Analiza utjecaja predistezanja na povećanje naprezanja u arteriji nakon ugradnje stenta

master's thesis

• Title (english): Effects of pre-stretch on arterial wall stress after stenting
• Author: Dominik Rukljač
• Mentor: Igor Karšaj (mentor)
• Mentor: Lana Virag (komentor)
• Granter: University of Zagreb; Faculty of Mechanical Engineering and Naval Architecture; Zagreb
• Defense date and country: 2021-01-21, Croatia
• Scientific / art field, discipline and subdiscipline: TECHNICAL SCIENCES; Mechanical Engineering; General Mechanical Engineering (Construction)

Abstract

Ateroskleroza je bolest kod koje dolazi do nakupljanja aterosklerotskog plaka u stijenci krvne žile. Povećano nakupljanje plaka može dovesti do opstrukcije krvnog protoka, a kao dodatna komplikacija javlja se tromb koji može uzrokovati moždani ili srčani udar. Uobičajeni tretman kojim se osigurava povrat protoka krvi u ateroskleroznoj žili je ugradnja stenta. Endovaskularno ugrađen proširivi kardiovaskularni stent lokalno širi krvnu žilu na mjestu stenoze i na taj način ponovno uspostavlja normalni protok krvi. U dosta slučajeva, javlja se ponovno sužavanje (restenoza). Mogući uzrok restenoze je povećanje naprezanja u krvnoj žili uslijed ugradnje stenta što posljedično može uzrokovati povećanu proizvodnju kolagenskih vlakana u stijenci žile. Radiologijskim slikovnim metodama moguće je snimiti in vivo geometriju arterija opterećenih krvnim tlakom. Kako nije poznata neopterećena geometrija arterije, često se koristi opterećena geometrija kao referentna konfiguracija. Modeliranje se temelji na unaprijed pretpostavljenim predistezanjima. Cilj rada je pokazati utjecaj iznosa predistezanja i krutosti stijenke na raspodjelu naprezanja nakon endovaskularnog liječenja, a time i njegovu uspješnost. Kako sam iznos predistezanja ovisi o starosti i stadiju bolesti, cilj rada je provjeriti utjecaj nepoznatog predistezanja na raspodjelu naprezanja u stijenci krvne žile nakon ugradnje stenta.
Korištenjem UMAT-a (eng. user subrutine), u ovom diplomskom radu, prikazana je implementacija neo-Hooke i Holzapfel–Gasser–Ogden (HGO) hiperelastičnih materijalnih modela s predistezanjem u programski paket Abaqus kako bi se izradio što realističniji model karotidne arterije. Taj model dalje je korišten za opisivanje ponašanja aterosklerozne stijenke u koji se ugrađuje stent. Također, s obzirom da predistezanja unutar HGO modela ne moraju biti ista i za izotropni i anizotropni dio funkcije unutarnje energije, neopterećena konfiguracija nije istovremeno i konfiguracija bez naprezanja. U radu je pokazano da nakon rasterećenja arterije ostaju rezidualna naprezanja te se nakon rezanja arterijski prsten otvori, a kut otvaranja ovisi o početnim predistezanjima i njihovoj razlici. U Abaqusu je izrađen i sklopni model s dodanim aterosklerotskim plakom zadanih dimenzija i geometrije te samostalno izrađenim karotidnim stentom.

Abstract (english)

Atherosclerosis is a disease in which atherosclerotic plaque accumulates in the wall of blood vessels. Increased plaque deposition can lead to an obstruction of blood flow, and as an additional complication, a thrombus occurs with potential of causing can a stroke or heart attack. A common treatment for ensuring heathy blood flow within the atherosclerotic vessel is stent implantation. An endovascularly implanted dilated cardiovascular stent locally dilates a blood vessel at the site of stenosis and thus restores normal blood flow. In many cases restenosis occurs. A possible cause of restenosis is an increase in mural stress in a blood vessel due to the stent implantation, which in turn can cause increased production of collagen fibers within the vessel wall. Using radiological imaging methods, it is possible to record the in vivo geometry of arteries loaded with blood pressure. As the unloaded geometry of the artery is unknown, the loaded geometry is often used as the reference configuration. Modeling is based on pressumed pre-stretches. The amount of pre-stretch is expected to affect the stress distribution after endovascular treatment and thus its success. As the amount of pre-stretch itself depends on the age of patient and stage of the disease, the aim of this study is to check the influence of unknown prestressing on the stress distribution in the blood vessel wall after stent implantation.
Using the UMAT (eng. user subrutine), in this thesis it will be demonstrated the implementation of neo-Hooke and Holzapfel – Gasser – Ogden (HGO) hyperelastic material models with pre-stretch into the Abaqus software package to construct a carotid artery model. This model was further used to describe the behavior of the atherosclerotic wall into which the stent is implanted. Also, since the pre-stretches within the HGO model do not have to be the same for the isotropic and anisotropic part of the internal energy function, the unloaded configuration is not at the same time stress-free. In this thesis it is shown that after unloading the artery, residual stresses are remaining and after cutting the arterial ring, it opens, and the opening angle depends on the initial pre-stretches and their difference.

• Keywords: ateroskleroza; kardiovaskularni stent; predistezanje; restenoza; UMAT
• Keywords (english): atherosclerosis; cardiovascular stent; pre-stretch; restenosis; UMAT
• Language: croatian
• URN:NBN: urn:nbn:hr:235:246087
• Study programme: Title: Mechanical Engineering; Study programme type: university; Study level: graduate; Academic / professional title: magistar/magistra inženjer/inženjerka strojarstva (magistar/magistra inženjer/inženjerka strojarstva)
• Type of resource: Text
• File origin: Born digital
• Access conditions: Open access
• Created on: 2021-01-14 11:54:34