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A comparative assessment of deformation characteristics of self-expanding venous stents

University of British Columbia

Stents are medical devices that are widely used to treat vascular diseases through endovascular surgery. This minimally invasive surgery provides a faster recovery and fewer complications in comparison to other types of treatments. This device is available in various sizes and designs for deployment in a variety of blood vessels. The deformation characteristics of a stent contribute in a successful stent deployment and its long-term performance. A particular vascular disease and its location in the blood circulatory system require a stent with certain deformation characteristics. Accordingly, by studying these parameters for different stent designs, we can identify the most suitable stent for each type of disease. The main objective of this thesis is to develop an analytical method that predicts the deformation characteristics of self-expanding venous stents. The presented analytical method in this thesis is desirable for design, optimization and comparative assessments with less computation time and cost in comparison to finite element simulation. The unit-cell study forms the framework of the presented analytical method, which allows the analysis of the radial pressure, compliance, and foreshortening. The developed analytical method relies on two critical stages: 1. Defining the deformation characteristics in terms of unit-cell deformation mechanism, 2. Correlating unit-cell deformation mechanism to strut bending mechanics. These two stages are respectively validated through axisymmetric FE simulation and unit-cell FE simulation. The precision and accuracy of the method were found acceptable. Collapse, another critical deformation mode, was studied through the axisymmetric FE simulation. The structural instability and compliance contribute to the collapse deformation. Four different venous stent designs (Cook Vena, Cook Z, Luminexx, and Wallstent) are evaluated in terms of collapse, foreshortening, radial pressure, and compliance. Steel stents (Cook Z and Wallstent) are less compliant than Nitinol stents (Luminexx and Wallstent) and are more reliable to treat localized blood clots. The Nitinol stents are more efficient to be deployed close to body joints. Luminexx and Wallstent apply larger radial pressure and are the most reasonable choices for vital veins. If the final length of stent is critical (e.g. deployment close to branch orifice), Cook Z can be the best choice.

Text

2018-01-17

Attribution-NonCommercial-NoDerivatives 4.0 International

http://hdl.handle.net/2429/64398

Mechanical Engineering

University of British Columbia

UBCV

http://creativecommons.org/licenses/by-nc-nd/4.0/