Every heart is unique. There are many factors that can affect the size and shape of a person’s heart. People with heart disease may notice these differences more than others, because their hearts and major vessels are working harder to compensate for any impairments.
MIT engineers are hoping to help doctors tailor treatments to patients’ specific heart form and function, with a custom robotic heart. The team has developed a procedure to 3D print a soft and flexible replica of a patient’s heart. They can then control the replica’s action to mimic that patient’s blood-pumping ability.
The procedure involves first converting medical images of a patient’s heart into a three-dimensional computer model, which the researchers can then 3D print using a polymer-based ink. The result is a soft, flexible shell in the exact shape of the patient’s own heart. The team can also use this approach to print a patient’s aorta — the major artery that carries blood out of the heart to the rest of the body.
To mimic the heart’s pumping action, the team has fabricated sleeves similar to blood pressure cuffs that wrap around a printed heart and aorta. Each sleeve has a precisely patterned underside that resembles bubble wrap. When the sleeve is connected to a pneumatic system, researchers can tune the outflowing air to rhythmically inflate the sleeve’s bubbles and contract the heart, mimicking its pumping action.
Researchers can also inflate an additional sleeve around a printed aorta, which will constrict it. This constriction, they say, can be tuned to mimic aortic stenosis — a condition in which the aortic valve narrows, causing the heart to work harder to force blood through the body.
Doctors commonly treat aortic stenosis by surgically implanting a synthetic valve designed to widen the aorta’s natural valve. In the future, the team says that doctors could potentially use their new procedure to first print a patient’s heart and aorta, then implant a variety of valves into the printed model to see which design results in the best function and fit for that particular patient. Researchers and medical device companies could use the heart replicas to create realistic models for testing various therapies for heart disease.
“All hearts are different,” says Luca Rosalia, a graduate student in the MIT-Harvard Program in Health Sciences and Technology. “There are massive variations, especially when patients are sick. The advantage of our system is that we can recreate not just the form of a patient’s heart, but also its function in both physiology and disease.”
Rosalia and his coworkers report on their findings in a study that appears today in Science Robotics. MIT co-authors are Caglar Ozturk and DebkalpaGoswami, Jean Bonnemain and Sophie Wang. Also, James Weaver from Harvard University and Christopher Nguyen and Rishi Puri at the Cleveland Clinic in Ohio, are James Weaver and Benjamin Bonner.
Print and pump
In January 2020, team members, led by mechanical engineering professor Ellen Roche, developed a “biorobotic hybrid heart” — a general replica of a heart, made from synthetic muscle containing small, inflatable cylinders, which they could control to mimic the contractions of a real beating heart.
Shortly after those efforts, the Covid-19 pandemic forced Roche’s lab, along with most others on campus, to temporarily close. Rosalia did not give up and continued to tweak the heart-pumping design at her home.
“I recreated the whole system in my dorm room that March,” Rosalia recalls.
The lab reopened months later. The team continued to work on improving the control of heart-pumping sleeves, which was tested in animal and computer models. The team then developed sleeves and replicas of heart that were specific for each patient. They turned to 3D printing for this purpose.
“There is a lot of interest in the medical field in using 3D printing technology to accurately recreate patient anatomy for use in preprocedural planning and training,” notes Wang, who is a vascular surgery resident at Beth Israel Deaconess Medical Center in Boston.
An inclusive design
In the new study, the team took advantage of 3D printing to produce custom replicas of actual patients’ hearts. The team used a polymer-based dye that can be stretched and squeezed once it has dried.
Researchers used medical scans from 15 patients suffering from aortic stenosis to source their material. The team converted each patient’s images into a three-dimensional computer model of the patient’s left ventricle (the main pumping chamber of the heart) and aorta. To create an anatomically correct shell of the vessel and ventricle, they fed this model to a 3D printer.
They also created sleeves to wrap around printed forms. They tailored each sleeve’s pockets such that, when wrapped around their respective forms and connected to a small air pumping system, the sleeves could be tuned separately to realistically contract and constrict the printed models.
The researchers found that each model heart could be accurately reproduced by the researchers, allowing them to recreate the same heart pumping pressures and flows as in each patient.
“Being able to match the patients’ flows and pressures was very encouraging,” Roche says. “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.”
To test if the printed vessel and heart responds in the same way, the team went one step further. Some patients had valve implants to expand their aorta. Roche and her colleagues implanted identical valves in printed aortas that were modeled after each patient. They were able to activate the printed heart pump and observe that the valve produced similar improvements in flow as the actual patients after their surgery.
Finally, the team used an actuated printed heart to compare implants of different sizes, to see which would result in the best fit and flow — something they envision clinicians could potentially do for their patients in the future.
“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 Nguyen. “Once it’s up and running, clinicians could test different valve types and sizes and see which works best, then use that to implant.”
Roche believes that the patient-specific replicas can help to develop and identify optimal treatments for patients with challenging and unique cardiac geometries.
“Designing inclusively for a large range of anatomies, and testing interventions across this range, may increase the addressable target population for minimally invasive procedures,” Roche says.
This research was partially supported by the National Science Foundation and the National Institutes of Health.
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