Heart Valve.pdf

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Stent Design for a
Percutaneous Heart Valve
A Major Qualifying Project submitted to the Faculty of
WORCESTER POLYTECHNIC INSTITUTE
in partial fulfillment of the requirements for the
Degree of Bachelor of Science
Submitted By:
Hamresh D. Lutchmun
______________________________
Submitted On:
April 28, 2011
Submitted to:
Professor Gregory Fischer
_________________________________
Sponsoring Organizations:
Abiomed, Inc.
This report represents the work of a WPI undergraduate student submitted to the faculty as evidence of
completion of a degree requirement. WPI routinely publishes these reports on its
web site without editorial or peer review.
Acknowledgements
I would like to thank Scott Corbett for making this project possible and guidance throughout the
course of the project. I would also like to acknowledge Professor Greg Fischer for his counsel and
encouragement from first meeting we had. I would like to thank all the Abiomed Inc. employees who
shared their experience in the medical device industry and most notably Christian Rivera and Terry
Barnes who worked tirelessly at Abiomed and ensured a successful collaboration. I also want to
recognize my friends and family who answered present when I needed them most for the execution of
the project.
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Abstract
Surgical Valve Replacement is the standard of care for patients with severe aortic valve
calcification, which restricts blood flow from the left atrium to the rest of the body. Valve calcification is
common with aging but patients are often refused surgery due to comorbidities present. Minimally
invasive placement of tissue valves has recently been introduced to the market and has demonstrated
applicability to patients not qualified for open heart surgery. The purpose of this project is to design a
self-expanding Nitinol stent with features to enable attachment to a polyurethane valve, facilitate
deployment and repositioning as well as secure placement within the aortic annulus while avoiding
obstruction of the aortic nodes. The design was performed in collaboration with Nitinol stent
manufacturers, private consultants, and surgeons. Various stent configurations were designed and
ANSYS was used to conduct finite element analyses on the stent iterations. The most promising stent
design was ordered to be custom manufactured and the polyurethane valve was attached to the stent
for deployment and bench-top performance testing.
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Table of Contents
Acknowledgements........................................................................................................................................ i
Abstract ......................................................................................................................................................... ii
Table of Contents ......................................................................................................................................... iii
Table of Tables ............................................................................................................................................. vi
Table of Figures ........................................................................................................................................... vii
Introduction .................................................................................................................................................. 1
Background and Significance .................................................................................................................... 1
The Abiomed Inc. Approach...................................................................................................................... 3
Project Objectives ..................................................................................................................................... 4
Scope of Work ........................................................................................................................................... 4
Design Requirements ................................................................................................................................ 5
Methods/Procedural ............................................................................................................................. 5
Mechanical Strength/Stability .............................................................................................................. 5
Dynamics ............................................................................................................................................... 6
Cost ....................................................................................................................................................... 6
Background Information ............................................................................................................................... 7
Survey of Current Stent Designs ............................................................................................................... 8
Nitinol Stents - Material and Design Considerations .............................................................................. 15
Basics of Nitinol Stent Design ................................................................................................................. 21
FEM of Nitinol Stents .............................................................................................................................. 26
Abiomed Inc. Polyurethane Valve........................................................................................................... 29
Benefits ............................................................................................................................................... 30
Manufacture ....................................................................................................................................... 30
Attachment ......................................................................................................................................... 31
Methodology............................................................................................................................................... 33
Evaluation of Generic Stents ................................................................................................................... 33
Valve Attachment ................................................................................................................................... 39
Dip Casting .......................................................................................................................................... 39
Solvent Bonding .................................................................................................................................. 41
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Suturing ............................................................................................................................................... 44
Thermoforming ................................................................................................................................... 46
Stent Development ................................................................................................................................. 49
3D Modeling ........................................................................................................................................ 50
As-Cut Models ..................................................................................................................................... 62
Test Setup and Results ................................................................................................................................ 64
FEA Analysis ............................................................................................................................................ 64
Nitinol Model ...................................................................................................................................... 64
ANSYS Workbench 12.1 ...................................................................................................................... 66
Stent Preparation for Testing.................................................................................................................. 70
Crimper ............................................................................................................................................... 70
Thermoforming ................................................................................................................................... 70
Suturing ............................................................................................................................................... 73
Bench-top Testing ................................................................................................................................... 75
Dynamics ............................................................................................................................................. 75
Pressure Drop...................................................................................................................................... 75
Backflow .............................................................................................................................................. 76
Mock Circulatory Loop and Placement ............................................................................................... 76
Cycle test ............................................................................................................................................. 76
Discussion & Future Works ......................................................................................................................... 77
Discussion................................................................................................................................................ 77
Future Works .......................................................................................................................................... 77
Crown Stent 1...................................................................................................................................... 77
Half Diamond 1 ................................................................................................................................... 78
Finite Element Analysis ....................................................................................................................... 78
Cycle Tester ......................................................................................................................................... 78
Delivery System................................................................................................................................... 78
Bibliography ................................................................................................................................................ 79
Appendices.................................................................................................................................................. 82
Appendix A: Most Popular Stents ........................................................................................................... 82
Appendix B: French Catheter Scale ......................................................................................................... 86
Appendix C: Strut Measurements ........................................................................................................... 87
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