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PubMed2006

Macroporous hydrogels based on 2-hydroxyethyl methacrylate. Part 4: growth of rat bone marrow stromal cells in three-dimensional hydrogels with positive and negative surface charges and in polyelectrolyte complexes.

The growth of bone marrow stromal cells was assessed in vitro in macroporous hydrogels based on 2-hydro- xyethyl methacrylate (HEMA) copolymers with different electric charges. Copolymers of HEMA with sodium methacrylate (MA(-)) carried a negative electric charge, copolymers of HEMA with [2-(methacryloyloxy)ethyl] trimethylammonium chloride (MOETA(-)) carried a positive electric charge and terpolymers of HEMA, MA(-) and MOETA(+) carried both, positive and negative electric charges. The charges in the polyelectrolyte complexes were shielded by counter-ions. The hydrogels had similar porosities, based on a comparison of their diffusion parameters for small cations as measured by the real-time tetramethylammonium iontophoretic method of diffusion analysis. The cell growth was studied in the peripheral and central regions of the hydrogels at 2 hours and 2, 7, 14 and 28 days after cell seeding. Image analysis revealed the highest cellular density in the HEMA-MOETA(+) copolymers; most of the cells were present in the peripheral region of the hydrogels. A lower density of cells but no difference between the peripheral and central regions was observed in the HEMA-MA(-) copolymers and in polyelectrolyte complexes. This study showed that positively charged functional groups promote the adhesion of cells.

Animals↗
PubMed1987

Acetylcholinesterase as polyelectrolyte in reaction with cationic substrates.

It is shown that the salt effect in acetylcholinesterase-catalyzed hydrolysis of 2-(N-methylmorpholinium)-ethylacetate can be quantitatively described by the equation log(k2/KS) = log(k2/KS) degrees--psi log[M+Z] following from Manning's polyelectrolyte theory; the psi values for salts with univalent and bivalent cations at different pH values of the reaction medium were in accordance with the conclusions of the theory. Manning's polyelectrolyte theory seems to be a useful framework for studying salt effects in the reactions of charged substrates with enzymes as globular polyions.

Acetylcholinesterase↗
PubMed1990

Conformational transition and polyelectrolyte behaviour of a succinoglycan polysaccharide.

We report the chemical characterization and the relationship between the physicochemical properties and conformational change of a succinoglycan polysaccharide produced by Pseudomonas sp, NCIB 11592. The expected chemical structure is confirmed, with a ratio of D-glucose: D-galactose: pyruvate: succinate of 7:1:1:1. The molecular weight of the native form is 4.2 x 10(6) but after a single heating cycle through the disordered state the molecular weight is reduced to 3.0 x 10(6). The polymer has a polymolecularity index of 1.3 in both cases. The conformational change was studied by different methods which enabled us to define the exact nature of the ordered and disordered states. The conformational transition depends on the temperature, the ionic strength and the nature of the counterion. The polyelectrolyte behaviour is in favour of a single chain conformation with an intramolecular helix-coil transition. The enthalpy change during this transition is greater than that expected solely on the basis of the polyelectrolyte contribution. It may be associated with changes in solvation or a rearrangement of water molecules in close association with the polymer.

Calcium Chloride↗
PubMed1983

Polyelectrolyte behaviour in mucus glycoproteins.

Mucus glycoproteins isolated from a human ovarian cyst and the sputum of a cystic fibrotic exhibit a significant decrease in reduced viscosity with increase in ionic strength, I. The molecular weights of the glycoproteins showed little variation with I, implying that the change is conformational rather than a dissociation. This change is ascribed to a polyelectrolyte-type contraction rather than to a reduction in particle asymmetry. Guanidine hydrochloride acts as a classical electrolyte in the reversible suppression of charge effects, and not as a denaturing or dissociation agent. These observations help to resolve some discrepancies in earlier studies. The occurrence of polyelectrolyte effects in these glycoproteins is ascribed to flexibility of structure and to their content of N-acetylneuraminic acid. The ionic strength values necessary for different types of physical measurement are discussed.

Cystic Fibrosis↗
PubMed1980

Polyelectrolyte effects in DNA condensation by polyamines.

The conditions required for the counterion induced collapse of T7 bacteriophage DNA are briefly reviewed. Using Manning's counterion condensation theory we calculate a striking unity among collapse conditions: collapse occurs when from 89% to 90% of the DNA phosphate charges are neutralized by condensed counterions. The forces involved in collapsed DNA are investigated with emphasis on electrostatic repulsion. It is concluded that polyelectrolyte repulsion is the dominant force opposing collapse. Comparison of the results or polyelectrolyte repulsion calculation made using numerical methods and the Poisson-Boltzmann equation, with values of the attractive energies due to London dispersion interactions, leads to the conclusion that dispersion forces are probably large enough to cause collapse when the repulsions have been reduced by the presence of multivalent counterions.

Calorimetry↗
PubMed1981

The binding of divalent metal ions to polyelectrolytes in mixed counterion systems. I. The dye spectrophotometric method.

The dye spectrophotometric method for the measurement of the activity of divalent metal ions in polyelectrolyte solutions containing added electrolytes is discussed. The method is applied to mixtures containing the dextransulfate polyanion, NaCl, and MgCl2 or Ca2. A two wavelength ratio method as applied to polyelectrolyte solutions is compared to the standard method which makes use of the previous determination of the dye-metal ion formation constant. The ratio method is found to be a convenient and reliable method which is not influenced by decomposition of the dye or by statistical errors in the extrapolation procedure. The activity coefficients as determined by the two wavelength dye spectrophotometric method are compared to results of Donnan exclusion measurements, and of EMF measurements using a calcium ion selective electrode. The results of the spectrophotometric method are equal to those of the two other methods within the limits of error in the latter. The spectrophotometric measurements can extend to much lower ion activaties than the other two methods, and can be done in the presence of a large excess of added electrolyte, yielding results of considerably improved precision when compared to Donnan and EMF methods.

Journal Article↗
PubMed1991

Solution and gelling properties of polysaccharide polyelectrolytes.

Attention is focussed on the special class of polysaccharide polyelectrolytes belonging to the family of the microbial polysaccharides. But a few exceptions, these are high molecular weight water- soluble polycarboxylates with complex, regular structures. Complexity and regularity in primary structure--two features normally not shared by other polysaccharides of either vegetal or animal origin--quite naturally entail unique conformational propensities, special physico-chemical properties in bulk and in solution and, as a consequence, make these biopolymers of particular interest from both a basic research and an industrial standpoint. What is outlined in this presentation should demonstrate that for many exocellular microbial polycarboxylates the solution properties are, as expected, dictated by the conformation assumed by the polyelectrolytic chains which, in turn, are governed by several free energy terms in particular stemming from specific solvent-chain interactions, among which the coulombic contribution may play a minor role.

Circular Dichroism↗
PubMed1991

Limiting-laws of polyelectrolyte solutions. Ionic distribution in mixed-valency counterions systems. I: The model.

An extension of the counterion-condensation (CC) theory of linear polyelectrolytes has been developed for the case of a system containing a mixture of counterions of different valency, i and j. The main assumption in the derivation of the model is that the relative amount of the condensed counterions of the type i and j is strongly correlated and it is determined by the overall physical bounds of the system. The results predicted by the model are consistent, in the limiting cases of single species component, with those of the original CC theory. The most striking results are obtained for the cases of low charge density and excess of counterion species: in particular, an apparent positive "binding" cooperativity of divalent ions is revealed for small, increasing additions of M2+ ions to a solution containing a swamping amount of monovalent salt and a polyelectrolyte of low charge density. Apparent "competitive binding" of mono- and divalent ions derives as a bare consequence of the electrostatic interactions. Theoretical calculations of experimentally accessible quantities, namely single-(counter) ion activity coefficients, confirm the surprising predictions at low charge density, which qualitatively agree with the measured quantities.

Journal Article↗
PubMed2005

Polyelectrolyte multilayers functionalized by a synthetic analogue of an anti-inflammatory peptide, alpha-MSH, for coating a tracheal prosthesis.

Polyelectrolyte multilayer films made of poly (L-lysine) (PLL) and poly (L-glutamic acid) (PGA) have been functionalized by covalent binding of a synthetic analogue of the anti-inflammatory peptide, alpha-melanocyte-stimulating hormone (alpha-MSH) to PGA to create biologically active coatings for tracheal prostheses. The morphology and in vivo stability of the films were investigated by atomic force microscopy and confocal laser scanning microscopy, respectively. For the in vivo evaluation, 87 rats were implanted and examined for a period superior to 3 months. Histological analysis, performed 1 month after implantation, showed a fibroblast colonization of the periprosthetic side and a respiratory epithelium type on the endoluminal side of the implant for all the polyelectrolyte coatings tested. However, for prostheses modified by PGA ending multilayer films, a more regular and less obstructive cell layer was observed on the endoluminal side compared to those modified by PLL ending films. Systemic anti-inflammatory IL-10 production was only detected in rats implanted with prostheses functionalized by alpha-MSH, demonstrating, in vivo, the anti-inflammatory activity of the embedded peptide into multilayer architectures.

Animals↗
PubMed2005

Radiation synthesis of interpolymer polyelectrolyte complex and its application as a carrier for colon-specific drug delivery system.

Novel pH-sensitive interpolymer polyelectrolyte complex was synthesized by gamma radiation-induced copolymerization of acrylic acid (AAc) and dimethyl aminoethyl methacrylate (DMAEMA). pH-dependent swelling showed different phase transitions depending on the copolymer composition and also showed the interpolymer polyelectrolyte complex formation at pH values ranged from pH 3 to pH 4. FT-IR and TGA was employed to study the complex formation. The influence of copolymer composition and pH value of the surrounding medium on the type of water diffusion in the glassy polymer was discussed. The ability of the prepared copolymer to be used as drug carrier for colon-specific drug delivery system was estimated using ketoprofen as a model drug.

Acrylates↗
PubMed2005

Application of a polyelectrolyte complex coacervation method to improve seeding efficiency of bone marrow stromal cells in a 3D culture system.

High seeding efficiency with homogenous distribution of limited cell sources such as bone marrow stromal cells (BMSCs) are of clinical relevance in scaffold-based tissue engineering. Therefore, considerable research efforts have been invested to ameliorate the seeding efficiency in 3D scaffolds. Preliminary data demonstrated that indeed BMSCs were viable and were able to proliferate in a model 3D scaffold, i.e. Cytomatrix scaffold. However, the eventual practical application of BMSCs in such 3D scaffolds is limited by the low seeding efficiency of the cells within the scaffold. Here, we demonstrated that the cell seeding efficiency of BMSCs in the Cytomatrix scaffold can be improved significantly (t-test, p<0.05) by means of macroencapsulating the scaffold via the complex coacervation of a methylated collagen and terpolymer. The thickness and density of the polyeletrolyte complex can be modulated by the contact time between the methylated collagen and terpolymer to balance between cell entrapment efficacy and mass transfer impedance imparted by the complex. Porcine BMSCs were macroencapsulated in Cytomatrix scaffolds using various polyelectrolyte contact time and cultured under both static and dynamic conditions. Throughout the range of contact time investigated, macroencapsulation did not affect the viability of the porcine BMSCs in dynamic culture. However, the viability of the cells under static cultures was compromised with longer polyelectrolyte contact time. Therefore, this proposed method of macroencapsulation enables customization to achieve enhanced seeding efficiency without mass transfer impedance for different culture configurations.

Adipocytes↗
PubMed2005

Protection of mammalian cell used in biosensors by coating with a polyelectrolyte shell.

In order to detect xenoestrogens which induce perturbations of mammalian cells, design of biosensor using a mammalian cell line enable to detect these compounds is necessary. MELN cell line is suitable to detect estrogen activity, since they are stably transfect with an estrogen regulated luciferase gene. To realize this biosensor, it appeared necessary to add a protection to the mamalian cell, which is devoided, of the wall protecting yeasts or plant cells. With this aim in view, MELN cells have been isolated with a polyelectrolyte shell using the layer-by-layer technique. Among several polyelectrolyte-couples, the best cell survival (>80%) was obtained by alternating the polycation poly-diallyldimethyl ammonium chloride layer and the negatively charged poly-styrene sulfonate. We observed that the composition of the buffer used for layer-deposition was crucial to preserving cell viability, e.g. potassium ions were preferred to sodium ions during the coating. Furthermore, viability was increased when cells were allowed to recover for 2 h between each bilayer deposition. The use of engineered mammalian cells that synthesize luciferase as a response to exposure to estradiol, demonstrated that coating not only permits cell survival, but also allows essential metabolic functions, such as RNA and protein synthesis to take place. Capsule formation allows free diffusion of small molecules, while it prevents internalization in the cells of proteins larger than 60 kDa.

Ammonium Chloride↗
PubMed2006

Mechanical properties of single living cells encapsulated in polyelectrolyte matrixes.

We have studied the mechanical properties of encapsulated Saccharomyces cerevisiae yeast cells by performing AFM force measurements. Single living cells have been coated through the alternate deposition of oppositely charged polyelectrolyte layers and mechanically trapped into a porous membrane. Coated and uncoated cells in presence/absence of bud scars, i.e. scars resulting from previous budding events, have been investigated. No significant differences between encapsulated and bare cells could be inferred from AFM topographs. On the other hand, investigation on the system elasticity through the acquisition and analysis of force curves allowed us to put in evidence the differences in the mechanical properties between the hybrid cell/polyelectrolyte system and the uncoated cells. Analysis of the curves contact region indicates that the polyelectrolyte coating increases the system rigidity. Quantitative evaluation of the cell rigidity through the Hertz-Sneddon model showed that coated cells are characterized by a Young's modulus higher than the value obtained for uncoated cells and similar to the value observed on the bud scar region of uncoated cells.

Biomechanical Phenomena↗
PubMed2004

Micellar electrokinetic chromatography with polyelectrolyte complexes as micellar pseudo-stationary phases.

The separation of dansyl (DNS-AAs) and carbobenzoxy (CBZ-AAs) amino acids using micellar electrokinetic chromatography employing polyelectrolyte-surfactant complexes (PSC) formed in the reaction between polyacrylic acid (PAA) and dodecyltrimethylammonium bromide (DTAB) as pseudo-stationary phases was described. The PSCs were stabilized by hydrophobic interactions of alkyl chains of the surfactant ions and converted to an intramolecular micellar-like phase. The running buffer was a 50mM solution of sodium phosphate (pH 6.0) containing 4.6-20.2mM PSC, in which a part of carboxyl groups of PAA was blocked by aliphatic amines. For the systems with 7.9mM of PAA/DTAB complex (phi=0.30, phi-composition of water-soluble polyelectrolyte complex) as a pseudo-stationary phase, the peaks of six dansyl amino acids (DNS-AAs) were baseline resolved. The separation in this case is based on a complex distribution mechanism of the dansyl derivatives between the free buffer and the intramolecular micellar-like phase of the water-soluble PSC. On the other hand, the additives of PAA/DTAB complex (phi=0.30) to the running buffer does not essentially affect on the electrophoretic behaviour of the CBZ-AAs, the variant MEKC is not realized. The influence of the concentration of the complex of PAA/DTAB on the electrophoretic behaviour of analytes was investigated. Relative retentions and relative selectivities were used for describing electrophoretic behaviour of the amino acid derivatives.

Algorithms↗
PubMed2003

Potential distribution around a polyelectrolyte-coated spherical particle in a salt-free medium.

Simple analytic approximate expressions for the solution to the Poisson-Boltzmann equation around a spherical particle coated with an ion-penetrable polyelectrolyte layer in a salt-free medium containing counterions only are derived. The results of the calculation of the potential distribution using the approximate solution are found to be in good agreement with exact numerical results. It is shown that as in the case of a charged rigid particle, there is a certain critical value of the particle charge, separating two cases, that is, the low-particle-charge case and the high-particle-charge case. In the low-charge case the potential is essentially the same as if counterions were absent and thus the potential is proportional to the particle charge. In the high-charge case counterion condensation occurs in the polyelectrolyte layer region, so that the dependence of the potential on the particle charge is considerably suppressed.

Journal Article↗
PubMed2004

Preparation and adsorption of refined polyelectrolyte complex nanoparticles.

We report on bulk and surface properties of centrifuged nonstoichiometric polyelectrolyte complex (PEC) dispersions. PECs were prepared by mixing poly(diallyldimethylammonium chloride) (PDADMAC) and sodium poly(maleic acid-co-alpha-methylstyrene) (PMA-MS) at the monomolar mixing ratio of 0.6 and polymer concentration >/=1 mmol/l. Centrifugation of initial PEC dispersions revealed three phases: supernatant (SUP), coacervate (COAC), and an insoluble precipitate. Mass, turbidity, particle hydrodynamic radii (R(h)), and the titratable charge amount were determined for those phases. The turbid COAC phase consisted of 200-nm nanoparticles and carried 60% of the polymer mass and 20% of the titratable charge amount of the initial PEC dispersion. The SUP phase showed no turbidity and no such nanoparticles, but carried 80% of the initial titratable charge amount, presumably caused by excess polycations. Furthermore, linear dependences of turbidity and R(h) on COAC concentration was observed. COAC adsorption was studied at polyelectrolyte multilayer (PEM) modified silicon surfaces in dependence on both adsorption time and concentration using attenuated total-reflection-Fourier transform infrared (ATR-FTIR) spectroscopy. The adsorption data were fitted by the simple Langmuir model. Comparison of COAC particles and polystyrene latices revealed similar adsorption features. SEM and AFM measurements resulted in hemispherically shaped adsorbed COAC particles with coverages >/=25%, whose calculated volumes correlated well with those in dispersion obtained by PCS.

Journal Article↗
PubMed2004

Amperometric method for determining the degree of complexation of polyelectrolytes with cationic surfactants.

The complexation of sodium polystyrene sulfonate with monovalent cationic surfactants at a microsized liquid/liquid interface has been studied using electrochemistry. The method is based on measurement of surfactant ion transfer across the interface between two immiscible electrolyte solutions (ITIES). The complexation of various cationic surfactants (alkylpyridinium- and trimethylammonium-) with oligosized polystyrene sulfonate was measured. Binding isotherms were used to determine the degree of binding as a function of the surfactant chain length and type of head group. It was found that the hydrophobicity of the surfactant was the predominant factor. The effect of the polyelectrolyte chain length on the binding mechanism was studied using cetylpyridinium chloride as a complexing agent. It was found that binding affinity, as well as cooperativity of the binding process, decreases with decreasing polyelectrolyte chain length. Thermodynamics of surfactant binding was measured using titration microcalorimetry. The thermodynamic data obtained show that the enthalpy of surfactant binding is not dependent on polymer chain length, but an increase in chain length makes the binding process entropically more favorable.

Calorimetry↗
PubMed2004

Adsorption of organic compounds onto polyelectrolyte immobilized-surfactant aggregates on cellulosic fibers.

The adsorption of anionic surfactants with different hydrophobic chain lengths onto cellulose fibers pretreated with a cationic polyelectrolyte has been investigated. Five steps are involved in the adsorption process, which was ascribed to the formation of monolayer and bilayer surfactant aggregates. Electrostatic interaction between the residual surface charges followed by hydrophobic interaction among the alkyl chains are considered the main factors in the adsorption process. The adsorption of the anionic surfactant was found to greatly enhance the retention of organic compounds onto the polyelectrolyte-treated cellulose. The coadsorption phenomenon, which was dependent on the saturation level of the adsorbed surfactant, has been explained in terms of the accumulation of the organic solute on the hydrophobic core generated by the adsorbed layer.

Adsorption↗