Phase Analysis of the Cellulose Triacetate-Nitromethane System

A comprehensive study was made on the cellulose triacetate-nitromethane system to explore its phase separation within ranges 2–25 wt.% and −5÷+80°C by means of polarization light and electron microscopy, the turbidity spectrum method, differential thermal and X-ray analyses, and rheological techniques. The physical state of the polymer was identified within the phase coexistence boundaries on the phase diagram which included three types of phase separation (amorphous (with a UCST at Tcr=57∘C and ccr=7.3 wt.%), crystal, and liquid crystal). The boundaries of the regions determining the coexistence of the liquid crystal (LC) and the partly crystal phase were found to be inside the region of amorphous liquid-liquid phase separation. For cellulose ester-solvent systems, this state diagram is the first experimental evidence for the possibility of coexistence of several phases with amorphous, LC, and crystal polymer ordering

Influence of Chitosan Ascorbate Chirality on the Gelation Kinetics and Properties of Silicon-Chitosan-Containing Glycerohydrogels

The influence of the chirality of chitosan ascorbate on the gelation kinetics and the properties of hybrid silicon-chitosan-containing glycerohydrogels were studied with a deep estimation of the stereospecificity of chitosan polysalts with l- and d-ascorbic acid diastereomers and their biological effects. It has been established that l- and d-diastereomerically enriched chitosan ascorbates are characterized by a positive Cotton effect and differ in the wavelength of the maximum of the dichroic band (250 and 240 nm), as well as in the values of its specific ellipticity (21.8 × 105 and 39.2 × 105 deg·mL·dm−1·g−1), the sign of specific optical rotation (+ and −), the type of dispersion curves (anomalous and smooth), as well as the condensed phase morphology (anisodiametric particles with optical anisotropy and confocal domains of spherical shape, respectively). In the biomimetic sol-gel synthesis of silicon-chitosan-containing glycerohydrogels using silicon tetraglycerolate as a precursor, it was found that chitosan d-ascorbate retarded gelation. Thin congruent plates obtained from the corresponding glycerohydrogels based on chitosan d-ascorbate have higher mechanical strength and elasticity under uniaxial stretching and lower values of Young’s modulus. It has been shown that the systems based on chitosan d-ascorbate show the greatest antibacterial activity against Staphylococcus aureus 209P and Escherichia coli 113-13 and significantly promote the viability of normal human dermal fibroblasts. The results of our assessment of the biological properties of chitosan polysalts are unexpected, since ascorbic acid exhibits biological activity as its l-isomer only

Thermosensitive Chitosan-Containing Hydrogels: Their Formation, Properties, Antibacterial Activity, and Veterinary Usage

Mixtures of aqueous solutions of chitosan hydrochloride (CS·HCl, 1–4 wt.%) and Pluronic F-127 (Pl F-127, 25 wt.%) were studied using vibrational and rotational viscometry; the optimal aminopolysaccharide concentration (3 wt.%) and the CS·HCl:Pl F-127 ratio (30:70) to obtain a thermosensitive hydrogel were found. It was shown that at 4 °C, such mixed compositions were viscous liquids, while at 37 °C for 1–2 min, they undergo a thermally reversible transition to a shape-stable hydrogel with a developed level of structure formation, satisfactory viscosity and high mucoadhesive parameters (maximum pull-off force Fmax = 1.5 kN/m2; work of adhesion W = 66.6 × 10−3 J). Adding D-ascorbic acid to the hydrogel led to orientational ordering of the supramolecular structure of the mixed system and significantly improved mucoadhesion (Fmax = 4.1 kN/m2, W = 145.1 × 10−3 J). A microbiological study revealed the high antibacterial activity of the hydrogel against Gram-negative and Gram-positive bacterial strains. The treatment of mixed bacterial infection in cows demonstrated the possibility of the in situ formation of a viscoelastic gel and revealed its high therapeutic effect. It has been suggested that our thermosensitive mucoadhesive CS·HCl:Pl F-127 hydrogels could be considered as independent veterinary drugs and pharmaceuticals