György Ring

Investigation of Drug Eluting Stents

The clinical results of drug eluting stents [DESs] depend on the type of the coating, the coating technology and the dosage and efficiency of the drug. The current study shows our examinations on drug eluting stents. Different types of commercially available coronary stents were investigated. Various methods were used for these experiments, for example optical microscopy, confocal fluorescent microscopy, scanning electron microscopy and EDS analysis. The properties characterizing applicability of drug eluting stents and the changing of the coatings during expansion are shown.

Polyurethane Coating on Coronary Stents

Stents are special metallic or polymer endoprostheses of meshed structure and tube shape. Their function is to prevent restenosis in the arteries. Stents can be coated or uncoated. In the expanded part of the artery the chance of restenosis is bigger even without a stent so it is practical to coat the stents. The aim of this work is to present the results of the coating experiments made on the coronary stents. Three types of commercially available polyurethanes were used for these experiments. The coatings were produced by a dipping method. Electro-polished and non-electro-polished metallic sheets and stents were used for these experiments. Contact angle measurements were done to examine the wetting properties of the three different polyurethane coatings. The quality and the changing of the coatings were examined by different methods (stereomicroscope, scanning electron microscope and energy dispersive spectrometry).

Mechanical Behaviours of Coronary Stents

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.

Investigation of Coated Coronary Stents

In this study the main properties of coated coronary stents are shown, such as recoil, foreshortening, surface features and failures and the expansion properties. The types and the effects of active and passive coatings are introduced. The results of our examinations with different coated coronary stents are shown as well. The quality and the changing of the coatings were examined by different methods (stereomicroscopy, atomic force microscopy, scanning electron microscopy and EDS analysis).

Coronary stents' materials and examinations of surface and expansion features

In our study we summarise the materials and manufacturing technologies of coronary stents used nowadays. Different testing methods for stent’s features are presented and main expansion features such as recoil and foreshortening are determined. The most frequent failures caused by the expansion of the coronary stents are also shown.

Surface treatment and examination of Grade 2 and Grade 5 titanium

Surface characteristics play an important role in the implant-bone integration that is required for the long-term reliability of dental and orthopedic implants. In this paper, we investigate the effect of acid etching on the mass reduction and roughness of grade 2 and grade 5 Ti under controlled experimental conditions. Three different etching compounds were investigated: 30% HCl, 85% H 3 PO 4 and the compound of 30% (COOH) 2 × 2H 2 O and 30% H 2 O 2 in various treatment intervals under controlled temperature. Stereo microscopy, scanning electron microscopy, roughness and weight measurements were carried out on the samples. We found that neither 85% H 3 PO 4 nor the compound of 30% (COOH) 2 × 2H 2 O and 30% H 2 O 2 were able to remove the machining marks from the surface of Ti discs in our experimental setting. On the other hand, etching in 30% HCl yielded even surfaces both on Ti grade 2 and 5 discs. We also found that etching at higher temperatures in 30% HCl resulted in significant mass loss.

Stent Retention Measurement

This article introduces two original measurement methods (i.e. adhesive layer and pulloff edge) for the determination of the stent retention force, together with the results from these measurements. The measurement with the adhesive layer models and quantifies the stentobstruction occurring in the constrictions; meanwhile the pull-off edge method is based on modelling and quantifying the collisions and constrictions in the main catheter. For the evaluation of the measurements our research introduced the specific ‘stent pull-off’ force, which shows the force required for the ‘pull-off’ of the stent from the balloon, which is referred to as the stent unit length. This is the maximum force value shown on the retention diagram (insert diagram reference here). It is ascertainable, that the presence of the polyurethane coating and the increase of the pulling-speed are increasing the ‘stent pull-off’ force. During the test interval of the pull-off speed, the ‘stent pull-off’ force for the Chronoflex®-coated stents increased from 0.45 N/mm to 0.76 N/mm.

Haemocompatible Coatings of Coronary Stents

The main goal of the present study was to determine the surface features, surface failures and fatigue properties of coated coronary stents. The quality and the changing of the coatings were examined by different methods. In this paper, the results of the examinations with different coated coronary stents are introduced and the results of the coating experiments are shown as well.