Fatigue life prediction of a cobalt-chromium stent placed into an artery with atherosclerotic plaque

• Κύριος συγγραφέας: Παρασκευά, Χριστίνα-Λυδία
• Άλλοι συγγραφείς: Paraskeva, Christina-Lydia
• Γλώσσα: English
• Έκδοση: 2023
• Θέματα: Balloon-expandable stent; Fatigue; Finite element method; Goodman diagram; Atheromatic plaque; Διαστελλόμενο με μπαλόνι stent; Κόπωση; Μέθοδος πεπερασμένων στοιχείων; Διάγραμμα Goodman; Αθηρωματική πλάκα

Intravascular stents are medical implants expanded into stenotic arteries tο restore blood flow perfusion tο the downstream tissues. The stent is placed tο open the site of blockage with the dilation οf a balloon. The biomedical-industry for stents has been advanced rapidly and nowadays there are different types of stents, such as bare-metal stent, drug eluting stent, bio-absorbable stent, and a dual therapy stent (combination of both drug and bioengineered stent) [18] and with various characteristics. This advancement was facilitated by the simulation through Finite Element Modeling (FEM) in a computer-simulated virtual environment that allowed the exploration οf various stent designs and their failure modes in a very cost-effective and timely manner and has thus become an integral part in the design cycle οf stents, helping the bio-medical industry tο attain quicker turn-around times and a faster time tο market [15]. Even though stents are a good alternative tο treat narrowed or blocked vessels, stent fracture (SF) has attracted increasing attention and is identified as one cause fοr stent failures, because the fracture metal/polymer struts protruding into the lumen or arterial wall could trigger acute stent thrombosis οr lead to late in-stent restenosis [20, 63]. Repetitive mechanical forces within the artery may result in stent fracture after stent implantation. This diploma thesis aims to design a type οf stent and investigate the behavior-fatigue of a balloon expandable (BE) Cobalt-Chromium stent inside an idealized artery with atheromatic plaque under diastolic-systolic cyclic loading, employing Finite Element Method (FEM). The stent expansion and partial recoil under balloon inflation and deflation were simulated, as well as the simulation of the blood pressure cyclic loading. The methodology followed is based on a global computational approach composed of a mechanical finite element analysis and then followed by a fatigue analysis. There are many factors that affect the fatigue life of stents such as material properties, design, manufacturing, specificities of patient and loading conditions. In particular, its FLP is influenced by static loading during deployment οr cyclic loading caused by pulsatile blood pressure, bending, torsion, tension, and compression [36, 39]. In general, a stent is designed with approximately a 10-years in-vivo life tο be considered safe, as proposed by the FDA. In this study, Goodman method (under three different approaches) was used for the fatigue life prediction of the stent. The Goodman methos gives a global prediction of the fatigue life. Specifically, the results of the two goodman approaches showed that the stent was safe under fatigue loading conditions, whereas the use of the fe-safe software showed smaller cycles until failure.