Kinetics of the Initial Stage of Gelation in Chitosan Solutions Containing Glutaric Aldehyde: Viscometric Study

The effects of glutaric aldehyde concentration C _GA(in the range from 0.07 to 0.2 wt %) and temperature T(from 20 to 65°C) on the kinetics of an increase in the effective viscosity _effof aqueous solutions of chitosans (C _CH= 2.4 wt %, pH 3.6, and ionic strength I= 0.05) with molecular masses equal to 33 × 10⁴and 55 × 10⁴and the degrees of substitution at N-acetyl and amino groups of 0.08 and 0.90, respectively were studied. The kinetic curves _eff(t) exhibited the induction periods of a relatively slight increase in the viscosity of chitosan–glutaric aldehyde mixed solutions with time followed by the periods of a drastic increase in the viscosity. The former periods correspond to the formation of gel clusters; the latter periods, to the gelation over the whole volume of a solution. Optimal ranges of the parameters C _GAand Twere determined for the preparation of spherical gel particles of slightly cross-linked chitosan, which are used for the sorption of heavy metals from low-concentrated solutions.     

A study of the viscosity of hyaluronic acid solutions for the preparation of polyelectrolyte complexes with chitosan

The viscosity of hyaluronic acid solutions kept at different pH values was found to decrease in the following order of pH: 6.5 > 3.5 > 4.3, although acid hydrolysis occurred at a higher rate in the most acidic solution. The poorest stability of the solutions with pH 4.3 was attributed to the compaction of the macromolecules as a result of charge density redistribution along the polyacid chains.     

Synthesis and surface properties of aqueous solutions of chitosan derivatives and ethylene oxide sulfonic acids

The synthesis and surface properties of aqueous solutions of salts of chitosan and di-, tri-, and oligo(ethylene oxide) sulfonic acids are described. It is shown that, unlike chitosan acetate solutions, the solutions of chitosan oligo(ethylene oxide) sulfonate feature a pronounced surface activity and good foamforming properties; this makes the latter compounds candidates for use in foam technologies of fiber and textile finishing.     

Fabrication and properties of pH-sensitive nanostructured polyelectrolyte microparticles loaded with insulin

Thorough investigation and comparative study were conducted for insulin-loaded microparticles fabricated by consecutive adsorption of polyanions (dextran sulfate and chitosan sulfate) and polycations (chitosan and protamine) onto protein microaggregates. The possible regulation of insulin release from the particles by variation in polyelectrolyte pairs, in the number of their adsorption cycles and in pH of media was demonstrated. For all studied cases the microparticles showed protective action towards insulin inactivation at acid pH values and protein release at pH > 5, corresponding to human gastro-intestinal conditions.     

Pervaporation properties of thermally modified chitosan films

Pervaporation properties of chitosan films in a basic form prepared from thermally modified chitosan acetate in a salt form with respect to aqueous-organic media are studied. It is found that thermally treated films of smaller surface areas have higher permeability and selectivity than the initial chitosan film. A tenfold increase in the membrane surface area leads to a manyfold decrease in a permeate flux density through a thermally treated membrane as compared with an initial membrane and to the appearance of inverse selective permeability upon variations in a liquid phase composition. The results obtained are compared with the previous data. It is concluded that swelling complex polymeric materials are characterized insufficiently for explanation of specific transport properties with respect to low-molecular-weight substances that are capable of varying the supramolecular organization of a polymer.     

Immobilization of trypsin on polysaccharides upon intense mechanical treatment

Immobilization of a ptoteolytic enzyme, trypsin, on chitosan and cellulose was accomplished in the solid state under pressure and shear strain. Trypsin immobilized in this way retains 70—80% of the catalytic activity and exhibits prolonged action. The mechanical treatment allows introduction of a much larger amount of the active protein into a polymer matrix than the equilibrium sorption from solution.     

Reasons for unstable viscous properties of chitosan solutions in acetic acid

A decrease in the molecular mass of chitosan as a result of polymer degradation during storage of its acetic acid solutions has been simulated by means of mixing of chitosan fractions with different molecular masses. It has been shown that a decline in the polymer molecular mass is responsible for a reduction in the dynamic viscosity of chitosan solutions in acetic acid during their storage.     

Diffusion dynamics of motor-driven transport: gradient production and self-organization of surfaces

The interaction between cytoskeletal filaments (e.g., actin filaments) and molecular motors (e.g., myosin) is the basis for many aspects of cell motility and organization of the cell interior. In the in vitro motility assay (IVMA), cytoskeletal filaments are observed while being propelled by molecular motors adsorbed to artificial surfaces (e.g., in studies of motor function). Here we integrate ideas that cytoskeletal filaments may be used as nanoscale templates in nanopatterning with a novel approach for the production of surface gradients of biomolecules and nanoscale topographical features. The production of such gradients is challenging but of increasing interest (e.g., in cell biology). First, we show that myosin-induced actin filament sliding in the IVMA can be approximately described as persistent random motion with a diffusion coefficient (D) given by a relationship analogous to the Einstein equation (D = kT/gamma). In this relationship, the thermal energy (kT) and the drag coefficient (gamma) are substituted by a parameter related to the free-energy transduction by actomyosin and the actomyosin dissociation rate constant, respectively. We then demonstrate how the persistent random motion of actin filaments can be exploited in conceptually novel methods for the production of actin filament density gradients of predictable shapes. Because of regularly spaced binding sites (e.g., lysines and cysteines) the actin filaments act as suitable nanoscale scaffolds for other biomolecules (tested for fibronectin) or nanoparticles. This forms the basis for secondary chemical and topographical gradients with implications for cell biological studies and biosensing.     

Preparation and investigation of solutions of chitosan derivatives with long-chain hydrophilic substituents

The preparation of aqueous solutions of chitosan oligo(ethylene oxide) sulfonate and special features of their viscosity and foam-stabilizing properties are described. It is shown that the complete dissolution of the chitosan derivative takes place at a degree of substitution of at least 0.75. An increase in the degree of substitution to 1 leads to a decrease in the viscosity of solutions; however, the viscosity of solutions of chitosan oligo(ethylene oxide) sulfonate in all cases greatly exceeds that of solutions of chitosan acetate of the same concentration. Unlike chitosan acetate solutions, the solutions of chitosan oligo(ethylene oxide) sulfonate have a higher stability and more pronounced foam-stabilizing properties.