The science of prosthetics has been advancing by leaps and bounds over the last few years, and research into soft robotics has been especially complementary. The same techniques that go into making a robot arm that flexes and turns like a real one can go into making more complex, subtle organs — like the heart, as Swiss researchers have demonstrated.

One problem with artificial hearts is that metal and plastic mechanisms can be difficult to integrate with tissue, or damage the blood because of their unnatural movement style.

A small team at ETH, led by doctoral student Nicholas Cohrs, has created what they say is the first artificial heart that’s entirely soft, with its pumping mechanism achieved by causing the silicone ventricles to pump just like a real heart.

Well, not exactly like a real heart — in-between the ventricles isn’t just a wall but a chamber that fills and deflates to create the pumping action. But it’s close.

The heart was created using a 3D-printed method that lets the researchers make a complex inner structure while still using soft, flexible material as its structure. The whole thing is basically one single part (a “monoblock”), so there’s no need to worry about how different internal mechanisms fit together — except at the input and output ports, where blood would come and go.

In tests the heart worked quite well, pushing a blood-like fluid along against body-like pressures. There is, of course, a catch.

This heart is a proof of concept, not built for actual implantation — so the materials they made it from don’t last more than a few thousands beats. That’s about half an hour, depending on your heart rate (and if you’re breaking in a new one, it’s probably pretty high). But the plan, obviously, is to have materials and designs that work for much longer than that.

“As a mechanical engineer, I would never have thought that I would ever hold a soft heart in my hands,” said Anastasios Petrou, the grad student who led the testing, in an ETH Zurich news release. “I’m now so fascinated by this research that I would very much like to continue working on the development of artificial hearts.”

The researchers’ work is published this week in the journal Artificial Organs (naturally).