Engineers at ETH Zurich used 3-D printing to make a soft, artificial heart made of the implantable material, according to research published last week in the journal Artificial Organs.
Though the "proof-of-concept" structure cannot beat for more than about 30 minutes at a stretch, the artificial heart nevertheless possesses left and right ventricles, pumps a liquid resembling blood and weighs about the same as a natural human heart.
Wendelin Stark, a professor of functional materials engineering at the Swiss science and technology university, made the pulsing heart, along with his doctoral student Nicholas Cohrs and other researchers, using a wax casting technique.
"We do not print the heart directly, but a mold, which allows us to make the silicone (structure) with the chamber geometries incorporated," Cohrs explained in an email. "We chose silicone because it is an established material in medicine and implants and is available from many suppliers in implantable grades."
Looking to the future, Cohrs said that silicone offers the greatest flexibility for optimization of an artificial heart.
Design of the soft artificial heart began at the Zurich Heart Project, a collaboration of 20 research groups from various disciplines and institutions in Zurich and Berlin. Their combined efforts are aimed at creating technologies to replace blood pumps, which have disadvantages such as malfunctioning parts. In pursuit of their goals, Zurich Heart Project researchers have designed a testing environment and even created a fluid with a similar viscosity as blood to simulate the human cardiovascular system.
Stark, Cohrs and other members of their group made use of this testing environment when developing their soft artificial heart.
"We chose 3-D printing because it is a very versatile technique, which allows the manufacturing of specific and detailed geometries very well," Cohrs wrote, adding that it is also a "very fast" technique.
The soft artificial heart weighs 390 grams, or about 0.86 pounds or 13.8 ounces. Though it lacks atria, the upper chambers of the human organ, the heart has both a right and a left ventricle, which are separatedby an additional chamber rather than a septum found in a human heart. Pressurized air inflates and deflates this central chamber, replacing the muscle contraction of the human heart, and this is how the artificial heart is able to pump fluid with comparable viscosity to human blood.
Currently, some heart transplant patients require ventricular assist devices -- essentially mechanical pumps that can support a failing circulatory system -- as a "bridge" before their procedures. Yet these devices "are often also used as destination therapy for older patients," who, because of their age, are not eligible for heart transplants, explained Cohrs.
His soft artificial heart might someday fulfill that purpose, he said, though the "final goal is, of course, to be able to supply an artificial heart" -- a patient-specific structure that works as well as a natural heart.
"It will take years for sure," Cohrs said, adding that improvements are necessary before "we can start thinking about that."
Dr. Stephen H. Little, a cardiologist with the Houston Methodist DeBakey Heart & Vascular Center and medical director of the center's valve clinic for heart disease, said the artificial heart developed by Cohrs and Stark is "pretty impressive."
The team created "a specific blend of 3-D printed materials that could hold their configuration under multiple cycles" for 30 to 45 minutes, and although they "weren't very specific about how they got it to beat -- they got it to beat," said Little, who was not involved in the research.
He noted that this "engineering feat" is "a long way from where anyone else is."
"The problem with the heart is, it's beating and moving," Little said. There's "a lot of medical 3-D printing happening," but most of it is in "materials that don't have to move."
"You can put in a hip bone, a jawbone, a piece of cell plate; you can 3-D print in titanium, ceramic or hard plastics," he said, yet when it comes to making a beating heart, that is "an order of magnitude tougher." As a result, "cardiology is fairly far behind other medical fields."
"There's a lot of interest in the pediatric world for some of the incredibly complex surgeries that need to be performed for little kids that are born with congenital heart problems," Little said. Increasingly, pediatric surgeons use3-D-printed models to plan complicated and specific procedures.
"One of the advantages of 3-D printing is, you can take a patient's clinical image, which can either be a CAT scan or an MRI or 3-D echocardiography ... and you can reproduce it and create a 3-D model," he said. With that, a surgeon can plan a procedure that might take 45 minutes versus three hours without a model.
Instead of just one material, 3-D printing can blend a dozen materials, Little explained, adding that this capability is bringing models closer to structures that actually look and feel like a heart.
"You can have a model with hard materials representing calcification, soft materials representing valve structures, slightly harder material representing heart muscle," he said.
"The other big application that we do with 3-D printing is medical education and patient education," Little said. Although surgeons can show patients hand puppets and diagrams and try to explain "this is your heart, and this is what we're going to do," that's not nearly as effective as a 3-D model.
"If a picture's worth a thousand words, then holding a printed model of your own heart and pointing to where the problem is and what you're going to fix, that's got to be worth a million words," he said. "It doesn't matter what language you're using, a translator or not, they hold the heart and see what you're doing -- and they get it. That's a low-hanging fruit application, but it's one of the most impactful.
"3-D printing is creating its role still. Nobody quite knows exactly what to do with it, but they're all excited to do something," Little said, adding that the challenge moving forward is funding. Who pays for the model? Is it paid out of a hospital's operating budget, philanthropy funds or patient billing?
Little hopes that someday, insurance providers can be convinced that if they spend, say, $500 or $1,000 to 3-D-print a model, the patient might spend fewer days in a hospital, and they'll actually save money.
Every patient, every heart, and every heart problem is different, explained Little. "People come in a million varieties, but most devices come in just one or two sizes. How this generic device should go into this specific patient, that's where the value of 3-D printing comes in."
Creating patient-specific artificial hearts may be years away, but it is a worthy goal, said Little.
The rising number of cardiovascular disease patients -- some requiring surgical procedures -- also suggests that 3-D-printed hearts would become an increasingly valuable commodity worldwide.
Cardiovascular diseases include most anything that can go wrong with the heart and blood vessels, including plaque buildup and clots, leading to heart attacks and stroke. Each year, cardiovascular diseases take nearly 17.5 million lives -- currently, this is about 31% of all deaths globally -- and this number continues to climb, according to the World Health Organization.
In the United States, more than 80 million people have some form of cardiovascular disease, which causes nearly one in four deaths each year -- nearly 610,000 people. Heart transplants may not be the solution to every heart condition, but the United Network for Organ Sharing counts 67,301 heart transplants performed in the United States from January 1, 1988, to June 30, 2017.
With natural hearts in short supply, an artificial heart would be an achievement valued by patients worldwide.
"If this is possible is another question," Cohrs said, "but it is definitely the goal."