T. A. Akopova

Solid state production of cellulose-chitosan blends and their modification with the diglycidyl ether of oligo(ethylene oxide)

Abstract Blends of the naturally occurring polysaccharides, cellulose and chitosan, obtained in the solid phase by the combined action of high pressure and shear deformation using various equipment, were studied. It was shown by IR-spectroscopy that the system of hydrogen bonds formed between hydroxyl and amino groups of the polysaccharides undergoes a qualitative change. This provides evidence that the blending of polysaccharides occurs at the molecular level. A mechanism of cellulose–chitosan blend formation in the presence of a diepoxide as a crosslinking agent was also studied. It was established that the crosslinking agent reacts predominantly at the amino groups of chitosan, with the formation of a three-dimensional network, cellulose macromolecules being located within and partially bound with this network by the crosslinks. It is shown that the formation of the aforementioned structures results in the insolubility of cellulose–chitosan compositions in acidic and alkaline aqueous media.

Investigation of properties of chitosan obtained by solid-phase and suspension methods

The properties and fractional composition of chitosan prepared by the suspension method and by solid-phase deacetylation of chitin under conditions ofjoint action of high pressure and shear deformations was studied. Elemental analysis, particle size distribution analysis, viscosimetry, potentiometry, and other experimental techniques were used in the study. The specific features of chitosan obtained by solid-phase extrusion were examined.

Effect of direct-current discharge treatment on the surface properties of chitosan-poly(L,L-lactide)-gelatin composite films

The surface of films made from a chitosan-poly(L,L-lactide)-gelatin mixture stabilized with a grafted-copolymer fraction has been modified by dc discharge treatment, as well as that of films made of the individual components. The surface properties of the films (wettability, surface energy), the chemical structure of surface layers, and their morphology have been examined by goniometric measurement of contact angles, X-ray photoelectron spectroscopy, and scanning electron microscopy.

Solid-state synthesis of amphiphilic chitosan-polyethylene systems by the maleinization of both components

N-acylated chitosan modified by maleic anhydride was prepared by the method of the solid-state synthesis (Bridgman anvils, semipilot extruder). In contrast to the synthesis under homogeneous conditions, solid-state acylation is accompanied by the reaction of imidization of the formed amic acid as well as by reaction through double bonds, thus leading to the formation of derivatives of succinic anhydride. By simultaneous or subsequent interaction of chitosan modified with maleic anhydride with a PE matrix, either modified or not modified with maleic anhydride, new chitosan-polyethylene composite materials are prepared, and these composites are characterized by the combined valuable medicinal and biochemical properties of chitosan and high mechanical characteristics of the polyolefin component. The above composites are of obvious interest as amphiphilic sorbents, which are highly resistant to the action of aggressive media, as well as antimicrobial and biodegradable PE-based materials.

Investigation of interaction of chitosan with solid organic acids and anhydrides under conditions of shear deformation

Chitosan interaction with stearic, oxalic, malonic, and succinic acids and with phthalic, succinic, and maleic anhydrides under shear deformation was investigated. It was shown that under these conditions the production of corresponding chitosan derivatives takes place. On the basis of elemental analysis, potentiometric titration, and IR spectroscopy data, the possible mechanisms of the reaction are discussed.

Compatibility of cells of the nervous system with structured biodegradable chitosan-based hydrogel matrices

Hydrogel matrices for cell cultivation have been generated by two-photon laser polymerization of unsaturated chitosan derivatives and methacrylated hyaluronic acid. The adhesive and toxic properties of the matrices have been assessed, and the matrices have been shown to have a good compatibility with primary hippocampal cell cultures. The formation of morphologically normal neural networks by cells of the nervous system cultured on the surface of hydrogel matrices has been observed. The metabolic status of dissociated hippocampal cells cultured on the matrices was similar to that of the control cultures, as shown by the results of MTT reductase activity assay. Thus, matrices based on unsaturated polysaccharide derivatives crosslinked by laser irradiation showed good compatibility with differentiated cells of the nervous system and considerable potential for use in neurotransplantation.

Solid state synthesis of chitosan and its unsaturated derivatives for laser microfabrication of 3D scaffolds

Chitosans with various degrees of deacetylation and molecular weights and their allyl substituted derivatives were obtained through a solvent-free reaction under shear deformation in an extruder. Structure and physical-chemical analysis of the samples were carried out using nuclear magnetic resonance (NMR), ultraviolet (UV) and infrared radiation (IR) spectroscopy. Photosensitive materials based on the synthesized polymers were successfully used for microfabrication of 3D well-defined architectonic structures by laser stereolithography. Study on the metabolic activity of NCTC L929 cultured in the presence of the cured chitosan extracts indicates that the engineered biomaterials could support adhesion, spreading and growth of adherent-dependent cells, and thus could be considered as biocompatible scaffolds.

The study of the interaction between chitosan and 2,2-bis(hydroxymethyl)propionic acid during solid-phase synthesis

New polymer salts and N-acetylated chitosan derivatives are prepared in an extruder by the method of solid-phase synthesis via the interaction of chitosan and 2,2-bis(hydroxymethyl)propionic acid. The effect of the initial component ratio and temperature on the yield and structure of the target products is studied. Joint deformation of solid components at room temperature is found to cause the quantitative formation of salt bonds between carboxylic groups of the acid and amino groups of chitosan. At elevated temperatures of synthesis, the corresponding acetylated derivatives with a degree of substitution of amino groups varying from 0.16 to 0.43 are prepared. The relaxation and phase transitions in the polymer salts and acetylated chitosan derivatives and their sorptional activity are studied. The films prepared from aqueous solutions of the new salt modification of chitosan are characterized by a homogeneous structure and improved mechanical characteristics relative to those of the films based on chitosan acetates. An additional thermal treatment of the products of the solid-phase synthesis leads to the formation of crosslinked and water-swollen materials that can be used for the development of novel polymeric chitosan-based membranes and sorbents.

Chitosan-g-lactide copolymers for fabrication of 3D scaffolds for tissue engineering

Chitosan-g-oligo (L, D-lactide) copolymers were synthesized and assessed to fabricate a number of 3D scaffolds using a variety of technologies such as oil/water emulsion evaporation technique, freeze-drying and two-photon photopolymerization. Solid-state copolymerization method allowed us to graft up to 160 wt-% of oligolactide onto chitosan backbone via chitosan amino group acetylation with substitution degree reaching up to 0.41. Grafting of hydrophobic oligolactide side chains with polymerization degree up to 10 results in chitosan amphiphilic properties. The synthesized chitosan-g-lactide copolymers were used to design 3D scaffolds for tissue engineering such as spherical microparticles and macroporous hydrogels.

Modification of the chitosan structure and properties using high-energy chemistry methods

Literature on the modification of the natural polymer chitosan using high-energy chemistry methods (treatment by a low-temperature plasma, with an electron beam, energetic ions, or γ-iradiation) has been surveyed. The basic chitosan treatment procedures and facilities used in the processes have been described. The instrumental techniques used to study changes in the chemical structure and properties of modified chitosan have been considered. Data showing the possibility of using modified chitosan in medicine and biotechnology have been presented.