Russian team tests new polymeric coating for vascular stents

A group of researchers of the Institute of Biophysics (Russian Academy of Sciences), Krasnoyarsk regional clinical hospital and Krasnoyarsk regional department of morbid anatomy under the guidance of .I. Gitelzon, Academician of Russian Academy of Sciences, have tested characteristics of a new polymeric coating for vascular stents. Intravascular stents processed by the polymeric coating have advantages as compared to standard metallic ones.

Intravascular stenting of arteries is one of the most frequent operations in cardiovascular surgery. Stents (metal woven fabric cylinders) are inserted into a vessel with injured inner wall to avoid its destruction, thrombi formation or vasoconstriction. Unfortunately, metal stents provoke thrombi formation. To enhance stent biocompatibility, it is possible either to modify metal surface of implant or to apply biocompatible coatings. The Krasnoyarsk researchers have chosen this way. They used polymers of fatty acids' oxyderivatives (polyhydroxyalkanoates or PHAs) - biocompatible and biodegradable materials of microbe origin. PHAs, which practically do not provoke immune reactions, are highly believed in by vascular sturgeons who are planning to make prosthetic cardiac valves of this material and to use it for angioplasty.

The PHA synthesis, isolation and purification technique was developed in the Institute of Biophysics (Siberian Branch, Russian Academy of Sciences). The technique allows to get high-purity samples tolerant to contact with blood. The researchers carried out all necessary investigations, including acute and chronic experiments with laboratory animals, and made sure that PHAs are biocompatible with cells, tissues and the organism as a whole.

The polymer was used to cover stents for peripheral vessels made of nitinol - nickel/titanium alloy - produced by Komed Ltd., Moscow (technology of this process also had to be developed). Intravascular stents (0.8 mm in diameter, 10 mm long) were introduced under anaesthetic into the femoral artery of laboratory dogs. Investigations carried out in 2 and 12 weeks after the operation proved that vessels were patent in all cases, artery lumen was not constricted. Stems with polymeric coating have proved to be better in every respect than metal ones. With their implantation, inflammatory reaction is much weaker, therefore they caused significantly less reactive changes of the vascular wall and did not provoke thrombi formation.

Within 12 weeks all stents, as expected, grew into vessel tissues, having plunged into its wall. In case of nitinol stent with polymeric coating, the wall of a vessel practically did not thicken, while in the vessels with metal stent it was significantly thicker than the standard. So, the results demonstrate significant advantages of a new intravascular stent material.

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