3D Printed Metamaterials Used for Patient-Specific Heart Valve Models May Help Cardiac Patients

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Every year, tens of thousands of people are diagnosed with heart valve disease, and of these people, transcatheter aortic valve replacement (TAVR) is considered a good option for those considered to be at high risk for open-heart surgery complications. The prosthetic valves come in many sizes from different manufacturers, but if the replacement doesn’t have the proper fit, paravalvular leakage can occur when blood flows around the prosthetic, instead of through it. If the right prosthetic is used from the get-go, this complication can be avoided and patient outcomes improved. Now, researchers with the Georgia Institute of Technology (Georgia Tech) and the Piedmont Heart Institute, which is part of Piedmont HealthCare, are trying to improve the success rate of TAVR, by using new 3D printing technologies and medical imaging to make patient-specific heart valve models that imitate the physiology of real heart valves.

“Paravalvular leakage is an extremely important indicator in how well the patient will do long term with their new valve. The idea was, now that we can make a patient-specific model with this tissue-mimicking 3-D printing technology, we can test how the prosthetic valves interact with the 3-D printed models to learn whether we can predict leakage,” Zhen Qian, the Chief of Cardiovascular Imaging Research at Piedmont Heart Institute, said.

“In preparing to conduct a valve replacement, interventional cardiologists already weigh a variety of clinical risk predictors, but our 3-D printed model gives us a quantitative method to evaluate how well a prosthetic valve fits the patient.”

Submerged valve model during flow testing. [Image: Rob Felt, Georgia Tech]

The 3D printed models, made using CT scans of 18 valve replacement surgery patients’ hearts, behave a lot like real heart valves, and so are able to predict leakage with a high level of accuracy. A special metamaterial design was used to make the models, which were fabricated on a multi-material 3D printer so researchers could better control design aspects, like curving wavelengths and diameter, so it really mimics the real tissue; they can even recreate valve conditions like arterial wall stiffness and calcium deposition.

Metamaterials are able to morph to their environment, and make up a new class of engineered surfaces that can perform multiple nature-defying tasks, such as manipulating light and shaping sound, which has its own medical applications. Furthermore, 3D printing and 3D modeling is increasingly helping physicians work with transcatheter aortic devices, as Dr. Dee Dee Wang from the Henry Ford Health System has told 3DPrint.com before, with advanced technologies aiding medical professionals and the patients whose lives they work to save.

Zhen Qian, Chief of Cardiovascular Imaging Research at Piedmont Heart Institute, and Kan Wang, a researcher at Georgia Tech, at the Structural Heart Research & Innovation Laboratory, part of Emory University’s Carlyle Fraser Heart Center within the Division of Cardiothoracic Surgery. [Image: Rob Felt, Georgia Tech]

Chuck Zhang, a professor at Georgia Tech’s Stewart School of Industrial and Systems Engineering, said, “Previous methods of using 3-D printers and a single material to create human organ models were limited to the physiological properties of the material used. Our method of creating these models using metamaterial design and multi-material 3-D printing takes into account the mechanical behavior of the heart valves, mimicking the natural strain-stiffening behavior of soft tissues that comes from the interaction between elastin and collagen, two proteins found in heart valves.”

Stiff, wavy microstructures were embedded into the softer material during 3D printing, in order to imitate this interaction between collagen and elastin.

Zhang said, “These 3-D printed valves have the potential to make a huge impact on patient care going forward.”

Graphical abstract

The results of the research team’s study were published in a paper, titled “Quantitative Prediction of Paravalvular Leak in Transcatheter Aortic Valve Replacement Based on Tissue-Mimicking 3D Printing,” in the JACC: Cardiovascular Imaging journal; authors include Zhen Qian, Kan Wang, Shizhen Liu, Xiao Zhou, Vivek Rajagopal, Christopher Meduri, James R. Kauten, Yung-Hang Chang, Changsheng Wu, Chuck Zhang, Ben Wang, Mani A. Vannan.

Dozens of radiopaque beads were added to each 3D printed model, in order to measure the tissue-imitating material’s displacement. Then, inside a controlled, warm water testing environment that matched the human body’s temperature, a similarly sized prosthetic valve that had been used in an actual valve replacement was implanted in the model; researchers took care to put the valves exactly where they had been used during the original procedure.

Medical imaging showed the location of the beads before and after the experiment, and software analyzed the images to see how well the prosthetic valves worked inside the 3D printed models; specifically, it looked for any “inconsistencies representing areas where the prosthetic wasn’t sealed well against the wall of the valve,” as Georgia Tech notes.

Inside the 3D printed model of a heart valve. Black regions represent the location of calcium deposits. [Image: Rob Felt, Georgia Tech]

Each of these inconsistencies was given a value, and all of the values formed what’s called a bulge index. The team determined that a higher index correlated with the patients who had more leakage during valve replacement. The 3D printed models were not only able to predict the leakage, but also duplicate the severity and location of leakage complications.

“The results of this study are quite encouraging. Even though this valve replacement procedure is quite mature, there are still cases where picking a different size prosthetic or different manufacturer could improve the outcome, and 3-D printing will be very helpful to determine which one,” said Qian.

The team isn’t done yet – they will keep working to optimize the 3D printing process and metamaterial design, in hopes of one day using the 3D printed heart valves as a pre-surgical planning tool.

Qian explained, “Eventually, once a patient has a CT scan, we could create a model, try different kinds of valves in there, and tell the physician which one might work best. We could even predict that a patient would probably have moderate paravalvular leakage, but a balloon dilatation will solve it.”

We’ve seen 3D printed heart valve models used for training purposes before, so it’s not a huge leap to think they could be used for surgical planning. Just as Qian said, even though TAVR is not a new procedure, it never hurts to have an extra planning tool in place. Discuss in the TAVR forum at 3DPB.com.

[Source: Georgia Tech]

 

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