Date of Award

1-1-2018

Document Type

Dissertation

Degree Name

Ph.D.

Department

Mechanical Engineering

First Advisor

Ali Nejatbakhsh Azadani, Ph.D.

Keywords

Computational modeling, Inverse finite element analysis, In-vitro experiments, Long-term durability, Stress and strain distributions, Transcatheter aortic valve

Abstract

Transcatheter aortic valve replacement (TAVR) is an established therapy alternative to surgical valve replacement in high-risk and intermediate-risk patients with severe aortic stenosis. Currently, although TAVR is an alternative and less-invasive treatment for high-risk and intermediate-risk patients, surgical aortic valves replacement (SAVR) was still considered as the gold standard for low-risk patients. TAVR could potentially be applied to lower-risk younger patients if the indications can be safely expanded to the patients and transcatheter aortic valve (TAV) long-term durability can match with that of surgical bioprostheses. In contrast to surgical aortic valves (SAVs), there have been limited clinical data on the long-term durability of TAV devices. In the absence of enough long-term valve durability data, accurate structural simulations and computational modeling become an integral part of the evaluation. Thus, the objectives of this dissertation were to employ in-vitro experiments and inverse finite element (FE) analyses to obtain accurate material properties of soft tissue employed in commercial available TAVs and then to implement them in computational simulations to determine leaflet stress and strain distributions for proper assessment of the TAVs long-term durability. Therefore, the main goal of this study was to develop an automated computational framework to minimize the peak stress on the leaflets under and optimize the TAV leaflet shape under physiological loading conditions. In addition, the impact of incomplete TAV expansion and thickness reduction on leaflet stress and strain distribution was assessed in this dissertation.

The results of this study showed that 2-3mm incomplete TAV stent expansion induced localized high stress regions within the TAV commissures, while 4-5mm incomplete stent expansion induced localized high stress regions within the belly of the TAV leaflets during the diastolic phase of the cardiac cycle. This study also presented three-dimensional anisotropic mechanical properties of leaflets used in Carpentier-Edwards PERIMOUNT Magna, Edwards SAPIEN 3 and Medtronic CoreValve. The optimized material parameters for each valve were implemented in FE simulations to assess the leaflet deformation and stress distribution. The results showed the CoreValve had the lowest peak stress value at the identical pressure value during diastole compared to the CE PERIMOUNT Magna and Edwards SAPIEN 3. Eventually, within the chosen design parameters in the optimization framework, we have achieved new designs for TAVs leaflet geometry in which the peak stress was 8.2% and 30.3% less than the corresponding surgical valves for 23 and 26 mm diameters, respectively. In addition, the leaflet peak stress of best TAV design obtained from the optimization framework showed the leaflet peak stress was 74.8% lower than the Edwards SAPIEN 3 TAV. The developed optimization framework may provide a more reliable TAV design with longer valve durability in comparison currently available designs. The present work presents a reliable approach to determine mechanical properties of pericardial valves and compare leaflet stress and strain distribution among different bioprostheses under physiological loading conditions.

Provenance

Received from ProQuest

Rights holder

Mostafa Abbasi

File size

210 p.

File format

application/pdf

Language

en

Discipline

Mechanical engineering, Biomechanics, Biomedical engineering

Share

COinS