I. P. Dobrovol’skaya

Specific features of chitosan-montmorillonite interaction in an aqueous acid solution and properties of related composite films

The rheological properties of chitosan solutions in a 2% aqueous solution of acetic acid with added montmorillonite nanoparticles and the mechanical properties and structural organization of chitosan-based composite films are studied. The interaction between the polymer functional groups and surface charges of nanoplatelets is confirmed by conductometric and potentiometric measurements. With the use of a X-ray diffraction analysis, it is shown that the nanoparticles in films are in the exfoliated and intercalated states. The incorporation of up to 10 wt % modified montmorillonite nanoparticles into the chitosan matrix results in a successive increase in rigidity and a decrease in the elongation at break.

Structure and characteristics of chitosan-based fibers containing chrysotile and halloysite

With the use of the methods of X-ray diffraction and electron microscopy, chitosan fibers prepared by coagulation into an alcohol-alkali mixture are shown to possess a two-phase structure containing C- and O-type crystallites. These fibers and composite fibers containing halloysite and Mg chrysotile nanotubes are characterized by anisotropic structure, i.e., by the orientation of both chitosan crystallites and Mg chrysotile particles along the fiber axis. A comparison of the rates of shear induced by passing of a polymer solution through a die and the data of rheological studies allows the conclusion that the structuring of chitosan solution under the applied field of shear stresses and the orientation of polymer macromolecules and filler nanotubes occur. An increase in the draw ratio during fiber spinning does not assist orientation of polymer crystallites but, in contrast, increases surface defectiveness and leads to the nucleation of longitudinal cracks; as a result, the strength of fibers decreases. The introduction of 5 wt % Mg chrysotile into the chitosan matrix markedly increases the mechanical characteristics of the composite fibers owing to the reinforcing action of oriented filler nanotubes.

Influence of spinning conditions on properties of chitosan fibers

Chitosan fibers were prepared by a coagulation method involving spinning from an acetic-acid solution (2%) of polymer (4%) in basic alcoholic solution. The influence of feed rate and shear rate of the polymer solution and the degree of orientational drawing on the structure and mechanical properties of the fibers were studied. The optimum spinning parameters were determined. The chitosan fibers had an anisotropic structure with the macromolecules oriented primarily along the fiber axis.

Supramolecular structure of chitin nanofibrils

The structure of chitin nanofibrils as a promising filler for bioresorbable suture materials and matrixes for cellular technologies and tissue engineering is investigated via the methods of X-ray diffraction and scanning electron microscopy. It is shown that the powder microparticles obtained via lyophilization of an aqueous dispersion of chitin nanofibrils have a band structure with a cross-sectional size of 30 μm and a thickness of 0.1 μm. The bands consist of nanoparticles 25 nm in thickness and 400–500 nm in length. The chitin nanofibrils are composed of two crystallites with cross-sectional sizes of 11–12 nm and b axes perpendicular to the nanofibril axis. The chitin nanofibrils tend to form planar elements with a layered structure on both the microlevel and the nanolevel. The addition of chitin nanofibrils to a chitosan solution leads to a rise in its viscosity. However, the action of shear stresses leads to a substantial decrease in the chitosan-chitin solution viscosity, a phenomenon that is due to the presence of planar anisodiametric nanoparticles of chitin.

Structure and characteristics of film composites based on methyl cellulose, poviargol, and montmorillonite

The structure of film composites based on methyl cellulose and fillers, such as montmorillonite and silver nanoparticles stabilized by poly(vinylpyrrolidone) (Poviargol), is studied by X-ray diffraction. In the composite, montmorillonite nanoparticles exist in the exfoliated state; when the content of the nanoparticles is below 7 wt %, the crystallinity of methyl cellulose increases. Owing to the presence of the filler and structural ordering of the matrix, elastic characteristics improve and the degradation temperature of the composites increases. The X-ray structural data show that the Ag particles in the methyl cellulose-Poviargol composite are 30 nm in size. The introduction of up to 20 wt % Poviargol assists the crystallization of methyl cellulose. The strength and strain characteristics of the film composites based on methyl cellulose and Poviargol make it possible to use these composites in medicine and agriculture.

Changes in the supramolecular structure of heat-resistant polyimide fibers in the course of thermal treatment

Changes in the supramolecular structure of heat-resistant fibers based on polyimide PM were studied by X-ray diffraction analysis and NMR spectroscopy.

Properties of Film Materials Based on Composite Nanofibers from Aliphatic Copolyamide and Carbon Nanotubes for Tissue Engineering

The investigation of the dependence of effective viscosity on shear rate for a water-alcohol solution of an aliphatic copolyamide and its mixtures with single-wall carbon nanotubes reveals that additives of the nanoparticles in the amount of 0.5 wt % lead to a substantial reduction in the effective viscosity as the shear rate rises. The measurement of the surface tension and electrical conductivity of the solutions bearing 0.1–2.0 wt % of the nanotubes allows one to choose an optimal mode for electrospinning of the composite nanofibers based on the aliphatic copolyamide. The introduction of carbon nanofibers reduces the specific resistance of the material to 8.9 × 109 Ω m, but increases the elastic modulus. The lack of cytotoxicity of the resulting materials and the high proliferative activity of human dermal fibroblasts on their surface allow one to use the film materials based on the composite nanofibers in cell technologies and as matrices for tissue engineering.

Biological resorption of fibers from chitosan in endomysium and perimysium of muscular tissue

The resorption of fibers from chitosan implanted into emdomysium and perimysium of the rat’s broadest muscle of the back is comparatively studied in vivo by the scanning electron microscopy and histologic analysis methods. It is shown that the mechanism and rate of resorption of the fibers from chitosan depend on the fiber localization in the muscular tissue. Implantation of chitosan fibers into endomysium, where they have been in direct contact with muscle fibers, results in 14 days in the formation of transverse cracks, fiber fragmentation, and their partial resorption. Complete resorption of fibers in endomysium is observed in 30 days. Fibers implanted into perimysium maintain integrity in 7 days of the experiment, and a fibrous tissue is formed around the fibers. There is no destruction of chitosan fibers in 45 days of the exposition. The biocompatibility of the chitosan fibers is confirmed by the effective adhesion and proliferation mesenchyme stem cells on their surface.

Thermochemical structural transformations of polyoxadiazoles

Changes in the physical and chemical structure of polyoxadiazole upon high-temperature heat treatment of Arselon fiber in inert and oxidizing atmosphere were studied. The role of the morphological rearrangement of the polymer in the turbostratic nucleation of carbon structures was determined. The mechanism of the thermochemical degradation and intramolecular cyclization of intermediate and final polyheterocyclic compounds formed in the process was elucidated.

Matrices based on chitosan nanofibers for cell technologies

A material constituting a nonwoven mat consisting of intersecting fibers 100 to 400 nm in diameter was fabricated by the electrospinning of a chitosan solution supplemented with a biocompatible polymer. Optimal compositions of solution and electrospinning conditions were selected. The material was tested for cultivating mesenchymal stem cells. The adhesion and proliferation rate of the stem cells applied on the surface of nanofiber matrix were investigated. The good compatibility of the obtained material with stem cells was shown.