that exhibit interesting opto-electronic properties.

This paper reports the synthesis and opto-electronic properties of different conjugated polymers that contain the diimine complexes of ruthenium or rhenium. Conjugated poly(phenylene vinylene)s that contain aromatic 1,3,4-oxadiazole and 2,2'-bipyridine units on the main chain were synthesized by the palladium catalyzed olefinic coupling reaction. Other types of polymers based on 1,10-phenanthroline bis(2,2-bipyridyl) ruthenium(II) or chlorotricarbonyl rhenium(I) complexes were also synthesized by the same reaction. In general, these polymers exhibit two absorption bands due to the pi - pi transition of the conjugated main chain and the d-pi* metal-to-ligand charge-transfer transition of the metal complex. As a result, the photosensitivity of the polymers beyond 500 nm was enhanced. Charge-carrier mobility measurements showed that the presence of metal complexes could facilitate the charge-transport process, and the enhancement in carrier mobility was dependent on the metal content in the polymer. In addition, we have also demonstrated that the ruthenium complex could act as both photosensitizer and light emitter. Photovoltaic cells were constructed, and they were subjected to irradiation with a xenon arc lamp. Under illumination, the short circuit current and the open circuit voltage were measured to be 0.05 mAcm(-2) and 0.35 V, respectively. The polymers were fabricated into single-layer emitting devices, and light emission was observed when the device was subjected to forward bias. The maximum luminance was determined to be 300 cdm(-2), and the external quantum efficiency was approximately 0.05 to 0.2%. Although the efficiency was relatively low when compared with other devices based on organic materials, we have demonstrated the first examples of using transition metal complexes for both photovoltaic and light-emitting applications.

Journal Article↗

PubMed2006

pi-Conjugated chelating polymers with charged iridium complexes in the backbones: synthesis, characterization, energy transfer, and electrochemical properties.

A series of pi-conjugated chelating polymers with charged iridium (Ir) complexes in the backbones were synthesized by a Suzuki polycondensation reaction, leading to homogeneous polymeric materials that phosphoresce red light. The fluorene and bipyridine (bpy) segments were used as polymer backbones. 5,5'-Dibromobipyridine served as a ligand to form a charged iridium complex monomer with 1-(9'9-dioctylfluorene-2-yl)isoquinoline (Fiq) as the cyclometalated ligand. Chemical and photophysical characterization confirmed that Ir complexes were incorporated into the backbones as one of the repeat units by means of the 5,5'-dibromobipyridine ligand. Chelating polymers showed almost complete energy transfer from the host fluorene segments to the guest Ir complexes in the solid state when the feed ratio was 2 mol %. In the films of the corresponding blend system, however, energy transfer was not complete even when the content of Ir complexes was as high as 16 mol %. Both intra- and intermolecular energy-transfer processes existed in this host-guest system, and the intramolecular energy transfer was a more efficient process. All chelating polymers displayed good thermal stability, redox reversibility, and film formation. These chelating polymers also showed more efficient energy transfer than the corresponding blended system and the mechanism of incorporation of the charged Ir complexes into the pi-conjugated polymer backbones efficiently avoided the intrinsic problems associated with the blend system, thus offering promise in optoelectronic applications.

Journal Article↗

PubMed2006

Noncovalent functionalization and solubilization of carbon nanotubes by using a conjugated Zn-porphyrin polymer.

A highly soluble, conjugated Zn-porphyrin polymer was synthesized and found to strongly interact with the surface of single-walled carbon nanotubes, producing a soluble polymer-nanotube complex. Successful complexation required the addition of trifluoroacetic acid to the solvent (THF). It was found that the complex remained soluble after excess free polymer was removed from solution, and could be centrifuged at high speed with no observable sedimentation. Furthermore, the polymer-nanotube assembly resulted in enhanced planarization and conjugation within the porphyrin polymer, which was manifested in a 127 nm bathochromic shift of the Q-band absorption. Control experiments with the Zn-porphyrin monomer indicated that homogeneous solutions could be prepared by means of sonication, but the monomer-nanotube interactions were significantly weaker, leading to nanotube precipitation within minutes. Atomic force microscopy (AFM) studies indicated that the polymer enables exfoliation of nanotube bundles and is able to "stitch" multiple nanotubes together into a series of long, interconnected strands.

Journal Article↗

PubMed2007

Layer-by-layer deposition of rhenium-containing hyperbranched polymers and fabrication of photovoltaic cells.

Multilayer thin films were prepared by the layer-by-layer (LBL) deposition method using a rhenium-containing hyperbranched polymer and poly[2-(3-thienyl)ethoxy-4-butylsulfonate] (PTEBS). The radii of gyration of the hyperbranched polymer in solutions with different salt concentrations were measured by laser light scattering. A significant decrease in molecular size was observed when sodium trifluoromethanesulfonate was used as the electrolyte. The conditions of preparing the multilayer thin films by LBL deposition were studied. The growth of the multilayer films was monitored by absorption spectroscopy and spectroscopic ellipsometry, and the surface morphologies of the resulting films were studied by atomic force microscopy. When the pH of a PTEBS solution was kept at 6 and in the presence of salt, polymer films with maximum thickness were obtained. The multilayer films were also fabricated into photovoltaic cells and their photocurrent responses were measured upon irradiation with simulated air mass (AM) 1.5 solar light. The open-circuit voltage, short-circuit current, fill factor, and power conversion efficiency of the devices were 1.2 V, 27.1 mu A cm(-2), 0.19, and 6.1x10(-3) %, respectively. The high open-circuit voltage was attributed to the difference in the HOMO level of the PTEBS donor and the LUMO level of the hyperbranched polymer acceptor. A plot of incident photon-to-electron conversion efficiency versus wavelength also suggests that the PTEBS/hyperbranched polymer junction is involved in the photosensitization process, in which a maximum was observed at approximately 420 nm. The relatively high capacitance, determined from the measured photocurrent rise and decay profiles, can be attributed to the presence of large counter anions in the polymer film.

Journal Article↗

PubMedDate not supplied

Molecular sieving of lambda phage DNA in polyacrylamide solutions as a function of the molecular weight of the polymer.

Electrophoresis of lambda phage DNA was carried out in solutions at various concentrations of uncrosslinked polyacrylamide of 0.6, 1, 5 and 9 x 10(6) molecular weight (Mw) with narrow Mw distribution. By inspection of mobilities in the various concentration ranges, it appears that mobilities decrease, and retardation increases, with increasing Mw. The relation between electrophoretic retardation and the Mw of the polymer was also interpreted (i) in the manner previously applied to nonlinear Ferguson plots and compatible with the Ogston model; and (ii) empirically, on the basis of the first derivatives of the functions describing the Ferguson plots at the polymer concentrations used. Interpretation (i) shows that the retardation increases linearly in the order of 0.6, 1, 5 and 9 x 10(6) Mw of polyacrylamide. Interpretation (ii) shows a nonlinear increase of retardation in the Mw range 5 to 9 x 10(6), and a decrease in retardation as Mw is raised from 0.6 to 5.0 x 10(6). Hypothetically, interpretation (ii) can be explained mechanistically by a progressive change, as the polymer size is increased, from a collision with the surface of the polymer fiber to one occurring after permeation in the interior of a random-coiled fiber. Interpretation (i) may fail to detect that change due to the large difference between DNA mobility in solutions of the smallest polymer and the free mobility. DNA peak detection in all of the four size classes of polyacrylamide in solution is limited to relatively narrow ranges of polymer concentration.(ABSTRACT TRUNCATED AT 250 WORDS)

Acrylic Resins↗

PubMedDate not supplied

Advances in DNA electrophoresis in polymer solutions.

DNA electrophoresis in gels and solutions of agarose and polyacrylamide was objectively evaluated with regard to separation efficiency at optimal polymer concentrations. In application to DNA fragments, polyacrylamide gels were superior for separating fragments of less than 7800 bp, and agarose gels are the best choice for larger fragments. Agarose solutions are nearly as good as polyacrylamide gels for small DNA (< 300 bp). Agarose solutions have a higher efficiency than polyacrylamide solutions for DNA of less than 1200 bp. Separation efficiency sharply decreases with increasing length of DNA. Retardation in polyacrylamide solutions was found to depend on polymer length in a biphasic fashion. The choice of resolving polymer concentrations depends on the progressive stretching of DNA in proportion to polymer concentration. The rate of that stretching appears higher in polyacrylmide solution than in gels or in liquid or gelled agarose. Application of polymer solutions to capillary electrophoresis raises further problems concerning agarose plugs, DNA interactions with the polymers, operation at low field strength and long durations as well as detection sensitivity.

Acrylic Resins↗

PubMed1994

Capillary zone electrophoresis of DNA fragments in a novel polymer network: poly(N-acryloylaminoethoxyethanol).

Migration of DNA fragments in the 51 to 21226 bp size range has been investigated by capillary zone electrophoresis in entangled solutions of linear poly(N-acryloylaminoethoxyethanol) from 8 to 16%. Plots of log mobility vs. log size (in base pairs, bp) clearly evidence three different migration regimes: according to Ogston (i.e. as spherical globules) up to 200 bp, reptation without stretching up to 3-4000 bp and reptation with partial stretching for larger fragments. Guidelines on the % polymer to be used for optimum resolution can be obtained from plots of peak spacing (in seconds per base pair) vs. % of polymer in solution and from standard plots of peak resolution vs. % polymer. An optimum linear poly(N-acryloylaminoethoxyethanol) concentration, allowing for good resolution of most fragments, from small to large, is found in the range 10% to 12% polymer (as opposed to conventional polyacrylamide, where a sharp maximum is obtained at 6% polymer). It is hypothesized that in situ polymerization allows for formation of a large distribution of polymer sizes, thus facilitating simultaneous separation of short and long DNA fragments based on the principle that shorter polyacrylamide chains will sieve shorter DNA fragments and vice versa. Due to the fact that the novel monomer is 500 times more resistant to hydrolysis and more hydrophilic than acrylamide, its polymeric solutions allow repeated sample injections (> 35) with minimal absolute standard deviations (of the order of +/- 3%). No carry-over nor sample precipitation at the injection port is experienced with the new matrix composed of poly(N-acryloylaminoethoxyethanol).

Acrylic Resins↗

PubMed1994

Interpenetrating polymer network (IPN) as a permanent joint between the elements of a new type of artificial cornea.

The combination at the interface between two chemically identical polymers was investigated by light and electron (scanning, transmission) microscopy. The polymers constitute elements of a new type of artificial cornea in which the peripheral skirt is made from spongy poly(2-hydroxyethyl methacrylate) (PHEMA) and the central optical zone from homogeneous, transparent PHEMA. Their two-phase combination along the boundary fulfill formally the requirements for an interpenetrating polymer network (IPN). The procedure for the manufacture of prosthesis was described in detail. Thin and ultrathin sections excised from the interface region were investigated using microscopic techniques. Light microscopy allowed the measurement of the diffusion path length of transparent PHEMA into sponge, which was approximately 0.5 mm. Transmission electron microscopy revealed a cellular-like morphology as well as larger segregated zones, which indicated network interpenetration on a molecular level and also a relatively poor miscibility of the two polymers despite their identical chemical structure. The latter was interpreted as a result of the submicroscopic restraints imposed by polymer I (sponge) upon polymer II. This study provides evidence that the interface combination of the prosthetic elements should be regarded as a gradient homo-IPN. This system offers a union between elements much stronger than those previously reported in artificial corneas.

Biocompatible Materials↗

PubMed2004

Effect of composition of interpenetrating polymer network hydrogels based on poly(acrylic acid) and gelatin on tissue response: a quantitative in vivo study.

The local tissue response of the biomaterial is the most important criteria for determination of its biocompatibility. In the present study, full and semi-interpenetrating polymer networks (IPN) based on polyacrylic acid (AAc) and gelatin (Ge) crosslinked with 0.5 mol % N,N'-methylene bisacrylamide (BAm) and 4% glutaraldehyde (GA), respectively, were evaluated for tissue response in rats. IPNs with varying ratios of AAc and Ge were implanted subcutaneously in rats. Gentamicin sulfate (GS)-loaded IPN samples were also studied to evaluate the possible therapeutic use of these polymers. The site of implantation was biopsied and processed for light microscopy (LM) with image analysis for assessment of tissue reaction at 2-, 6-, and 12-week intervals. The tissue reaction was evaluated as a function of composition and time. The degree of neutrophil, lymphocyte and macrophage infiltration, fibrosis, granuloma formation, integration with extracellular matrix, vascular proliferation, and damage of adjacent structures were assessed. Polymers with >66% crosslinked Ge (Gx) showed persistence of acute inflammatory reaction till 3 months, with marked tissue injury and fibrosis. On the other hand, high crosslinked AAc (Ax) content showed chronic inflammatory reaction with high macrophage infiltration. Macrophages took active part in phagocytosis, degradation, and removal of polymers without granuloma formation or significant giant cell reaction. The IPNs with acrylic acid and gelatin in the ratio of 1:1 showed least tissue reaction and thus appeared to be most biocompatible. The majority of the polymers showed integration with extracellular matrix and growth of capillaries in and around the polymer. The heamogram, liver and renal function tests, and histology of vital organs were all normal. GS loading showed no additional local or systemic reaction suggesting the potential usefulness of the hydrogels as carrier for drugs such as GS.

Acrylic Resins↗

PubMedDate not supplied

Dynamics of tumor imaging with Gd-DTPA-polyethylene glycol polymers: dependence on molecular weight.

Macromolecular contrast media offer potential advantages over freely diffusible agents in magnetic resonance (MR) imaging outside the central nervous system. To identify an optimum molecular weight for macromolecular contrast media, the authors studied a novel macromolecular contrast agent, gadolinium diethylenetriaminepentaacetic acid polyethylene glycol (DTPA-PEG), synthesized in seven polymer (average) molecular weights ranging from 10 to 83 kd. Twenty-eight rabbits bearing V2 carcinoma in thighs underwent T1-weighted spin-echo imaging before injection and 5-60 minutes and 24 hours after injection of the Gd-DTPA-PEG polymers or Gd-DTPA at a gadolinium dose of 0.1 mmol/kg. Tumor region-of-interest measurements were obtained at each time point to determine contrast enhancement dynamics. Blood-pool enhancement dynamics were observed for the Gd-DTPA-PEG polymers larger than 20 kd. Polymers smaller than 20 kd displayed dynamics similar to those of the freely diffusible agent Gd-DTPA. Above the 20 kd threshold, tumor enhancement was more rapid for smaller polymers. The authors conclude that the 21.9-kd Gd-DTPA-PEG polymer is best suited for clinical MR imaging.

Animals↗

PubMed1992

Control of drug release with a combination of prodrug and polymer matrix: antitumor activity and release profiles of 2',3'-diacyl-5-fluoro-2'-deoxyuridine from poly(3-hydroxybutyrate) microspheres.

Drug release was controlled by a combination of prodrug and polymer matrix. Prodrugs of 5-fluoro-2'-deoxyuridine with different physicochemical properties were synthesized by esterification with aliphatic acids (propionate, n-butyrate, and n-pentanoate). Microspheres containing these ester prodrugs were prepared with poly(3-hydroxybutyrate) of three molecular weights (65,000, 135,000, and 450,000). The release rates from the spheres depended on both the lipophilicity of the prodrug and the molecular weight of the polymer. Regardless of the polymer, the relative release rates were propionate greater than butyrate greater than pentanoate. The release of butyrate and pentanoate from the spheres consisting of low-molecular-weight polymer (M(r), 65,000) was faster than that from the spheres of higher molecular weight (M(r), 135,000 or 450,000). A single intraperitoneal injection of spheres of the highest molecular weight polymer containing butyrate or pentanoate resulted in higher antitumor effects against P388 leukemia in mice than did free prodrugs given over a period of five consecutive days. The polymer sphere itself showed low toxicity to and good biocompatibility with mice and rats.

Animals↗

PubMed1993

Microencapsulation of drugs with aqueous colloidal polymer dispersions.

Sustained-release polymer particles containing drugs with various solubility characteristics (ibuprofen, theophylline, guaifenesin, and pseudoephedrine HCl) were prepared with colloidal polymer dispersions in a completely aqueous environment as an alternative to conventional microencapsulation techniques, which use organic solvents. Spherical particles were prepared by spraying or dropping dilute sodium alginate solutions (0.67%, w/w) containing the dissolved or dispersed drug and colloidal polymer particles into calcium chloride solutions. The gelled particles, which formed by ionotropic gelation of the polysaccharide with calcium ions, were dried and cured at 60 degrees C to cause fusion of the colloidal polymer particles into a homogeneous matrix system. Actual drug contents close to 50% and encapsulation efficiencies of between 80 and 98% were achieved with all drugs. Guaifenesin and ibuprofen acted as plasticizers for the ethyl cellulose pseudolatex, whereas with theophylline and pseudoephedrine HCl, dibutyl sebacate had to be added as a plasticizer to yield a nondisintegrating polymer matrix. The stirring time before separation of the particles from the gelation medium had to be minimized with the water-soluble drugs to maximize drug loading; however, it was not critical with the water-insoluble drugs. Drug release was a function of the solubility of the drug, drug loading, and the type of polymer dispersion used.

Capsules↗

PubMed1994

A theoretical and experimental study of additive effects of physical aging and antiplasticization on the water permeability of polymer film coatings.

The effects of physical aging and antiplasticization on the water transport properties of glassy cellulose acetate film-coated tablets were investigated. The gradual approach toward thermodynamic equilibrium during physical aging decrease the free volume of the polymers. This decrease in free volume is accompanied by a decrease in the transport mobility, with concomitant changes in those properties of the polymer that depend on it. Antiplasticization arises from an interaction between the polymer and the plasticizer molecules and decreases the molecular mobility of the polymer and plasticizer. This effect was confirmed by mechanical measurements of polymer free films at the same experimental temperature. We have studied the additive effect of aging and antiplasticizing to see if the individual effects would interfere with one another, as might be expected if the same free volume were involved in each. The pronouncedly additive effects of physical aging and antiplasticization on the water permeability can be found in cellulose acetate film-coated tablets that were affected by longer physical aging time and lower plasticizer concentration. A theoretical study suggested that the free volume in the glassy polymer should consist of at least two independent parts, one of which is affected by annealing and the other by antiplasticization.

Cellulose↗

PubMed1995

Effects of polyacrylic polymers on the lumenal proteolysis of peptide drugs in the colon.

The in-vitro effectiveness of polyacrylic acid polymers in inhibiting degradation of insulin, calcitonin, and insulin-like growth factor-I by colonic lumenal contents was determined. Further, the effect of Carbopol 974P, a polyacrylic acid polymer, on colonic absorption of insulin in rats was studied. The results revealed that Carbopol 934P, 971P, and 974P all strongly inhibited microbial proteolytic activities against insulin, calcitonin, and insulin-like growth factor-I. Inhibition by Carbopol polymers was complete or almost complete when the concentration of each polymer in saline or in 50 or 100 mM Tris buffer was 0.4%, where the pH of the medium was lower than 5. The extensive inhibition by these polyacrylic acid polymers seems to correlate with their ability to acidify the incubation medium. Further, in-situ absorption studies showed that Carbopol 974P increased the pharmacological availability of colonic insulin. In summary, Carbopol polymers are useful in minimizing colonic proteolysis of peptide drugs.

Acrylic Resins↗

PubMed2006

Nanoscience of single polymer chains revealed by nanofishing.

The invention of atomic force microscopy (AFM) enabled us to study the statistical properties of single polymer chains by a method called "nanofishing," which stretches a single polymer chain adsorbed on a substrate with its one end by picking it at the other end. A force-extension curve obtained for a single polystyrene chain in a Theta solvent (cyclohexane) shows good agreement with a worm-like chain model and, therefore, gives microscopic information about entropic elasticity. Furthermore, the nanofishing technique can be used for dynamic viscoelastic measurement of single polymer chains. An AFM cantilever is mechanically oscillated at its resonant frequency during the stretching process. This technique enables the estimation of quantitative and simultaneous elongation-dependent changes of stiffness and viscosity of a single chain with the use of a phenomenological model. In this study, the effect of solvent on viscosity in low extension regions reveals that the viscosity is attributed to monomer-solvent friction. Thus, static and dynamic nanofishing techniques are shown to give powerful experimental proofs for several basic questions in polymer physics. The techniques are expected to reveal hidden properties of polymer chains or polymer solutions by any types of macroscopic measurements in the future.

Journal Article↗

PubMed1997

Multiple attachment mechanisms of corneal epithelial cells to a polymer--cells can attach in the absence of exogenous adhesion proteins through a mechanism that requires microtubules.

The initial adhesion of epithelial cells is recognized as a critical determinant in the epithelialization of a polymer. Previously, the attachment of a variety of cell types to a polymer has been shown to be mediated by fibronectin and/or vitronectin that adsorb onto the polymer surface from the serum used to supplement the culture medium. Such an attachment reaction, dependent upon exogenous cell-adhesive proteins, is likely to involve the actin cytoskeleton and integrin receptors on the cell surface. In the current study, we have examined the attachment of recently isolated corneal epithelial cells to tissue culture polystyrene in the absence of such exogenous cell-adhesive proteins. Under these circumstances, there is an alternative mechanism of attachment operative between corneal epithelial cells and the polymer surface which is essentially independent of the adsorption of serum-derived fibronectin and vitronectin. This is an unusual phenomenon not previously observed with other normal cell types. The presence of cycloheximide inhibited this alternative attachment mechanism in corneal epithelial cells, indicating the role of newly synthesized proteins in this reaction. Additionally, we found that cell attachment to the polymer surface in the absence of cell-adhesive proteins was substantially inhibited by the presence of demecolcine, but not by cytochalasin B, thereby demonstrating the involvement of microtubules rather than actin microfilaments in this reaction. In the presence of serum-derived fibronectin and vitronectin, the attachment of corneal epithelial cells to a polymer may involve dual attachment mechanisms.

Actins↗