Papers by Author: Eszter Bognár

Abstract: Devices used in the field of medical technology require high biocompatibility. Medical devices that are made from stainless steel have good biocompatible properties, but polymer coatings can radically improve it. One of the most important quality of the coating is adhesion, and this was our rationale for developing a polymer adhesion testing protocol. In our research, two biocompatible polymers were compared, polyurethane (PUR) and poly-(DL-lactic-co-glycolic acid) (PDLG). Surface-treated stainless steel sheets were used as carrier for polymer layers. The adhesive properties of different layers were compared. Adhesion of the coatings was characterised by concentration of coating solution and surface roughness of the carriers, and some phenomena were observed.

Abstract: The goal of this research was to create a surface topography that would promote cell attachment onto Ultrafine-grained Grade 2 Titanium. Morphologies that assist the deposition of bone tissue and reduce colonisation by unwelcome bacteria onto dental implant surfaces are created most often by sand-blasting, chemical etching, or these two in combination. Discs of thickness 2 mm from the machined base material were prepared for this study. After machining, the samples were chemically etched. Three etchants were used: 30 % HCl and 85% H₃PO₄, and the two in combination. The etching temperatures were 20 °C, 40 °C, and 60 °C, the etching times were 5 minutes and 120 minutes. The surface morphologies of the discs were examined by confocal microscope and scanning electron microscope (SEM), and compared to the machined-only samples as reference values. Samples treated in the 30% HCl solution at 40 °C for 120 minutes and then in the 85 % H₃PO₄ solution at the same temperature and time altered macro and micromorphology together in ways which assist the attaching of bone.

Abstract: The guidewire is a small diameter, steerable wire which facilitates the navigation of the interventional devices such as stent, balloon, or coil in endovascular intervention. The guidewire has an elongated flexible body and a relatively more flexible ribbon tip. The elongated body (shaft) is tapered to the ribbon tip. The composition of the helical coil formed ribbon tip is different than the elongated body. In this article we demonstrate the correlation between the material composition and the kinking resistance of guidewire. The identified metal composition of the core wire was 18-8 stainless steel and the helical coil composed of platinum-nickel alloy and the material of tip bond was tin. The kink angle which caused permanent deformation were significantly higher on the helical coil (=68,3^o) due to the higher flexibility of the helical coil than that was found on the shaft portion (=55^o) (p=0,00032). The remnant angel induced by 90^o kinking on the helical coil was significantly lower (=15^o) than that was observed on the shaft portion (=23,9^o) (p=0,00046). The deformation of the helical coil was smaller due to the higher flexible properties of the platinum-nickel alloy material against the stainless steel.

Abstract: As a result of the collective efforts of engineers and physicians modern medicine is one of the most developed discipline nowadays. The invention of stents is one of the most important result of these works. With development of stents artery narrowing, which can often lead to death, can be efficiently treated. The stent is a biocompatible mesh, which is inserted into the narrowed section of the artery to dilate and prop up its wall hereby it ensures continuous blood flow. The bio-and haemocompatibility of stents have to be sufficient to avoid significant recurrent stenosis (restenosis). Better biocompatibility can be achieved using surface treatments such as chemical etching, electropolishing and coatings. In our research we developed self-expandable stents made of shape memory Ni-Ti alloy called nitinol. In this article the present stage of our work, the electropolishing experiments are summarized. A new electropolishing cell was worked out by using special stent holder to lead the current to the stent, which made possible the even electropolishing of the stent surface. The electrolyte, which was applied, contains less than 5% of perchloric acid. A current interval was determined which will be sufficient to determine the optimal polishing parameters, such as polishing time and current density with further researches.

Abstract: Almost half of the deaths in the European Union are a consequence of cardiovascular diseases, which can be reduced significantly by dietary changes, physical activity and suitable medications. Since changing lifestyle and healthcare is a slow process, a more efficient and quicker solution is to improve medical devices. Stents are mesh-structured implants, which support arterial wall and allow dilatation of the narrowed section. The material analyses of stents removed from cadavers allow further development and improvement of these special devices. Despite of the widespread application of stents, not many publications deal with their technical analysis and most of them have a medical approach. This paper presents a technical analysis of three stents removed from cadavers. The results may promote the evaluation of the stent development. Until now these kind of feedback was missing from the improvement cycle.

Abstract: The present study focus on the chemical etching of shape memory nickel-titanium (nitinol) alloy stents made by laser cutting. Application of nitinol stents widely spread in case of atherosclerosis of peripheral vessels. This type of stent has to have appropriate surface quality, flexibility and strength. The aim of chemical etching is removing the burr, which arises during the laser cutting. Etching is one step of the production of stents. The appropriate parameters allow the laser burned surface and most of protruding material removing without significant damage of stent shape. During these experiments etching time was changed. After etching the cross section area was determined by metallographic examinations. The results of the examinations show the relationship between the etching time and the cross-section area. The analysis of measurement data revealed the change of etching velocity. Before and after etching the samples was examined by scanning electron microscopy (SEM). The different surfaces also were compared and the findings were discussed.

Abstract: 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.

Abstract: The rate of restenosis can be decreased by the usage of drug eluting stents compared to bare metal stents. The aim of this work was the optimization of micro sprayed polymer coatings for medical applications and the examination of drug absorbing and releasing properties of these coatings. Control groups were bare metal stent models (316 LVM type austenitic stainless steel tube slices). Different types of medical grade polyurethane granules were applied onto the stent surface. Various methods were used for the examination of the surface and coating quality, such as optical microscopy, scanning electron microscopy and atomic force microscopy.

Abstract: The aim of this study is to examine some key properties of medical polyurethane coatings on coronary stents such as thickness and size of pores on the surface of austenitic stainless steel (316L). Plates were used as carrier instead of real stents, because they are too expensive and difficult to work with. The carriers were dipped into the solution of polyurethane and tetrahydrofuran. Solutions of 1 to 5 wt % were prepared for the experiments and the numbers of the dipping were changed. The coatings were examined with Atomic Force Microscope (AFM). In contact mode detailed images with good contrast were made about the coatings. These images were processed with image processing algorithms in MATLAB and with the image analysis software belonging to the AFM instrument.

Abstract: 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.