Volt-ampere characteristics of an ion-plasma system for treating the internal surface of hollow cardiovascular implants

Abstract

The creation of thrombus-resistant artificial vascular endoprostheses is a pressing issue in cardiology. To address this issue, it has been proposed to modify the surface of polymer vascular grafts and catheters using the ion-plasma method. However, the inner surface of shunts and catheters is inaccessible for ion beam treatment with a planar electrode geometry. To treat the inner surface of such polymer tubes, a special ion-plasma system was created, including a hollow tubular high-voltage electrode into which the tube to be treated was placed. A stream of nitrogen gas passed through the tube, while high-voltage pulses were applied to the electrode, causing a plasma discharge in the tube. As a result, the inner surface of the tube was bombarded with ions of the process gas until a carbonized layer appeared. This study determines the volt-ampere characteristics of the created plasma system depending on the linear dimensions of the tube, the applied voltage, and the volumetric gas flow rate. Low-temperature spatial plasma is characterized by the Child-Langmuir law, according to which the current–voltage curve is approximated by a power function. However, in our study, an exponential nature of the volt-ampere characteristics depending on the applied voltage was observed. The difference between the experimental and theoretical data can be explained by the additional influence of secondary electron emission and the spraying of polymer material in the tube. The exponential nature of the dependence of the current on the applied voltage can also be explained by the theory of electrical discharge in a hollow cathode. The results of this work contribute to the creation of a physical theory of ion treatment of the inner surface of hollow polymer products such as vascular shunts and catheters.