Soft robotic models are patient-specific and can help zero in on the best implant for an individual.
Massachusetts Institute of Technology
No two hearts beat alike. The size and shape of the heart can vary from one person to the next. These differences can be particularly pronounced for people living with heart disease, as their hearts and major vessels work harder to overcome any compromised function.
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. The underside of each sleeve resembles precisely patterned 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.
The
researchers can also inflate a separate sleeve surrounding a printed aorta to
constrict the vessel. 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.
The heart replicas could also be used by research labs and the medical device industry as realistic platforms for testing therapies for various types of 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 colleagues report their results in a study appearing today in Science Robotics. MIT
co-authors include Caglar Ozturk, Debkalpa Goswami, Jean Bonnemain, Sophie
Wang, and Ellen Roche, along with Benjamin Bonner of Massachusetts General
Hospital, James Weaver of Harvard University, and Christopher Nguyen, Rishi
Puri, and Samir Kapadia at the Cleveland Clinic in Ohio.
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. Undeterred, Rosalia continued tweaking
the heart-pumping design at home.
"I recreated the whole system in my dorm room that
March," Rosalia recalls.
Months
later, the lab reopened, and the team continued where it left off, working to
improve the control of the heart-pumping sleeve, which they tested in animal
and computational models. They then expanded their approach to develop sleeves
and heart replicas that are specific to individual patients. For this, they
turned to 3D printing.
"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. They used a polymer-based ink that, once
printed and cured, can squeeze and stretch, similarly to a real beating heart.
As
their source material, the researchers used medical scans of 15 patients
diagnosed with aortic stenosis. 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. They fed this model into a 3D printer
to generate a soft, anatomically accurate shell of both the ventricle and
vessel.
The
team also fabricated sleeves to wrap around the 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 showed that for each model heart, they could accurately recreate
the same heart-pumping pressures and flows that were previously measured in
each respective 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."
Going a step further, the team aimed to replicate some of the interventions that a handful of the patients underwent, to see whether the printed heart and vessel responded in the same way. Some patients had received valve implants designed to widen the aorta.
Roche and her colleagues implanted similar valves in the
printed aortas modeled after each patient. When they activated the printed
heart to pump, they observed that the implanted valve produced similarly
improved flows as in actual patients following their surgical implants.
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 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."
Ultimately,
Roche says the patient-specific replicas could help develop and identify ideal
treatments for individuals with unique and challenging 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 supported, in part, by the National Science Foundation, the National Institutes of Health, and the National Heart Lung Blood Institute.
