Abstract
The biocompatibility of body implants made from polytetrafluoroethylene (PTFE) is inadequate; therefore, the surface should be grafted with biocompatible molecules. Because PTFE is an inert polymer, the adhesion of the biocompatible film may not be appropriate. Therefore, the PFTE surface should be modified to enable better adhesion, preferably by functionalization with amino groups. A two-step process for functionalization of PTFE surface is described. The first step employs inductively coupled hydrogen plasma in the H-mode and the second ammonia plasma. The evolution of functional groups upon treatment with ammonia plasma in different modes is presented. The surface is saturated with nitrogen groups within a second if ammonia plasma is sustained in the H-mode at the pressure of 35 Pa and forward power of 200 W. The nitrogen-rich surface film persists for several seconds, while prolonged treatment causes etching. The etching is suppressed but not eliminated using pulsed ammonia plasma at 35 Pa and 200 W. Ammonia plasma in the E-mode at the same pressure, but forward power of 25 W, causes more gradual functionalization and etching was not observed even at prolonged treatments up to 100 s. Detailed investigation of the XPS spectra enabled revealing the surface kinetics for all three cases.
Highlights
Polymers are often used for the synthesis of vascular grafts because of their chemical and mechanical properties
The samples were exposed to ammonia plasma in the second step to functionalize the surface film with nitrogen-containing groups
The results showed that the maximal concentration of nitrogen in the surface film as probed by X-ray photoelectron spectroscopy (XPS) was 12 at.%, irrespective of the plasma parameters
Summary
Polymers are often used for the synthesis of vascular grafts because of their chemical and mechanical properties. A handful of different polymers were found useful for grafts, including polyethylene terephthalate, polyurethane, polytetrafluorethylene, silk and a variety of silicones [1,2,3,4,5] All those materials exhibit different behaviors when in contact with human or animal blood. The non-treated polymers exhibit moderate hemocompatibility, which is reflected in activation of blood platelets, the surface transformation of blood proteins and non-controlled accumulation, the poor proliferation of vascular endothelial cells and rapid proliferation of soft muscle cells. All these effects may lead to serious complications such as thick neointimal formation, thrombosis and restenosis. Various techniques for modification of the surface properties have been reported in the scientific literature [9]; most of them involve the deposition of a thin film of bio-compatible materials
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