ИСТИНА

Nowadays there is a huge problem with human hypersensitivity and it is very important to try to minimize the probable risks connected with it. Therefore it would be very useful to find a media, which is absolutely biocompatible and, at the same time, can dissolve polymers suitable for different biomedical purposes, such as wound dressing, drug delivery, cancer diagnosis and tissue engineering. Carbonic acid behaves just like this kind of media. If we saturate water with pressurized carbon dioxide, the pH will decrease down to the values lower than 3.0 with the increase of pressure up to the hundreds atmospheres. Thus, as a result, polymers in carbonic acid can protonate, become polyelectrolytes and dissolve. Сarbonic acid combines two important properties thanks to which it appears to be very convenient solvent for biomedical applications. Those are strong antimicrobial activity at the stage of coating formation on some medical device and remaining biocompatibility when using this device with the adsorbed coating in the human body. Moreover, when changing the dissolving power of “usual” solvents the inhomogeneity and strong gradients occur. On the contrary, when using carbonic acid we can depressurize whole volume of the reactor simultaneously at the same time i.e. increase the pH inside very homogeneously. To develop the methodological recommendations of the best regime of dissolution of polymers in biocompatible solvent - carbonic acid, it is extremely important to detect and explain the conformation of the macromolecules in this solvent. However it is very challenging to investigate the conformation of the macromolecules, solubilized in water saturated with CO2 under high pressure by means of the commonly used methods for conformational characterization of polymers in solutions, such as light scattering, small-angle neutron and X-Ray scattering. Indeed the solutions of polymer in carbonic acid exist only in the pressurized tightened metal autoclave. Therefore, using of ex situ atomic force microscopy as a tool to observe macromolecules as adsorbed on mica from polymer solution 4th International Solvothermal and Hydrothermal Association Conference – ISHA 2014 in carbonic acid seems to be very promising at least it can provide direct information on the morphology of polymer structures, which spontaneously adhered to the substrate during exposure in the autoclave at high pressure. Therefore, the combination of the method of direct adsorption on a substrate of single macromolecules from highly pressurised solvent with further analysis of their conformation with atomic force microscopy seems to be very promising. In our laboratory we succeeded in dissolution of such polycations in solutions in carbonic acid as chitosan, poly(2-vinylpiridine), poly(4-vinylpiridine) and in fabrication of micelles from copolymers of polystyrene and poly(4-vinylpiridine) in such medium. We succeeded in adsorption of rather smooth, uniform polymer films from such solutions. Closer look with atomic force microscopy at the films of chitosan revealed that they are composed by rather persistent elongated rod-like structures (Fig. 1). Micelles were also investigated with atomic force microscopy and transmission electron microscopy.