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New 3D-Printed Heart Model Pumps New Life into Prosthetic Valve Testing

In a paper published in Science Robotics, engineers from MIT have developed a procedure to 3D-print a soft robotics-enabled replica of a patient’s heart and aorta. The model is custom-fit to each patient and capable of recreating the haemodynamics of aortic stenosis and any congenital defects the patient may have.

No two hearts beat the same

Aortic stenosis (AS) is a narrowing of the aortic valve orifice caused by reduced mobility of the valve leaflets, leading to elevated transaortic pressure gradients, pressure overload, and left ventricular remodelling. It affects about 1.5 million people in the United States and has a low survival rate if left untreated. Aortic valve replacement is the preferred treatment to improve blood flow and alleviate symptoms, and it is estimated that 80,000 to 85,000 aortic valve replacement procedures are performed every year in the United States. There are currently no effective pharmacological treatments for AS. In order to improve the durability, performance, and safety of aortic prosthetic valves, there is a growing demand for the creation of more advanced versions.

To evaluate the performance of prosthetic aortic valves, hydrodynamic models are often used. However, these models are limited in their use, and there is a growing need for high-fidelity patient-specific platforms. Hydrodynamic platforms that integrate patient-specific aortic replicas have been developed for studies of AS, but these models rely on rigid, idealized components and do not recreate patient-specific anatomies and haemodynamics. More advanced models which use 3D printing have also been developed, but there are still several problems which limit their clinical relevance. These include the inability to achieve real-time tunability with stiff 3D-printed models and the use of traditional pumps that cannot model the diastolic dysfunction caused by LV remodelling processes observed in most patients with AS.

Building a heart

To address this issue, the research team from MIT set out to create a heart replica that was not only patient-specific, but was also soft and flexible to allow for adjustments, and that accurately mimicked the patient’s blood pumping abilities.

The researchers used medical scans of 15 patients diagnosed with aortic stenosis and converted medical images of the patient’s left ventricle and aorta into a 3D computer model. They then 3D printed the computer model with a polymer-based ink. The result is a soft, flexible, anatomically accurate shell in the shape of the patient’s heart. To mimic the heart’s pumping action, the researchers fabricated robotic sleeves that wrap around the printed heart and aorta – similar to blood pressure cuffs. Again, these sleeves were tailor-made for each patient, and when connected to a pneumatic system, researchers caould tune the outflowing air to rhythmically inflate the sleeve’s bubbles and contract the heart, mimicking its pumping action. The sleeve wrapped around the aorta could also be inflated to constrict the vessel and mimic aortic stenosis.

The soft robotic model (which was validated against clinical data) successfully recapitulates patient-specific haemodynamics of aortic stenosis and secondary ventricular remodelling. “Being able to match the patients’ flows and pressures was very encouraging,” said Ellen Roche, senior author of the study. “We’re not only printing the heart’s anatomy, but also replicating its mechanics and physiology. That’s the part that we get excited about.”

Figure 1 ¦ Showing the different steps involved in building the patient-specific hydrodynamic model

Ready for the clinic

One of the notable aspects of this new model is how fast the turnaround time for building it is. “Patients would get their imaging done, which they do anyway, and we would use that to make this system, ideally within the day,” says co-author Christopher Nyugen. “Once it’s up and running, clinicians could test different valve types and sizes and see which works best, then use that to implant.” Moreover, as these heart models are patient-specific, the use of these models could expand the cohort of patients who are eligible for aortic valve replacement, as well as increase the efficacy and get the best fit for each patient. “Designing inclusively for a large range of anatomies, and testing interventions across this range, may increase the addressable target population for minimally invasive procedures,” says Ellen Roche. The heart replicas could also be used by research labs and the medical device industry as realistic platforms for testing therapies for various other types of heart disease.