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Query: UMLS:C0267964 (PAA)
 2,561 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

In this work we describe experiments designed to understand the human platelet adhesion to human umbilical vein endothelial cells (HUVECs) cultured on various kinds of chemically cross-linked anionic hydrogels, which were synthesized by radical polymerization. HUVECs could proliferate to sub-confluent or confluent on poly(acrylic acid) (PAA), poly(2-acrylamido-2-methyl-propane sulfonic acid sodium salt) (PNaAMPS), and poly(sodium p-styrene sulfonate) (PNaSS) gels. The proliferation behavior was not sensitive to the cross-linker concentration of the gels. However, the platelet adhesion on the HUVECs cultured on these gels showed different behavior, as revealed by human platelet adhesion test in static conditions. Only a few platelets adhered on the HUVEC sheets cultured on PNaAMPS gels with 4 and 10mol% cross-linker concentrations, and completely no platelet adhered on the HUVEC sheets cultured on PNaSS gels with 4 and 10mol% cross-linker concentrations. On the other hand, a large number of platelets adhered on the HUVECs cultured on PAA gels with 1, 2mol% cross-linker concentrations and PNaAMPS gel with 2mol% cross-linker concentration. Furthermore, the study showed that promote of the glycocalyx of HUVECs with transforming growth factor-beta(1) (TGF-beta(1)) decreased platelet adhesion, and degrade the glycocalyx with heparinase I increased platelet adhesion. The results suggested that the glycocalyx of cultured HUVECs modulates platelet compatibility, and the amount of glycocalyx secreted by HUVECs dependents on the chemical structure and cross-linker concentration of gel scaffolds. This result should be applied to make the hybrid artificial blood vessel composes of gels and endothelial cells with high platelet compatibility.
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PMID:Platelet adhesion to human umbilical vein endothelial cells cultured on anionic hydrogel scaffolds. 1718 48

Binary brushes constituted from two incompatible polymers can be used in the form of ultrathin polymeric layers as a versatile tool for surface engineering to tune physicochemical surface characteristics such as wettability, surface charge, chemical composition, and morphology and furthermore to create responsive surface properties. Mixed brushes of oppositely charged weak polyelectrolytes represent a special case of responding surfaces that are sensitive to changes in the pH value of the aqueous environment and therefore represent interesting tools for biosurface engineering. The polyelectrolyte brushes used for this study were composed of two oppositely charged polyelelctrolytes poly(2-vinylpyridine) (P2VP) and poly(acrylic acid) (PAA). The in-situ properties and surface characteristics such as as surface charge, surface tension, and extent of swelling of these brush layers are functions of the pH value of the surrounding aqueous solution. To test the behavior of the mixed polylelctrolyte brushes in contact with biosystems, protein adsorption experiments with globular model proteins were performed at different pH values and salt concentrations (confinement of counterions) of the buffer solutions. The influence of the pH value, buffer salt concentration, and isoelectric points (IEP) of the brush and protein on the adsorbed amount and the interfacial tension during protein adsorption as well as the protein adsorption mechanism postulated in reference to recently developed theories of protein adsorption on polyelectrolyte brushes is discussed. In the salted regime, protein adsorption was found to be similar to the often-described adsorption at hydrophobic surfaces. However, in the osmotic regime the balance of electrostatic repulsion and a strong entropic driving force, "counterion release", was found to be the main influence on protein adsorption.
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PMID:In-situ investigation of the adsorption of globular model proteins on stimuli-responsive binary polyelectrolyte brushes. 1719 Apr 85

The structural and functional properties of ultrathin (<5 nm) poly(aniline) (PANI) films deposited on indium-tin oxide (ITO) have been investigated using electrochemical and attenuated total reflection (ATR) spectroscopy methods. Layer-by-layer (LbL) self-assembly was used to form films composed of one and two bilayers of PANI and poly(acrylic acid) (PAA), as well as single PANI layers of approximately monolayer thickness. PANI deposited on an ITO electrode is electroactive at neutral pH, both with and without codeposition of an acid dopant such as PAA. In the absence of PAA, it is hypothesized that the acidic surface groups on ITO can function as the counterion. The pH response of PANI single layer, (PANI/PAA)(1), and (PANI/PAA)(2) films was examined using both potentiometry and ATR spectroscopy. Near-Nernstian potentiometric responses over pH 3-9 were observed for all three types of films, consistent with the weak acid-base behavior expected of polymers assembled in a LbL film. The ATR spectral sensitivity to pH increases as the number of layers in the film increases, with the highest sensitivity achieved by monitoring the absorbance at 800 nm (predominately due to the emeraldine salt form) of (PANI/PAA)(2) films. Codeposition of PANI and PAA appears to produce a wide distribution of strengths of acidic and basic sites in the film and thus a large linear dynamic range, up to six pH units. The water contact angle of (PANI/PAA)(2) is approximately 16 degrees, which is considerably more hydrophilic than either the PANI single layer or (PANI/PAA)(1) films ( approximately 40 degrees ). This film is shown to be a suitable substrate for deposition of a planar supported phospholipid bilayer. The supported membrane is highly impermeable to protons, which makes this architecture useful for monitoring transmembrane charge transport.
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PMID:pH-sensing properties of poly(aniline) ultrathin films self-assembled on indium-tin oxide. 1729 39

The effect of varying the fraction of charged monomer units of the polyion in aqueous polyion-oppositely charged surfactant complex salts has been investigated. The complex salts used were based on cetyltrimethylammonium (C16TA+) with three different polymeric counterions: poly(acrylate) (PA-) or poly(acrylate) copolymerized with either dimethylacrylamide (PA-/DAM) or N-isopropylamide (PA-/NIPAM). The charge density of the polyion was varied by either adding poly(acrylic) acid (PAA) to the C16TAPA complex salt (annealed charges) or by varying the fraction of uncharged units in the C16TAPA/DAM or C16TAPA/NIPAM complex salts (quenched charges). The formed phases were studied visually between crossed polarizers and by small angle X-ray scattering (SAXS). Both types of complex salts (annealed and quenched) formed hexagonal phases at high fractions of charged monomers and low water contents. Upon increasing the water content, a cubic phase of the Pm3n space group was found. Upon further addition of water, a miscibility gap with the cubic phase in equilibrium with pure water was found. Decreasing the fraction of charged monomers in the annealed complex salt resulted in an increase of the curvature of the surfactant aggregates. Only at very low (<0.05) fractions of charged monomers did the packing of the surfactant aggregates lose long-range order, and eventually, the miscibility gap disappeared. For the quenched complex salts, the changes upon decreasing the fraction of charged monomers in the polyion were similar, but the loss of long-range order occurred at much higher fractions of charged monomers. The average surfactant aggregation number in the surfactant aggregates, which was similar for the annealed and quenched systems, decreased when the fraction of charged monomers was decreased.
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PMID:Phase behavior of aqueous polyion-surfactant ion complex salts: effects of polyion charge density. 1738 70

We report the influence of polyelectrolyte (PE) multilayer films prepared from poly(styrene sulfonate)-poly(acrylic acid) (PSS-PAA) blends, deposited in alternation with poly(allylamine hydrochloride) (PAH), on film wettability and the adsorption behavior of the protein immunoglobulin G (IgG). Variations in the chemical composition of the PAH/(PSS-PAA) multilayer films, controlled by the PSS/PAA blend ratio in the dipping solutions, were used to systematically control film thickness, surface morphology, surface wettability, and IgG adsorption. Spectroscopic ellipsometry measurements indicate that increasing the PSS content in the blend solutions results in a systematic decrease in film thickness. Increasing the PSS content in the blend solutions also leads to a reduction in film surface roughness (as measured by atomic force microscopy), with a corresponding increase in surface hydrophobicity. Advancing contact angles (theta) range from 7 degrees for PAH/PAA films through to 53 degrees for PAH/PSS films. X-ray photoelectron spectroscopy measurements indicate that the increase in film hydrophobicity is due to an increase in PSS concentration at the film surface. In addition, the influence of added electrolyte in the PE solutions was investigated. Adsorption from PE solutions containing added salt favors PSS adsorption and results in more hydrophobic films. The amount of IgG adsorbed on the multilayer films systematically increased on films assembled from blends with increasing PSS content, suggesting strong interactions between PSS in the multilayer films and IgG. Hence, multilayer films prepared from blended PE solutions can be used to tune film thickness and composition, as well as wetting and protein adsorption characteristics.
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PMID:Polyelectrolyte blend multilayer films: surface morphology, wettability, and protein adsorption characteristics. 1739 99

Nano-sized crystals of calcined hydroxyapatite (HAp) having spherical morphologies were fabricated by calcination at 800 degrees C for 1 h with an anti-sintering agent surrounding the original HAp particles and the agent was subsequently removed by washing after calcination. The original HAp particles were prepared by a modified emulsion system, and surrounded with poly(acrylic acid, calcium salt) (PAA-Ca) by utilizing a precipitation reaction between calcium hydroxide and poly(acrylic acid) adsorbed on the HAp particle surfaces in an aqueous medium. In the case of calcination without PAA-Ca, micron-sized particles consisting of sintered polycrystals were mainly observed by scanning electron microscopy, indicating the calcination-induced sintering among the crystals. On the other hand, most of the crystals calcined with the anti-sintering agent were observed as isolated particles, and the mean size of the HAp crystals was around 80 nm. This result indicates that PAA-Ca and its thermally decomposed product, CaO, surrounding the HAp crystals could protect them against calcination-induced sintering during calcination at 800 degrees C. The HAp crystals calcined with PAA-Ca showed high crystallinity, and no other calcium phosphate phases could be detected.
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PMID:Nano-sized ceramic particles of hydroxyapatite calcined with an anti-sintering agent. 1745 Aug 45

The formation of polyelectrolyte complexes (PECs) from oppositely charged linear polyelectrolytes (PELs) was studied using static light scattering at various salt concentrations. The PELs used were poly(allylamine hydro chloride) (PAH) and the two polyanions poly(acrylic acid) (PAA) and poly(methacrylic acid) (PMAA). Physical characteristics such as the radii of gyration, molecular weights, and water contents of the PECs were determined at various molar mixing ratios. Despite relatively small differences in chemical structure between PAA and PMAA, fairly large differences were detected in these physical characteristics. Generally, PECs comprising PMAA were larger and contained more water. Moreover, by using cryogenic transmission electron microscopy, transmission microscopy and atomic force microscopy, shape and structure of the prepared PECs were investigated both in solution and after drying. The PECs were found to be spherical in solution and the shape was retained after freeze-drying. PECs adsorbed on silica surfaces and dried in air at room-temperature still showed a three-dimensional structure. However, the relatively low aspect ratios indicated that the PECs collapsed significantly due to interactions with the silica during adsorption and drying. At intermediate ionic strengths (1-10 mM), stagnation point adsorption reflectometry (SPAR) showed that the adsorption of low charged cationic PAH-PAA PECs on silica surfaces increased if the pH value was increased from pH 5.5 to 7.5.
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PMID:New insights into the structure of polyelectrolyte complexes. 1749 66

Nanostructure changes with the Krafft transition of complexes of poly(acrylicacid) with octadecyltrimethylammonium (PAA-OTA) in the aqueous solutions at various NaCl concentrations (Cs) from 20 to 400 mM, were studied making temperature-scanning small-angle X-ray scattering (SAXS) experiments and differential scanning calorimetric (DSC) measurements. For the PAA-OTA complex in the solution at a higher temperature than 25 degrees C, four SAXS peaks with a spacing ratio of 1:31/2:41/2:71/2, indicating the 2D hexagonal structure, were observed at Cs below 100 mM and two SAXS peaks with a spacing ratio of 1:2, indicating the lamella structure, were observed at Cs above 200 mM. For the complex in the solution at a lower temperature than 22 degrees C, a broad SAXS peak was observed at the scattering vector q = 1.2 nm-1 when the Cs was less than 200 mM but not when Cs was 400 mM. Two peaks with a spacing ratio 1:2, indicating the lamella structure, were also observed for the complex in the solution at 8 degrees C. The DSC data demonstrated that the nanostructure changes were accompanied with the endothermic enthalpy change. On the basis of the experimental results, the salt concentration dependent nanostructures are discussed.
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PMID:Nanostructure changes with Krafft transitions of polyelectrolyte-surfactant complexes in aqueous NaCl solutions. 1755 53

The layer-by-layer deposition of two polyelectrolytes, quaternized poly(dimethylaminoethyl methacrylate chloride) (MADQUAT) and poly(acrylic acid) (PAA) on a silica substrate was investigated using optical reflectometry, as a function of pH (pH 4, 5.5 and 9), ionic strength (10(-3) to 10(-1) M) and type of salt. Attention was given to the successive deposited weights and to the corresponding deposited charge densities within the ten first deposited layers. Results show a change of growth regime between an early stage where the substrate had a dominating influence in the build-up and a second stage where the polymer uptake was ruled essentially by polymer-polymer interactions. The pH was seen to influence the growth via the charge densities of silica (first stage) and PAA (first and second stages). The increase of NaCl concentration induced an increase of the film weight between 10(-3) and 10(-2) M, but the trend was more sophisticated between 10(-2) and 10(-1) M where the polymer uptake increased in the first stage of the growth and decreased in subsequent layers. The film weight increased in accordance with the rank of ions in the Hofmeister series. AFM images revealed a heterogeneous film morphology with bumps and valleys, which was explained by a growth mechanism made of the successive formation and growth of polymer complexes.
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PMID:Early steps in layer-by-layer construction of polyelectrolyte films: the transition from surface/polymer to polymer/polymer determining interactions. 1765 98

Adsorption on ZnO of sodium poly(acrylate) (PAA), sodium poly(styrene sulfonate) (PSS) and a monomer surfactant [hydroxyethylidene diphosphonate (HEDP)] was investigated in suspensions initially equilibrated at pH 7. Results demonstrate interplay in the adsorption mechanism between zinc complexation, salt precipitation, and ZnO dissolution. In the case of PAA, the adsorption isotherm exhibits a maximum attributed to the precipitation of zinc polyacrylate. PSS and HEDP formed high-affinity adsorption isotherms, but the plateau adsorption of HEDP was significantly lower than that of PSS. The adsorption isotherm of each additive is divided into two areas. At low additive concentration (high zinc/additive ratio), the total zinc concentration in the solution decreased and the pH increased upon addition. At a higher additive ratio, zinc concentration and pH increased with the organic concentration. The increase in pH is due to the displacement of hydroxyl ions from the surface and the increase in zinc concentration results from the dissolution of ZnO due to the complexation of zinc ions by the organics. The stability of the ZnO dispersions was investigated by measurement of the particle size distribution after addition of various amounts of polymers. The three additives stabilized the ZnO dispersions efficiently once full surface coverage was reached.
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PMID:Adsorption mechanism and dispersion efficiency of three anionic additives [poly(acrylic acid), poly(styrene sulfonate) and HEDP] on zinc oxide. 1772 Jan 81


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