壳聚糖基聚电解质复合物在生物医学领域的应用

近年来,国内外对壳聚糖在生物医学领域的应用研究十分活跃。壳聚糖在低pH时带正电荷,在溶液中可与带负电荷的聚离子形成聚电解质复合物。壳聚糖基聚电解质复合物除了具有壳聚糖的生物相容性,还表现出良好的物理化学性质,在药物控制释放体系、蛋白质分离、生物酶以及细胞固定化等领域具有广泛应用。本文重点介绍壳聚糖与几种天然的或合成的聚阴离子形成的聚电解质复合物及其在生物医学领域的应用。     

脱乙酰壳多糖─羧甲基纤维素聚电解质复合物的合成和药物控制释放研究

本文研究合成条件对脱乙酰壳多糖─羧甲基纤维素聚电解质复合物的组成、结构及药物控制释放性能的影响。结果表明,反应介质的ｐＨ值对生成的脱乙酰壳多糖─羧甲基纤维素聚电解质复合物的组成和结构的影响最大,在ｐＨ值５．５合成的脱乙酰壳多糖─羧甲基纤维素聚电解质复合物具有较好的药物控释性能。     

脱乙酰壳多糖-羧甲基纤维素聚电解质复合物的合成和药物控制释放研究

本文研究合成条件对脱乙酰壳多糖－羧甲基纤维素聚电解质复合物的组成、结构及药物控制释放性能的影响。结果表明，反应介质的ｐＨ值对生成的脱乙酰壳多糖－羧甲基纤维素聚电解质复合物的组成和结构的影响最大，在ｐＨ值５．５合成的脱乙酰壳多糖－羧甲基纤维素聚电解质复合物具有较好的药物控释性能。     

Water-soluble nonstoichiometric polyelectrolyte complexes of chitosan with a polystyrenesulfonate anion

Chitosan complexes that meet the performance criteria of water-soluble nonstoichiometric polyelectrolyte complexes have been first prepared via the interaction of chitosan with excess polystyrenesulfonate anions in acidic media. Thus, the region of the existence of soluble complexes can be narrowed down through a decrease in the degree of polymerization of a lyophilizing polyanion until fully degenerates as in the case of oligomeric anions. The critical concentration of a salt that brings about phase separation decreases with an increase in the relative content of a blocking chitosan in a mixture and depends on the ratio of chain lengths of polymer components. This is also typical of nonstoichiometric polyelectrolyte complexes. The results of this study may be useful for designing soluble chitosan complexes with polyanions, including those of biological origin.     

Nonstoichiometric polyelectrolyte complexes of chitosan soluble in neutral solutions

The technique of preparing nonstoichiometric polyelectrolyte complexes of chitosan soluble in neutral solutions is developed. Chitosan complexes soluble in neutral solutions and meeting the behavioral criteria of water-soluble nonstoichiometric polyelectrolyte complexes are prepared via mixing of strongly acidic solutions of chitosan and polystyrenesulfonate anions taken in a nonequimolar charge-charge ratio and subsequent neutralization of the products by a solution of alkali. Thus, the region of existence of soluble complexes narrows with a decrease in the length of the host polyanion up to its full degeneration in the case of oligomeric anions. The critical concentration of a salt that brings about phase separation decreases with an increase in the relative content of the guest chitosan in a mixture and depends on the ratio of chain lengths of polymer components.     

The rheology of hydrogels based on chitosan–gelatin (bio)polyelectrolyte complexes

Influence of the chitosan concentration in the low-concentrated acidic hydrogels formed by (bio)polyelectrolyte chitosan–gelatin complexes (at a constant gelatin concentration of 1%) was studied by shearing in steady flow and linear oscillations. These complexes, including native gelatin, demonstrate clearly expressed viscoelastic properties. Viscoelastic properties correlated well with the non-Newtonian behavior of hydrogels (according to the Cox–Merz rule). Increasing the chitosan concentration (from 0.1% to 0.6%) results in exponential growth of the apparent viscosity, yield stress, and storage modulus. However, a further increase in chitosan concentration to 0.8% leads to a reduction in these rheological parameters due to the electrostatic repulsion of similarly charged polyelectrolyte complexes under the high concentration of these complexes. The macro-rheological properties of chitosan–gelatin gels are mainly determined by the colloidal structure of sol-precursors in solutions. The yield stress dependence on the radius of the dispersed particles is of square type. Electron photomicrographs showed that the introduction of even small quantities of chitosan leads to radical changes in the supramolecular structure of the gelatin gel.     

Pervaporation and properties of chitosan-poly(acrylic acid) complex membranes

Polyelectrolyte complex membranes between chitosan as a cationic polyelectrolyte and poly(acrylic acid) as an anionic species were prepared by blending two polymer solutions in different ratio. Characterization of chitosan-poly(acrylic acid) complex membrane was investigated by Fourier transform-infrared (FT-IR), wide angle X-ray diffractometer, dielectric analyzer. Their mechanical properties were studied by universal testing machine. The swelling of polyelectrolyte membranes was studied. Thermal properties of polyelectrolyte membranes from chitosan and poly(acrylic acid) by varying blend ratios showed a shift in transition temperatures of polyelectrolyte complexes. Polyelectrolyte complex membranes from chitosan and poly(acrylic acid) had pH sensitive characteristics as determined by FT-IR studies and swelling behaviors. Pervaporation performances were investigated with various organic mixtures; water-ethanol, water-isopropanol, methanol-methyl t-butyl ether mixtures. An increase of poly(acrylic acid) content in the polyelectrolyte complex membranes affected the swelling behavior and pervaporation performance of water-ethanol mixture. Permeation flux decreased and the water concentration in the permeate was close to 100% upon increasing the feed alcohol concentration.     

Formation and properties of positively charged colloids based on polyelectrolyte complexes of biopolymers

Formation of colloids based on polyelectrolyte complexes (PECs) was mainly studied with synthetic polyelectrolytes. In this study, we describe the elaboration of positively charged PEC particles at a submicrometer level obtained by the complexation between two charged polysaccharides, chitosan as polycation and dextran sulfate (DS) as polyanion. The complexes were elaborated by dropwise addition of default amounts of DS to excess chitosan. Quasi-elastic light scattering was used to investigate in detail the influence of the characteristics of components (chain length, degree of acetylation) and parameters linked to the reaction of complexation (molar mixing ratio, ionic strength, concentration in polymer) on the sizes and polydispersity of colloids. Chain length of chitosan is the major parameter affecting the dimensions of the complexes, high molar mass chitosans leading to the largest particles. Variations of hydrodynamic diameters of PECs with the molar mass of chitosan are consistent with a mechanism of particle formation through the segregation of the neutral and then hydrophobic blocks of the polyelectrolyte complexed segments. Resulting particles display probably a structure constituted by a neutral core surrounded by a chitosan shell ensuring the colloidal stabilization. Such a structure was evidenced by measurements of electrophoretic mobilities revealing that the positive charge of particles was decreasing with pH, in relation with the neutralization of excess glucosamine hydrochloride moieties.     

Polymer colloid complexes of chitosan with sodium dodecyl sulfate in water-alcohol media

The formation of polymer colloid complexes based on chitosan and sodium dodecyl sulfate in aqueous ethanol media was studied. The infl uence of the composition of water-ethanol mixtures on the parameters of surfactant binding with chitosan, on the stability of the complexes, on the phase state of the system, and on the colloid-chemical properties of the complexes was analyzed. Addition of small (up to 34 vol %) amounts of ethanol to water enhances the intensity of binding of sodium dodecyl sulfate with the polyelectrolyte and promotes formation of insoluble associates.     

Supramolecular Systems from Natural Polymers and Maleic Polyelectrolytes

Summary: The formation of polyelectrolyte complexes by interaction between chitosan and maleic acid copolymers as strong/weak dibasic polyanions was investigated. The interaction between the sodium salt of maleic acid copolymers with styrene or vinyl acetate and the chitosan hydrochloride in aqueous solution was followed by potentiometric, conductometric and turbidimetric titration. The effect of the added low molecular salt on the complex formation was also investigated. The precipitated complexes were analyzed by FTIR spectroscopy and TG analysis. Preliminary layer-by-layer deposition experiments were performed to obtain thin films.     

Polyelectrolyte complexes from polysaccharides: formation and stoichiometry monitoring

Colloids were obtained from non-stoichiometric polyelectrolyte complexes with two polysaccharides of opposite charge: chitosan and dextran sulfate (DS) as the polycation and polyanion, respectively. The complexes were elaborated by a one-shot addition of the polymer in default to the one in excess. The colloids were positively or negatively charged according to the nature of the polymer in excess. Dynamic light scattering (DLS) demonstrated that particles were formed at a very early stage in the complexation process. The consumption of the excess polyelectrolyte was monitored with a dye assay specific for dextran sulfate (toluidine blue) or chitosan (orange II). From these experiments, two different mechanisms of colloidal PEC formation were evidenced, according to the nature of the polymer in excess. On adding chitosan to DS in excess, regular consumption of the polyanion was observed at a constant stoichiometry, in the 1.5 to 1.85 range (sulfate residues for one glucosamine group), according to the molar mass of the polycation. When DS was added to chitosan in excess, the overall stoichiometry varied from ca. 6 (glucosamine residues for one sulfate group) down to 1 as the charge molar mixing ratio R=n+/n- decreased from 20 to 1. The existence of various mechanisms, according to the nature of the polymer in excess, could be attributed to the differences in chemical reactivity (strong vs low) of the ion in excess and the conformation and flexibility of the macromolecular chains related to their electrostatic potential.     

Characteristics of Interactions in the Pectin–Chitosan System

Interpolymeric complexes have been obtained from citric pectin and chitosan, the latter synthesized from crab chitin. The composition and structure of complexes obtained from different ratios of the components were studied by IR spectroscopy, rheological investigation of gel structure, and mathematical modelling of system properties. Rheological investigation of the processes involved in the formation of interpolymeric complexes with gel structures from citric pectin and chitosan was conducted in moderately concentrated solutions containing different ratios of the components. It was shown that the toughness of the gel structures was determined by the ratio of the amounts of the heterogeneous polymers. The toughest product (τ=121.4 Pa) was obtained by use of equimolar quantities of pectin and chitosan. With deviation of the composition of the mixture from equimolar the toughness of the gel decreased. It is proposed that the polyelectrolyte pectin–chitosan complex with a network structure is formed at the expense of electrostatic interaction between positively charged amino groups at C-2 of the chitosan pyranose ring and negatively charged carboxyl groups at the C-5 of the pectin pyranose ring.     

Water-soluble nonstoichiometric polyelectrolyte complexes of modified chitosan

A modified polysaccharide that, in each deacetylated unit, carries a functional secondary amino group and a quaternized amino group that provides a positive charge and solubility to the polymer throughout the pH range is prepared by the alkylation of primary amino groups of chitosan with glycidyltrimethylammonium chloride. The mixing of modified chitosan solutions with solutions of polystyrenesulfonate or polymethacrylate anions in neutral solutions gives rise to negatively charged nonstoichiometric polyelectrolyte complexes soluble and stable under physiological conditions. The effects of pH, ionic strength, the degree of polymerization, the nature of the lyophilizing polyanion, and the charge-to-charge ratio of components on the boundaries of existence of soluble complexes are ascertained. The collected experimental data may serve as a basis for designing biocompatible and biodegradable means useful for the delivery of genetic material and drugs to living cells.     

Polymer colloids formed by polyelectrolyte complexation of vinyl polymers and polysaccharides in aqueous solution

The polyelectrolyte complex formed from the polyanion and polycation was studied by turbidimetry, static and electrophoretic light scattering, and elementary analysis. Sodium salts of polyacrylate (PA) and heparin (Hep) were chosen as the polyanion, and hydrochloric salts of poly(vinyl amine) (PVA) and chitosan (Chts) as the polycation. Although these vinyl polymers and polysaccharides have remarkably different backbone chemical structures and linear charge densities, all the four combinations PA-PVA, PA-Chts, Hep-PVA, and Hep-Chts provide almost stoichiometric polyelectrolyte complexes which are slightly charged owing to the adsorption of the excess polyelectrolyte component onto the neutral complex. The charges stabilize the complex colloids in aqueous solution of a non-stoichiometric mixture, and the aggregation number of the complex colloids increases with approaching to the stoichiometric mixing ratio. The mixing ratio dependence of the aggregation number for the four complexes is explained by the model proposed in the previous study.     

Soluble–insoluble polyelectrolyte complex of quaternized chitosan with DIVEMA (pyran copolymer)

To endow chitosan with solubility in the whole pH-range without loss of functionality of the amino groups, the cationic polysaccharide was exhaustively alkylated yielding N-[(2-hydroxy-3-trimethylammonium) propyl]chitosan chloride (QCht). Each alkylated unit of QCht contained both quaternary amino group and secondary amino group. Recently we demonstrated that QCht forms with nucleic acids of soluble polyelectrolyte complexes stable at physiological conditions and capable of cell transfection in vitro. In the current work, the anionic counterpart of QCht was hydrolyzed copolymer of divinyl ether and maleic anhydride (DIVEMA) which is known to possess some anti-tumor and immune stimulating activity and use as a drug carrier in anti-tumor drug delivery systems. According to the potentiometry data and ζ-potential measurements, almost all carboxylic groups of DIVEMA were able to form ion pairs with QCht. In aqueous and water–salt solutions, formation of either soluble or insoluble complexes was controlled by pH, ionic strength, a ratio of the oppositely charged groups, and degree of polymerization of the chains following general rules revealed on studying polyelectrolyte complexes of polycarboxylic acids. These findings evidence plausible advantages of the complex formation as the non-covalent modification that imparts to both polyelectrolytes of the ability for reversible soluble–insoluble transformation under enzyme-friendly conditions.     

脱乙酰甲壳质和卡拉胶在溶液中的反应及其复合物性质研究

脱乙酰甲壳质(CTS)和卡拉胶(CGN)在溶液中反应生成不溶于水的沉淀,红外光谱分析及相反离子含量测定证明,CTS和CGN分子间的联结是以CTS分子中的-NH_3~+与CGN分子中的-SO_3~-通过静电相互作用来实现的。形成的聚电解质复合物N/S摩尔比在较宽的范围内依赖于反应混合溶液组成比、pH值及CTS的脱乙酰度。不同条件下形成的复合物具有不同的形态结构,当CTS分子与CGN分子上的电荷密度接近时,电镜观察到的复合物呈纤维状结构。复合物不溶于二甲基亚砜及CH_3COCH_3/KBr/H_2O(20∶20∶60wt)三元溶剂,在加热时溶于浓甲酸和稀盐酸,其溶解性随CTS脱乙酰度的增加而降低,CTS和CGN形成的聚电解质复合物具有一定的抗血凝性。     

Water-soluble polyplexes of modified chitosan

The alkylation of primary amino groups of chitosan with glycidyltrimethylammonium chloride yields the modified cationic polysaccharide that carries, in practically every deacetylated unit, a secondary amino group and a quaternized amino group that provide the solubility of the polymer over the whole range of pH values. The mixing of solutions of modified chitosan and nucleic acid in neutral solutions at various ratios gives soluble DNA-containing polyelectrolyte complexes (polyplexes) that preserve stability under physiological conditions. The effects of the pH, ionic strength, and charge-to-charge ratio of polymer components on the boundaries of existence of soluble polyplexes both negatively and positively charged are elucidated. The collected experimental data may serve as a basis for designing biocompatible and biodegradable means for the delivery of genetic material and drugs to living cells.     

Polyelectrolyte complex nanoparticles from chitosan and poly(acrylic acid) and Polystyrene‐block‐poly(acrylic acid)

Interpolymer polyelectrolyte complexes of chitosan (CS) with poly(acrylic acid) homopolymers and polystyrene‐block‐poly(acrylic acid) diblock copolymers were prepared and characterized. The influence of the positive/negative charge balance (charge ratio), pH, and ionic strength were thoroughly studied by dynamic light scattering. The existence of a strong polyelectrolyte effect was also highlighted in this study. Domains of stability, in which nanoparticle sizes are smaller than 100 and 200 nm for complexes of CS with the homopolymer and copolymer, respectively, were identified and confirmed by scanning electron microscopy and atomic force microscopy. The charged nature of the surface of the nanoparticles was evidenced by Zeta potential measurements. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012     

Formation of soluble chitosan–carrageenan polyelectrolyte complexes

The formation process of soluble chitosan (C)/κ-carrageenan (K) complexes was studied. It was shown that soluble complexes were obtained preferentially by mixing the starting components at given ratios whereas soluble complexes were formed only over a narrow range of starting-component ratios by titration of K with C. The formation of C/K polyelectrolyte complexes was confirmed by gel-permeation chromatography and centrifugation in a Percoll gradient. The formation process of C/K complexes depended on the C molecular weight and the concentrations and ratios of starting polysaccharides. It was shown that unbound components in addition to the complex remained in the mixture upon mixing carrageenan with high-molecular-weight C (C-HM) in 1:1.5 and 1:30 ratios (mol/mol) whereas low-molecular-weight C (C-LM) was bonded completely to the polyanion.     

Stabilization of Liposomes by Polyelectrolytes: Mechanism of Interaction and Role of Experimental Conditions

ζ-potential measurements on LUVs allow to evidence the influence of pH, ionic salt concentration, and polyelectrolyte charge on the interaction between polyelectrolyte (chitosan and hyaluronan) and zwitterionic lipid membrane. First, chitosan adsorption is studied: adsorption is independent on the chitosan molecular weight and corresponds to a maximum degree of decoration of 40% in surface coverage. From the dependence with pH and independence with MW, it is concluded that electrostatic interactions are responsible of chitosan adsorption which occurs flat on the external surface of the liposomes. The vesicles become positively charged in the presence of around two repeat units of chitosan added per lipid accessible polar head in acid medium down to pH = 7.2. Direct optical microscopy observations of GUVs shows a stabilization of the composite liposomes under different external stresses (pH and salt shocks) which confirms the strong electrostatic interaction between the chitosan and the lipid membrane. It is also demonstrated that the liposomes are stabilized by chitosan adsorption in a very wide range of pH (2.0 < pH < 12.0). Then, hyaluronan (HA), a negatively charged polyelectrolyte, is added to vesicles; the vesicles turn rapidly negatively charged in presence of adsorbed HA Finally, we demonstrated that hyaluronan adsorbs on positively charged chitosan-decorated liposomes at pH < 7.0 leading to charge inversion in the liposome decorated by the chitosan-hyaluronan bilayer. Our results demonstrate the adsorption of positive and/or negative polyelectrolyte at the surface of lipidic vesicles as well as their role on vesicle stabilization and charge control.