Abstract
The hemocompatibility of vascular grafts made from poly(ethylene terephthalate) (PET) is insufficient due to the rapid adhesion and activation of blood platelets that occur upon incubation with whole blood. PET polymer was treated with NHx radicals created by passing ammonia through gaseous plasma formed by a microwave discharge, which allowed for functionalization with amino groups. X-ray photoelectron spectroscopy characterization using derivatization with 4-chlorobenzaldehyde indicated that approximately 4% of the –NH2 groups were associated with the PET surface after treatment with the gaseous radicals. The functionalized polymers were coated with an ultra-thin layer of heparin and incubated with fresh blood. The free-hemoglobin technique, which is based on the haemolysis of erythrocytes, indicated improved hemocompatibility, which was confirmed by imaging the samples using confocal optical microscopy. A significant decrease in number of adhered platelets was observed on such samples. Proliferation of both human umbilical vein endothelial cells and human microvascular endothelial cells was enhanced on treated polymers, especially after a few hours of cell seeding. Thus, the technique represents a promising substitute for wet-chemical modification of PET materials prior to coating with heparin.
Highlights
Cardiovascular diseases represent the major cause of death in the modern world
This observation is explained by extensive formation of NHx radicals in ammonia plasma
After 20 min, the concentration is approximately twice as high as in the untreated samples, and it increases to 4 times greater after 30 min; for longer times, the ratio approaches infinity because the concentration for the case of untreated samples approaches zero. These results illustrate the favorable hemocompatibility of materials with functionalized polymer surfaces with amino groups treated by ammonia plasma flowing afterglow followed by covalent binding of a thin heparin layer onto the groups, which act as anchor sites for the heparin molecules
Summary
Cardiovascular diseases represent the major cause of death in the modern world. Treating such diseases is often achieved by surgery, during which inefficient blood vessels are bypassed or replaced with synthetic ones. The most popular anticoagulant is heparin, a glycosaminoglycan (GAG) that is rich in –SO3− functional groups [4] This GAG acts as an anticoagulant due to its binding to antithrombin (AT), the major inhibitor of coagulation proteases thrombin and Factor Xa, via a specific pentasaccharide sequence that contains a 3-O-sulfatesulfated glucosamine residue. This high-affinity pentasaccharide induces a conformational change in AT that accelerates the rate of factor Xa inhibition by at least two orders of magnitude but has very little to no effect on the rate of thrombin inhibition. Heparin was covalently bound to the polymer surface according to Scheme 1. Multistep strategy for the molecular binding of heparin to ammonia plasma-treated poly(ethylene terephthalate) (PET) surface
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