| Περίληψη: | 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.
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