Antibacterial activity and biocompatibility of a chitosan-γ-poly(glutamic acid) polyelectrolyte complex hydrogel

In this study, we prepared a polyelectrolyte complex (PEC) hydrogel comprising chitosan as the cationic polyelectrolyte and γ-poly(glutamic acid) (γ-PGA) as the anionic polyelectrolyte. Fourier transform infrared spectroscopy revealed that ionic complex interactions existed in the chitosan-γ-PGA PEC hydrogels. The compressive modulus increased upon increasing the degree of complex formation in the chitosan-γ-PGA PEC hydrogel; the water uptake decreased upon increasing the degree of complex formation. At the same degree of complex formation, the compressive modulus was larger for the chitosan-dominated PEC hydrogels; the water uptake was larger for the γ-PGA-dominated ones. Scanning electron microscopy images revealed the existence of interconnected porous structures (pore size: 30-100 μm) in all of the chitosan-γ-PGA PEC hydrogels. The chitosan-γ-PGA PEC hydrogels also exhibited antibacterial activity against Escherichia coli and Staphylococcus aureus. In addition, in vitro cell culturing of 3T3 fibroblasts revealed that all the chitosan-γ-PGA PEC hydrogels were effective in promoting cell proliferation, especially the positively charged ones (chitosan-dominated). Therefore, the chitosan-γ-PGA polyelectrolyte hydrogel appears to have potential as a new material for biomedical applications.     

Polyelectrolyte complex micelles composed of c-raf antisense oligodeoxynucleotide-poly(ethylene glycol) conjugate and poly(ethylenimine): effect of systemic administration on tumor growth

An antisense oligodeoxynucleotide (ODN) delivery system based on polyelectrolyte complex (PEC) micelles composed of an ODN-poly(ethylene glycol) (PEG) conjugate and polyethylenimine (PEI) was demonstrated. The PEC micelles having a core/shell structure were spontaneously formed in an aqueous solution by ionic interactions between ODN part in the conjugate and PEI. The ODN/PEI polyelectrolyte complex formed an inner core while PEG chains surrounded it as a shell. The morphology of the micelles was visualized as a separate sphere by atomic force microscopy (AFM). When the micelles containing a c-raf antisense ODN were intravenously administered into tumor-bearing nude mice, significant antitumor activities against human lung cancer were observed. The intravenously injected micelles also showed significantly higher accumulation level in the solid tumor region compared to that of naked ODN.     

Molecular dynamics simulation of polyelectrolyte with oppositely charged monomeric and dimeric surfactants

Interactions of anionic polyelectrolyte (PE) with cationic monomeric (MS) and dimeric surfactants (DS) have been investigated by coarse-grained molecular dynamics (MD) simulation. A PE/surfactant mixture is observed to evolve over time into micellar complex of increasing size. The critical aggregation concentration (CAC) is qualitatively found to be much lower than the critical micellization concentration (CMC) of the free surfactant. Compared to the monomeric analog, a DS interacts more strongly with the oppositely charged polyion chain. The equilibrium complex size becomes larger with increasing surfactant concentration. Simulation results are consistent with experimental observations and reveal that the electrostatic and hydrophobic interactions play an important role in the formation of micellar complex.     

Affinity precipitation of monoclonal antibodies by nonstoichiometric polyelectrolyte complexes

The nonstoichiometric polyelectrolyte complex (PEC) formed by poly(methacrylic acid) (degree of polymerization 1830) (PMAA)and poly(N-ethyl-4-vinyl-pyridinium bromide) (degree of polymerization 530) (PEVP) undergoes reversible precipitation from aqueous solution at any desired pH-value in the range 4.5–6.5 depending on the ionic strength and PEVP/PMAA ratio in the complex. The antigen, inactivated glyceraldehyde-3-phosphate dehydrogenase (GAPDH) from rabbit was covalently coupled to PEVP. The resulting GAPDH–PEVP/PMAA complex was used for the purification of antibodies from a 6G7 clone specific towards inactivated GAPDH. The crude extract was incubated with GAPDH-containing PEC and the precipitation of the PEC was carried out at 0.01 M NaCl and pH 4.5, 5.3, 6.0 and 6.5 using PEC with PEVP/PMAA ratios of 0.45, 0.3, 0.2 and 0.15, respectively. Purified antibodies were eluted at pH 4.0 where PECs of all compositions used were insoluble.PEC precipitation is accompanied only by small nonspecific coprecipitation of proteins. Precipitated PEC could be dissolved at pH 7.3 and used repeatedly. This revised version was published online in July 2006 with corrections to the Cover Date.     

Biodegradable interpolyelectrolyte complexes based on methoxy poly(ethylene glycol)-b-poly(alpha,L-glutamic acid) and chitosan

We synthesized methoxy poly(ethylene glycol)-b-poly(alpha,L-glutamic acid) (mPEGGA) diblock copolymer by ring-opening polymerization of N-carboxy anhydride of gamma-benzyl-L-glutamate (NCA) using amino-terminated methoxy polyethylene glycol (mPEG) as macroinitiator. Polyelectrolyte complexation between mPEGGA as neutral-block-polyanion and chitosan (CS) as polycation has been scrutinized in aqueous solution as well as in the solid state. Water-soluble polyelectrolyte complexes (PEC) can be formed only under nonstoichiometric condition while phase separation is observed when approaching 1:1 molar mixing ratio in spite of the existence of hydrophilic mPEG block. This is likely due to mismatch in chain length between polyanion block of the copolymer and the polycation or hydrogen bonding between the components. Hydrodynamic size of primary or soluble PEC is determined to be about 200 nm, which is larger than those reported in some literatures. The increase in polyion chain length of the copolymer leads to the increase in the hydrodynamic size of the water-soluble PEC. Formation of spherical micelles by the mPEGGA/CS complex at nonstoichiometirc condition has been confirmed by the scanning electron microscopy observation and transmission electron microscopy observations. The homopolymer CS experiences attractive interaction with both mPEGA and PGA blocks within the copolymer. Competition of hydrogen bonding and electrostatic force in the system or hydrophilic mPEG segments weakens the electrostatic interaction between the oppositely charged polyions. The existence of hydrogen bonding restrains the mobility of mPEG chains of the copolymer and completely prohibits crystallization of mPEG segments. In vitro culture of human fibroblasts indicates that mPEGGA/CS-based materials have potential in biomedical application, especially in tissue engineering.     

Chitosan–Chondroitin Sulfate Based Matrix Tablets for Colon Specific Delivery of Indomethacin

The different approaches for targeting orally administered drugs to the colon include coating with pH-dependent polymers, design of time-release dosage forms, and the utilization of carriers that are degraded exclusively by colonic bacteria. The aim of the present study was to develop a single unit, site-specific drug formulation allowing targeted drug release in the colon. Matrix tablets were prepared by wet granulation using cross-linked chitosan (ChI) and chondroitin sulfate (ChS) polysaccharides as binder and carrier. ChS was used to form polyelectrolyte complexes (PEC) with ChI, and its potential as a colon-targeted drug carrier was investigated. Indomethacin was used as a model drug. The ChI and ChS PEC was characterized by Fourier transform infrared spectroscopy (FTIR), differential scanning calorimetry (DSC) and powder X-ray diffraction studies (XRD). The matrix tablets were tested in vitro for their suitability as colon-specific drug delivery systems. FTIR demonstrated that the PEC forms through an electrostatic interaction between the protonated amine (NH₃⁺) group of ChI with the free carboxylate (COO⁻) group and sulfate (SO₄²⁻) group of ChS. DSC and XRD indicated that the PEC has different thermal characteristics from ChI or ChS. The dissolution data demonstrates that the dissolution rate of the tablet is dependent upon the concentration of polysaccharide used as binder and matrix and time of cross-linking. The study confirmed that selective delivery of indomethacin to the colon can be achieved using cross-linked ChI and ChS polysaccharides.     

New evidence of the nonequilibrium nature of the "slow modes" of diffusion in polyelectrolyte solutions

The time-dependent behavior of the dissolution of polyelectrolyte powders in pure water and moderate ionic strength aqueous solvent was monitored by flowing dissolving material through an online filter, and then through a multiangle light scattering unit, a refractometer, and a capillary viscometer. When the polyelectrolytes were dissolved in solutions of moderate ionic strength, their dissolution behavior was similar to that of neutral polymers. When dissolved in pure water, however, there was consistently a small population of aggregates that appeared at the beginning of the dissolution process, which then rapidly diminished. For large pore filtration, the aggregates reached a final low level, and slowly disappeared over the span of many days, whereas for small pore filtration the aggregates disappeared completely over a scale of minutes. The real-time data, together with size exclusion chromatography analysis, shed light on previously unanswered questions concerning the nonequilibrium nature of this small population of polyelectrolyte aggregates in low ionic strength solutions, and its relation to the "extraordinary phase" of diffusion (or "slow modes"). Further evidence is also provided that both angular scattering maxima due to interpolyion correlations and the maximum of reduced viscosity vs polyion concentration ("electroviscous" effect) at low ionic strength are equilibrium properties that are unrelated to these aggregates.     

Radii of gyration of sodium carboxymethylcellulose in aqueous and mixed solvent media from viscosity measurement

The viscosities of three sodium carboxymethylcellulose samples with molecular weights of 90,000 [degree of substitution (DS): 0.7], 250,000 (DS: 0.9), and 700,000 (DS: 0.9) have been reported in water and methanol–water mixtures in salt-free and salt-containing solutions at 35 °C. The results were analyzed in terms of a phenomenological approach for the viscosity of polymer solutions to determine the intrinsic viscosities [η] of the polyelectrolyte samples. This contribution presents a new and convenient method for the determination of the root-mean-square radii of gyration of the polyion chains using the [η] values obtained as a function of the added salt concentration. The polyion coils are found to expand at low ionic strength and these collapse drastically with increasing ionic strength. Addition of methanol to the medium in which these samples are dissolved causes a contraction of the polyion chains, although this influence is less pronounced than that of the added salt.     

Dehydration from alcohols by polyion complex cross-linked chitosan composite membranes during evapomeation

This study describes the dehydration of an ethanol/water azeotrope during evapomeation using polyion complex cross-linked chitosan composite (q-Chito-PEO acid polyion complex/PES composite) membranes, constructed from quaternized chitosan (q-Chito) and poly(ethylene oxydiglycolic acid) (PEO acid) on a porous poly(ether sulfone) (PES) support. Both the q-Chito/PES composite and the q-Chito-PEO acid polyion complex/PES composite membranes showed high water permselectivity for an ethanol/water azeotrope. Both the permeation rate and the water permselectivity of the q-Chito/PES composite membranes were enhanced by increasing the degree of quaternization of the chitosan molecule because the affinity of the q-Chito/PES composite membranes for water was increased by introducing a quaternized ammonium group into the chitosan molecule. q-Chito-PEO acid polyion complex/PES composite membranes prepared from an equimolar ratio of carboxylate groups in the PEO acid versus quaternized ammonium groups in the q-Chito showed the maximum separation factor for water permselectivity without lowering the permeation rate. With an increasing molecular weight of PEO acid, the separation factor for water permselectivity increased, but the permeation rate almost did not change. The mechanism responsible for the separation of an ethanol/water azeotrope through the q-Chito-PEO acid polyion complex/PES composite membranes was analyzed by the solution-diffusion model. The permeation rate, separation factor for water permselectivity, and evapomeation index of q-Chito-PEO acid 400 polyion complex/PES composite membrane with an equimolar ratio of carboxylate groups in PEO acid 400 and ammonium groups in q-Chito were 3.5 x 10(-1) kg/(m(2) hr), 6300, and 2205, respectively, and very high membrane performance. The separation factor for water permselectivity for aqueous solutions of n-propyl and isopropyl alcohol was also maximized at an equimolar ratio of carboxylate groups and ammonium groups and was greater than that for an ethanol/water azeotrope. The above results were discussed from the viewpoint of the physical and chemical structure of the q-Chito-PEO acid polyion complex/PES composite membranes and the permeants.     

Hybrid Photoelectrochemical Water Splitting Systems: From Interface Design to System Assembly

Photoelectrochemical (PEC) water splitting has attracted increasing attention due to its potential to mitigate energy and environmental issues. Hybrid PEC systems containing semiconductor photosensitizers and molecular catalysts are reported to be highly active and stable for water splitting with great potential for facilitating clean fuels production. In this review, following a showcasing of the fundamental details of hybrid PEC systems for water splitting, semiconductor/molecular catalyst interface designs are highlighted, with a focus on interfacial physicochemical interactions and binding, and interfacial energetics and dynamics for efficient charge transfer. Recent advances in hybrid system assemblies for PEC water splitting are also briefly introduced. Finally, future challenges and directions in the field of hybrid PEC water splitting for solar energy conversion are reviewed. The current review provides state‐of‐the‐art strategies for optimized interface design for creating highly active and stable PEC water splitting assemblies.     

Block polyelectrolyte networks from poly(acrylic acid) and poly(ethylene oxide): sorption and release of cytochrome C

A new family of block polyelectrolyte networks containing cross-linked poly(acrylic acid) (PAA) and poly(ethylene oxide) (PEO) was synthesized by copolymerization of acrylic acid and bisacrylated PEO (10 kDa). Two materials with different PEO/PAA ratios were compared with a weakly cross-linked PAA homopolymer network. The networks bound a cationic protein, cytochrome C, due to the polyion coupling, leading to the network contraction. After binding the protein the block polyelectrolyte networks were more porous compared to a homopolymer network, facilitating protein absorption within the gel. The protein was released by adding Ca2+ ions or a polycation. Ca2+ ions migrated within the gels and reacted with PAA chains, thus displacing the protein. The polycation transfer into hydrogels, as a result of polyion substitution reactions, was inhibited by the excess of PEO chains in the block polyelectrolyte networks. Overall, these findings advance development of functional polyelectrolyte networks for immobilization and controlled release of proteins.     

Changes in the water binding characteristics of the cell walls from transgenic Nicotiana tabacum leaves with enhanced levels of peroxidase activity

Pore size in the cell wall matrix may affect cell wall–water relations, particularly under osmotic stress. Cross linkage of plant cell wall matrix polymers is an important step in the formation of this structure and peroxidases have been proposed to catalyse the cross-linking of phenolic constituents. Transgenic tobacco ( Nicotiana tabacum ) plants expressing a basic tomato peroxidase gene (TPX2) showed increased apoplastic ferulic acid peroxidase activity in mature leaves. This enhanced activity was not associated with a decreased leaf growth. Differential scanning calorimetry (DSC) of control dried cell walls showed a putative glass transition, after Ca²⁺ removal, that was absent in the transgenic line. This would indicate that transgenic walls were more rigid. DSC analysis of water-hydrated cell wall preparations distinguished two pools of water, freezable and non-freezable water. The amount of non-freezable water, which corresponds to strongly bound water, was higher in the transgenic line (64 versus 55%). DSC thermograms of the transgenic cell wall were displaced to lower temperatures, and this may be interpreted as the result of a stronger interaction between this freezable water and this wall. Water sorption and desorption isotherms, obtained at relative humidity ranging from 5 to 93%, demonstrated the presence of very strongly bound water in the transgenic cell walls that was absent in controls. Water sorption–desorption hysteresis of the isotherms was evident in the control wall but not in the transgenic line. These changes in cell wall–water interaction seem to be relevant at the organ level because leaf discs of transgenic plants maintained higher relative water content than control discs, at water potentials between −1.05 and−2.31 MPa.     

Polycomplexes – potential for bioseparation

This review discusses the properties of complexes formed by proteins with polyelectrolytes (PPC) and two polyelectrolyte molecules of opposite charge (PEC). The most highly charged polymers with ionic groups in each monomer unit are considered in this paper. There are all reasons to regard PEC as macromolecular compounds produced as a result of equilibrium reactions with inherent permanent exchange of polyions in water-salt solutions. They combine two properties that might appear at first sight to be mutually exclusive, i.e. rather high stability and lability. Introduction of bioaffinity ligands endows PEC with the recognition capacity sufficient for the purposes of bioseparation and bioanalysis. Antibody-PEC conjugates were successfully used in the immunoassay combining the advantages of both homogeneous and heterogeneous assays and for modeling of chaperone action. The unique properties of polyelectrolyte complexes in combination with bioaffinity ligands makes them promising for the development of highly efficient means of protein isolation, new immunoassay procedures and creation of reversibly soluble biocatalysts. This revised version was published online in July 2006 with corrections to the Cover Date.     

Novel composite blend microbeads of sodium alginate coated with chitosan for controlled release of amoxicillin

Composite blend microbeads of sodium alginate (NaAlg) with sodium carboxymethyl cellulose (NaCMC) containing magnesium aluminum silicate (MAS) particles and enteric coated with chitosan have been prepared to achieve controlled release (CR) of amoxicillin in stomach environment. The composite beads have been characterized by X-ray diffraction (XRD) to study drug distribution, DSC for understanding thermal stability and Fourier transform infrared (FTIR) spectroscopy to investigate chemical interactions as well as to assess the structure of the drug-loaded formulations. Surface morphology of the beads was investigated by scanning electron microscopy (SEM). The size distribution of beads loaded with drug as studied by particle size analyzer was in the range of 745-889 μm. The beads exhibited quite widely varying encapsulation efficiencies from 52 to 92%. Equilibrium swelling of the beads measured in water and in vitro release of amoxicillin in pH 1.2 medium suggests that drug release depends on polymer blend composition, concentration of MAS and extent of enteric coating.     

The effect of counter-ion substitution on the transport properties of polyelectrolyte solutions

The effects of counter-ion substitution in aqueous polyelectrolyte solutions (chondroitin sulfate) on the two main transport phenomena of the ionic species, self-diffusion and electrical mobility, were studied experimentally by tracer methods and dynamic light scattering. The data were analyzed with respect to counter-ion condensation and stoichiometric substitution of low-ionic counterions by high-ionic charge ones and compared to Manning's theory. Substitution effects on the apparent charge of the macro-ion were derived from the transport data using an extended Nernst-Einstein relationship and discussed in the light of the condensation effect in polyelectrolyte solutions. The effective charge of the polyion (i.e., its residual charge after condensation of counter-ions) and the charge difference between the substituting counter-ions appear determinant in the mechanism of substitution.     

Calorimetric studies of the interaction between sodium alginate and sodium dodecyl sulfate in dilute solutions at different pH values

Interactions between the polyelectrolyte sodium alginate (NaAlg) and the anionic surfactant sodium dodecyl sulfate (SDS) have been investigated by microcalorimetric techniques. The polymer-surfactant interactions were observed between NaAlg and SDS at different pH values in dilute solution. The thermodynamic parameters for their interaction process are evaluated from the results of the observed dilution enthalpy curves. As the pH value of the solution decreases from 7 to 6, NaAlg polymers have an obvious effect on the cmc of SDS as a simple salt, which indicates no association between SDS and NaAlg owing to electrostatic repulsion. With the progressive decrease of pH value from 5 to 3, the hydrophobic segments in the alginate chains are increasing and the hydrophilic segments decreasing, and the aggregation between SDS and alginate due to hydrophobic interactions is observed.     

Sorption of wheat seed lectin by polyelectrolyte complexes of chitosan

The possible application of polyelectrolyte complexes (PEC) of chitosan and copolymers of maleic acid with N-vinylpyrrolidone, styrene, and ethylene and/or chitin cross-linked sorbents (CCLS) synthesized on the basis of PEC for sorption of wheat germ agglutinin (WGA) was studied. The synthesis of spherically granulated sorbents was shown. Compared to unmodified chitosan, there was a significant increase in sorption of WGA by the PEC: PEC, 2.5-fold, and CCLS, from 3.5-fold to 7-fold.     

Electroviscosity of polyelectrolyte solutions

A theoretical expression for the electroviscous effect in polyelectrolyte solutions, caused by the distortion of counterion-distribution and counterion flow around a polyion under a velocity gradient of solvent flow, was obtained to elucidate the characteristic behaviour of the viscosity of highly charged polyelectrolyte solutions observed at low salt concentration. The derivation of the theory was performed on the basis of the Navier-Stokes-Onsager equation, Poisson equation, and diffusion equations for low molecular ions by the use of a cell model (free-volume model) for a polyion. Energy dissipation was obtained without directly solving these equations. It was found that the derived expression of viscosity explained the experimental results satisfactorily, and that the streaming potential effect caused by the counterion flow played an essential role in the increase in viscosity of polyelectrolyte solutions at finite polymer concentration and low salt concentration ranges.     

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.     

Facile preparation of well-defined near-monodisperse chitosan/sodium alginate polyelectrolyte complex nanoparticles (CS/SAL NPs) via ionotropic gelification: A suitable technique for drug delivery systems

Polymeric nanoparticles have emerged as a promising approach for drug delivery systems. We prepared chitosan (CS)/sodium alginate (SAL) polyelectrolyte complex nanoparticles (CS/SAL NPs) via a simple and mild ionic gelation method by adding a CS solution to a SAL solution, and investigated the effects of molecular weight of the added CS, and the SAL:CS mass ratio on the formation of the polyelectrolyte complex nanoparticles. The well-defined CS/SAL NPs with near-monodisperse particle size of about 160 nm exhibited a pH stable structure, and pH responsive properties with a negatively or positively charged surface. The so-called “electrostatic sponge” structure of the polyelectrolyte complex nanoparticles enhanced their drug-loading capacity towards the differently charged model drug molecules, and favored controlled release. We also found that the drug-loading capacity was influenced by the nature of the drugs and the drug-loading media, while drug release was affected by the solubility of the drugs in the drug-releasing media. The biocompatibility and biodegradability of the polyelectrolytes in the polyelectrolyte complex nanoparticles were maintained by ionic interactions. These results indicate that CS/SAL NPs can represent a useful technique for pH-responsive drug delivery systems.