[Estimation of biocompatibility of fibers with large mechanical resistance]

Aramid fibers from aromatic polyamide group are plastic materials with high mechanical resistance to breaking, small elongation and low mass. They have obtained numerous technical usage for products carrying high mechanical forces and resistance to consumption. Application of aramid in alloplasty would satisfy the grafts with high mechanical resistance. However, the biological influence and biostability of aramid is unknown and univocal. Research of the degree of biocompatibility of aramid fibres in comparison with commonly used polyester fibres with known and accepted biological reaction was the purpose of the study. The research included in the first phase: physicochemic properties, hemolytic action, cytotoxity degree, intracutaneous reactivity of aqueous extracts, in the second phase: estimation of tissue reaction after implantation the early and distant period, estimation of systemic and local induction of proinflammatory cytokines IL-1beta ad IL-6 after implantation. In physicochemic studies of aqueous extracts from fibers proper electric conductivity and dry residue were determined. The research of toxic action was carried out on frozen sperm of a bull estimating the survival time of sperm cells in the tested aqueous extracts. The estimation of hemolytic was conducted on human erythrocytes according to the method based on photometric measurement of blood supernatant and aqueous extracts. The research of irritating action measured with the changes of colour and size reaction after intracutaneous injection of aqueous extracts was carried out on rabbits. The research of the local reaction of soft tissue after implanting of aramid and polyester fibers into back muscles and into the peritoneal cavity was carried on 90 rats. Estimation was performed in early period, that is to 90th, and distant period, that is to the 360th day after implantation. The estimation of the local reaction of cartilaginous tissue was performed on 24 rabbits after implantation on 60, 90, 180, 270 and 360 days of aramid and polyester fibers into xiphoid process of sternum. The quantitative microscopic estimation of the local reaction of tissue after implantation of fibers was performed using punctual estimation of tissue reaction. The research of proinflammatory cytokines IL-1beta and IL-6 induction after implantation of aramid and fibers into peritoneal cavity was performed on 85 mice Balb/c. the level IL-1beta and IL-6 was determined in the serum of peripheral blood of mouse and in peritoneal fluid in 3rd, 7th, 14th and 21st day after implantation. The results were compared with control of operative and spontaneous production of proinflammatory cytokines in non-operated animals. A rubber medical drain constituted the control of the tested cytokines induction. The determinations were made with ELISA method. The tests of resistance to biocorrosion in electronic scanning microscope were performed after implantation of fibers into peritoneal cavity of rats for 180 and 360 days. Biostability of mechanical properties of fibers after remaining for 360 days in the application of the tested breaking force in the knot and in the dynamic system of cyclic strain of fibers (with strength 20N and 1Hz). In the tests of aqueous extracts from fibers comparative pH (aramid--6.42 and polyester 6.35), four-time higher proper electric conductivity (aramid 45.5; polyester 11.0) and five-time higher-dry mass of residue after vaporization of extracts from aramid fibers in comparison with polyester fibers (aramid--10.4 mg, polyester--2.1 mg) were observed. In biological tests of aqueous extracts toxic, hemolytic or irritating action was not observed. The local reaction soft tissues after implantation of aramid and polyester fibers was similar. Macroscopically it was characterized with producing on the third day thin, transparent membrane which in distant period, was whitish, thicker and strongly connected with the implanted fibers and surrounding tissues. In the microscopic tests the reaction was characterized with a short-lasting exudative phase less intense around the aramid fibers and a proliferating phase led to producing a capsule from newly created areolar tissue sharply separated from muscles undergoing collagenization in the cicatrization phase. The produced connective tissue capsule from the side of the graft both around aramid and polyester had the cellular character with the presence of single giant multinucleated cells till the 360th day after implantation. From the side of the muscles the connective tissue streak had more dense character and in distant period consisted mainly of collagenous fibers with hyalinization features. The reaction of cartilaginous tissue after implantation both kinds of fibers from the 90th to the 360th day was similar. It was characterized with producing cartilaginous tissue and locally fibrous tissue with a large amount of intercellular substance. Connective tissue showed hyalinization features and was transformed into cartilaginous tissue. According to the punctual estimation of reaction the tested fibers caused minimal reaction. In the testes of level of proinflammatory cytokines IL-1beta and IL-6 their constant presence on the low level in the serum of mouse blood and in the peritoneal fluid was observed. aramid fibers did not induce an increase of the level IL-1beta and IL-6, whereas polyester fibers in the 3rd day after surgery stimulated locally their moderate increase. The influence of surgery on the local induction IL-1beta and IL-6 was statistically essential in the 3rd day. The rubber medical drain was strong inductor of mediators of inflammation IL-1beta and IL-6. In physiocomechanical fatigue-testing and in SEM in the period to 360th day after implantation, biocorrosion of aramid and polyester fibers was not observed. The value of breaking force of aramid fibers was twice higher and the resistance to cyclic fatigue was over two hundred times higher in comparison to polyester fibers. Those differences were statistically significant (p < 0.001). On the basis of the performed tests it is possible observed that aramid fibers cause minimal tissue reaction compared with the observed one around polyester fibers, they do not cause local nor systemic stimulation of proinflammatory cytokines IL-1beta and IL-6. aramid fibers show essentially higher statistic and dynamic mechanical resistance in comparison with polyester fibers; they not undergo biocorosion and they can be useful to increase mechanical resistance of medical materials or as independent biomaterial resistant to high mechanical forces.