S. N. Chvalun

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.

Initial stages of growth of poly(p-xylylene) coatings: AFM study

The morphology of poly(p-xylylene) ultrathin films prepared by vapor deposition polymerization on the surface of single-crystal silicon (100) and on the cleaved surface of mica at a substrate temperature of 20°C has been studied by atomic force microscopy. At the initial stage, the growth of the poly(p-xylylene) coating follows the island mechanism. Within the framework of pyramidal model of island growth, the mean diffusion length for monomer p-xylylene is calculated: For the single-crystal silicon, this parameter is 15 ± 3 nm; for the cleaved surface of mica, 9 ± 2 nm. The nature of the substrate and defects on its surface show a peculiar effect on the structure of the poly(p-xylylene) coating. Thus, at a low monomer flow, nucleation of polymer islands on the surface of silicon is predominantly homogeneous, whereas on the cleaved surface of mica, it is heterogeneous. A change in the monomer flow significantly affects the rate of nucleation of polymer islands.

Biodegradable multi-liposomal containers

The method of preparing biodegradable multi-liposomal containers via modification of anionic liposomes with a cationic polymer and subsequent adsorption of the obtained liposome-polymer cationic complex on the surfaces of negatively charged polylactide micelles with grafted polyoxyethylene chains is described. Liposomes preserve their integrity in a ternary micelle-polycation-liposome complex, a circumstance that allows the complex to be used as a multi-liposomal container for encapsulation of bioactive compounds.

Effect of low molecular additives on the electrospinning of nonwoven materials from a polyamide-6 melt

The effect of low molecular additives on the structure and properties of polyamide-6-based nonwoven materials obtained via electrospinning from a melt is studied. The introduction of up to 10% salts of higher fatty acids into the polymer melt leads to a decrease in its viscosity and to an increase in its electrical conductivity, thereby making it possible to produce nonwoven materials with an average fiber diameter of <1.5 µm. With the use of DSC, IR spectroscopy, and X-ray diffraction, it is shown that, in nonwoven materials based on polyamide-6, the metastable γ form of crystals prevails, while, in the native polymer, the stable a form predominates. The resulting materials demonstrate high filtration characteristics, and their surface properties are close to superhydrophobic.

Migration and Proliferative Activity of Mesenchymal Stem Cells in 3D Polylactide Scaffolds Depends on Cell Seeding Technique and Collagen Modification

We analyzed viability of mesenchymal stem cells seeded by static and dynamic methods to highly porous fibrous 3D poly-L-lactide scaffolds with similar physical and chemical properties, but different spatial organization modified with collagen. Standard collagen coating promoted protein adsorption on the scaffold surface and improved adhesive properties of 100 μ-thick scaffolds. Modification of 600-μ scaffolds with collagen under pressure increased proliferative activity of mesenchymal stem cells seeded under static and dynamic (delivery of 100,000 cells in 10 ml medium in a perfusion system at a rate of 1 ml/min) conditions by 47 and 648%, respectively (measured after 120-h culturing by MTT test). Dynamic conditions provide more uniform distribution of collagen on scaffold fibers and promote cell penetration into 3D poly-L-lactide scaffolds with thickness >600 μ.

Electrospinning of Non-Woven Materials from the Melt of Polyamide-6 with Added Magnesium, Calcium, and Zinc Stearates

Polyamide-6 fibres of diameter 2-3 μm could be produced from the melt by adding (2-10 mass%) divalent metal (Mg, Ca, Zn) stearates, which caused the viscosity to decrease and the electrical conductivity of the melt to increase, whereas the diameter of pure polymer fibres was >20 μm. Differential scanning calorimetry, IR spectroscopy, and x-ray structure analysis found that the supramolecular structure of polyamide-6 in non-woven materials differed considerably from that of the starting polymer. Whereas the α-form of the crystals dominated in the granules, the metastable γ-form dominated in non-woven materials spun from both pure polymer and those with added stearates. Non-woven materials were wetted according to the Wenzel model with a petal effect being observed.

Rheological Features of Fiber Spinning from Polyacrylonitrile Solutions in an Electric Field. Structure and Properties

Spatially ordered fibers of diameter 260-990 nm were produced by electrospinning from polyacrylonitrile (PAN) solutions. The influence of the rheological properties of solutions of PAN and its copolymers was investigated over a broad range of molecular weights during fiber spinning in an electric field. The structural and tensile properties of the fibers were studied.

Proliferative and Differentiation Potential of Multipotent Mesenchymal Stem Cells Cultured on Biocompatible Polymer Scaffolds with Various Physicochemical Characteristics

Biocompatibility of film and fibrous scaffolds from polylactide-based polymers and the relationship between their architecture and the functional characteristics of mesenchymal stem cells were studied. Cell culturing on polylactide-based film and fibrous matrixes did not deteriorate cell morphology and their proliferation and differentiation capacities. The rate of cell proliferation and penetration in microporous 3D matrices with the same porosity parameters and pore size depended on their spatial organization. The above materials can be used as scaffolds for mesenchymal stem cells for creation of tissue engineering implants. The scaffold size and structure should be determined by the defects in the organs in which the regeneration processes have to be stimulated.

Nanocomposite nonwoven materials based on polyamide-6 and montmorillonite, prepared by electrospinning of the polymer melt

The effect of montmorillonite on the structure and properties of nonwoven microfibrous materials based on polyamide-6 and prepared by electrospinning of the polymer melt was studied. Addition of 3% montmorillonite into the melt increases its viscosity and electrical conductivity, with the mean diameter of the formed fibers increasing from 8 to 12 μm. As shown by X-ray diffraction, IR spectroscopy, and differential scanning calorimetry, pellets of the pristine polyamide are characterized by prevalence of crystals of the stable α-form, whereas in the composites and nonwoven materials the metastable γ-form prevails. Addition of montmorillonite only slightly influences the contact angles, and the resulting materials exhibit nearly superhydrophobic properties.

Structure and optical characteristics of poly(p-phenylenevinylene) prepared by vapor deposition polymerization

Films based on poly(p-phenylenevinylene) are prepared by pyrolitic polymerization of α,α′-dichloro-p-xylene. During monomer precipitation, the temperature on a substrate is 25, 50, or −196°C. Subsequent annealing of the precursor at 250°C yields the final product: the copolymer of p-phenylenevinylene and p-xylylene with an approximate composition of 4: 1. The surface morphology, structure, and optical characteristics of the polymer are studied. The mean-square surface roughness of the precursor is 5 nm. Thermal treatment increase the samples’ roughness up to 10 nm. When the precursor is transformed into poly(p-phenylenevinylene), the roughness coefficient decreases from 0.85 ± 0.05 to 0.74 ± 0.05 owing to the formation of a rougher surface. Characterization of the optical characteristics of the synthesized poly(p-phenylenevinylene) shows that the maximum effective conjugation chain length achieves 12 units in the copolymer prepared when the temperature on the substrate is −196°C. As the temperature on the substrate increases, the conjugation length decreases to 8 units upon precipitation. Luminescence analysis reveals the effective excitation-energy transfer from short chain fragments of poly(p-phenylenevinylene) to long chain fragments. Electron parameters of the material are estimated: i.e., the band gap, the Huang-Rhys factor, the Stokes shift, and the oscillation energy of molecules.