Hydrophobic Modification of Chitosan via Reactive Solvent-Free Extrusion.

Hydrophobic derivatives of polysaccharides possess an amphiphilic behavior and are widely used as rheological modifiers, selective sorbents, and stabilizers for compositions intended for various applications. In this work, we studied the mechanochemical reactions of chitosan alkylation when interacting with docosylglycidyl and hexadecylglycidyl ethers in the absence of solvents at shear deformation in a pilot twin-screw extruder. The chemical structure and physical properties of the obtained derivatives were characterized by elemental analysis, FT-IR spectroscopy, dynamic light scattering, scanning electron microscopy, and mechanical tests. According to calculations for products soluble in aqueous media, it was possible to introduce about 5-12 hydrophobic fragments per chitosan macromolecule with a degree of polymerization of 500-2000. The length of the carbon chain of the alkyl substituent significantly affects its reactivity under the chosen conditions of mechanochemical synthesis. It was shown that modification disturbs the packing ability of the macromolecules, resulting in an increase of plasticity and drop in the elastic modulus of the film made from the hydrophobically modified chitosan samples.

Multicomponent Non-Woven Fibrous Mats with Balanced Processing and Functional Properties.

The mimicking of the architectonics of native tissue, biodegradable non-woven fibrous mats is one of the most promising forms of scaffolding for tissue engineering. The key properties needed for their successful application in vivo, such as biodegradability, biocompatibility, morphology, mechanical properties, etc., rely on their composition and appropriate 3D structure. A multicomponent system based on biodegradable synthetic (polycaprolactone, oligo-/polylactide) and natural (chitosan, gelatin) polymers, providing the desired processing characteristics and functionality to non-woven mats fabricated via the electrospinning technique, was developed. The solid-state reactive blending of these components provided a one-step synthesis of amphiphilic graft copolymer with an ability to form stable ultra-fine dispersions in chlorinated solvents, which could be successfully used as casting solvents for the electrospinning technique. The synthesized graft copolymer was analyzed with the aim of fractional analysis, dynamic laser scattering, FTIR-spectroscopy and DSC. Casting solution characteristics, namely viscosity, surface tension, and electroconductivity, as well as electrospinning parameters, were studied and optimized. The morphology, chemical structure of the surface layer, mechanical properties and cytocompatibility were analyzed to confirm the appropriate functionality of the formed fibrous materials as scaffolds for tissue engineering.

Solid-State Synthesis of Water-Soluble Chitosan-g-Hydroxyethyl Cellulose Copolymers.

Graft copolymers of chitosan with cellulose ether have been obtained by the solid-state reactive mixing of chitin, sodium hydroxide and hydroxyethyl cellulose under shear deformation in a pilot twin-screw extruder. The structure and composition of the products were determined by elemental analysis and IR spectroscopy. The physicochemical properties of aqueous solutions of copolymers were studied as a function of the composition, and were correlated to the mechanical characteristics of the resulting films to assess the performance of new copolymers as coating materials, non-woven fibrous materials or emulsifiers for interface stabilization during the microparticle fabrication process.

Chitosan-g-oligo/polylactide copolymer non-woven fibrous mats containing protein: from solid-state synthesis to electrospinning.

Graft-copolymers based on bioresorbable synthetic (oligo-/polylactide) and natural (chitosan and collagen/gelatin) components were synthesized through solid-state reactive co-extrusion and used for fabrication of fibrous non-woven mats via the electrospinning technique. The effect of the macromolecular features of the initial components on the copolymer characteristics was evaluated using FTIR-spectroscopy, differential scanning calorimetry and elemental analysis. Dynamic light scattering analysis showed that the copolymers have a tendency to form stable ultra-fine dispersions with a mean size of macromolecular aggregates of 150 nm within chlorinated solvents. The copolymer-containing non-woven fibrous mats were fabricated via an electrospinning procedure using chloroform as a solvent. An effect of the copolymer composition on the casting solution's viscosity, conductivity and surface tension was evaluated. Scanning electron microscopy showed that the obtained mats consist of randomly distributed fibers with a mean size of ∼5 µm and a more complex morphology than mats fabricated from neat polylactide. The proposed mechanochemical approach to obtain hybrid copolymeric compositions differs from typical liquid-phase methods in terms of high efficiency, simplicity and cleanness.

Genetic variation of the nine Profiler Plus loci in Russians.

This paper presents allele frequency distributions from a representative population sample of the Russian Federation for the nine loci (D3S1358, vWA, FGA, D8S1179, D21S11, D18S51, D5S818, D13S317 and D7S820) which constitute the commercially available Profiler Plus PCR amplification kit. DNA samples of 402 Russian individuals from 57 regions of the Russian Federation were amplified in a multiplex reaction with subsequent genotyping using an ABI Prism 377 DNA sequencer. The population data obtained for genotype and allele frequencies conformed to Hardy-Weinberg expectations (HWE).