Katarína Vizárová

Depolymerization reactions of hyaluronic acid in solution.

Samples of microbial sodium hyaluronate were degraded by heating, ultrasonication ultraviolet (UV) and gamma-ray irradiation and enzymatic treatment. The weight-average molecular weight, Mw, of hyaluronate in 0.15 M NaCl and 0.06 M Na2HPO4 was determined by gel filtration with UV detection. The Mw of the degraded samples varied from 8 x 10(4) to 1.38 x 10(6). Depolymerization processes can be described by linear relationship (1/Mw)2 = f(t) in the case of ultrasonic treatment and by non-linear relationships in the cases of heating and UV irradiation at 257 nm. Gamma-ray irradiation and enzymatic treatment caused chemical degradation and depolymerization to oligosaccharides, respectively.

Modification of layered atelocollagen: enzymatic degradation and cytotoxicity evaluation

Two kinds of layered atelocollagen materials cross-linked with hexamethylene diisocyanate (HMDIC), starch dialdehyde and glyoxal were enzymatically treated by bacterial collagenase. Evaluating collagenase digestion assay for these material showed progressive differences, particularly in the group of samples cross-linked with HMDIC. This should offer the possibility of programmed enzymatic degradation. These materials may be toxicologically acceptable as proven by the short-term test used for cytotoxicity evaluation.

Modification of layered atelocollagen by ultraviolet irradiation and chemical cross-linking: structure stability and mechanical properties

Physical and chemical modifications of atelocollagen materials have been carried out to improve their physical, chemical and biological properties. We have studied the influence of physical modification using ultraviolet irradiation and of chemical modification using hexamethylene diisocyanate on the physical properties of layered atelocollagen materials. The study evaluated the structural stability of cross-linked materials using swelling experiments. Influence on mechanical properties is also discussed.

Relationship between the decrease of degree of polymerisation of cellulose and the loss of groundwood pulp paper mechanical properties during accelerated ageing

During natural ageing, paper undergoes colour changes and becomes brittle. It is mainly due to the degradation of cellulose, the main component of paper fibres. From the viewpoint of conservation/protection of paper-based information carriers, as well as of the utilisation of secondary fibres, knowledge of the impact of a decrease of the degree of polymerisation (DP) of cellulose on mechanical properties of paper becomes of key importance. In this paper, correlations between the decrease of DP of cellulose and the loss of paper folding endurance (FE) using three model samples (pure cellulose, groundwood pulp paper, and degraded groundwood pulp paper) at accelerated ageing were investigated. The existence of such correlations between DP and FE is supported by experimental results; the correlations are linear for pure cellulose and groundwood pulp paper ageing, while exponential correlation was observed in case of degraded groundwood pulp paper. The results indicate that the rate of paper degradation can be evaluated by means of the rate of glycosidic bonds breaking in cellulosic polymer chains both for cellulose and groundwood pulp paper.

Peculiar rheological properties of dilute aqueous solutions of polymers in contact with a rotating disc

Abstract The anomalous decrease of apparent solution viscosity (measured by a rheoviscometric system with a metal disc) below the viscosity of pure water was monitored by studying highly diluted solutions of water-soluble polymers. The phenomenon suddenly vanishes below 35°C, which is not the case for a simple drag reduction. It is suggested that the explanation is in the complex functioning of drag reduction and viscoelastic behaviour of the adsorbed polymer layer at the metal disc.