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PubMed2006

Spontaneous assembly of viruses on multilayered polymer surfaces.

The idea that randomly arranged supermolecular species incorporated in a network medium can ultimately create ordered structures at the surface may be counterintuitive. However, such order can be accommodated by regulating dynamic and equilibrium driving forces. Here, we present the ordering of M13 viruses, highly complex biomacromolecules, driven by competitive electrostatic binding, preferential macromolecular interactions and the rigid-rod nature of the virus systems during alternating electrostatic assembly. The steric constraints inherent to the competitive charge binding between M13 viruses and two oppositely charged weak polyelectrolytes leads to interdiffusion and the virtual 'floating' of viruses to the surface. The result is the spontaneous formation of a two-dimensional monolayer structure of viruses atop a cohesive polyelectrolyte multilayer. We demonstrate that this viral-assembled monolayer can be a biologically tunable scaffold to nucleate, grow and align nanoparticles or nanowires over multiple length scales. This system represents an interface that provides a general platform for the systematic incorporation and assembly of organic, biological and inorganic materials.

Acrylic Resins↗
PubMed2001

p-Sulfonatocalix[6]arene is an effective coacervator of poly(allylamine hydrochloride).

p-Sulfonatocalix[6]arene is shown to form insoluble complexes with poly(allylamine hydrochloride) when the charge balance between the negative calixarene sulfonate groups matches the positive charge carried by the polyelectrolyte, this makes this glycosylaminoglycan analog an interesting candidate for controlled release systems in the case of proteins encapsulated in mesoscopic complexes with polyelectrolytes.

Journal Article↗
PubMed2002

Preferential adsorption of fluorescing fulvic and humic acid components on activated carbon using flow field-flow fractionation analysis.

Activated carbon treatment of drinking water is used to remove natural organic matter (NOM) precursors that lead to the formation of disinfection byproducts. The innate hydrophobic nature and macromolecular size of NOM render it amenable to sorption by activated carbon. Batch equilibrium and minicolumn breakthrough adsorption studies were performed using granular activated carbon to treat NOM-contaminated water. Ultraviolet (UV) absorption spectroscopy and flow field-flow fractionation analysis using tandem diode-array and fluorescence detectors were used to monitor the activated carbon sorption of NOM. Using these techniques, it was possible to study activated carbon adsorption properties of UV absorbing, fluorescing and nonfluorescing, polyelectrolytic macromolecules fractionated from the total macromolecular and nonmacromolecular composition of NOM. Adsorption isotherms were constructed at pH 6 and pH 9. Data were described by the traditional and modified Freundlich models. Activated carbon capacity and adsorbability were compared among fractionated molecular subsets of fulvic and humic acids. Preferential adsorption (or adsorptive fractionation) of polyelectrolytic, fluorescing fulvic and humic macromolecules on activated carbon was observed. The significance of observing preferential adsorption on activated carbon of fluorescing macromolecular components relative to nonfluorescing components is that this phenomenon changes the composition of dissolved organic matter remaining in equilibrium in the aqueous phase relative to the composition that existed in the aqueous phase prior to adsorption. Likewise, it changes the composition of dissolved organic matter remaining in equilibrium in the aqueous phase relative to the adsorbed phase. This research increases our understanding of NOM interactions with activated carbon which may lead to improved methods of potable water production.

Adsorption↗
PubMed1981

Ionic control of immobilized enzymes. Kinetics of acid phosphatase bound to plant cell walls.

When an enzyme is bound to an insoluble polyelectrolyte it may acquire novel kinetic properties generated by Donnan effects. It the enzyme is homogeneously distributed within the matrix, a variation of the electrostatic partition coefficient, when substrate concentration is varied, mimics either positive or negative co-operativity. This type of non-hyperbolic behaviour may be distinguished from true co-operativity by an analysis of the Hill plots. If the enzyme is heterogeneously distributed within the polyelectrolyte matrix, an apparent negative co-operativity occurs, even if the electrostatic partition coefficient does not vary when substrate concentration is varied in the bulk phase. If the partition coefficient varies, mixed positive and negative co-operativities may occur. All these effects must be suppressed by raising the ionic strength in the bulk phase. Attraction of cations by fixed negative charges of the polyanionic matrix may be associated with a significant decrease of the local pH. The magnitude of this effect is controlled by the pK of the fixed charges groups of the Donnan phase. The local pH cannot be much lower than the value of this pK. This effect may be considered as a regulatory device of the local pH. Acid phosphatase of sycamore (Acer pseudoplatanus) cell walls is a monomeric enzyme that displays classical Michaelis-Menten kinetics in free solution. However, when bound to small cell-wall fragments or to intact cells, it has an apparent negative co-operativity at low ionic strength. Moreover a slight increase of ionic strength apparently activates the bound enzymes and tends to suppress the apparent co-operativity. At I0.1, or higher, the bound enzyme has a kinetic behavior indistinguishable from that of the purified enzyme in free solution. These results are interpreted in the light of the Donnan theory. Owing to the repulsion of the substrate by the negative charges of cell-wall polygalacturonates, the local substrate concentration in the vicinity of the bound enzyme is smaller than the corresponding concentration in bulk solution. The kinetic results obtained are consistent with the view that there exist at least three populations of bound enzyme with different ionic environments: a first population with enzyme molecules not submitted to electrostatic effects, and two other populations with molecules differently submitted to these effects. The theory allows one to estimate the proportions of enzyme belonging to these populations, as well as the local pH values and the partition coefficients within the cell walls.

Acid Phosphatase↗
PubMed2004

Nanoscale surface engineered living cells with extended substrate spectrum.

We report on cell surface engineering of living microorganisms by using Layer-by-Layer (LbL) technology to extend the substrate spectrum. The yeast Arxula adeninivorans LS3 (Arxula) was employed as a model organism and biological template. By using LbL technology, Arxula cells were encapsulated by polyelectrolyte and enzyme layers. The biological activity of the Arxula was retained after the encapsulation process. The polymeric capsule surrounding the Arxula provides a stable interface for surface engineering of living cells. LbL of polyelectrolytes followed by an enzyme layer of lactate oxidase were assembled. The outer enzyme layer provides an additional biological function for Arxula to convert the unfavourable substrate lactate into the favourable substrate pyruvate, thus extending the substrate spectrum of the organism. Moreover, capsule stability and enzyme conjugate stability of the surface engineered Arxula were studied.

Journal Article↗
PubMed2006

Electrostatic interactions in dissipative particle dynamics using the Ewald sums.

The electrostatic interactions in dissipative particle dynamics (DPD) simulations are calculated using the standard Ewald [Ann. Phys. 64, 253 (1921)] sum method. Charge distributions on DPD particles are included to prevent artificial ionic pair formation. This proposal is an alternative method to that introduced recently by Groot [J. Chem. Phys. 118, 11265 (2003)] where the electrostatic field was solved locally on a lattice. The Ewald method is applied to study a bulk electrolyte and polyelectrolyte-surfactant solutions. The structure of the fluid is analyzed through the radial distribution function between charged particles. The results are in good agreement with those reported by Groot for the same systems. We also calculated the radius of gyration of a polyelectrolyte in salt solution as a function of solution pH and degree of ionization of the chain. The radius of gyration increases with the net charge of the polymer in agreement with the trend found in static light scattering experiments of polystyrene sulfonate solutions.

Journal Article↗
PubMed2004

Higher-order assembly of microtubules by counterions: from hexagonal bundles to living necklaces.

Cellular factors tightly regulate the architecture of bundles of filamentous cytoskeletal proteins, giving rise to assemblies with distinct morphologies and physical properties, and a similar control of the supramolecular organization of nanotubes and nanorods in synthetic materials is highly desirable. However, it is unknown what principles determine how macromolecular interactions lead to assemblies with defined morphologies. In particular, electrostatic interactions between highly charged polyelectrolytes, which are ubiquitous in biological and synthetic self-assembled structures, are poorly understood. We have used a model system consisting of microtubules (MTs) and multivalent cations to examine how microscopic interactions can give rise to distinct bundle phases in biological polyelectrolytes. The structure of these supramolecular assemblies was elucidated on length scales from subnanometer to micrometer with synchrotron x-ray diffraction, transmission electron microscopy, and differential interference contrast microscopy. Tightly packed hexagonal bundles with controllable diameters were observed for large trivalent, tetravalent, and pentavalent counterions. Unexpectedly, in the presence of small divalent cations, we have discovered a living necklace bundle phase, comprised of 2D dynamic assemblies of MTs with linear, branched, and loop topologies. This new bundle phase is an experimental example of nematic membranes. The morphologically distinct MT assemblies give insight into general features of bundle formation and may be used as templates for miniaturized materials with applications in nanotechnology and biotechnology.

Animals↗
PubMed1977

Cryoenzymology in mixed solvents without cosolvent effects on enzyme specific activity.

Water-soluble polyelectrolytes in interaction with proteins are described. These polyelectrolytes make it possible to investigate enzyme-catalyzed reactions in cooled mixed solvents without the usual effects of their organic solvent component on enzyme specific activity. The applicability of techniques developed is illustrated by results obtained on several systems. The possibility of an electrostatic "sorting out" of solvents and its potentialities in cryoenzymology are discussed.

Cold Temperature↗
PubMedDate not supplied

Biological cells as templates for hollow microcapsules.

Microcapsules in the micrometer size range with walls of nanometer thickness are of both scientific and technological interest, since they can be employed as micro- and nano-containers. Liposomes represent one example, yet their general use is hampered due to limited stability and a low permeability for polar molecules. Microcapsules formed from polyelectrolytes offer some improvement, since they are permeable to small polar molecules and resistant to chemical and physical influences. Both types of closed films are, however, limited by their spherical shape which precludes producing capsules with anisotropic properties. Biological cells possess a wide variety of shapes and sizes, and, thus, using them as templates would allow the production of capsules with a wide range of morphologies. In the present study, human red blood cells (RBC) as well as Escherichia coli bacteria were used; these cells were fixed by glutardialdehyde prior to layer-by-layer (LbL) adsorption of polyelectrolytes. The growth of the layers was verified by electrophoresis and flow cytometry, with morphology investigated by atomic force and electron microscopy; the dissolution process of the biological template was followed by confocal laser scanning microscopy. The resulting microcapsules are exact copies of the biological template, exhibit elastic properties, and have permeabilities which can be controlled by experimental parameters; this method for microcapsule fabrication, thus, offers an important new approach for this area of biotechnology.

Biotechnology↗
PubMedDate not supplied

The use of additives to modulate the release of a sparingly water soluble drug entrapped in PLA50 microparticles.

One of the major problems raised by the microencapsulation of drugs which are sparingly soluble in water is the difficulty to achieve a controlled and total release of the drug. It was previously shown that the microencapsulation of a model water insoluble drug, namely 1-[2-(4-fluorobenzoyl)aminoethyl]-4-(7-methoxynaphthyl) piperazine hydrochloride (FAMP) with a hydrophilic additive like low molar mass poly(ethylene glycol)s (PEG) can fulfil these requirements, provided all the drug + additive matter is in contact with the surrounding liquid medium via open pores and percolating channels. In this paper, PEG was replaced by other additives, selected because of their potential ability to increase the solubility of FAMP in pH = 7.4 isosomolar phosphate buffer (PBS). The idea was that increasing the solubility locally in microparticles could allow the drug to be released, despite its poor solubility in aqueous media like body fluids, and be absorbed before recrystallization. The solubility in PBS of FAMP mixed with additive, in the form of solid dispersions, was determined for various additives, namely citric acid, dimyristoyl DL-alpha-phosphatidyl choline (DMPC), poloxamer copolymers of different compositions and poly(dodecyl L-lysine citramidate) (PLCAC12(100)), an aggregate-forming hydrophilic polyelectrolyte containing 100%, hydrophobizing ester groups which can accommodate lipophilic compounds in hydrophobic pockets present in the aggregates. PEG was taken as a reference. It was found that DMPC, some poloxamers and the hydrophobized polyelectrolyte do increase the solubility of FAMP in PBS. Investigation was made of the release of FAMP from ground microparticles, whose loads were composed of FAMP combined with these solubilization-promoting additives. It was found that the release rate of FAMP from such systems can be increased and modulated to achieve an in vitro sustained release over a 20-30 day period and secure exhaustion of the particles at the end of this period.

Benzamides↗
PubMed2005

Studies on the drug release properties of nano-encapsulated indomethacin microparticles.

Indomethacin micro-crystals sized approximately 2 microm have been encapsulated with polyelectrolyte multi-layers for the purpose of controlled release. Charged linear poly (dimethyldiallyl ammonium chloride) (PDDA) and poly (styrene sulphonate) (PSS) were alternatively deposited on approximately 2 microm drug micro-crystals. The release of indomethacin from coated micro-crystals was measured in aqueous solutions of pH 1.4 and 6.8. The polyelectrolyte multi-layer capsule thickness was proved to control. The results provided a method of achieving prolonged drug release through self-assembly of polymeric shells on drug microcrystals.

Anti-Inflammatory Agents, Non-Steroidal↗
PubMed2005

Application of self-assembled ultra-thin film coatings to stabilize macromolecule encapsulation in alginate microspheres.

Alginate-based hydrogels have several unique properties that have enabled them to be used as a matrix for the entrapment of a variety of enzymes, proteins and cells for applications in bioprocessing, drug delivery and chemical sensing. However, control over release rates or, in some cases, stable encapsulation remains a difficult goal, especially for small particles with high surface-area-to-volume ratios. In this work, the potential to limit diffusion of macromolecules embedded in alginate spheres with nanofilm coatings was assessed. Alginate microspheres were fabricated using an emulsification process with high surfactant concentration to form beads in the size range of 2-10 microm. Using calcium chloride for ionotropic gelation, dextran was encapsulated in the gel phase by mixing with the alginate in solution. The exterior surface was then modified with polyelectrolyte coatings using the layer-by-layer self assembly technique. Leaching studies to assess retention of dextran with varying molecular weights confirmed that the application of multi-layer thin films to the alginate microspheres was effective in reducing leaching rate and total loss of the encapsulated material from the microspheres. For the best case, the rate of release for dextran of 2,000,000 Dalton molecular weight decreased from 1% h(-1) in bare microspheres to 0.1% h(-1) in polyelectrolyte-coated microspheres. The effectiveness of nanofilms reducing loss of the encapsulated macromolecules was found to vary between different polycation materials used. These studies support the feasibility of using these microsystems for development of long-term stable encapsulated systems, such as implantable biosensors.

Alginates↗
PubMed2005

Alginate-coated alginate-polyethyleneimine beads for prolonged release of furosemide in simulated intestinal fluid.

Furosemide-loaded calcium alginate (ALG), calcium alginate-polyethyleneimine (ALG-PEI) and alginate-coated ALG-PEI (ALG-PEI-ALG) beads were prepared by ionotropic/polyelectrolyte complexation method to achieve controlled release of the drug. Effects of several formulation factors on the characteristics of the beads were investigated. Although variation in formulation factors did not influence the drug-loading efficiency (DLE) of ALG beads, rapid release of the drug in simulated intestinal fluid (SIF) could not be prevented. PEI treatment of ALG beads, however, prolonged the drug release considerably. Ionic interaction, as appeared from FTIR studies, between alginate and PEI led to the formation of polyelectrolyte complex membrane, the thickness of which was dependent on the conditions of PEI treatment as demonstrated by scanning electron microscopy (SEM). The membrane acted as a physical barrier to drug release from ALG-PEI beads. Alginate coating of ALG-PEI beads further prolonged the release of the drug by increasing membrane thickness and reducing swelling of the beads possibly by blocking the surface pores. Differential scanning calorimetry (DSC) study indicated that drug was not degraded by PEI treatment. The release data from ALG-PEI beads showed a good fit in power law expression, whereas the release data from ALG-PEI-ALG beads were found to fit in modified power law expression, and the mechanism of drug release changed from super case II transport to nearly Fickian transport, depending on the degree of gelation and formation of polyelectrolyte complex membrane.

Alginates↗
PubMed1997

The interaction of DNA with intercalating agents probed by sodium-23 NMR relaxation rates.

We have investigated the changes of Na-23 NMR spin-lattice and spin-spin relaxation rates of Na-DNA in dilute aqueous solutions, induced by the intercalating drugs ethidium, propidium, 6,7-dihydro-pyrido[2',1':3,4]pyrazino[1,2-f]-phenanthridinediium dihydrate (dq2pyp) and by the electrostatic binder Mg2+. It has been found that the Na-23 spin-lattice relaxation is monoexponential, while the spin-spin relaxation follows a biexponential law. From the linear trends of the relaxation rates observed in the titration experiments of Na-DNA with the drugs we inferred the validity of a two-site model in the fast exchange limit. The relaxation rates of sodium in the bound state have been estimated by using the fraction of bound sodium ions per phosphate charge, predicted by the counterion condensation theory, and the number of sodium ions released per bound drug, calculated from salt dependent equilibrium binding studies. The results show that the addition of the competitors slow down the broad component of the spin-spin relaxation rate of bound sodium in the order dq2pyp approximately propidium < ethidium < Mg2+. This reduction is shown to be due mainly to the decrease of the quadrupolar coupling constant for the slow motions, thus indicating a decrease of the average electric field gradient at the sodium ions close to the DNA surface. We also show that the broad component of the spin-spin relaxation rate linearly correlates with the relative non-polyelectrolyte free energy. This result is discussed in terms of the non-polyelectrolyte interactions affecting R2bB, which can be partitioned into stacking interaction and interactions involving the molecular moieties of the intercalators exposed to the solvent in the minor groove.

Binding, Competitive↗
PubMed1998

Counterion condensation revisited.

We review some of the characteristic properties of the structure of polyelectrolyte solutions: the condensed layer of counterions that forms abruptly at a critical threshold charge density on the polymer chain; the more diffuse Debye-Hückel cloud, which is spatially distinct from the condensed layer; and the entropic release of counterions from the condensed layer as a driving force for the binding of oppositely charged ligands. We present a reminder of the basis of our current understanding in a variety of experiments, simulations, and theories; and we attempt as well to clarify some misunderstandings. We present a new analysis of a lattice model that suggests why the limiting laws for polyelectrolyte thermodynamics have proved to be accurate despite the neglect of polymer-polymer interactions in their original derivation. We sketch recent progress in constructing a potential between counterion and polyion. A counterion located in the interface between condensed layer and Debye cloud is repelled from the polyion, creating a sharp boundary between the two counterion populations.

Electrolytes↗
PubMed2002

Coagulation for treatment of paint industry wastewater.

In the present study, the coagulation of paint industry wastewater was examined. Ferrous and aluminum sulphate and polyaluminum chloride (PACl) were used as coagulation agents and the influence of the coagulant dose and effective pH on the quality of treated wastewater was investigated. Optimum pH for FeSO4 addition was near 9.7, the required coagulant dose was about 2 g/L and average process efficiency varied between 30 and 80% in COD and between 70 and 99% in turbidity terms, for a wide spectrum of wastewater batches. In the case of Al2(SO4)3, no pH adjustment was needed and process efficiency varied between 70 and 95% in COD and between 90 and 99% in turbidity terms, for an effective dose of 2.5 g/L. Further improvement of process efficiency was possible by raising the pH of the supernatant liquid after alum-sludge sedimentation to 10. In the case of PACl optimum pH was around 7 and process efficiency was about 98% based on both quality parameters, for an effective dose of 4 g/L. Cationic polyelectrolytes were proved to have a higher potential vs. coagulation than anionic ones when acting as primary coagulants. Combination of Al2(SO4)3 or PACl with polyelectrolytes resulted in high process efficiencies, while maintaining liquid pH values at acceptable limits.

Alum Compounds↗
PubMed2005

A configurable three-dimensional microenvironment in a microfluidic channel for primary hepatocyte culture.

We have developed a technique for the in situ three-dimensional (3D) immobilization of primary rat hepatocytes within a localized matrix in a microfluidic channel that provides a 3D microenvironment incorporating both a configurable 3D matrix and fluid perfusion. This is based on the laminar flow complex coacervation of a pair of oppositely charged polyelectrolytes, i.e., methylated collagen and a terpolymer of HEMA-MMA-MAA. 3D collagen matrices were formed with minimal gelation times (<8 min), were able to entrap cells under aqueous noncytotoxic conditions, and permitted culture media to be perfused in the microchannel by virtue of the spatial confinement of the 3D matrix on one side of the channel. The architecture and stability of the collagen matrix could be configured by the use of different material combinations and changes in the polyelectrolyte flow rates and retention time. Primary rat hepatocytes cultured for 24 h in the 3D matrix within the microchannel showed comparable or enhanced cytochrome P450 7-ethoxyresorufin-O-deethylation activity with static controls. The configurable 3D microenvironment in the microfluidic channel may be a potential 3D culture model of primary hepatocytes for drug testing applications.

Animals↗
PubMed2006

Enzymatic fluorescent microsphere glucose sensors:evaluation of response under dynamic conditions.

Most previous attempts at the development of a "smart tattoo" for glucose monitoring in diabetes--implantable fluorescent microspheres that can be implanted intradermally and interrogated transdermally using light--have focused on the encapsulation of a competitive binding assay for glucose within hydrogel microspheres or polyelectrolyte microcapsules. We recently reported on the development of a microsphere sensor based on an enzymatic scheme, combined with an oxygen-quenched fluorescent reporter element. A novel feature of this design is the use of polyelectrolyte multilayer nanofilms, which are assembled stepwise on the surface of the microspheres, for modulation of glucose and oxygen mass transport, allowing them to be designed for sensitive and safe operation within the "oxygen deficit" present in the skin. In this work, a flow-through sensor testing apparatus was used to demonstrate the reversible response of the sensors under controlled, dynamic conditions. The sensors were shown to be sensitive over at least 0-140 mg/dL glucose, with a response time of less than 2 min. This report also identifies some current problems with the approach, and gives potential solutions towards the development of a practical implantable sensor for glucose monitoring in diabetes.

Biosensing Techniques↗