N. R. Kil’deeva

A study of cryostructuring of a polymer system. 39. Poly(vinyl alcohol) composite cryogels filled with chitosan microparticles

Composite macroporous poly(vinyl alcohol) (PVA) cryogels have been prepared by cryogenic treatment (freezing at −20°C for 12 h followed by defrosting at a rate of 0.03°C/min) of dispersions of chitosan particles swollen in an aqueous 120 g/L PVA solution. The elasticity moduli and fusion temperatures have been determined for corresponding samples, and their microstructure has been investigated by optical microscopic examination of their thin sections. The rigidity and heat endurance of the PVA-chitosan composite cryogels have been shown to increase with filler concentration. In addition, the rheological properties of initial dispersions have been studied and the appearance of adhesion contacts between discrete and continuous phases has been revealed already at the stage of dispersion preparation. The optical microscopic investigations of the morphological features of the initial dispersions and the microstructure of the composites have established a relatively uniform distribution of filler particles in the bulk of composite cryogels. It has been shown that chitosan particles incorporated into the matrix of the macroporous PVA cryogel are capable of sorbing heavy metal ions—in particular, bivalent copper ions—from aqueous solutions.

A Study of cryostructuring of polymer systems. 41. Complex and composite poly(vinyl alcohol) cryogels containing soluble and insoluble forms of chitosan, respectively

Complex macroporous poly(vinyl alcohol) (PVA) cryogels have been obtained by cryogenic treatment (freezing at–20°C for 12 h followed by defrosting at a rate of 0.03°C/min) of PVA–chitosan hydrochloride mixed solutions. The subsequent alkaline treatment of the cryogels has resulted in the transformation of the water-soluble salt form of chitosan into its insoluble basic form, which coagulates inside the bulk of the continuous phase of PVA cryogel into small particles with sizes of 2–5 µm. In the resulting composite cryogels, these particles play the role of an “active” filler, which increases the rigidity and heat endurance of the gel material. It has been shown that the sorption capacity of such chitosan particles entrapped into the bulk of composite cryogels with respect of bivalent copper ions is noticeably higher than the sorption capacity of ground chitosan particles incorporated as a discrete filler into the continuous phase PVA cryogels. The study of the properties of PVA–chitosan hydrochloride mixed solutions revealed that these polymers are, to a large extent, compatible with one another in a common solvent at a low ionic strength. Therefore, liquidliquid phase separation of these systems due to the thermodynamic incompatibility of macromolecules of different natures is observed only upon increasing the ionic strength by adding a low-molecular-mass salt (NaCl, 0.15 mol/L) to the solution.

Peculiarities of obtaining biocompatible films based on chitosan cross linked by genipin

The results of a study of gelation peculiarities in chitosan solutions in the presence of a cross-linking agent of natural origin and biocompatible properties of films obtained on the basis of the chitosan-solution–genipin gelling system are presented. The possibility of controlling the swelling degree of the films from 300 to 1800% are shown.

Biodegradablescaffolds based on chitosan: Preparation, properties, and use for the cultivation of animal cells

The influence of the conditions of the formation of chitosan hydrogels crosslinked with glutaraldehyde (GA) or genipin (the polysaccharide molecular weight, pH level, and concentration of the chitosan solution) on the gel time and the properties of biopolymer scaffolds for tissue engineering obtained by the freeze-drying of hydrogels was studied. The resulting scaffolds had different structures (morphology, degree of anisotropy, average pore size) and moisture-retaining capacities. The cytotoxicity of biodegradable scaffolds based on chitosan with a low content of genipin and GA was studied for the first time. Using the L929 mouse fibroblasts model line, we demonstrated that scaffolds based on chitosan with a molecular weight of 320 and 190 kDa crosslinked with genipin and GA (0.005 and 0.01 mol/mol of chitosan amino groups) are biocompatible. Using confocal laser microscopy, we demonstrated that the cells are uniformly distributed in all scaffold samples and they successfully grew and proliferated when cultured in vitro for 4 days.

Electrospinning of Biodegradable Polymer Scaffolds

Ultrathin fibers could be prepared by nozzle-less electrospinning from solutions of biodegradable polyhydroxybutyrate (PHB) polyesters and its mixture with polycaprolactone in CHCl3. The formation region of the continuous network of linkages that was required for stable electrospinning of the fibers was established by studying the PHB solution viscosity as a function of concentration. It was found that microscopic amounts of HCl could regulate the viscosity of solutions of high-molecular-weight PHB.

Films of a Biodegradable Polyester Mixture with Antimicrobial and Proteolytic Activity

The possibility of preparing a biomaterial based on a mixture of biocompatible and biodegradable polymers, polyhydroxybutyrate and polycaprolactone, was studied. Samples for laboratory tests were prepared by forming films from an emulsion of solutions of biologically active compounds in a solution of the polymers in an organic solvent. Trypsin was used as the proteolytic component. Films containing chlorhexidine digluconate, pefloxacin, and furazolidone were studied in order to find the optimum antimicrobial component. The optimum composition of the molding mixture for preparing films with the optimal properties, i.e., trypsin activity 52.5% of the initial value, vapor permeability 4.5 mg/cm2, furazolidone desorption rate 25% Cτ/C∞, and properties 90% stable after storing in normal saline, was determined.

Surgical Sutures Modified with Polysaccharide Composites

Method development for improving the biocompatibility of fibroin sutures by forming surface layers of biopolymer polyelectrolyte complexes was studied. The rheological properties of aqueous alcohol solutions of the polysaccharides chitosan and hyaluronic acid were compared. Two-component silk threads coated with the polyelectrolyte complex of chitosan and hyaluronic acid were prepared by depositing layers. The resulting threads could be used in general surgery to suture post-operative wounds and as mesothreads for compression plastic surgery.

A study of cryostructuring of polymer systems. 43. Characteristics of microstructure of chitosan-containing complex and composite poly(vinyl alcohol) cryogels

The microstructure of complex and composite poly(vinyl alcohol) (PVA) cryogels containing water-soluble chitosan hydrochloride (ChHC) of dispersed particles of water-insoluble chitosan base (Ch), respectively, has been studied by optical microscopy and attenuated total reflection FTIR spectroscopy. The macroporous morphology of cryogels has been studied using preparations in the form of thin (~10 μm) sections and discs 1 mm thick. The introduction of non-gelling additives (NaCl and ChHC) into an initial PVA solution causes significant changes in the size and shapes of macropores in the complex cryogels formed by freezing–defrosting, as compared with the pores in the samples obtained under the same conditions without additives. The reasons for the changes are the process of phase segregation and the influence of low- and high-molecular-weight electrolytes on crystallization of ice, which plays the role of a porogen upon cryotropic gelation of aqueous PVA solutions. As a result of an alkaline treatment of the complex cryogels, which transforms ChHC into Ch, microcoagulation of chitosan yields discrete, almost spherical, particles with sizes of about 1–5 μm. IR spectral studies have shown that concentration gradients of the gelling and nongelling polymers arise along the thickness of the gel discs, with PVA concentration prevailing near the lower surface and ChHC or Ch concentration dominating near the upper surface of the disc.

A study of the viscosity of hyaluronic acid solutions for the preparation of polyelectrolyte complexes with chitosan

The viscosity of hyaluronic acid solutions kept at different pH values was found to decrease in the following order of pH: 6.5 > 3.5 > 4.3, although acid hydrolysis occurred at a higher rate in the most acidic solution. The poorest stability of the solutions with pH 4.3 was attributed to the compaction of the macromolecules as a result of charge density redistribution along the polyacid chains.

Preparation of Biologically Active Film-Forming Materials Based on Polyphosphate-Modified Chitosan

The processes of preparing film-forming materials based on chitosan with surface modification and ionic cross-linking using sodium tripolyphosphate and potassium pyrophosphate respectively were studied. Optimum cross-linking conditions were identified by studying the interactions of chitosan with different levels of amino group protonation with polyphosphates with different numbers of ionized groups. These studies showed that changes in the duration of treatment of films allowed the level of swelling to be varied over the range 165% to 148% for potassium pyrophosphate and from 196% to 80% for sodium tripolyphosphate. Studies of the kinetics of study drug release showed that changes in the conditions used for modification with polyphosphates could increase the duration of release of the biologically active components to 8 h.