Q: Tell us a little about the human heart.
A: The human heart is our pumping machine. Our pump works 24/7 from the first moment of life until we die. The heart is a large two-sided muscle that continuously pumps. You have the left side and the right side. The left side is where the oxygenated blood is pumped into your body, via the aorta into the extremities and brain. This is the high-pressure side. And then you have the right side where the blood comes back from your body with a low amount of oxygen, which is later pumped into your lungs.
The right side, where the blood returns, is in the low-pressure domain. Each side has two individual chambers. In total, we have four chambers, each with an inflow orifice and an outflow orifice. All of these openings are gated by valves. The human heart has four heart valves: the left side (the aortic heart valve) and the right side (the pulmonary heart valve).
The one we are talking about, the aortic valve, is the most significant for people with heart valve conditions. That is where the blood leaves your left ventricle with high pressure going directly into the aorta. From the aorta, blood leaves the heart and goes down into your body and up to your brain. So, this is the heart valve that sees the highest loading throughout its lifetime, in terms of blood flow, in terms of pressure differences, and is exposed to really strong physical loading.
Q: How common is it for heart valves to break down? What impact does it have on the person when that happens?
A: The aortic valve has three small parts called leaflets. These are very flexible little wing-like sails that can open easily and move the blood through. On the other hand, they also close easily to prevent blood from flowing back. Over time (with aging) they can calcify which prevents the leaflets from opening and closing easily.
Calcification increases over time, that’s a typical pathological event in the human body, vessels, and arteries. It’s not hard to imagine that once you see the accumulation of heart calcifications in these very flexible tissues, the heart valve won’t function perfectly anymore. The valve has trouble opening, and that needs to happen because the blood needs to go out into the aorta. And that leads to the heart working too hard, and eventually, the valve needs to be replaced. Valves were first replaced with surgical devices. These were rings with little plastic or metallic structures that could open and close, but they required open heart surgery to place them into the human body. Now, roughly 20 years later, a new system has developed. Transcatheter devices can be placed into your body with the transcatheter, with a catheter device that enters your femoral artery. And this is what it’s called, TAVI devices.
Q: How is SimInSitu attempting to rectify the problem of the artificial valve with biodegradable polymers?
A: There is a new class of devices becoming available. Even the substitute devices, these TAVI devices, over time, deteriorate, lose performance, and must be replaced. What can you do if the patient has them longer than 10-15 years? The best solution would be if the function is restored through your tissue, if your body could help or could develop a solution, restoring the original function of the heart valve. Over the past 15 years, there’s been a new strategy developing that uses biodegradable synthetic material. Once it is placed into your body, it attracts certain types of cells that start to infiltrate it and start to produce new tissue, and at the same time, the synthetic material starts to biodegrade. This is a balanced process between synthetic tissue being degraded and resorbed over time and, likewise, at the same time, new tissue being generated. Theoretically, you could build in whatever geometry you would like to have, and your body could recreate new structures. This is a promising strategy but challenging. If it’s your tissue, there is no further risk that this will deteriorate because it’s a living organism.
Q: What challenges have SimInSitu encountered while trying to make this groundbreaking technology a reality?
A: This technology is developed by several research organizations, but also companies are working on that topic, and they have been working on that technological problem for quite a few years developing products and testing them in different environments. All these high-risk products need to be tested in clinical trials before they can go to the market. This is a very long, risky, and expensive process. Our idea with SimInSitu is to use computational methods to help medical device companies develop their products faster. Providing computational methods and simulation tools that allow the test of devices and healthcare solutions in a computational computer environment in a virtual patient environment accelerates the development process. For three and a half years, we have worked with medical device companies that use this technology and have experience in these biodegradable technologies to develop tools that can help them develop these products faster and safer in the long term.
Q: How are you using advanced computer modeling and simulation to help address the challenges of the biodegradable part?
A: Our main goal in this project is to develop two platforms. A platform is effectively a computer model that can be used to simulate how these devices could evolve within a given patient. We have two classes of devices for which we want to develop these platforms. And within these two platforms, we need to ensure that we have the right material models developed that can simulate the biological process of degradation and restoration. We are simulating a biological process. That material is changing: it is growing, and it’s changing its dimensions and its mechanical properties. Another group is the patient models, where we have a group that is collecting true patient data through a clinical center and using this data to generate patient-specific models from real patients who are undergoing classic TAVI treatments.
We can see how these classic devices are performing over time and we can use this data to build and validate our models. There are also different kinds of computational domains: material modeling, mechanical structural modeling, and blood flow. And because it’s a valve, the blood flow and the interaction with these valve components is the key element to simulate. Although it sounds simple, it’s a huge challenge. Fluid-structure interaction, or FSI, is one of the biggest building blocks but also one of the biggest challenges to put in these models because they are very computationally demanding.
A key objective of the SimInSitu project besides developing advanced simulation tools for complex systems, is establishing the credibility of these models as well. This is generally done through VVUQ, which stands for Verification, Validation & Uncertainty Quantification, and which is a structured approach to make sure that the predictions done with the computer model are trustworthy. Our experience in the VVUQ domain increased tremendously, which we discussed and shared with other industries, like aerospace and automotive. We realized there is a lack of deep understanding and experience in using these methods as part of your daily job in a company or research institute. We at 4RealSim are trying to improve this situation by offering also dedicated training.
Q: Is there another layer of complexity in doing a patient-specific series of tests?
A: The methods we’re using are not different, whether it’s a generic heart or a specific heart. The difference is that based on the availability of imaging data, specifically high-resolution MRI and high-resolution CT data, we have more access to patient-specific data. And that means we can reconstruct for a given patient the exact anatomy. During one cardiac cycle, during one heartbeat, we can make multiple snapshots. With a certain CT MRI technology, we can see how the heart is changing and how it’s getting bigger and smaller, and we can use this data to reconstruct the specific anatomy of that patient. We can also simulate for a specific patient where the calcification in these leaflets is based on the imaging data. This requires a lot of automation processes. So the whole model generation is done from clinical data, from CT MRI, M data, then going through what’s called segmentation model generation, and then you need to build this computer model and put the right boundary conditions on top.
Q: Did you find a preference or value in using one type of simulation software over another?
A: We have multiple software simulations in this consortium and SimInSitu, but I would say 80% of the work is on a structural level. So, finite element methods. And here we are working exclusively with Abaqus because it is well established in the industry and also in academics, and especially because it has huge flexibilities in subroutine programming especially for user-defined materials. Abaqus is very strong, and all of our partners who are somehow involved in the modeling of finite elements work with Abaqus. That’s our workhorse.
Q: Tell me what impact this work you’re doing might have on the world someday. What do you think the dream scenario is?
A: The dream scenario is that we have established a way of working and building these models that get acceptance in the industry and also from regulators. So one day we can develop a product and can also provide the regulatory agency with a large amount of computational data. If we can establish that, it would be the biggest success story that I can foresee. I cannot look into the future and realistically see that we can solve everything on the computer. I will always consider that this has to be a mix of real clinical data with computational data. But if that amount can be increased and we have the methods in place, and also all the external stakeholders, then this will be a huge success. I’m quite positive that we can do this. With all the work that is going on in so many sites, on so many projects, developing into what is called good simulation practice standards, into official standards from ASME that deal with computation methods, with medical devices, our work here, and the work of other consortiums. I’m quite optimistic that this path is going forward and will make a big contribution in the future.
Q: I love simulation because…
A: I love simulation because it’s a challenge and because it allows me to do things that would be so complicated to see in a test environment or a laboratory environment.
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Katie is the Editor of the SIMULIA blog, an expert in engineering and scientific communication, and a strategic digital marketer. Katie has a BA in English and Writing from the University of Rhode Island and a MS in Technical Communication from Northeastern University. She is also a proud SIMULIA advocate, passionate about democratizing simulation for all audiences. Katie is a native Rhode Islander but now lives just over the border in southeast Massachusetts. She is a true New Englander and loves sharing all the cool things NE has to offer. She enjoys a variety of hobbies including history, astronomy, science/technology, science fiction, true crime, fashion and anything associated with nature and the outdoors. She is also mom to a 4-year old budding engineer and two crazy rescue pups.