Preparation of aromatic polyamidines and their transformation in polybenzimidazoles

Polymers with amidine groups –NH–C(=NH)– in main chain were synthesized by two different approaches. The first strategy consists in polyaddition of dinitriles and diamines in acidic ionic liquids (ILs) which act as catalyst and solvent, while the second approach is based on polycondensation of 4,4'-oxybis(benzoic acid) diamide and diamines in Eaton’s reagent (ER). The resulting polyamidines (PADs) with Mw up to 25 000 g/mol possess thermal stability on air up to 288°C, and good solubility in polar organic solvents. Moreover dehydrocyclization of obtained PADs into polybenzimidazoles (PBIs) under the action of various oxidants was also studied in this work. The crosslinked films based on PBI and poly(amino imide) resin (PAIR) possess high mechanical characteristics. It has been proved that the crosslinked films based on PBI matrix are perspective materials for design the phosphoric acid electrolyte membranes for the medium temperature fuel cells

Functionalization of chitosan with carboxylic acids and derivatives of them: Synthesis issues and prospects of practical use: A review

The review is devoted to the current state of the investigation works concerning chitosan functionalization with carboxylic acids and derivatives of them, including oxidized carbon nanoparticles such as graphene oxide, oxidized nano diamonds and oxidized carbon nanotubes. The examples of a use of chitosan derivatives in the pharmacology, the regenerative medicine, and other areas are given

Fabrication of Conductive Tissue Engineering Nanocomposite Films Based on Chitosan and Surfactant-Stabilized Graphene Dispersions

Chitosan (CS)/graphene nanocomposite films with tunable biomechanics, electroconductivity and biocompatibility using polyvinylpyrrolidone (PVP) and Pluronic F108 (Plu) as emulsion stabilizers for the purpose of conductive tissue engineering were successfully obtained. In order to obtain a composite solution, aqueous dispersions of multilayered graphene stabilized with Plu/PVP were supplied with CS at a ratio of CS to stabilizers of 2:1, respectively. Electroconductive films were obtained by the solution casting method. The electrical conductivity, mechanical properties and in vitro and in vivo biocompatibility of the resulting films were assessed in relation to the graphene concentration and stabilizer type and they were close to that of smooth muscle tissue. According to the results of the in vitro cytotoxicity analysis, the films did not release soluble cytotoxic components into the cell culture medium. The high adhesion of murine fibroblasts to the films indicated the absence of contact cytotoxicity. In subcutaneous implantation in Wistar rats, we found that stabilizers reduced the brittleness of the chitosan films and the inflammatory response

From Aggregates to Porous Three-Dimensional Scaffolds through a Mechanochemical Approach to Design Photosensitive Chitosan Derivatives

The crustacean processing industry produces large quantities of waste by-products (up to 70%). Such wastes could be used as raw materials for producing chitosan, a polysaccharide with a unique set of biochemical properties. However, the preparation methods and the long-term stability of chitosan-based products limit their application in biomedicine. In this study, different scale structures, such as aggregates, photo-crosslinked films, and 3D scaffolds based on mechanochemically-modified chitosan derivatives, were successfully formed. Dynamic light scattering revealed that aggregation of chitosan derivatives becomes more pronounced with an increase in the number of hydrophobic substituents. Although the results of the mechanical testing revealed that the plasticity of photo-crosslinked films was 5–8% higher than that for the initial chitosan films, their tensile strength remained unchanged. Different types of polymer scaffolds, such as flexible and porous ones, were developed by laser stereolithography. In vivo studies of the formed structures showed no dystrophic and necrobiotic changes, which proves their biocompatibility. Moreover, the wavelet analysis was used to show that the areas of chitosan film degradation were periodic. Comparing the results of the wavelet analysis and X-ray diffraction data, we have concluded that degradation occurs within less ordered amorphous regions in the polymer bulk