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PubMed2002

Viability, adhesion, and bone phenotype of osteoblast-like cells on polyelectrolyte multilayer films.

The aim of this study was to develop new biocompatible coatings for bone implants by the alternating deposition of oppositely charged polyelectrolytes. Polyelectrolyte films were built up with different terminating layers on which SaOS-2 osteoblast-like cells and human periodontal ligament (PDL) cells were grown. The terminating layer was made of one of the following polyelectrolytes: poly(ethylene imine) (PEI), poly(sodium 4-styrenesulfonate) (PSS), poly(allylamine hydrochloride) (PAH), poly(L-glutamic acid) (PGA), or poly(L-lysine) (PLL). Cell adherence, viability, stability of osteoblast phenotype, and inflammatory response were studied. Adherence and viability were good on all terminating layers except the PEI-terminating layer, which was cytotoxic. Maintenance of osteoblast phenotype marker expression was observed on PSS- and PGA-terminating films for both cell types, whereas downregulation, associated with the induction of Interleukin-8 (IL-8) secretion, was detected on PEI and PAH for both cell types and on PLL for PDL cells. These results suggested a good biocompatibility of PSS- and PGA-ending films for PDL cells and of PSS-, PGA-, and PLL-terminating films for SaOS-2 cells. As a result, polyelectrolyte multilayer films could emerge as new alternatives for implant coatings.

Alkaline Phosphatase↗
PubMed2000

Polyelectrolyte-Induced Aggregation of Microcrystalline Cellulose: Reversibility and Shear Effects.

The polyelectrolyte-induced aggregation of microcrystalline cellulose (MCC) was studied by focused beam reflectance measurement (FBRM) to determine the reversibility of MCC aggregation under high-shear conditions. A correlation was established between the mean chord length output of FBRM probing a high-shear zone with the mean particle size (laser diffraction) of an aliquot extracted from the low-shear bulk mixing zone. Flocs formed by addition of a cationic polyelectrolyte were ruptured by shear forces of mixing and did not reaggregate at low mixing intensities. Flocs formed by addition of both polyelectrolyte and colloidal silica sols were found to reaggregate at low shear quite reversibly following high-shear degradation. The Kolmolgoroff microscale, eta, was determined using a three-compartment mixing model for the FBRM experiments, and the minimum aggregate adhesion forces were calculated to be approximately 3 nN under the experimental mixing conditions. Shear-dependent FBRM studies are also used to estimate the radial dependence of particle adhesion forces within an aggregate. AFM-based surface force measurements between model anionic surfaces (mica and glass beads) showed more reversible adhesion forces in the presence of colloidal silica than with cationic polyelectrolyte only. A descriptive model of the interfaces giving rise to the observed MCC aggregation and adhesion behavior is proposed. Copyright 2000 Academic Press.

Journal Article↗
PubMed2001

Desorption of Low-Charge-Density Polyelectrolyte Adlayers in Aqueous Sodium n-Dodecyl Sulfate Solution.

The association between low-charge-density polyelectrolytes adsorbed onto negatively charged surfaces (mica and silica) and an anionic surfactant, sodium dodecyl sulfate (SDS), has been investigated using surface force measurements, ellipsometry, and XPS. All three techniques show that the polyelectrolyte desorbs when the SDS concentration is high enough. The XPS study indicates that desorption starts at a SDS concentration of ca. 0.1 unit of cmc (8x10(-4) M) and that the desorption proceeds progressively as the SDS concentration is increased. Surface force measurements show that for the polyelectrolyte studied here, having 1% of the segments charged, the desorption proceeds without any swelling of the adsorbed layer. This behavior differs from that observed when polyelectrolytes of greater charge density are used. Copyright 2001 Academic Press.

Journal Article↗
PubMed1980

Modulation of human polymorphonuclear leukocyte chemotaxis by leukocyte extracts, bacterial products, inflammatory exudates, and polyelectrolytes.

Human polymorphonuclear leukocytes (PMN) chemotaxis was tested during exposure to leukocyte and platelet extracts, a variety of polyelectrolytes, inflammatory exudates, and bacterial products. The chemoattractants employed were either zymosan-activated serum or supernatant from autolyzed Staphylococcus aureus. Chemotaxis to both chemoattractants was markedly inhibited by leukocyte and platelet extracts; inflammatory exudates; anionic polyelectrolytes, DNA, hyaluronic acid, liquoid; and by cationic polyelectrolytes, histone, protamine base, protamine sulfate, and myeloperoxidase. Inhibition was also found with elastase, collagenase, pepstatin, and epsilon-amino-caproic acid. Bacterial products, such as lipoteichoic acid and lipopolysaccharides, and extracts of human dental plaque inhibited chemotaxis. No inhibition of chemotaxis was observed with heparin (< 10 micrograms/ml), chondroitin sulfate, phosphatidylethanolamine and phospatidylserine. Indeed, chondroitin sulfate markedly enhanced chemotaxis and antagonized the inhibitory effect of leukocyte or platelet extract. None of the agents employed was toxic to PMN as judged by trypan blue exclusion. These observations suggest that cationic polyelectrolytes and inflammatory exudates influence PMN surfaces, modifying interaction with chemoattractants. Assessment of the role of PMN chemotaxis in host defense against microbial invaders requires evaluation of the response in the presence of agents likely to be present in inflamed tissues.

Chemotaxis, Leukocyte↗
PubMed2005

Controlled release of dexamethasone from microcapsules produced by polyelectrolyte layer-by-layer nanoassembly.

PURPOSE: In an effort to expand the application of core-shell structures fabricated by electrostatic layer-by-layer (LbL) self-assembling for drug delivery, this study reports the controlled release of dexamethasone from microcrystals encapsulated with a polyelectrolyte shell. METHODS: The LbL self-assembly process was used to produce dexamethasone particles encapsulated with up to five double layers formed by alternating the adsorption of positively charged poly(dimethyldiallyl ammonium chloride), negatively charged sodium poly(styrenesulfonate) and depending on the pH positively or negatively charged gelatin A or B onto the surface of the negatively charged dexamethasone particles. The nano-thin shells were characterized by quartz crystal microbalance measurements, microelectrophoresis, microcalorimetry, confocal microscopy, and scanning electron microscopy. In vitro release of dexamethasone from the microcapsules suspended in water or carboxymethylcellulose gels were measured using vertical Franz-type diffusion cells. RESULTS: Sonication of a suspension of negatively charged dexamethasone microcrystals in a solution of PDDA not only reduced aggregation but also reduced the size of the sub-micrometer particles. Assembly of multiple polyelectrolyte layers around these monodispersed cores produced a polyelectrolyte multilayer shell around the drug microcrystals that allowed for controlled release depending on the composition and the number of layers. CONCLUSIONS: Direct surface modification of dexamethasone microcrystals via the LbL process produced monodispersed suspensions with diffusion-controlled sustained drug release via the polyelectrolyte multilayer shell.

Capsules↗
PubMed1977

Limiting laws and counterion condensation in polyelectrolyte solutions. IV. The approach to the limit and the extraordinary stability of the charge fraction.

The limiting laws for polyelectrolyte solutions developed in previous papers of this series have been amply confirmed by measurement. A surprising result of the accumulated data is that the limiting polyelectrolyte charge fraction (fraction of fixed charges uncompensated by condensed counterions in the limit of zero concentration), persists up to concentrations of 0.1 M or even higher. Here the theory is extended in a simple manner to finite concentrations, and the stability of the charge fraction is found to be firmly based on consequences of the long-range polyelectrolyte field. The associated counterions are assumed to translate freely in a region centered on the contour axis of the polyion. The numerical value of the free volume is determined self-consistently from the axial charge density of the polyelectrolyte and is used as the general framework within which specific binding effects are treated.

Calcium Chloride↗
PubMed1991

Viscosity and scattering of very weakly charged polyelectrolytes.

Careful examination of the concentration range where both intrinsic viscosity and light scattering show a polyelectrolyte effect, even for singly charged halato-telechelic ionomers in DMF, together with the neutron scattering results at higher concentration show that weakly charged polymers may be a very useful tool to understand the complicated effects of coulombic interaction in polyelectrolyte solutions. A theoretical framework is given for a systematic study of such weakly charged polymers. The current state of understanding is presented of the properties of solutions of strong polyelectrolytes and of charged rigid particles. Finally it is shown how the transposition to weak polyelectrolytes solutions sheds light on the respective contributions of intra- and intermolecular interactions.

Journal Article↗
PubMed1995

Intrinsic binding effects in mixed counterionic polyelectrolyte systems: extension of condensation theory and comparison with voltammetric data.

Voltammetric speciation data for the potassium/zinc/polymethacrylate system, recently obtained for various charge densities of the polyelectrolyte (Díaz-Cruz et al., Anal. Chim. Acta, 264 (1992) 163) and for different concentrations of monovalent counterions (van den Hoop and van Leeuwen, Anal. Chim. Acta, 273 (1993) 275), are compared with theoretical predictions computed according to a new thermodynamic model developed by Paoletti et al. (Biophys. Chem., 41 (1991) 73) and recently extended by Benegas and Paoletti (in preparation). The model allows: (i) the simultaneous condensation of both monovalent and divalent counterions and (ii) can account for a certain specific affinity of the polyelectrolyte for one type of the counterion over the other. For various charge densities of the polyelectrolyte, experimentally obtained speciation data for the K/Zn/PMA system agree well with theoretical predictions by considering an extra reduced molar affinity energy of -4RT for the Zn(2+) polyelectrolyte binding. The agreement between experimental and theoretical values for the distribution of Zn(2+) ions over the free and bound state becomes less perfect for relatively high concentrations of monovalent counterions.

Journal Article↗
PubMed2005

Endothelial cell--interactions with polyelectrolyte multilayer films.

The seeding of endothelial cells (ECs) on biomaterial surfaces became a major challenge, allowing to improve the non-thrombogenic properties of these surfaces. Recently, the use of polyelectrolyte films has been suggested as a new versatile technique of surface modification aimed at tissue engineering. In this study, we evaluate the adhesion properties of ECs on two types of polyelectrolyte films ending either by poly(D-lysine) (PDL), or poly(allylamine hydrochloride) (PAH), and compared them to data obtained on PDL or PAH monolayers, glass and fibronectin (Fn)-coated glass. ECs seeded on polyelectrolyte films showed a good morphology, allowing ECs to resist physiological shear stress better compared to ECs seeded on glass or Fn. The expression of beta1 integrins was slightly lower on polyelectrolyte films than on control surfaces. However, the phosphorylation of focal adhesion kinase, involved in the transduction of adhesion signal, was not modified on PAH ending films compared to control surfaces; whereas it became lower on PDL ending films. Finally, PAH ending films improve strongly ECs adhesion without disturbing the adhesion mechanism, necessary for the development of a new endothelium. These types of films or similar build-ups could thus be used in the future as a way to modify surfaces for vascular tissue engineering.

Actins↗
PubMed2005

A new radiochemical method to investigate ion binding with polyelectrolytes.

A new method for investigating the binding of ions with polyelectrolytes has been developed. This method, based on Donnan equilibrium and an isotope exchange between the electrolyte and polyelectrolyte, can distinguish territorial from specific binding of ions and can determine fractions of ions bound with the polyion. This method can determine ion binding with polyelectrolytes in a wide range of polyelectrolyte concentrations in multicomponent solutions. The method was tested with radioactive tracers 22Na+, 36Cl- and heparin sodium salt. The influence of the ionic strength on the Na+ binding with heparin was investigated at 310 K. In the limit of zero ionic strength, all Na+ ions are bound to heparin, but only 45% of them are exchangeable. Thus Na+ ions can be bound both territorially and specifically. The fraction of bound ions decreases rapidly with increasing ionic strength. The fraction of the specifically bound ions becomes negligible when the ionic strength exceeds 0.01 M, whereas the fraction of territorially bound ions can be neglected at ionic strengths higher than 0.45 M.

Electrolytes↗
PubMed2004

Flocculation of cellular suspensions by polyelectrolytes.

The regularities, kinetics and mechanisms of flocculation of Escherichia coli and B. thuringiensis var. israelensis (Bti) cellular suspensions by water-soluble polymers-and first of all cationic polyelectrolytes of different charge density and stiffness of the macromolecule chain have been investigated. The effect of the focculant dose and nature, its charge density, the hydrophobic-hydrophilic balance in macromolecule, the suspension concentration, the mode of adding the reagent, the pH and the medium composition on the degree of aggregation of cells both in perikinetic regime and in a flowing system is considered. It has been shown that the main laws of microorganism's suspension flocculation are the same as the laws of flocculation of inorganic dispersions but at the same time the first process is much more complicated because the cell-flocculant interactions are strongly affected by products of cell metabolism, components of the culture liquor, pH value, electrolyte content as well as by the changing structure of the cell surface. On the basis of complex measurements of polymer adsorption and its effect on the electrokinetic potential and degree of aggregation of cells, a conclusion is made that the aggregation of E. coli cells by flexible polyelectrolytes like polydiethylaminoethylmetacrylate and its copolymers with acrylic acid, acrylamide and vinylpyrrolidone is due to charge neutralization, while the flocculation in the presence of rigid-chain chitosan and its derivatives is caused mainly by "bridging" between cells via adsorbed macromolecules. Extraction of cells from suspension can be enhanced by combination of electroflotation and flocculation by cationic polyelectrolytes. It has been shown that dilute suspensions of Bti bacteria can be effectively flocculated and concentrated using different cationic and anionic polyelectrolytes that is necessary for its formulation and use as anti-mosquito agent.

Bacillus thuringiensis↗
PubMed2005

Selective transport of ions and molecules across layer-by-layer assembled membranes of polyelectrolytes, p-sulfonato-calix[n]arenes and Prussian Blue-type complex salts.

Our recent studies in the field of ultrathin membranes prepared upon layer-by-layer assembly of various polyionic compounds such as polyelectrolytes, calixarenes and polyelectrolytes, and metal hexacyanoferrate salts such as Prussian Blue are reviewed. It is demonstrated that polyelectrolyte multilayers can be used (a) as nanofiltration and reverse osmosis membranes suitable for water softening and seawater desalination and (b) as molecular sieves and ion sieves for size-selective separation of neutral and charged aromatic compounds. Furthermore, hybrid membranes of p-sulfonato-calixarenes and cationic polyelectrolytes showing specific host-guest interactions with permeating ions are described. The membranes exhibit high selectivities for distinct metal ions. Finally, it is demonstrated that purely inorganic membranes of Prussian Blue (PB) and analogues can be prepared upon multiple sequential adsorption of transition metal cations and hexacyanoferrate anions. Due to the porous lattice of PB, the membranes are useful as ion filters able to separate cesium from sodium ions, for example.

Calixarenes↗
PubMed2005

Polyelectrolytes as new matrices for secondary ion mass spectrometry.

Significant enhancements in ion yields in time-of-flight secondary ion mass spectrometry (TOF-SIMS) are observed when water-soluble analytes are mixed with a polyelectrolyte, e.g., poly(diallyldimethylammonium chloride) or poly(sodium 4-styrenesulfonate), and then deposited in the layer-by-layer method on a surface. This previously unobserved effect is demonstrated for 5-chloro-8-methoxyquinoline appended diaza-18-crown-6, 5-(2-aminoethoxy)methyl-5-chloro-8-methoxyquinoline appended diaza-18-crown-6, acridine, 9-anthracenecarboxylic acid, and ferrocenecarboxylic acid. By optical ellipsometry film thicknesses range from ca. 5-20 angstroms. X-ray photoelectron spectroscopy shows significantly less analyte in the polyelectrolyte-analyte films than in the neat analytes. However, TOF-SIMS generally shows significant enhancements in ion yields from the polyelectrolyte films compared with either the neat compounds or the compounds solubilized with acid or base and then dried on a surface. These significant enhancements in ion yields also appear to extend to analyte fragments and cationized molecular species. Some enhancement is also observed for dried droplets of analytes mixed with a polyelectrolyte on surfaces.

Complex Mixtures↗
PubMed2005

Adsorption of cationic polyelectrolyte at the solid/liquid interface and dispersion of nanosized silica in water.

Adsorption of cationic polyelectrolyte, a homopolymer of maleimide propyl trimethylammonium chloride (MPTMAC), on silica nanoparticles from aqueous solution was studied. The adsorbed amount of MPTMAC and the adsorption layer thickness from solutions of different pH, polyelectrolyte concentration, salt type, and salt concentration were measured. The adsorbed amount exhibited a maximum as a function of the electrolyte concentration. The onset of the decline in the adsorbed amount depended on the type of counterions. The thickness of the adsorption layer increased gradually with increased of electrolyte concentration and leveled off at high electrolyte concentration. The enhanced adsorption in the presence of Na2SO4 can be explained by the bivalent SO4(2-) causing a better shielding effect. With increasing pH the adsorbed amount of MPTMAC increased, whereas the thickness of an adsorbed layer of MPTMAC decreased. At low polyelectrolyte concentrations unstable silica suspensions were observed from a stability test. At high polyelectrolyte concentrations the higher particle coverage caused electrosteric stabilization of the dispersion. However, further increase in MPTMAC concentration after saturated adsorption would flocculate the dispersed system. At low pH, MPTMAC tending to create a loops or tails conformation stabilized the suspension.

Journal Article↗
PubMed2006

Polyelectrolyte adsorption layers studied by streaming potential and particle deposition.

Adsorption of a cationic polyelectrolyte, polyallylamine hydrochloride (PAH), having a molecular weight of 70,000 on mica was characterized by the streaming potential method and by deposition of negative polystyrene latex particles. Formation of PAH layers was followed by determining the apparent zeta potential of surface zeta as function of bulk PAH concentration. The zeta potential was calculated from the streaming potential measured in the parallel-plate channel formed by two mica plates precovered by the polyelectrolyte. The experimental data were expressed as the dependence of the reduced zeta potential zeta/zeta0 on the PAH coverage Theta(PAH), calculated using the convective diffusion theory. It was found that for the ionic strength of 10(-2) M, the dependence of zeta/zeta0 on Theta(PAH) can be reflected by the theoretical model formulated previously for surfaces covered by colloid particles. The electrokinetic measurements were complemented by particle deposition experiments on PAH-covered mica surfaces. A direct correlation between the polymer coverage and the initial deposition rate of particles, as well as the jamming coverage, was found. For ThetaPAH > 0.3 the initial deposition rate attained the value predicted from the convective diffusion theory for homogeneous surfaces. The initial deposition rates for surfaces modified by PAH were compared with previous experimental and theoretical results obtained for heterogeneous surfaces formed by preadsorption of colloid particles. It was revealed that negative latex deposition occurred at surfaces exhibiting negative apparent zeta potential, which explained the anomalous deposition of particles observed in previous works. It was suggested that the combined electrokinetic and particle deposition methods can be used for detecting adsorbed polyelectrolytes at surfaces for coverage range of a percent. This enables one to measure bulk polyelectrolyte concentrations at the level of 0.05 ppm.

Journal Article↗
PubMed2005

Controlled release from fibers of polyelectrolyte complexes.

Controlled release systems for delicate compounds, such as proteins, often suffer the drawbacks of decreased bioactivity and low encapsulation efficiency. This study introduces the concept of producing drug-loaded fibers from interfacial polyelectrolyte complexation. Chitosan-alginate fibers were produced by pulling from the interface between two polyelectrolyte solutions at room temperature. Depending on the component properties, the release time of encapsulated components from these fibers can range from hours to weeks. Dexamethasone was completely released within 2 h, whereas charged compounds such as BSA, PDGF-bb, and avidin showed sustained release for 3 weeks. The fibers were able to release PDGF-bb in a steady fashion for over 3 weeks without an initial burst. Furthermore, the bioactivity of PDGF-bb was retained over this period. Release kinetics could be controlled by the inclusion of heparin, which contains specific binding sites for various growth factors. By varying the alginate/heparin ratios in the anionic polyelectrolyte solution, the release of PDGF-bb could be significantly altered. In this study, interfacial polyelectrolyte complexation has been demonstrated to be a promising technique for producing drug-loaded fibers with high encapsulation efficiency, sustained release kinetics, and capacity to retain the bioactivity of the encapsulants.

Alginates↗
PubMed2005

Effect of polyelectrolyte conditioning on the enhanced dewatering of activated sludge by application of an electric field during the expression phase.

Activated sludge is known to be poorly dewaterable due to its high surface charge density and the extreme solids compressibility, even after polyelectrolyte conditioning. The application of an electric field during pressure dewatering (PDW) of sludge can enhance the dewaterability by the electroosmosis effect. A comparative study was conducted to investigate the additional effect of an electric field, applied during the expression phase, on the dewatering course of polyelectrolyte conditioned sludge, compared to mere PDW. It was found that the application of an electric field markedly improved the dewatering kinetics for all sludge samples, regardless of the conditioning treatment. Although the conditioning polyelectrolyte characteristics and dose had a major effect on the PDW of sludge, the conditioning history did not have a significant effect on the electroosmotic water transport efficiency during the sludge expression phase. By means of on-line streaming potential measurements and fractionated filtrate electrophoretic mobility measurements, it could be demonstrated that even at high polyelectrolyte doses, leading to positively charged sludge flocs, negative surface charges were still present inside the sludge matrix. During the expression of the sludge cake, when liquid is forced to move through the floc inside pores, these negative surface charges hampered PDW, but enhanced electroosmotic dewatering. Electroosmosis is therefore an appropriate technique to remove the water fraction that is associated with these negative surface charges.

Acrylates↗
PubMed2000

Analysis of potentiometric titrations of heterogeneous natural polyelectrolytes in terms of counterion condensation theory: application to humic acid.

A model, developed within the framework of the counterion condensation theory of linear polyelectrolytes, is presented in this paper to describe the acid-base properties of linear polyelectrolytes, consisting of several types of functional ionizable groups. This formalism has been successfully applied to Fluka humic acid under salt-free conditions, as well as in the presence of supporting simple 1:1 salt (KNO3) at three different concentrations. As part of this approach, the charge density of the humic acid is obtained from the activity coefficient measurements of potassium counterions at different humic acid concentrations at a constant degree of dissociation of the polyelectrolyte. The humic acid average charge density was found to be 0.80 +/- 0.05. Using the present model, we are able to satisfactorily describe the experimental data obtained from acid-base potentiometric titrations. Four main functional groups making up the polymer are determined through their fractional abundances (Xi) and intrinsic pK (pK0i) values. The fractional abundances remained constant and independent of the ionic strength, indicating that the humic acid constitution does not depend on the concentration of excess salts. The pK0i values show a small change with ionic strength, which can be explained by the polyelectrolytic behavior of the solution.

Algorithms↗