With too few donor hearts to satisfy the 123,000 patients awaiting a heart transplant, engineers have been working to design an artificial heart. The artificial hearts approved by the FDA are rigid devices attached to external pumps to mimic how the heart pushes blood through the body. Now researchers from Cornell University have designed an artificial heart made of foam that can pump a higher rate of fluid than other soft artificial hearts, according to a study published recently in the journal Advanced Materials.

The heart is made of flexible silicone and was inspired by soft robotics and artificial muscles, which can fit naturally in the body and interact gently with organic tissues. Unlike rigid artificial hearts, the foam heart is porous, which allows air to flow through it and allow it to beat, the way blood moves through blood vessels to make hearts beat, as New Scientist reports. This means that the heart’s design can be much simpler than other artificial hearts. An external pump, made of metals that don’t react in the body, pushes air and fluid through the artificial heart; a thin plastic coating around the foam prevents it all from leaking.

The foam heart is off to a promising start, but it’s not ready to be put into humans quite yet. The foam heart only contains two chambers, unlike typical human hearts, which have four. The researchers didn’t test if the foam’s property changes at higher temperatures like those that might be found in the body. And even though the device pumps more fluid than any other soft artificial heart, the speed at which it does so is still limited—and if the heart overinflates, the foam tears. In future work, the researchers will change some of the foam’s ingredients to make it less susceptible to tearing and make the air pathways simpler so that the heart can inflate more quickly.

Check out the material in action, via New Scientist:

Heart Disease photo

Correction, Friday, October 2: this article previously stated that the artificial heart in question was the “most powerful” yet, but this is not the case. It is, in-fact, the highest-pumping soft artificial heart in terms of pumping rate. We have updated the article to reflect this and sincerely regret the error.