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At least 649 records · Page 36Linked to original sources
PubMed1993

Polyvinyl alcohol plasma deposited nylon 4 membrane for hemodialysis.

Polyvinyl alcohol (PVA) is a hydrophilic and blood compatible material, but it is easily hydrolyzed in aqueous solution. Various methods, including chemical crosslinking and gamma-ray irradiation, have been investigated by many researchers for overcoming the instability of PVA in aqueous solution. This study suggests a new hemodialysis membrane, which is prepared by plasma depositing vinylacetate (VAc) onto annealled nylon 4 membrane, followed by hydrolysis treatment. This improves the blood compatibility of nylon 4 and overcomes the hydrolysis problem of PVA. In addition to conventional plasma deposition, the plasma initiated interpenetrating network (IPN) method is also investigated. The new hemodialysis membranes prepared by both conventional plasma deposited VAc onto nylon 4 (PPVA/N4) and IPN polymer of plasma initiated VAc onto nylon 4 (PIPVA/N4 IPN) show significant improvement in blood compatibility. However, the solute permeabilities of PIPVA/N4 IPN membranes are higher than those of PPVA/N4 membranes. The permeabilities of NaCl, vitamin B12, and albumin for membranes prepared by IPN at 80 W, 30 sec plasma deposited conditions, i.e., the optimized conditions, are 3.614, 0.070, and 0.000 x 10(-5) cm2/min, respectively. The mole ratio of adsorbed fibrinogen to adsorbed albumin (the mole ratio F/A) for this membrane is 0.20, and it also shows excellent blood compatibility in this study.

Biocompatible Materials↗
PubMed2003

Electrochemical deposition of hydroxyapatite with vinyl acetate on titanium implants.

A novel approach to electrochemical processing of hydroxyapatite (HA) coating was explored. Vinyl acetate was added in the electrolytes of calcium and phosphorous in order to improve the adhesion between HA coating and titanium substrate. X-ray powder diffractometer (XRD) spectra indicated that the vinyl acetate did not interfere with the deposition of HA on the surface of titanium cathodes. X-ray photoelectron spectroscopy (XPS) and scanning electron microscope (SEM) results revealed that both vinyl acetate and HA were deposited on the titanium cathodes. The vinyl acetate changed the HA crystalline morphology in the deposition layer. The shape and growth direction of the HA crystals in the coating with vinyl acetate differed from those of HA deposition along. The addition of vinyl acetate increased the coating strength considerably, even though further improvement is needed for clinical applications. Moreover, a preliminary study of the bioactivity showed that osteoblastic cells exhibited higher cell proliferation potential on the HA/vinyl acetate coating than on that of pure HA.

Adhesiveness↗
PubMed2004

Effect of chemical structure and composition of the resin phase on mechanical strength and vinyl conversion of amorphous calcium phosphate-based composites.

The mechanical properties of recently developed bioactive, antidemineralizing/remineralizing, amorphous calcium phosphate (ACP)-based composites need improvement. The objective of this study was to elucidate the effect of structure and composition of resins on the biaxial flexure strength (BFS) and the degree of conversion (DC) of composites attained after photo-polymerization. Two series of 2,2-bis[p-(2'-hydroxy-3'-methacryloxypropoxy)phenyl]propane (Bis-GMA)/triethylene glycol dimethacrylate (TEGDMA)/X (X being a neutral or acidic comonomer) ternary resins were prepared and mixed with a mass fraction of 40% of zirconia-hybridized ACP. Both unfilled copolymers and their composites were evaluated for BFS (dry and wet specimens after 2 weeks of immersion in buffered saline) and for DC (after 24 h at 23 degrees C). It was found that for the neutral X monomers, no correlation existed between the hydrophobic/hydrophilic character of the X monomer and the BFS values of the immersed composites. A flexible monomethacrylate yielded copolymers and composites with the highest DC. For the resins utilizing the acidic comonomers, methacrylic acid and mono-4-(methacryloyloxy) ethyltrimellitate (4MET), dry composites with improved BFS values were obtained. 4MET composites exhibited the least loss of strength of all the ternary resin ACP materials. The effect of acidic X on DC was most pronounced for maleic acid copolymers.

Biocompatible Materials↗
PubMed1992

The use of modified divinylbenzene-polystyrene resins in the separation of fermentation products. A case study utilizing amino acids and a dipeptide.

The adsorption of phenylalanine, aspartic acid, asparagine and aspartame from phosphate-buffered aqueous solutions with modified divinyl-benzene-polystyrene resins has been investigated using high pressure liquid chromatography (HPLC). The pH studied was 2.8, the temperature range was 293-313 K and the ionic strength was maintained at 1.0 mol dm-3. Over the range of variables investigated, the adsorption isotherms are linear and may be characterized by temperature and pH-dependent apparent adsorption equilibrium constants, characteristic of the resin-adsorbate system. By studying the dependence on temperature of this adsorption constant, heats of adsorption and entropy of adsorption have been estimated. In terms of the heat liberated on adsorption, the amino acids and a dipeptide can be ranked thus: aspartame > phenylalanine > aspartic acid > asparagine.

Adsorption↗
PubMed2005

Characterization of physico-mechanical properties of indomethacin and polymers to assess their suitability for hot-melt extrusion processs as a means to manufacture solid dispersion/solution.

The objective of the study was to characterize the physical and viscoelastic properties of binary mixtures of drug and selected polymers to assess their suitability for use in the hot-melt extrusion (HME) process as a means to improve solubility by manufacturing either solid dispersion or solid solution. Indomethacin (INM) was selected as a model drug. Based on comparable solubility parameters, the selected polymers were Eudragit EPO (EPO), polyvinylpyrrolidone/vinyl acetate copolymer (PVP-VA), polyvinylpyrrolidone K30 (PVPK30), and poloxamer 188 (P188). The various drug and polymer systems were characterized for thermal and rheological properties as a function of drug concentration to provide an insight into miscibility and processibility of these systems. From the thermal analysis studies, a single T(g) was observed for the binary mixtures of INM/EPO, INM/PVP-VA, and INM/PVPK30, indicating miscibility of drug and polymer in the given ratios. In the case of mixtures of INM/P188, two melting endotherms were observed with decreasing drug melting point as a function of polymer concentration indicating partial miscibility of drug in polymer. As part of the rheological evaluation, zero rate viscosity (eta(o)) and activation energy (E(a)) was determined for the various systems using torque rheometer at varying shear rates and temperatures. The eta(o) for binary mixtures of drug and EPO, PVP-VA and PVPK30 were found to be significantly lower as compared to pure polymer, indicating disruption of the polymer structure due to miscibility of the drug. On the other hand, INM/P188 mixtures showed a higher eta(o) compared to pure polymer indicating partial miscibility of drug and polymer. With respect to E(a), the mixtures of INM/EPO showed an increase in E(a) with increasing drug concentration, suggesting antiplasticization effect of the drug. These findings corroborate the thermal analysis results showing increase T(g) for the various binary mixtures. The mixtures of INM/PVP-VA showed a decrease in the E(a) with the increasing drug concentration suggesting a plasticization effect of the drug. The understanding of thermal and rheological properties of the various drug/polymer mixtures help established the processing conditions for hotmelt extrusion (such as extrusion temperatures and motor load) as well as provided insight into the properties of the final extrudates. Using the actual hot-melt processing, a model was developed correlating the zero rate viscosity to the motor load determined by rheological evaluation.

Acrylates↗
PubMed2007

Impact of antinucleants on transdermal delivery of testosterone from a spray.

The goal was to explore whether the incorporation of antinucleant polymers into a testosterone spray formulation could stabilize a putative supersaturated state and improve the delivery of the drug across the skin. Several antinucleants were screened using differential scanning calorimetry (DSC) and two candidates showed particular promise: a cyclodextrin derivative (RAMEB) and a vinylpyrrolidone/vinyl acetate copolymer (Kollidon VA64). These agents also improved significantly the long-term stability of saturated solutions of the drug. Further, using the method of mixed cosolvents, it was possible to create, in the presence of 5% w/v antinucleant polymer, supersaturated ethanol/propylene glycol/water (4:1:1 v/v) solutions of the drug with degrees of saturation between 1.4 and 2.6; however, these metastable systems existed only transiently under carefully controlled conditions and had reverted back to equilibrium solubilities of the drug within 6 h. When the same solutions were administered to hairless rat skin in vitro from mechanical sprays, no improvement in testosterone delivery, relative to a nonstabilized control, was observed. It appears, therefore, that the in situ crystallization process of the drug is more complex and incompletely understood (and cannot be predicted from DSC experiments). The complicated evaporation/volatilization process, which takes place when a spray is pulverized, requires better characterization before the use of supersaturation for testosterone delivery can be optimized.

Administration, Cutaneous↗
PubMed1976

Vinyl acetate casts of emphysematous rat lungs.

Emphysema was induced in rats by chronic exposure to a papain aerosol according to established methods. The emphysematous changes were evaluated by previously described histological and biochemical parameters and by a new method employing infiltration of the lungs with vinyl acetate to make casts of the air spaces of the pulmonary tree. The weights and gross and microscopic appearance of the casts demonstrated the emphysematous changes in lungs of the papain-treated rats. Vinyl acetate casting may offer a new and useful tool in evaluating experimental induction of emphysema in rats.

Acetates↗
PubMed1990

Computer automated structure evaluation of antifungal 1-vinylimidazoles, 1,2-disubstituted propenones, and azolylpropanolones.

The Computer Automated Structure Evaluation (CASE) program has been applied to a series of 1-vinylimidazoles, 1,2-disubstituted propenones, and azolylpropanolones exhibiting in vitro antifungal properties. Relevant molecular fragments were obtained for activity against the fungal strains Candida albicans, Aspergillus fumigatus, and Trichophyton asteroides. Fragments were utilized as descriptors to derive quantitative structure-activity relationships (QSAR) within each respective biological endpoint. A high degree of correlation was observed between fragments derived from C. albicans and A. fumigatus. The relevant activating and inactivating fragments from each of the respective biological endpoints analyzed are discussed.

Alkenes↗
PubMed2006

One-pot synthesis of polysaccharide 3,5-dimethylphenylcarbamates having a random vinyl group for immobilization on silica gel as chiral stationary phases.

Different kinds of vinyl groups were randomly introduced onto the glucose units of cellulose 3,5-dimethylphenylcarbamates by a one-pot method using the bifunctional reagents dec-1-ene-10-isocyanate, 2-isocyanatoethyl methacrylate, and methacryloyl chloride. The chiral recognition properties of the prepared derivatives were then evaluated by coating and immobilizing them on silica gel as HPLC packing material. Immobilization was carried out by radical copolymerization with a vinyl comonomer, 1,5-hexadiene, in toluene at 80 degrees C. The effects of the structures and content of the vinyl groups on the immobilization and on enantioseparations were investigated. This one-pot method was also extended to the synthesis of amylose 3,5-dimethylphenylcarbamates having a random vinyl group. Comparisons of the chiral resolution powers of our laboratory-made packing materials and the newly commercialized Chiralpak IA with immobilized amylose 3,5-dimethylphenylcarbamate and Chiralpak IB with immobilized cellulose 3,5-dimethylphenylcarbamate are discussed.

Amylose↗
PubMed2006

Vinyl polymers as non-viral gene delivery carriers: current status and prospects.

Since the first application of polymers as non-viral gene delivery systems in 1965 by Vaheri and Pagano using functionalised dextran (A. Vaheri and J. S. Pagano, "Infectious poliovirus RNA: a sensitive method of assay", Virology 1965, 27, 434-6), a large number of different polymers have been developed, studied and compared for application as DNA carriers. Vinyl-based polymers are one type of polymers that have gained considerable interest. The interest in developing this particular type of polymer is partly related to the straightforward way in which large amounts of these polymers can be prepared by radical (co)polymerisation. This opens up a path for establishing a wide range of structure-property relations using polymer libraries. The present review aims to give an overview of past and ongoing research using vinyl-based gene delivery systems. The application of cationic, neutral and zwitterionic polymers as DNA carriers is summarised and discussed. [structure: see text] Chemical structure of DEAE-functionalised dextran.

Animals↗
PubMed2006

Vinyl sulfones: synthetic preparations and medicinal chemistry applications.

Vinyl sulfones have long been known for their synthetic utility in organic chemistry, easily participating in 1,4-addition reactions and cycloaddition reactions. This functional group has also recently been shown to potently inhibit a variety of enzymatic processes providing unique properties for drug design and medicinal chemistry. This review includes traditional methods used for the synthesis of vinyl sulfones, but focuses mainly on newer reactions applied to vinyl sulfones, including olefin metathesis, conjugate reduction, asymmetric dihydroxylation (AD), and the use of vinyl sulfones to arrive at highly functionalized targets, all illustrating the rich and versatile chemistry this group can efficiently perform. In addition, geminal disulfones are discussed with respect to their formation, reactions, and medicinal applications of this underutilized functional group.

Chemistry, Pharmaceutical↗
PubMed2003

Proton transfer reaction ion trap mass spectrometer.

Proton transfer reaction mass spectrometry is a relatively new field that has attracted a great deal of interest in the last few years. This technique uses H(3)O(+) as a chemical ionization (CI) reagent to measure volatile organic compounds (VOCs) in the parts per billion by volume (ppbv) to parts per trillion by volume (pptv) range. Mass spectra acquired with a proton transfer reaction mass spectrometer (PTR-MS) are simple because proton transfer chemical ionization is "soft" and results in little or no fragmentation. Unfortunately, peak identification can still be difficult due to isobaric interferences. A possible solution to this problem is to couple the PTR drift tube to an ion trap mass spectrometer (ITMS). The use of an ITMS is appealing because of its ability to perform MS/MS and possibly distinguish between isomers and other isobars. Additionally, the ITMS duty cycle is much higher than that of a linear quadrupole so faster data acquisition rates are possible that will allow for detection of multiple compounds. Here we present the first results from a proton transfer reaction ion trap mass spectrometer (PTR-ITMS). The aim of this study was to investigate ion injection and storage efficiency of a simple prototype instrument in order to estimate possible detection limits of a second-generation instrument. Using this prototype a detection limit of 100 ppbv was demonstrated. Modifications are suggested that will enable further reduction in detection limits to the low-ppbv to high-pptv range. Furthermore, the applicability of MS/MS in differentiating between isobaric species was determined. MS/MS spectra of the isobaric compounds methyl vinyl ketone (MVK) and methacrolein (MACR) are presented and show fragments of different mass making differentiation possible, even when a mixture of both species is present in the same sample. However, MS/MS spectra of acetone and propanal produce fragments with the same molecular masses but with different intensity ratios. This allows quantitative distinction only if one species is predominant. Fragmentation mechanisms are proposed to explain the results.

Journal Article↗
PubMed1978

Congenital central nervous system malformations and vinyl chloride monomer exposure: a community study.

Incidence rates for central nervous system (CNS) malformations in infants born to residents of Kanawha County, West Virginia, 1970-1974, were significantly higher than comparable United States rates during those years. Since Kanawha County contains a polyvinyl chloride (PVC) polymerization plant, a case-control study was conducted on the possible relationship between the occurrence of CNS defects and parental occupational or residential exposure to vinyl chloride monomer emissions from this plant. No relationship with parental occupation was found. While a tendency was noted for residences of case families to be located in an area northeast of the plant, this observation did not entirely correlate with existing data on local patterns of wind direction and air pollution.

Abnormalities, Drug-Induced↗