A heart of gold may be hard to find, but a heart of silicone may be within reach.

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.

Testing a soft artificial heart

The full announcement:

ETH researchers from the Functional Materials Laboratory have developed a silicone heart that beats almost like a human heart. In collaboration with colleagues from the Product Development Group Zurich, they have tested how well it works

It looks like a real heart. And this is the goal of the first entirely soft artificial heart: to mimic its natural model as closely as possible. The silicone heart has been developed by Nicholas Cohrs, a doctoral student in the group led by Wendelin Stark, Professor of Functional Materials Engineering at ETH Zurich. The reasoning why nature should be used as a model is clear. Currently used blood pumps have many disadvantages: their mechanical parts are susceptible to complications while the patient lacks a physiological pulse, which is assumed to have some consequences for the patient.

“Therefore, our goal is to develop an artificial heart that is roughly the same size as the patient’s own one and which imitates the human heart as closely as possible in form and function,” says Cohrs. A well-functioning artificial heart is a real necessity: about 26 million people worldwide suffer from heart failure while there is a shortage of donor hearts. Artificial blood pumps help to bridge the waiting time until a patient receives a donor heart or their own heart recovers.

The soft artificial heart was created from silicone using a 3D printing, lost-wax casting technique; it weighs 390 grams and has a volume of 679 cm3. “It is a silicone monoblock with complex inner structure,” explains Cohrs. This artificial heart has a right and a left ventricle, just like a real human heart, though they are not separated by a septum but by an additional chamber. This chamber is in- and deflated by pressurized air and is required to pump fluid from the blood chambers, thus replacing the muscle contraction of the human heart.

Thinking in a new direction

Anastasios Petrou, a doctoral student of the Product Development Group Zurich, led by Professor Mirko Meboldt evaluated the performance of this soft artificial heart. The young researchers have just published the results of the experiments in the scientific journal Artificial Organs.

They proved that the soft artificial heart fundamentally works and moves in a similar way to a human heart. However, it still has one problem: it currently lasts for about only 3,000 beats, which corresponds to a lifetime of half to three quarters of an hour. After that, the material can no longer withstand the strain. Cohrs explains: “This was simply a feasibility test. Our goal was not to present a heart ready for implantation, but to think about a new direction for the development of artificial hearts.” Of course, the tensile strength of the material and the performance would have to be enhanced significantly.

Zurich Heart brings researchers together

Cohrs and Petrou met in the Zurich Heart Project, a flagship project of University Medicine Zurich that brings together 20 research groups from various disciplines and institutions in Zurich and Berlin. Part of the research focuses on improvements on existing blood pumps, such as how to reduce blood damage induced from the mechanical parts of the pump, while others explore extremely elastic membranes or more biocompatible surfaces. This is done in close collaboration with the clinicians in Zurich and Berlin.

The lively exchanges among the researchers also helped this Zurich Heart sub-project. Doctoral students of Product Development Group Zurich, who are working on new technologies for blood pumps, have developed a testing environment with which they can simulate the human cardiovascular system. The researchers of the silicone heart made use of this testing environment for their development process which also included the use of a fluid with comparable viscosity as human blood. “Currently, our system is probably one of the best in the world,” says Petrou proudly.

Researching the heart is an appealing task, and Cohrs and Petrou would both like to remain in this research field. “As a mechanical engineer, I would never have thought that I would ever hold a soft heart in my hands. I’m now so fascinated by this research that I would very much like to continue working on the development of artificial hearts,” says Petrou.

Source: ETH news

  • VIDEO: Watch a report about the 3D printed heart at https://www.youtube.com/watch?v=YUYNXeHfTdQ

“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.

Future applications

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 separated by 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.”

‘Engineering feat’

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 use 3-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.”

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