This Soft Artificial Heart May One Day Shorten the Heart Transplant List

ETH Zurich
ETH Zurich

If the heart in the Functional Materials Laboratory at ETH Zurich University were in a patient in an operating room, its vital signs would not be good. In fact, it would be in heart failure. Thankfully, it's not in a patient—and it's not even real. This heart is made of silicone.

Suspended in a metal frame and connected by tubes to trays of water standing in for blood, the silicone heart pumps water at a beat per second—a serious athlete's resting heart rate—in an approximation of the circulatory system. One valve is leaking, dripping onto the grate below, and the water bins are jerry-rigged with duct tape. If left to finish out its life to the final heartbeat, it would last for about 3000 beats before it ruptured. That's about 30 minutes—not long enough to finish an episode of Grey's Anatomy

Nicolas Cohrs, a bioengineering Ph.D. student from the university, admits that the artificial heart is usually in better shape. The one he holds in his hands—identical to the first—feels like taut but pliable muscle, and is intact and dry. He'd hoped to demonstrate a new and improved version of the heart, but that one is temporarily lost, likely hiding in a box somewhere at the airport in Tallinn, Estonia, where the researchers recently attended a symposium.

Taking place over the past three years, the experimental research is a part of Zurich Heart, a project involving 17 researchers from multiple institutions, including ETH, the University of Zurich, University Hospital of Zurich, and the German Heart Institute in Berlin, which has the largest artificial heart program in Europe.


Heart failure occurs when the heart cannot pump enough blood and oxygen to support the organs; common causes are coronary heart disease, high blood pressure, and diabetes. It's a global pandemic, threatening 26 million people worldwide every year. More than a quarter of them are in the U.S. alone, and the numbers are rising.

It's a life-threatening disease, but depending on the severity of the condition at the time of diagnosis, it's not necessarily an immediate death sentence. About half of the people in the U.S. diagnosed with the disease die within five years. Right now in the U.S., there are nearly 4000 people on the national heart transplant list, but they're a select few; it's estimated that upwards of 100,000 people need a new heart. Worldwide, demand for a new heart greatly outpaces supply, and many people die waiting for one.

That's why Cohrs, co-researcher Anastasios Petrou, and their colleagues are attempting to create an artificial heart modeled after each patient's own heart that would, ideally, last for the rest of a person's life.

Mechanical assistance devices for failing hearts exist, but they have serious limitations. Doctors treating heart failure have two options: a pump placed next to the heart, generally on the left side, that pumps the blood for the heart (what's known as a left ventricular assist device, or LVAD), or a total artificial heart (TAH). There have been a few total artificial hearts over the years, and at least four others are in development right now in Europe and the U.S. But only one currently has FDA approval and CE marking (allowing its use in European Union countries): the SynCardia total artificial heart. It debuted in the early '90s, and since has been implanted in nearly 1600 people worldwide.

While all implants come with side effects, especially when the immune system grows hostile toward a foreign object in the body, a common problem with existing total artificial hearts is that they're composed of hard materials, which can cause blood to clot. Such clots can lead to thrombosis and strokes, so anyone with an artificial heart has to take anticoagulants. In fact, Cohrs tells Mental Floss, patients with some sort of artificial heart implant—either a LVAD or a TAH—die more frequently from a stroke or an infection than they do from the heart condition that led to the implant. Neurological damage and equipment breakdown are risky side effects as well.

These complications mean that total artificial hearts are "bridges"—either to a new heart, or to death. They're designed to extend the life of a critically ill patient long enough to get on (or to the top of) the heart transplant list, or, if they're not a candidate for transplant, to make the last few years of a person's life more functional. A Turkish patient currently holds the record for the longest time living with a SynCardia artificial heart: The implant has been in his chest for five years. Most TAH patients live at least one year, but survival rates drop off after that.

The ETH team set out to make an artificial heart that would be not a bridge, but a true replacement. "When we heard about these problems, we thought about how we can make an artificial heart that doesn't have side effects," he recalls.


Using common computer assisted design (CAD) software, they designed an ersatz organ composed of soft material that hews closely to the composition, form, and function of the human heart. "Our working hypothesis is that when you have such a device which mimics the human heart in function and form, you will have less side effects," Cohrs says.

To create a heart, "we take a CT scan of a patient, then put it into a computer file and design the artificial heart around it in close resemblance to the patient's heart, so it always fits inside [the body]," Cohrs says.

But though it's modeled on a patient's heart and looks eerily like one, it's not identical to the real organ. For one thing, it can't move on its own, so the team had to make some modifications. They omitted the upper chambers, called atria, which collect and store blood, but included the lower chambers, called ventricles, which pump blood. In a real heart, the left and right sides are separated by the septum. Here, the team replaced the septum with an expansion chamber that is inflated and deflated with pressurized air. This action mimics heart muscle contractions that push blood from the heart.

The next step was to 3D-print a negative mold of the heart in ABS, a thermoplastic commonly used in 3D printing. It takes about 40 hours on the older-model 3D printers they have in the lab. They then filled this mold with the "heart" material—initially silicone—and let it cure for 36 hours, first at room temperature and then in an oven kept at a low temperature (about 150°F). The next day, they bathed it in a solvent of acetone, which dissolved the mold but left the printed heart alone. This process is essentially lost-wax casting, a technique used virtually unchanged for the past 4000 years to make metal objects, especially bronze. It takes about four days.

The resulting soft heart weighs about 13 ounces—about one-third more than an average adult heart (about 10 ounces). If implanted in a body, it would be sutured to the valves, arteries, and veins that bring blood through the body. Like existing ventricular assist devices and total artificial hearts on the market, it would be powered by a portable pneumatic driver worn externally by the patient.


In April 2016, they did a feasibility test to see if their silicone organ could pump blood like a real heart. First they incorporated state-of-the-art artificial valves used every day in heart surgeries around the world. These would direct the flow of blood. Then, collaborating with a team of mechanical engineers from ETH, they placed the heart in a hybrid mock circulation machine, which measures and simulates the human cardiovascular system. "You can really measure the relevant data without having to put your heart into an animal," says Cohrs.

Here's what the test looked like.

"Our results were very nice," Cohrs says. "When you look at the pressure waveform in the aorta, it really looked like the pressure waveform from the human heart, so that blood flow is very comparable to the blood flow from a real human heart."

Their results were published earlier this year in the journal Artificial Organs.

But less promising was the number of heartbeats the heart lasted before rupturing under stress. (On repeated tests, the heart always ruptured in the same place: a weak point between the expansion chamber and the left ventricle where the membrane was apparently too thin.) With the average human heart beating 2.5 billion times in a lifetime, 3000 heartbeats wouldn't get a patient far.

But they're making progress. Since then, they've switched the heart material from silicone to a high-tech polymer. The latest version of the heart—one of which was stuck in that box in the Tallinn airport—lasts for 1 million heartbeats. That's an exponential increase from 3000—but it's still only about 10 days' worth of life.

Right now, the heart costs around $400 USD to produce, "but when you want to do it under conditions where you can manufacture a device where it can be implanted into a body, it will be much more expensive," Cohrs says.

The researchers know they're far from having produced an implantable TAH; this soft heart represents a new concept for future artificial heart development that could one day lead to transplant centers using widely available, easy-to-use design software and commercially available 3D-printers to create a personalized heart for each patient. This kind of artificial heart would be not a bridge to transplantation or, in a few short years, death, but one that would take a person through many years of life.

"My personal goal is to have an artificial heart where you don't have side effects and you don't have any heart problems anymore, so it would last pretty much forever," Cohrs says. Well, perhaps not forever: "An artificial heart valve last 15 years at the moment. Maybe something like that."

10 Radiant Facts About Marie Curie

Photo Illustration by Mental Floss. Curie: Hulton Archive, Getty Images. Background: iStock
Photo Illustration by Mental Floss. Curie: Hulton Archive, Getty Images. Background: iStock

Born Maria Salomea Skłodowska in Poland in 1867, Marie Curie grew up to become one of the most noteworthy scientists of all time. Her long list of accolades is proof of her far-reaching influence, but not every stride she made in the fields of chemistry, physics, and medicine was recognized with an award. Here are some facts you might not know about the iconic researcher.

1. Marie Curie's parents were teachers.

Maria Skłodowska was the fifth and youngest child of two Polish educators. Her parents placed a high value on learning and insisted that all their children—including their daughters—receive a quality education at home and at school. Maria received extra science training from her father, and when she graduated from high school at age 15, she was first in her class.

2. Marie Curie had to seek out alternative education for women.

After collecting her high school diploma, Maria had hoped to study at the University of Warsaw with her sister, Bronia. Because the school didn't accept women, the siblings instead enrolled at the Flying University, a Polish college that welcomed female students. It was still illegal for women to receive higher education at the time so the institution was constantly changing locations to avoid detection from authorities. In 1891 Maria moved to Paris to live with her sister, where she enrolled at the Sorbonne to continue her education.

3. Marie Curie is the only person to win Nobel Prizes in two separate sciences.

Marie Curie and her husband, Pierre Curie, in 1902.
Marie Curie and her husband, Pierre Curie, in 1902.
Agence France Presse, Getty Images

In 1903, Marie Curie made history when she won the Nobel Prize in physics with her husband, Pierre, and with physicist Henri Becquerel for their work on radioactivity, making her the first woman to receive the honor. The second Nobel Prize she took home in 1911 was even more historic: With that win in the chemistry category, she became the first person to win the award twice. And she remains the only person to ever receive Nobel Prizes for two different sciences.

4. Marie Curie added two elements to the Periodic Table.

The second Nobel Prize Marie Curie received recognized her discovery and research of two elements: radium and polonium. The former element was named for the Latin word for ray and the latter was a nod to her home country, Poland.

5. Nobel Prize-winning ran in Marie Curie's family.

Marie Curie's daughter Irène Joliot-Curie, and her husband, Frédéric Joliot-Curie, circa 1940.
Marie Curie's daughter Irène Joliot-Curie, and her husband, Frédéric Joliot-Curie, circa 1940.
Central Press, Hulton Archive // Getty Images

When Marie Curie and her husband, Pierre, won their Nobel Prize in 1903, their daughter Irène was only 6 years old. She would grow up to follow in her parents' footsteps by jointly winning the Nobel Prize for chemistry with her husband, Frédéric Joliot-Curie, in 1935. They were recognized for their discovery of "artificial" radioactivity, a breakthrough made possible by Irène's parents years earlier. Marie and Pierre's other son-in-law, Henry Labouisse, who married their younger daughter, Ève Curie, accepted a Nobel Prize for Peace on behalf of UNICEF, of which he was the executive director, in 1965. This brought the family's total up to five.

6. Marie Curie did her most important work in a shed.

The research that won Marie Curie her first Nobel Prize required hours of physical labor. In order to prove they had discovered new elements, she and her husband had to produce numerous examples of them by breaking down ore into its chemical components. Their regular labs weren't big enough to accommodate the process, so they moved their work into an old shed behind the school where Pierre worked. According to Curie, the space was a hothouse in the summer and drafty in the winter, with a glass roof that didn't fully protect them from the rain. After the famed German chemist Wilhelm Ostwald visited the Curies' shed to see the place where radium was discovered, he described it as being "a cross between a stable and a potato shed, and if I had not seen the worktable and items of chemical apparatus, I would have thought that I was been played a practical joke."

7. Marie Curie's notebooks are still radioactive.

Marie Curie's journals
Hulton Archive, Getty Images

When Marie Curie was performing her most important research on radiation in the early 20th century, she had no idea of the effects it would have on her health. It wasn't unusual for her to walk around her lab with bottles of polonium and radium in her pockets. She even described storing the radioactive material out in the open in her autobiography. "One of our joys was to go into our workroom at night; we then perceived on all sides the feebly luminous silhouettes of the bottles of capsules containing our products […] The glowing tubes looked like faint, fairy lights."

It's no surprise then that Marie Curie died of aplastic anemia, likely caused by prolonged exposure to radiation, in 1934. Even her notebooks are still radioactive a century later. Today they're stored in lead-lined boxes, and will likely remain radioactive for another 1500 years.

8. Marie Curie offered to donate her medals to the war effort.

Marie Curie had only been a double-Nobel Laureate for a few years when she considered parting ways with her medals. At the start of World War I, France put out a call for gold to fund the war effort, so Curie offered to have her two medals melted down. When bank officials refused to accept them, she settled for donating her prize money to purchase war bonds.

9. Marie Curie developed a portable X-ray to treat soldiers.

Marie Curie circa 1930
Marie Curie, circa 1930.
Keystone, Getty Images

Marie's desire to help her adopted country fight the new war didn't end there. After making the donation, she developed an interest in x-rays—not a far jump from her previous work with radium—and it didn't take her long to realize that the emerging technology could be used to aid soldiers on the battlefield. Curie convinced the French government to name her Director of the Red Cross Radiology Service and persuaded her wealthy friends to fund her idea for a mobile x-ray machine. She learned to drive and operate the vehicle herself and treated wounded soldiers at the Battle of the Marne, ignoring protests from skeptical military doctors. Her invention was proven effective at saving lives, and ultimately 20 "petite Curies," as the x-ray machines were called, were built for the war.

10. Marie Curie founded centers for medical research.

Following World War I, Marie Curie embarked on a different fundraising mission, this time with the goal of supporting her research centers in Paris and Warsaw. Curie's radium institutes were the site of important work, like the discovery of a new element, francium, by Marguerite Perey, and the development of artificial radioactivity by Irène and Frederic Joliot-Curie. The centers, now known as Institut Curie, are still used as spaces for vital cancer treatment research today.

Why Does Your Arm Hurt After You Get a Flu Shot?

Pornpak Khunatorn/iStock via Getty Images
Pornpak Khunatorn/iStock via Getty Images

If you’ve ever gotten a flu shot, you may have felt soreness in your upper arm for a day or two afterward. That’s just a sign the vaccine is working, immunologists say.

The flu vaccine works by introducing your body to a foreign substance called an antigen (in this case, the antigen is a deactivated or “dead” virus similar to the flu virus). Being exposed to an antigen “primes” immune system cells, preparing them to create antibodies should they ever encounter the foreign substance again [PDF]. The inactive virus in the vaccine can’t make you sick, but it does help sensitize your immune system to potential threats. Essentially, the vaccine puts your body on high alert for anything resembling the flu virus, enabling you to fight off infections and illnesses faster and more effectively than you could otherwise.

In the process of battling the inactive flu virus introduced by the flu vaccine, your immune system also releases mediators like histamine, which causes inflammation. In the event of infection, inflammation is important because it helps your body fight invaders and repair damaged tissue. But it’s also what causes soreness. The flu shot is usually injected into your upper arm, which is why the early immune response—and any pain—tends to be localized there.

Roughly one in five people have this type of painful reaction, immunologist Richard Zimmerman told Popular Science. If you’re susceptible to soreness after receiving a flu shot, there are a few steps you can take to alleviate the pain. Dr. Juanita Mora of the American Lung Association recommends taking an ibuprofen about two hours before getting the shot.

“You can also try icing the injection site to reduce redness and swelling,” Dr. Mora said.

It’s also important to move your arm around after receiving the shot so the vaccine isn’t quite so concentrated in one place. Barring that, you could always try getting the vaccine in your non-dominant arm so that any pain won’t interfere with your everyday activities.

Any pain is worth it, though: Even if you’ve never gotten the flu before, there’s always a chance you could get it in the future. And getting a flu shot also contributes to herd immunity, helping protect higher-risk populations (like children, older adults, and chronically ill individuals) who often can’t receive the flu vaccine for themselves. Keeping up-to-date on vaccines is one of the easiest ways individuals can contribute to community health.

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