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At least 1,693 records · Page 94Linked to original sources
PubMed1996

Factors contributing to the temperature rise during polymerization of resin-modified glass-ionomer cements.

Part of the setting reaction of a resin-modified glass-ionomer cement (RMGIC) is a photoinitiated polymerization. As a result of the polymerization exotherm, the temperature of the cement may rise during setting. This study investigated the temperature rise for two liner/base- and two restorative-type RMGICs. The effects of factors such as specimen thickness, exposure time and environment temperature were investigated. The thermal diffusivity of the cements was also evaluated. Temperatures were measured using a thermocouple embedded in the centre of 6-mm diameter specimen discs of 1, 2, or 3 mm thickness. The exposure times used to cure the specimens varied from 15 to 60 s. The test were carried out at either 25 or 37 degrees C. The temperature rises attributable to the polymerization reaction ranged from 11 to 26 degrees C for the liner/base cements and from 8 to 17 degrees C for the restorative cements. Increasing the specimen thickness reduced the temperature rise only when inadequate exposure times were used. Raising the environmental temperature resulted in a smaller temperature rise. The thermal diffusivities were determined from cylindrical specimens. These ranged from 1.9 x 10(-3) to 2.5 x 10(-3) cm2 s-1, the lining cements showing lower values than the restorative materials.

Chemical Phenomena↗
PubMed1997

Action of eugenol as a retarder against polymerization of methyl methacrylate by benzoyl peroxide.

This study was undertaken to examine an effect of eugenol on polymerization of methyl methacrylate (MMA) by benzoyl peroxide (BPO) and 2,2'-azobisisobutyronitrile (AIBN) in the presence of eugenol. The induction period and initial rate of polymerization (IRP) were determined from polymerization curves of MMA using differential scanning calorimetry (DSC). The induction period increased with increasing concentration of eugenol in both BPO and AIBN systems. The IRP decreased as the concentration of eugenol in both BPO and AIBN systems. The IRP decreased as the concentration of eugenol increased. Its decreasing rate in the BPO system was higher than that in the AIBN system. In the BPO system, the IRP was reduced to zero at 0.5 mol% of eugenol. Eugenol in the BPO system was an efficient retarder, although the decrease in IRP was relatively small, below 0.05 mol%. Eugenol was an inhibitor even at high concentration in the AIBN system. The suppressible effect of eugenol appears to be due to the interaction between free radicals from BPO and eugenol.

Benzoyl Peroxide↗
PubMed2003

The problem of allergy in ecotoxicology of polymeric materials.

In the program of initial toxicological test, the estimation of allergenic activity of some names of polymeric compositions, which are used in the polygraphic industry and when painting and decorating dwelling houses and social purpose premises, had been carried out. Most of the investigated compositions have different degrees of allergenicity. In order to unify the works in this field, we suggest the basic circuit of the estimation of allergenicity of polymeric materials, the final stage of which provides for the compiling of register of potentially allergenic polymeric materials.

Allergens↗
PubMed2002

Binding of polymeric IgG to fibronectin in extracellular matrices: an in vitro paradigm for immune-complex deposition.

We have previously shown a biochemical interaction between fibronectin (Fn) and polymeric immunoglobulins (Igs), that we localized to the fourth and fifth N-terminal type I repeats (4F1.5F1) in Fn and the Fc portion of IgG. Therefore, we hypothesized that Fn, as a constituent of the extracellular matrix (ECM) may directly bind circulating immune complexes (ICs) causing their deposition, thereby contributing to the pathogenesis of IC diseases. As an in vitro paradigm to test this idea, we have generated Fn-containing ECMs from varied cells in culture and demonstrated a saturable dose-dependent binding of aggregated (agg) IgG, as a prototype of ICs, as well as the binding of both heat and cold aggregated purified type I cryoglobulins (CGs) to these ECMs. No binding was observed to ECMs (Matrigel) that do not contain Fn. Characteristic of our previous findings, polymeric but not monomeric IgG bound to the acellular Fn-containing ECMs. To further demonstrate the specificity of the interaction and implicate matrix Fn in the binding of aggIgG, complete inhibition of binding of aggIgG to Fn was achieved by blocking Fn on the ECMs with anti-Fn antiserum and by preincubation of the Ig aggregates with anti-human IgG antibodies. By competing the binding interaction with fluid phase Fn and the Ig-binding site on Fn, 4F(1).5F(1), 70% inhibition was obtained. Additional experiments performed with purified CGs show that an identical dose-dependent increase in Fn binding occurred using both preformed and forming cryoprecipitates suggesting that Fn does not confer cryoprecipitation of CGs and that the specific association of Fn with cryoprecipitates probably results from their polymeric configuration. Our results support the notion that Fn, as it exits in expanding ECMs characteristic of glomerulonephropathies and rheumatoid synovial disease, specifically interacts with complexed/polymeric Igs, thereby perpetuating IC deposition and playing a role in the pathogenesis of IC diseases.

Antigen-Antibody Complex↗
PubMed1997

Late events in assembly determine the polymeric structure and biological activity of secretory IgM.

IgM antibodies can be secreted in at least two functional polymeric forms that can be distinguished according to subunit composition. While IgM hexamers comprise six H2L2 monomeric subunits, pentamers contain an additional polypeptide, the J chain. In the presence of high abundance J chain protein, IgM pentamers are preferentially assembled at the expense of hexamers. To determine the mechanism by which J chain regulates the assembly process, we defined the point at which J chain is added to assembling polymers. We found no evidence for the presence of J chain in small IgM assembly intermediates of IgM, suggesting that it was not stably associated with these complexes. However, J chain was found associated with large polymeric IgM complexes exhibiting sedimentation properties of intracellular pentameric structures. These complexes were frequently not completely covalently assembled; however, complete covalent assembly of J chain-containing pentameric complexes did occur prior to their maturation in the Golgi. These data argue that pentameric structures are the substrate for J chain incorporation into assembling IgM and suggest that the incorporation of J chain is thermodynamically favored over the addition of a sixth monomeric subunit into an assembling polymer. We conclude that late events in IgM polymer assembly, specifically the insertion of J chain, the exclusion of an additional monomeric subunit, and the covalent closure of the pentameric IgM molecule, determine the polymeric structure and, consequently, the biological activity of secreted IgM.

Animals↗
PubMed1997

Monovalent and polymeric 5N-thioacetamido sialosides as tightly-bound receptor analogs of influenza viruses.

A possible approach to the development of synthetic inhibitors of influenza virus attachment to host cells is based on the anchoring of the minimum receptor determinant of influenza virus, sialic acid, to a polymeric carrier. In this study, the effect of substitution of oxygen by sulphur in the 5N-acetyl moiety of sialic acid on the binding of monovalent and polymeric sialosides by A and B influenza virus strains was investigated. The polymeric inhibitor with pendant 5N-thioacetylneuraminic acid residues was found to be more broadly active against different virus stains that the one prepared from the Neu5Ac ligand.

Influenza A virus↗
PubMed2002

Calyculin A-induced endothelial cell shape changes are independent of [Ca(2+)](i) elevation and may involve actin polymerization.

Changes in endothelial cell (EC) shape result in inter-EC gap formation and subsequently regulate transendothelial passage. In this work, we investigated the effects of protein phosphorylation (induced by inhibition of protein phosphatases) on EC shape changes. Treatment of bovine pulmonary artery endothelial cells (BPAEC) with calyculin A (100 nM, an inhibitor of protein Ser/Thr phosphatases 1 and 2A) resulted in cell retraction, surface bleb formation and cell rounding. Trypan blue and electrophysiological experiments suggested that the plasma membrane of these rounded cells maintained functional integrity. Calyculin A-induced morphological changes were strongly inhibited by staurosporine, but not affected by specific inhibitors of the myosin light chain (MLC) kinase, protein kinases A, C and G, and tyrosine kinases. The calyculin A effects were not mimicked by phorbol myristate acetate, dibutyryl cAMP, 8-bromo-cGMP or ionomycin. Cytochalasin B (an inhibitor of actin polymerization) almost completely abolished such shape changes while colchicine (an inhibitor of microtubule polymerization) had no inhibitory effect at all. Ca(2+) imaging experiments showed that the morphological changes were not associated with any global or local cytosolic Ca(2+) concentration ([Ca(2+)](i)) elevation. The results suggest that calyculin A unmasked the basal activities of some protein Ser/Thr kinases other than MLC kinase and protein kinases A, C and G; these unknown kinases might cause BPAEC shape changes by a mechanism involving actin polymerization but not [Ca(2+)](i) elevation.

Actins↗
PubMed1999

Carp liver actin: isolation, polymerization and interaction with deoxyribonuclease I (DNase I).

The aim of this study was to isolate and to characterize actin from the carp liver cytosol and to examine its ability to polymerize and interact with bovine pancreatic DNase I. Carp liver actin was isolated by ion-exchange chromatography, followed by gel filtration and a polymerization/depolymerization cycle or by affinity chromatography using DNase I immobilized to agarose. The purified carp liver actin was a cytoplasmic beta-actin isoform as verified by immunoblotting using isotype specific antibodies. Its isoelectric point (pI) was slightly higher than the pI of rabbit skeletal muscle alpha-actin. Polymerization of purified carp liver actin by 2 mM MgCl(2) or CaCl(2) was only obtained after addition of phalloidin or in the presence of 1 M potassium phosphate. Carp liver actin interacted with DNase I leading to the formation of a stable complex with concomitant inhibition of the DNA degrading activity of DNase I and its ability to polymerize. The estimated binding constant (K(b)) of carp liver actin to DNase I was calculated to be 1.85x10(8) M(-1) which is about 5-fold lower than the affinity of rabbit skeletal muscle alpha-actin to DNase I.

Actins↗
PubMed1997

Polymeric controlled delivery for immunization.

Current vaccine technology has limitations; for example, most vaccines require repeat administration for long-term protection, and immunity at mucosal surfaces is difficult to achieve. In animal models, polymeric controlled-release systems provide long-lasting systemic or mucosal immunoprotection, often after a single administration. Polymeric devices that deliver a controlled amount of antibody can provide passive immunity against genital herpes infections in mice; orally administered polymeric-microsphere-based vaccines produce enhanced immune responses in rodents and primates. These new delivery technologies have many desirable features, and so their use in humans could have a substantial impact on worldwide public health.

Animals↗
PubMed2002

Enhanced adjuvantic property of polymerized liposome as compared to a phospholipid liposome.

Liposome, although intensively researched as vaccine or drug delivery vehicle, has been of limited use due to the low and unpredictable long-term stability. In order to overcome such problems, polymerized liposome (PL) that could initiate polymerization under very mild reaction condition was examined and compared to a conventional liposome. The polymerizable lipid, 1,2-bis[12-(lipoyloxy)dodecanoyl]-sn-glycero-3-phosphorylcholine (DLL), was synthesized according to the literature, and 1,2-distearoyl-sn-glycero-3-phosphorylcholine (DSPC) was used as the conventional lipid counterpart. Polymerization of liposome was as easy and convenient as just shaking in pH 7.4 buffer. The protein encapsulation efficiency of DLL was higher than that of DSPC, and its protein release rate was lower. Immunoglobulin G (IgG) activity examined after intraperitoneal injection of antigen encapsulated by either DLL or DSPC showed that ca. 2 times as much antibody was formed by DLL-encapsulated lysozyme compared with DSPC-encapsulated form. The reasons for the superior adjuvantic properties of DLL and its future application as a drug delivery system are briefly discussed.

Adjuvants, Immunologic↗
PubMed1998

Mass transport enhancement by ultrasound in non-degradable polymeric controlled release systems.

In this work, an attempt was made to characterize mass transport enhancement in non-erodible polymeric matrices, caused by ultrasound. It was found that drug release rates from polymeric matrices exposed to ultrasound, can be controlled by modifying parameters like: ultrasound frequency, molecular weight of the incorporated drug and structure of the polymeric matrix (size of pores in the network). It is suggested that the enhancing effect of ultrasound on drug release from non-erodible polymers is due to the contribution of a convective term, generated by cavitation, without any destructive effect on morphology of the polymer. This phenomenon was found to be more pronounced in systems which are mass-transport limited.

Drug Carriers↗
PubMed1998

Incorporation of water-insoluble anticancer drug into polymeric micelles and control of their particle size.

A water-insoluble anticancer drug, KRN 5500 (KRN), was incorporated into polymeric micelles forming from poly(ethylene glycol-poly(amino acid) block copolymers by physical entrapment utilizing hydrophobic interactions between this drug and the poly(amino acid) chain block of the block copolymers. Three block copolymers were examined for this incorporation; poly(ethylene glycol)-poly(beta-benzyl l-aspartate) (PEG-PBLA) and its two derivatives obtained by partial hydrolysis at the beta-benzyl l-aspartate (BLA) units (PEG-P(Asp, BLA)) and by partial cetyl ester substitution at the BLA units (PEG-P(C16, BLA)), respectively. Among these block copolymers, considerable effects of the cetyl esterification were seen on KRN yield and particle size. Considerable differences in the KRN incorporation yield and particle size were also observed between DMF and DMS used as solvent to dissolve KRN and the block copolymers. Sonication was turned out to be an effective method to obtain a polymer micelles fraction in high efficiency, and sonication was considered to work for separating intermicellar associates into dispersed micelles. A KRN incorporation procedure by dialysis using PEG-P(C16, BLA) and DMSO (as solvent) followed by sonication brought about polymeric micelles of 71 nm in weight-average diameter. This shows successful incorporation of a water-insoluble drug into polymeric micelles by optimizing block copolymer structure and incorporation conditions.

Antibiotics, Antineoplastic↗
PubMed1998

Synthesis of bioadhesive poly(acrylic acid) nano- and microparticles using an inverse emulsion polymerization method for the entrapment of hydrophilic drug candidates.

Bioadhesive latices of water-swollen poly(acrylic acid) nano-and microparticles were synthesized using an inverse (W/O) emulsion polymerization method. They are stabilized by a co-emulsifier system consisting of SpanTM 80 and TweenTM 80 dispersed in aliphatic hydrocarbons. The initial polymerization medium contains emulsion droplets and inverse micelles which solubilize a part of the monomer solution. The polymerization is initiated by free radicals, and particle dispersions with a narrow size distribution are obtained. The particle size is dependent on the type of radical initiator used. With water-soluble initiators, for example ammonium persulfate, microparticles were obtained in the size range of 1 to 10 micrometer indicating that these microparticles originate from the emulsion droplets since the droplet sizes of the W/O emulsion show similar distribution. When lipophilic radical initiators, such as azobis-isobutyronitrile, are used, almost exclusively nanoparticles are generated with diameters in the range of 80 to 150 nm, due to the limited solubility of oligomeric poly(acrylic acid) chains in the lipophilic continuous phase. These poly(acrylic acid) micro- and nanoparticles yielded excellent bioadhesive properties in an in-vitro assay and may, therefore, be suitable for the encapsulation of peptides and other hydrophilic drugs.

Acrylic Resins↗
PubMed1997

Polymeric implants for cancer chemotherapy.

Cancer chemotherapy is not always effective. Difficulties in drug delivery to the tumor, drug toxicity to normal tissues, and drug stability in the body contribute to this problem. Polymeric materials provide an alternate means for delivering chemotherapeutic agents. When anticancer drugs are encapsulated in polymers, they can be protected from degradation. Implanted polymeric pellets or injected microspheres localize therapy to specific anatomic sites, providing a continuous sustained release of anticancer drugs while minimizing systemic exposure. In certain cases, polymeric microspheres delivered intravascularly can be targeted to specific organs or tumors. This article reviews the principles of chemotherapy using polymer implants and injectable microspheres, and summarizes recent preclinical and clinical studies of this new technology for treating cancer.

Journal Article↗
PubMed1998

Effect of a resin-modified glass ionomer liner on volumetric polymerization shrinkage of various composites.

OBJECTIVE: The aim of this study was to evaluate the volumetric polymerization shrinkage of a selection of composite resins alone, and in contact with a resin-modified glass ionomer (RMGI) liner. METHODS: Volumetric polymerization shrinkage was measured for five different composite resins by means of the Watts and Cash deflecting disk method. Shrinkage measurements were determined for 300 s for each composite alone, and when placed over pre-cured RMGI liner. Each sample was placed within a brass ring fixed to a glass microscope slide. A linear vertical displacement transducer (LVDT) was brought into contact with a flexible glass coverslip placed over the composite sample. On curing, the contraction of the setting composite sample caused distortion of the coverslip, the resulting deflection being recorded via the LVDT by means of data-logging software. All RMGI samples were prepared at 85% relative humidity (RH) and 35 degrees C. In all cases the composite was light-cured at ambient RH and 35 degrees C. RESULTS: Analysis of the data demonstrated statistically significantly less shrinkage for each composite when cured in contact with the set RMGI liner than when cured alone, at p < 0.001. SIGNIFICANCE: Use of an RMGI liner was found to significantly reduce volumetric polymerization contraction for all the light-curing composite resin restorative materials tested.

Analysis of Variance↗
PubMed2000

Influence of the effector peptide of MARCKS-related protein on actin polymerization: a kinetic analysis

The members of the MARCKS protein family, MARCKS (an acronym for myristoylated alanine-rich C kinase substrate) and MARCKS-related protein (MRP), interact with membranes, protein kinase C, and calmodulin via their effector domain, a highly basic segment composed of 24-25 amino acid residues. This domain is also involved in the interaction between MARCKS/MRP and actin. In this article we show that a peptide corresponding to the effector domain of MRP, the effector peptide, strongly influences the dynamics of actin polymerization. Depending on the stoichiometric ratio of effector peptide to actin the peptide either accelerates or retards the actin polymerization process, which takes place in the presence of near-physiological salt concentrations. A model is developed in which this phenomenon is explained by two independent nucleation processes involving free actin monomers and peptide-bound actin monomers, respectively. As a control, a possible regulatory mechanism has been investigated: we show that calmodulin inhibits the actin polymerizing activity of the MRP effector peptide, thereby validating our model approach.

Journal Article↗
PubMed2000

In vitro polymerization of mussel polyphenolic proteins catalyzed by mushroom tyrosinase.

The in vitro enzymatic polymerization of the polyphenolic protein purified from the mussels Aulacomya ater, Mytilus edulis chilensis and Choromytilus chorus was studied. Mushroom tyrosinase was used to oxidize the dopa residues present in these proteins, and polymerization was monitored by acid-urea polyacrylamide gel electrophoresis. The protein from A. ater polymerized at a faster rate than the other two. Amino acid analysis of the crosslinked protein showed a notable decrease in the content of dopa, but no significant change of other amino acids. This suggests that crosslink formation may be limited to the oxidized dopa derivatives of the protein molecules.

Agaricales↗
PubMed2003

Extracellular polymeric substances responsible for bacterial adhesion onto solid surface.

The influence of extracellular polymeric substances (EPS) on bacterial cell adhesion onto solid surfaces was investigated using 27 heterotrophic bacterial strains isolated from a wastewater treatment reactor. Cell adhesion onto glass beads was carried out by the packed-bed method and the results were discussed in terms of the amount of each EPS component produced and cell surface characteristics such as zeta potential and hydrophobicity. Protein and polysaccharides accounted for 75-89% of the EPS composition, indicating that they are the major EPS components. Among the polysaccharides, the amounts of hexose, hexosamine and ketose were relatively high in EPS-rich strains. For EPS-poor strains, the efficiency of cell adhesion onto glass beads increased as the absolute values of zeta potential decreased, suggesting that electrostatic interaction suppresses cell adhesion efficiency. On the other hand, the amounts of hexose and pentose exhibited good correlations with cell adhesiveness for EPS-rich strains, indicating that polymeric interaction due to the EPS covering on the cell surface promoted cell adhesion. It was concluded that, if the EPS amount is relatively small, cell adhesion onto solid surfaces is inhibited by electrostatic interaction, and if it is relatively large, cell adhesion is enhanced by polymeric interaction.

Bacteria↗