This Squishy 3D-Printed Human Heart Feels Like the Real Thing

In the intro to the HBO sci-fi series Westworld, a 3D printer churns out humanoid robots, delicately assembling the incredible complexities of the human form so that those robots can go on to—spoiler alert—do naughty things. It takes a lot of biomechanical coordination, after all, to murder a whole lot of flesh-and-blood people.

Speaking of: Researchers just made a scientific leap toward making 3D-printed flesh and blood a reality. Writing recently in the journal ACS Biomaterials Science & Engineering, a team described how they repurposed a low-cost 3D printer into one capable of turning an MRI scan of a human heart into a deformable full-size analog you can actually hold in your hand. Squeeze it, and it’ll give like the real thing. Slice it open, and you’ll find chambers. The idea isn’t to one day realize the homicidal humanoids of Westworld, but to give surgeons a better way to practice on a patient’s heart before an operation. The advance might eventually lead to fully-functioning 3D-printed hearts, and give medical device developers an unprecedented platform for testing their wares.

The researchers call their technique the Freeform Reversible Embedding of Suspended Hydrogels, or FRESH. They begin with a scan of a real heart and translate the data into something a 3D printer can read. Because the device works by depositing layers of material one on top of another, they run the 3D image through a slicer program. “For every layer, it basically defines the path that the material is going to be extruded, and then feeds that to the printer,” says Adam Feinberg, a biomedical engineer at Carnegie Mellon University who coauthored the new paper.

That printer churns out alginate—a squishy material derived from seaweed—that the researchers chose both for its low cost and likeness to the material properties of human heart tissue. But instead of it extruding it into air, as a normal 3D printer might do when building something out of plastic, this extrudes the ersatz heart into a container of support gel, specifically gelatin.

“The analogy I have is: Imagine you were printing inside of hair gel,” says Feinberg. Think of the little bubbles suspended in that bottle of gel—the material is providing enough support for them to float indefinitely, or at least until you squeeze the gel out of the bottle. In this case, the gelatin offers enough give for the needle of the 3D printer to slide through. “Whatever you extrude stays embedded in place, kind of like those air bubbles in hair gel,” Feinberg says.

And now for something completely different when it comes to the art of artificial hearts: jello shots. After the organ is done printing, the researchers need a way to dissolve the gel lattice that’s surrounding it, and they use a familiar method. “I think a lot of people have experienced this from using gelatin in baking or making jello shots,” says Feinberg. “It’s actually a liquid when you warm it up, but it becomes a solid gel when you cool it down. And so we take advantage of that.” When they’re ready to extract the heart, all Feinberg has to do is raise the bath to body temperature, melting away the support gel and leaving behind the 3D-printed structure.