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At least 1,243 records · Page 69Linked to original sources
PubMed1981

The rheological properties of polyelectrolyte cements. I. polycarboxylates.

The rheological behaviour of six setting carboxylate cements was studied by capillary techniques in the shear rate of 0.65-65 s-1 and the cements were found to behave as power law fluids. All cements became dilatant as setting progressed and the kinetics of apparent viscosity increase, were found to follow an exponential function of time, exp (mt), with m congruent to 0.5.

Acrylic Resins↗
PubMed1981

The rheological properties of polyelectrolyte cements II. Glass ionomers.

The rheological properties of two glass ionomer cements, ASPA and Fuji have been investigated. The viscosities of the liquid components of these systems have been found to be Newtonian up to a shear rate of 140 s-1 with values of 0.80 N m-2 s for ASPA and 1.8 N m-2 for Fuji. Capillary viscometry techniques have been employed to study the rheological changes accompanying setting. Both cements appear to behave as power law fluids, becoming progressively dilatant as setting proceeds. The apparent viscosities of the two systems are approximately equivalent displaying values of the order of 50 N m-2 s, at a shear rate of unity shortly after mixing.

Chemical Phenomena↗
PubMed1999

Development of cellulose sulfate-based polyelectrolyte complex microcapsules for medical applications.

Microencapsulation, as a tool for immunoisolation for allogenic or xenogenic implants, is a rapidly growing field. However most of the approaches are based on alginate/polylysine capsules, despite this system's obvious disadvantages such as its pyrogenicity. Here we report a different encapsulation system based on sodium cellulose sulfate and polydiallyldimethyl ammonium chloride for the encapsulation of mammalian cells. We have characterized this system regarding capsule formation, strength and size of the capsules as well as viability of the cells after encapsulation. In addition, we demonstrate the efficacy of these capsules as a "microfactory" in vitro and in vivo. Using encapsulated hybridoma cells we were able to demonstrate long-term release of antibodies up to four months in vivo. In another application we could show the therapeutic relevance of encapsulated genetically modified cells as an in vivo activation center for cytostatic drugs during tumor therapy.

Alginates↗
PubMed1992

The polyelectrolyte properties of elastin.

The charge structure and ionic interactions of elastin prepared from the pig thoracic aorta by acid, alkali, or CNBr extraction have been investigated by potentiometric titration and radiotracer techniques. The number of charged groups was consistent with the amino acid composition, comparable to elastin from other sources and insensitive to the method of preparation. The enthalpies of ionization of the basic groups were comparable for those previously found for proteins but those of the acidic groups were higher. Ionic interactions were predominantly electrostatic although a strong affinity for chloride ions was noted. Changes in ionic interactions as the elastin was stretched had a similar effect to an increase in the apparent fixed charge density of the tissue. Mechanical strain altered the protonation of the elastin and the pK of the carboxyl groups. Conversely, the conformation of the elastin network varied with ionic strength and pH, being particularly sensitive to the degree of ionization of the more basic groups and with the ionic strength and anion composition of the medium. We speculate that strain induced changes in the conformation of elastin altering its reactivity towards lipids, ions or matrix macromolecules or changes in its mechanical properties resulting from changes in its ionic environment may be of physiological or pathological importance.

Animals↗
PubMed1998

Ultrathin films of a polyelectrolyte with layered architecture

Posttransfer modification of preformed Langmuir-Blodgett films of poly(tert-butyl methacrylate) and poly(tert-butyl acrylate) by gaseous hydrochloric acid yields films with layered architecture of poly(methacrylic acid) and poly(acrylic acid), respectively. X-ray reflectivity and infrared spectroscopy confirm monolayer by monolayer transfer of the source polymers and their transformation to acid multilayer assemblies with retention of low surface roughnesses. The incorporation of cross-linking groups into the system offers the possibility for further chemical modification to produce ultrathin films of model networks desirable for bioadsorption studies and as hydrophilic spacing layers for tethered membranes.

Journal Article↗
PubMed1972

Polyelectrolyte flocculation as an aid to recovery of enteroviruses from oysters.

A simple and rapid method for recovering enteroviruses from oysters is described. A polycation sewage flocculant promoted cohesion of oyster solids and thereby aided separation of these from the viruses. Recovery of 80 to 100% of experimentally inoculated virus was achieved, and the suspension or extract obtained could be inoculated directly into tissue cultures or concentrated first for greater sensitivity.

Antibodies↗
PubMed1974

Polyelectrolyte nature of bacterial teichoic acids.

Several physicochemical properties of the teichoic acid of Bacillus subtilis 168 have been determined. The teichoic acid partial specific volume was found to be 0.57 ml/g. The apparent weight-average molecular weight of the polymer was 24,800. Sedimentation was strongly dependent on solvent. The sedimentation coefficient of the teichoic acid was found to have a value of s(20.w) (0) = 1.90S. In dilute buffers and distilled water, the teichoic acid possessed a rigid rod or extended conformation. Salts induced a loss of secondary structure in the polymer, resulting in a random coil configuration. Salt-induced structural changes in the teichoic acid were determined by viscosities, ultraviolet difference spectra, and inhibition of precipitation with concanavalin A. Divalent cations such as Mg(2+) had little effect on the teichoic acid structure. The salt-induced structural changes were reversible, as evidenced by return of the original properties upon dialysis of the teichoic acid against water. Sodium chloride inhibited the adsorption of bacteriophage ø25 to B. subtilis cell walls. Teichoic acid conformation may have a significant influence on the physiology of bacteria.

Adsorption↗
PubMed2004

Variational theory for a single polyelectrolyte chain revisited.

We reconsider the electrostatic contribution to the persistence length, le, of a single, infinitely long-charged polymer in the presence of screening. A Gaussian variational method is employed, taking le as the only variational parameter. For weakly charged and flexible chains, crumpling occurs at small length scales because conformational fluctuations overcome electrostatic repulsion. The electrostatic persistence length depends on the square of the screening length, le approximately kappa(-2), as first argued by Khokhlov and Khachaturian by applying the Odijk-Skolnick-Fixman (OSF) theory to a string of crumpled blobs. We compare our approach to previous theoretical works (including variational formulations) and show that the result le approximately kappa(-2), found by several authors comes from the improper use of a cutoff at small length scales. For highly charged and stiff chains, crumpling does not occur; here we recover the OSF result and validate the perturbative calculation for slightly bent rods.

Journal Article↗
PubMed2006

Spontaneous condensation in DNA-polystyrene- b-poly(l-lysine) polyelectrolyte block copolymer mixtures.

We investigated the condensation of calf thymus DNA by amphiphilic polystyrene(m)-b-poly(l-lysine)(n) block copolymers ( PS(m)-b- PLys(n), m, n = degree of polymerization), using small-angle X-ray scattering, polarized optical microscopy and laser scanning confocal microscopy. Microscopy studies showed that the DNA condenses in the form of fibrillar precipitates, with an irregular structure, due to electrostatic interactions between PLys and DNA. This is not modified by the presence of hydrophobic PS block. Scattering experiments show that the structure of the polyplexes corresponds to a local order of DNA rods which becomes more compact upon increasing n. It can be concluded that for DNA/ PS(m)-b- PLys(n) polyplexes, the balance between the PLys block length and the excess charge in the system plays an essential role in the formation of a liquid crystalline phase.

Binding Sites↗