ИСТИНА

It is well known, that a complex of the unique properties of chitosan materials causes their wide usage in many different areas of biomedical applications. Particular interest is provoked by a possibility to cover with chitosan the surfaces of biomedical devices (such as heart valve prostheses) by deposition from solutions in water saturated with CO2 under high pressure (i.e. from carbonic acid) [1]. Carbonic acid is an advanced solvent for polycations including chitosan as far as it is not only a biocompatible and yet antimicrobial medium, but additionally its dissolving power may be adjusted and tuned by means of purely physical factors, i.e., by variation of pressure. We performed a set of systematic expirements including deposition of chitosan macromolecules with different molecular weights and degrees of deacetylation (DA) on a model surface from solutions in carbonic acid. Then we analysed the conformation of the deposited macromolecules by means of an atomic force microscopy. The macromolecular conformation as deposited from carbonic acid on a model mica substrate was found to be rather peculiar: indeed, the polymer chains were deposited as rather extended persistent structures. There was no correlation observed between the average length of the nanostructures and their molecular weight. Therefore we made a conclusion that these “sigar-like” nanoobjects are aggregates consisting of several macromolecules. It was shown that the size of the aggregates increases with increasing of the number of charged units (DA). This can be explained by the dominance of the effect caused by the attraction of ionic pairs over the aggregate size stabilisation caused by the presence of charged units. It is known that a dipole-dipole interaction of ionic pairs promotes the aggregation of the macromolecules with each other. Indeed our experimental conditions correspond to the enhanced Manning condensation of counterions reducing the total net charge of the polyelectrolyte chains.