Ulm, Univ. Diss., 2007.

Ulm, Univ., Diss., 2008.

Ulm, Univ., Diss., 2007.

Ulm, Univ., Diss., 2008.

The plastic deformation of stent is investigated in this study and the effect of atherosclerotic artery on the stent deformation is studied. The relationship between different stent structure parameters; i.e., stent thickness, length, slot length ration and final deformation are also discussed. The elastic-plastic finite element models is employed in the deformation and residual stress analysis. The materials of balloon, stent and artery were assumed to be linear elastic, elasto-plastic and nolinear-elastic Odgen model, respectively. A typical Palmaz type stent is analyzed. The deformation and stress distributions of the stent are simulated with the inflation and the deflation of the angioplasty balloon. Results indicate that the considering of the atherosclerotic artery may affect the calculated stent deformation and stress distributions significantly.

Im Institut für Röntgendiagnostik der Universität Würzburg wurden in einem Zeitraum von bis zu 68 Monaten 168 Patienten mit PAVK der unteren Extremität mit einem oder mehreren Stents versorgt und anschließend regelmäßig kontrolliert. Insgesamt wurden 405 Stents implantiert. In den Nachkontrollen wurden die Stents mittels Röntgenzielaufnahmen in 2 Ebenen auf Frakturen sowie mit Hilfe der FKDS auf Restenosen oder Okklusionen untersucht. In der vorliegenden Studie wurden Ursachen für das Auftreten von Stentfrakturen ermittelt und ihre klinische Relevanz beurteilt. / In the department of radiology of the University of Würzburg 168 patients with peripheral artery disease in the lower extremity, which were treated with one or more stents, were examined over a period of 68 months. Overall there were 405 stents implanted. In follow-up examinations these stents were screened for fractures using two-plane x-ray imaging. Color duplex sonography was applied to detect restenosis and occlusion-rates. The aim of our study was to identify possible causes for stent fractures and to evaluate their clinical relevance.

Coronary stents are generally tubular-shaped expandable devices which function to hold open a segment of a blood vessel. They are particularly suitable for use to support and hold back a dissected lumen. This study aims to improve the existing designs of coronary stents through geometry design. This study focuses on the flexible mechanism and planar strut of a thin wall tubular stent to design a new type of coronary stent. A good coronary stent has to meet various requirements. First of all, a coronary stent has to be strong enough to support the wall of the blood vessel. Secondly, it has to be elastic enough. Thirdly, the longitudinal length shorten with dilatation should be as less as possible, otherwise it is difficult to implant precisely. Computer aided design software Pro Engineer is used to build the solid model and then CAE software ANSYS is used to analyze the dilatation of the new stent. After several modifications, a new type of stent with no longitudinal shortening is designed.

Zugl.: Berlin, Techn. Universiẗat, Diss.

Este estudo foi desenvolvido no Instituto de Pesquisas Energéticas e Nucleares IPEN mais especificamente, no Centro de Ciência e Tecnologia dos Materiais CCTM com apoio da empresa Innovatech. Foram estudados tubos de Co-Cr (L605) usados para fabricação de stents coronarianos, aplicação esta que pede um comportamento mecânico específico e biocompatibilidade. Os tubos de CoCr (L605) podem ser adquiridos em duas condições de história térmica: Trabalhado a frio ou com encruamento ou recozido. O tubo recozido se não estiver em condições para a aplicação, dificilmente será possível atingi-las com um novo tratamento térmico. O tubo encruado abre possibilidades para acertar as condições de tratamento térmico e obter a condição ideal de comportamento mecânico, sem comprometer outros aspectos importantes para a aplicação como biocompatibilidade. Foi selecionado um tubo de CoCr (L605) encruado e com uma quantidade grande de precipitados para os testes, foram selecionadas três faixas de temperatura para o tratamento térmico de recozimento uma abaixo do ponto de solubilização (1000°C), uma dentro da temperatura (1175°C) e uma terceira, mais próxima do ponto de fusão alcançável pelo forno (1250°C). Em cada temperatura foram usados quatro períodos de exposição ao forno( 4, 7, 10 e 15 minutos) totalizando uma matriz com 12 condições de tratamento térmico. Em cada tratamento térmico foram incluídas amostras para ensaio de tração e metalografia. O objetivo deste trabalho é estudar os efeitos dos tratamentos térmicos no comportamento mecânico e na microestrutura do material afim de levantar critérios para determinar os melhores parâmetros de tratamento térmico para a aplicação. / This study was developed at IPEN Institute of Energy and Nuclear Research more specifically in CCTM Materials Cience and Tecnology Center, with support of Innovatech Medical. It was studied Co-Cr (L605) tubes used for manufacture of coronary stents, this application require a specific mechanical behavior and biocompatibility. The tubes CoCr (L605) can be acquired in two conditions of thermal history: Cold worked or annealed. If the annealed tube doesn´t have the conditions for the application it is hardly possible to reach them with a new heat treatment. Hardened tube opens up more possibilities to adjust the conditions of thermal treatment and obtain the optimum condition of mechanical behavior without compromising other aspects important for application as biocompatibility. A tube CoCr (L605) Hardened and a relatively large amount of precipitates were selected for the tests, three temperature tracks have been selected for the thermal annealing treatment: below the temperature of solution aneealing(1000 ° C), at solution aneealing(1175 ° C) and a third temperature closest achievable by furnace (1250 ° C). For each temperature four periods of exposure where selected (4, 7, 10 and 15 minutes) totaling a matrix of 12 heat treatment conditions. In each heat treatment, samples for tensile testing and metallography were included. The objective of this work is to study the effects of heat treatment on mechanical behavior and microstructure of the material in order to raise criteria to determine the best heat treatment for the application.

La rétention aiguë d'urine est la complication la plus grave de l'hyperplasie bénigne de la prostate. Elle est aujourd'hui traitée en urgence par cathétérisation, ce qui expose le patient à un important risque infectieux. Dans le cadre de cette thèse, un stent urétral innovant a été développé afin de remplacer la cathétérisation. Ce stent utilise des échantillons filiformes d'alliage à mémoire de forme Nickel-Titane, lui conférant deux mémoires de forme distinctes au chauffage, et permettant ainsi une pose et une ablation simplifiées.Afin de convenablement dimensionner les éléments constitutifs de ce stent, un dispositif permettant la réalisation d'essais de flexion pure à haute déformation sur des échantillons de géométrie filiforme a été conçu. Ce dispositif a permis la caractérisation de fils et tubes de NiTi en flexion pure, ainsi que l'étude du phénomène de localisation qui est survenue lors de ces essais.Une méthode numérique permettant l'identification des lois de comportement matériau à partir d'essais expérimentaux à champ de contrainte non uniforme a été développée. Cette méthode a notamment permis d'identifier le comportement en compression uni-axiale de fils et tubes de NiTi, à partir de résultats expérimentaux obtenus en flexion pure et en traction uni-axiale. / Acute urinary retention is the major complication of benign prostatic hyperplasia. Today, the first line treatment consists in emergency catheterization, which often leads to urinary infection. This thesis aimed at developing an innovative nitinol based stent as a alternative treatment for acute urinary retention. Using a combination of NiTi wires and tubes, this stent is given two distinct shape memories during heating.The stent components are mostly loaded under pure bending during the stent activation. A pure bending apparatus allowing large deformations on slender specimens was thus designed. This device gave access to the NiTi wires and tubes behaviour under pure bending, and also provided information about localization phenomena during pure bending experiment.A numerical method able to identify the shear-stress shear-strain function from experimental pure torsion tests, and the stress strain function under compressive load from experimental uni-axial tensile and pure bending tests was also developed. This method was applied using afore-obtained numerical results to identify the NiTi wires and tubes behaviour under uni-axial compressive load.