Papers by Author: László Major

Abstract: The structure of diamond-like carbon thin films prepared by radio frequency chemical vapor deposition onto the surface of different corrosion resistant alloys (304, 316L and Iconel 617) used for coronary stent fabrication was investigated by Raman spectroscopy excited by visible (488 nm) and near-infrared (785 nm) light. The effect of electrochemical polishing of the alloy surface and that of Ar+ ion pre-treatment on the structure of the forming film was also studied in case of substrate made of 316L material. It was found that in spite of simultaneous preparation the character of the formed amorphous carbon films depends on the type of the alloy. The layer developed on the surface of Fe-rich stainless steels (316L and 304) showed the most diamond-like character, while the Ni-rich Inconel alloy promoted the formation of layer with high graphitic sp2 cluster content. The Ar+ pre-treatment enhanced the adhesion and the diamond-like properties of the film while the electrochemical polishing was found to be unfavorable concerning the diamond-like character of the layer.

Abstract: The role of the stents is to prevent restenosis. The rapid growth of stents’ application in the treatment of cardiovascular diseases resulted in the unique development of these implants. This is mainly due to the effective clinical trials, the success of which determined the use of these endoprostheses. In this study the surface properties of the coronary stents were described by using different methods (stereomicroscopy, scanning electron microscopy and energy dispersive analysis) before and after balloon expansion. Furthermore, the most frequent failures caused by the expansion were introduced. For investigating fatigue properties two high cycle fatigue test equipments were used: the first one simulates the bending stress, and the second one simulates the effect of the pulsating mechanical strain. Surface features of the stents were examined after the fatigue tests as well: macroscopic damages were not originated on the stents, and the implants were not broken down. Only small traces of fatigue occurred on the surface, which became rough; and slip lines and grain boundaries were outlined.