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PubMed2006

Salt-induced collapse and reexpansion of highly charged flexible polyelectrolytes.

We study the salt-dependent conformations of dilute flexible polyelectrolytes in solution via computer simulations. Low concentrations of multivalent salt induce the known conformational collapse of individual polyelectrolyte chains, but as the salt concentration is increased further this is followed by a reexpansion. We explicitly demonstrate that multivalent counterions can overcompensate the bare charge of the chain in the reexpansion regime. Both the degree of reexpansion and the occurrence of overcharging sensitively depend on ion size. Our findings are relevant for a wide range of salt-induced complexation phenomena.

Computer Simulation↗
PubMed2006

Collapse of spherical polyelectrolyte brushes in the presence of multivalent counterions.

We consider the interaction of multivalent counterions with spherical polyelectrolyte brushes (SPB). The SPB result if linear polyelectrolyte (PE) chains (contour length: 60 nm) are densely grafted to colloidal spheres of 116 nm in diameter. Dispersed in water, the surface layer consisting of chains of the strong PE poly(styrene sulfonic acid) (PSS) will swell. We demonstrate that successive addition of trivalent ions (La3+) leads to a collapse in which the surface layer is shrinking drastically. All findings are discussed on the base of a theoretical mean-field approach using the Donnan equilibrium. The ion exchange and a strong binding of trivalent ions by PE chains is followed up by a drop in the osmotic pressure inside the brush. This reduction is the driving force for the collapse. The strong ion-chain correlation is discussed with results obtained from molecular dynamics simulations.

Cations↗
PubMed2003

Encapsulated yeast cells inside Paramecium primaurelia: a model system for protection capability of polyelectrolyte shells.

One of the most promising applications of encapsulated living cells is their use as protected transplanted tissue into the human body. A suitable system for the protection of living cells is the use of nano- or microcapsules of polyelectrolytes. These shells can be deposited easily on top of the cells by means of a layer-by-layer technique. An interesting feature of the capsules is the possibility to control their properties on a nanometre level, tuning their wall texture via the preparation conditions. Here we introduce a model system to test the protection ability of polyelectrolyte capsules. Common bakery yeast cells were encapsulated. They were coated with a fluorescently labelled shell at conditions known to guarantee cell survival, and the cell interior was stained with DAPI. The protozoan Paramecium primaurelia was incubated with this double-stained living yeast and visualized by means of two-photon excitation fluorescence microscopy. Cross-sections of the dye-stained material as well as autofluorescence of the fixed protozoan allowed us to follow the digestion of the coated yeast with time. Our investigation reveals that capsules prepared under these deposition conditions are permeable to lysosomal enzymes, leading to degradation of the yeast inside the intact capsules. Our preliminary results indicate the suitability of the introduced model as a test system of this permeability.

Animals↗
PubMed1997

Synthetic strategies for the preparation of precursor polymers and of microcapsules suitable for cellular entrapment by polyelectrolyte complexation of those polymers.

The production of microcapsules suitable for the entrapment of mammalian cell by means of polyelectrolyte complexation has, of a necessity, led to the development of novel strategies for the preparation of relatively bioinert polymers which complex efficiently under unique conditions to produce a mechanically resilient membrane with efficient transport properties. In this communication we relate a brief overview of capsule-membrane forming systems for the immunoisolation (or potential immunoisolation) of mammalian cells, which are based upon the complexation of polyelectrolyte (PE) polymers; with emphasis on precursor synthesis and relationships between precursor polymer structure and capsule membrane stability.

Animals↗
PubMed1988

Poliovirus retention in soil columns after application of chemical- and polyelectrolyte-conditioned dewatered sludges.

The transport of poliovirus type 1 (strain LSc) was studied in Red Bay sandy loam columns that were treated with chemical- or polyelectrolyte-conditioned dewatered sludges and then leached with natural rainwater under saturated flow conditions. Poliovirus was concentrated in the alum and ferric chloride sludges that were produced following the flocculation of virus-seeded raw sewage. Virtually complete inactivation of the virus was observed following the flocculation of raw sewage or the stabilization of alum and ferric chloride sludges with lime at pH 11.5. Poliovirus was also concentrated in polyelectrolyte-conditioned dewatered sludge that was produced from virus-seeded, anaerobically digested sludge. Despite the saturated flow conditions for a sustained period, no viruses were detected in the leachates of the soil columns that were treated with these chemical and chemically treated sludges. Since the viruses were mostly associated with the solids in these sludge samples, it is believed that they were immobilized along with the sludge solids in the top portion of the soil columns.

Hydrogen-Ion Concentration↗
PubMed1969

Concentration of viruses from sewage and excreta on insoluble polyelectrolytes.

The concentration of viruses from sewage by adsorption on and elution from an insoluble cross-linked copolymer of maleic anhydride is described. Viruses either added to sewage or naturally contained in sewage were preferentially adsorbed to this polyelectrolyte at a pH range of 5.0 to 6.0 and were eluted at pH 8.0 to 9.0. In a 2-month survey of viruses in sewage in the spring (April to May 1968), when viruses are at low levels, efficient and economical detection of these agents was accomplished with the polyelectrolyte-concentration method. This method lends itself to the detection of viruses present in minute amounts in fecal samples, urine, sewage, and other natural waters. Large volumes of these fluids can be treated with the polymer described, and virus can be concentrated sufficiently for detection.

Adsorption↗
PubMed2006

Polyelectrolyte multilayer formation: electrostatics and short-range interactions.

We investigate the phenomenon of multilayer formation via layer-by-layer deposition of alternating charged polyelectrolytes. Using mean-field theory, we find that a strong short-range attraction between the two types of polymer chains is essential for the formation of multilayers. For strong enough short-range attraction, the adsorbed amount per layer increases (after an initial decrease), and finally it stabilizes in the form of a polyelectrolyte multilayer that can be repeated hundreds of times. For weak short-range attraction between any two adjacent layers, the adsorbed amount (per added layer) decays as the distance from the surface increases, until the chains stop adsorbing altogether. The dependence of the threshold value of the short-range attraction as function of the polymer charge fraction and salt concentration is calculated.

Computer Simulation↗
PubMed2004

Effects of counterion fluctuations in a polyelectrolyte brush.

We investigate the effect of counterion fluctuations in a single polyelectrolyte brush in the absence of added salt by systematically expanding the counterion free energy about Poisson-Boltzmann mean-field theory. We find that for strongly charged brushes, there is a collapse regime in which the brush height decreases with increasing charge on the polyelectrolyte chains. The transition to this collapsed regime is similar to the liquid-gas transition, which has a first-order line terminating at a critical point. We find that, for monovalent counterions, the transition is discontinuous in theta solvent, while for multivalent counterions, the transition is generally continuous. For collapsed brushes, the brush height is not independent of grafting density as it is for osmotic brushes, but scales linear with it.

Biophysics↗
PubMed2004

Effects of continuous water flow on the swelling properties of polyelectrolyte hydrogels.

We report the swelling behavior of a polyelectrolyte copolymer gel in water, which consists of poly(N-isopropylacrylamide) and sodium acrylate. The diameter of the cylindrical gels was measured at room temperature under a continuous flow of solvent water (equivalent to an infinite amount of water; open system). After a sufficient water flow, the diameter of the gel in the limited amount of water (closed system) was measured as a function of the temperature. The gel in the open system was found to shrink as a result of the continuous flow of water, and the gel in the closed system began to swell again at the phase transition point by increasing the temperature. The effects of the degree of initial ion exchange by the water flow on the macroscopic swelling behavior were discussed in terms of the exchange of counterions (the ion dissociation of carboxyl groups) and of the creation and destruction of intermolecular forces (hydrogen bonding). It was concluded that the amount of solvent water determines the environmental variables, such as the pH and ion concentration, which affects the swelling properties of polyelectrolyte hydrogels; intermediate re-swollen states can be observed in a closed system.

Journal Article↗
PubMed2004

Spherical polyelectrolyte block copolymer micelles: structural change in presence of monovalent salt.

Spherical polyelectrolyte block copolymer micelles were investigated as a function of added NaCl salt concentration using Small-Angle Neutron Scattering (SANS) and Light Scattering (LS). The micelles are formed by the self-association of charged-neutral copolymers made of a long deuterated polyelectrolyte moiety (NaPSS(d))251 and a short hydrophobic moiety (PEP)52. In presence of salt, the core shape and the aggregation number of the micelles are not affected. The hydrodynamic radius of the micelle is found to be identical to the radius of the whole micelle deduced from neutron scattering and thus the hydrodynamic radius is a valid measure of the corona thickness. At the lowest salt concentrations investigated the thickness of the corona, R(s), remains essentially constant and a contraction is observed above an added-salt concentration c(s) of 2 x 10(-2) M where this crossover concentration corresponds to the average ionic strength of the free counterions in the corona. The contraction takes place while maintaining a rod-like behavior of the chains at short scale and obeys to: R(s) approximately c(s)(-0.18). The exponent 0.18 suggests an electrostatic persistence length proportional to the Debye screening length.

Journal Article↗
PubMed2005

Volume exclusion effects in the ground-state dominance approximation for polyelectrolyte adsorption on charged interfaces.

We consider the problem of polyelectrolyte molecules adsorbing on oppositely charged interfaces. For sufficiently long chains, the ground-state dominance approximation can be used which results in a (semi-)analytical solution of the self-consistent field equations (aSCF). Whereas existing aSCF theory assumes a low polyelectrolyte density, here the required electrostatic corrections for a high polymer density are implemented. Adsorbed polymer excludes volume for the solvent and small ions, a volume effect that also leads to a reduced dielectric permittivity and a resulting polarization term in the exchange potential. Calculations show the influence of volume exclusion on the polymer density profile.

Adsorption↗
PubMed2006

Curved polymer and polyelectrolyte brushes beyond the Daoud-Cotton model.

We revise the classical Daoud-Cotton (DC) model to describe conformations of polymer and polyelectrolyte chains end-grafted to convex spherical and cylindrical surfaces. In the framework of the DC model, local stretching of chains in the brush does not depend on the degree of polymerization of grafted chains, and the polymer density profile follows a single-exponent power law. This model, however, does not correspond to a minimum in free energy of the curved brush. The nonlocal (NL) approximation exploited in the present paper implies the minimization of the overall free energy of the brush and predicts that the polymer density profile does not follow a single-exponent power law. In the limit of large surface curvature the NL approximation provides the same scaling laws for brush thickness and free energy as the local DC model. Numerical prefactors are however different. Extra extension of chains in the brush interior region leads to larger equilibrium brush thickness and lower free energy per chain. A significant difference between outcomes of the two models is found for brushes formed by ionic polymers, particularly for weakly dissociating (p H-sensitive) polyelectrolytes at low solution salinity.

Journal Article↗
PubMed2005

Monocyte activation on polyelectrolyte multilayers.

The adherence and activation of primary human monocytes was investigated on a polyelectrolyte multilayer film containing hyaluronic acid (HA) and poly-L-lysine (PLL). The sequential layer-by-layer deposition of the multilayer film was characterized by surface plasmon resonance. Eight alternating bilayers displayed an effective thickness of 16.15 nm with a total polymer coverage of 2.10 microg/cm2. For cell studies, HA-PLL multilayers were constructed on tissue culture polystyrene (TCPS) substrates and characterized by time of flight second ion mass spectrometry (ToF-SIMS) analysis. Principal component analysis of the ToF-SIMS spectra resolved no significant difference in surface chemistry between PLL-terminated and HA-terminated multilayer surfaces. Monocyte adhesion on PLL- and HA-terminated surfaces was measured by the lactate dehydrogenase assay and showed a significant decrease in cell adhesion after 24 h incubation. Cell viability measured by Live/Dead fluorescent staining showed significant cell death in the adherent cell population over these 24 h. Tumor necrosis factor-alpha (TNF-alpha) production, a measure of monocyte activation, was quantified by ELISA and normalized to the number of adherent monocytes. The activation of monocytes on PLL-terminated and HA-terminated surfaces was nearly identical, and both surfaces had TNF-alpha levels that were 8-fold higher than TCPS. These results demonstrate that sufficient PLL had diffused into the surface layer to direct monocyte adherence and to induce cytokine activation and cell death on the HA-terminated multilayer films. The diffusion of the second multilayer component to the coating surface should, thus, be taken into account in the design of polyelectrolyte-based biomaterial coating strategies.

Cell Adhesion↗
PubMedDate not supplied

Polyelectrolyte microshells as carriers for fluorescent sensors: loading and sensing properties of a ruthenium-based oxygen indicator.

A strategy for the design and fabrication of microcapsule-based fluorescent biosensors containing indicators and internal references is described. The rationale for this work is the physical immobilization and chemical separation of assay chemistry for use in biological environments. Using the general approach of depositing oppositely charged species on colloidal micro/nanotemplates, a sensor system employing polyelectrolyte microshells for uptake of functional molecules is proposed, and experiments to demonstrate the feasibility of nanoengineering the sensor properties are described in the context of an oxygen sensor. Methods for immobilization and entrapment of fluorescent indicator and reference dyes are shown, along with the pH dependence of this process. Embedded dyes are shown to be stable and retain their function, as demonstrated with oxygen-sensitivity experiments of loaded microcapsules. Although oxygen sensitivity is presented as an example of a specific application, the overall strategy is likely more generally useful. The work suggests that polyelectrolyte microshells may be used as a platform to develop novel sensors by entrapment of functional materials.

Biosensing Techniques↗
PubMed2006

Polyelectrolyte multilayer film coating and stability at the surfaces of oral prosthesis base polymers: an in vitro and in vivo study.

A new type of coating involving a layer-by-layer technique has been recently reported. This coating is composed of a polyelectrolyte multilayer film that confers specific properties on surfaces to which it is applied. Here, we studied the applicability of such a technique to the coating of oral prostheses, by first testing the construction of polyelectrolyte multilayer films on several polymers used in oral prosthesis bases, and, subsequently, by studying the stability of these coatings in vitro, in human saliva, and in vivo in a rat model. We demonstrated that the multilayered films are able to coat the surfaces of all tested polymers completely, thus increasing their wettability. We also showed that saliva does not degrade the film after 7 days in vitro and after 4 days in vivo. Taken together, our results establish that the layer-by-layer technique is suitable for the coating of oral devices.

Acrylates↗
PubMed2005

Comparison between normal saline and a polyelectrolyte solution for fluid resuscitation in severely dehydrated infants with acute diarrhoea.

UNLABELLED: The optimal intravenous solution for rehydration of infants and children with severe dehydration is debated. AIM: The aim was to compare the efficacy of a polyelectrolyte solution (group PS) with sodium chloride 0.9% solution (group NS) in rapid parenteral rehydration of severely dehydrated infants with acute diarrhoea. METHODS: Primary outcomes were volume and time to hydration. Secondary outcomes were urea, creatinine, electrolytes, glucose, arterial pH and bicarbonate levels. Patients were assigned randomly and openly to one of the two treatment groups. Severe dehydration was defined as one or more of the following associated with any other sign of dehydration: depressed consciousness, a weak or absent pulse or capillary refill time > 10 sec. Peripheral blood samples for chemical pathology were collected before and after rapid fluid therapy. The mean age of the 36 enrolled infants was 9.1 mths. All had depressed consciousness or severe hypotension/shock. The fluid infusion rate was 50 ml/kg/hr until haemodynamic stability was restored (absence of severe hypotension and two urine emissions). Fluid volume, time to rehydration and weight before and after rehydration were recorded. RESULTS: All infants recovered full pulse within 1 hr; most had a better level of consciousness or capillary refill <3 sec. Group NS (15 infants) showed (before and after treatment, respectively) a decrease of plasma potassium (3.4 to 3.1 mmol/L, p=0.07), bicarbonate (13.3 to 12.2 mmol/L, p=0.01) and glucose (8.2 to 5.8 mmol/L, p<0.01). Group PS (21 infants) showed a decrease of potassium (4.4 to 3.2 mmol/L, p<0.01) but an increase in bicarbonate (11.6 to 13.3 mmol/L, p<0.01) and glucose (11.4 to 14.8 mmol/L, p=0.08). CONCLUSION: Polyelectrolyte solution was as effective as normal saline on volume expansion and better for correcting acidosis.

Acidosis↗
PubMed2001

Enhanced nasal retention of hydrophobically modified polyelectrolytes.

Hydrophobically modified polyelectrolytes (HMP) are polymers with a high content of ionizable groups bonded to hydrophobic groups. Copolymers of poly(acrylic acid) and Pluronic surfactants constitute a special class of HMP whereby poly(propylene oxide) segments act as hydrophobes. The poly(propylene oxide) segments possess temperature-dependent aqueous solubility and the solutions of the Pluronic-poly(acrylic acid) copolymers (MW > 3,000,000) undergo a sol-gel transition when kept at body temperature. Due to the presence of the poly(acrylic acid) segments, the Pluronic-poly(acrylic acid) copolymers are bioadhesive. We have examined the hypothesis that the in-situ gelling polymer formulations of Pluronic-poly(acrylic acid) copolymers may have an enhanced retention in the nasal cavity. The effects of putative bioadhesive (Carbomer 934P) and thermogelling (Pluronic F127) polymers on nasal clearance were compared with Pluronic-poly(acrylic acid) copolymers using a rat model. The enhancement of the residence time of fluorescent labels by the Pluronic-poly(acrylic acid) copolymers was shown to be 5-8-fold that of Carbomer, and 3-6-fold that of Pluronic F127. The results unequivocally demonstrate the superior retention of the HMP that combines bioadhesive and thermogelling capabilities over either a bioadhesive polyelectrolyte or a polymer of a low molecular weight that undergoes a sol-gel transition.

Acrylic Resins↗