Wei Sun, Ph.D.(WS) is an associate professor in Biomedical Engineering at Georgia Institute of Technology. He is an expert in the field of heart valve mechanics. He was previously employed by Edwards Lifesciences, LLC. He also serves as a member of the ISO/TC 150/SC 2 – Cardiovascular implants and extracorporeal systems working committee with Rob Fraser (RF), ViVitro Lab Manager.
Wei and Rob spoke recently about Wei’s work in the Tissue Mechanics Lab, the ISO committee, and TAVR durability.
RF: As an associate professor at Georgia Tech you’re involved in a variety of projects. Will you give our readers a summary of what’s unique about the work you’re doing.
WS: We study heart valve biomechanics, left ventricle mechanics, as well as the ascending aorta aneurysm rupture potential—basically cardiovascular biomechanics. We use experimental methods, such as biaxial, uniaxial, and fatigue testing to characterize the tissues’ mechanical properties, then we put them into computer models to simulate their biomechanical behaviors and responses. We would look at valve performance to study the mechanism of valve failure, valve repair, and procedural failure – like TAVR procedural failure- the mechanism. That’s our research focus.
RF: It sounds like basic material characterization with the biaxial and uniaxial testing to translate this into a TAVR model, are you also testing on the full TAVR systems?
WS: We don’t test a full commercial TAVR valve in our lab. Basically we test pericardial tissues and then put their properties in the computational model. We created a generic TAVR valve model. It’s a computational model that mimics the key features of transcatheter valves. We can run simulations in the nominal shape, elliptical shape or oval shape, and look at the valve stress and strain distributions. From numeric simulations we can also look at how the TAVR stent interacts with the calcified aortic root, whether it is placed too high or too low and whether it is expanded too much. Will it cause aortic rupture, paravalvular leak, coronary occlusion, or blood flow obstruction?
RF: How is the work going? What reactions have you had from colleagues in the industry?
WS: We have been publishing in this area extensively. Some of our papers have had a pretty good impact. For example, our 2010 publication talks about how elliptical deployment is going to increase TAVR stress and have implications on the durability. At that time it was new, now it is well accepted that the elliptical configuration is not good.
RF: Yes, certainly your elliptical findings were great results. Are there any other highlights?
WS: We also work on modeling aortic aneurysm. We look at the ascending aortic aneurysm and its rupture potential. We work with Dr. Elefteriades at Yale University Medical Center. He’s a cardiac surgeon. He provided us patient tissue samples and imaging data, and we built computational models and run simulations. We also collaborate with Dr. James Duncan at Yale. He’s an imaging expert. We recently worked on statistical shape models for population-based modeling of the aortic valve.
RF: What are some of your future plans or goals?
WS: I think fatigue damage is going to be an issue for the TAVR valves. The 5 year durability data for the SAPIEN device look very good. We’re waiting to see at 7-8 years if this type of valve is going to show some particular issues. We’re getting towards that 7 years now.
I think the TAVR durability is going to be a concern. As TAVR goes to younger patients and low risk patients and is competing somewhat with surgical valve replacement, the durability is going to be a big issue. We did some computational fatigue models, tissue fatigue testing, and we just don`t have clinical results yet so we are waiting. That`s one of the interesting research areas we are studying.
RF: Based upon this fundamental research you are conducting, do you see any issues coming up?
WS: It`s hard to say. It`s predicting into the future. I have a good confidence in the companies who have a lot of surgical valve fabrication experience. They have in-house expertise and are rigorous. For the new companies- we have so many new start-ups with new valve designs- for those companies I think it’s going to be an issue because durability will not show until many years down the road. In 5-6 years, “are they really building a valve as good and rigorously as a well-established valve company?” is a big unknown.
RF: You have a unique perspective working in both industry and academia.
WS: One difference is that in academia you have more time to look at more details. In a company you have product deadlines and have to hit those targets for a product launch. The goal is really the same: To improve the patient’s healthcare. For me, I enjoy doing more fundamental basic science research. That’s the reason I go for academia. But I think for the valve industry, this is probably the best time. There are a lot of R&D activities, a lot of start-ups and opportunities for young people to grow. If you are a grad student, going into the valve industry is probably a good idea at this moment.
RF: But not for you. You’re happy where you are.
WS: (laughs) Yes, I am.
RF: We met while working on the ISO committee. Has it helped or influenced your work?
WS: Not directly because a lot of my work is fundamental basic research. But I really like my ISO work because it gives me a different perspective. I feel ISO standards have very rigorous wording. We discuss every single line to make sure it makes sense. Sometime we argue, sometimes we agree. It’s nice working with the representatives from different companies. In terms of technical learning, not that much.
Read more interviews with Cardiovascular Pioneers.