Printing Organs That Give

To a surgeon, a useful model organ needs to be more than a rigid plastic curio. It needs the feel of the real thing if it’s to be any good for practice. Now researchers have created a 3D printed organ with the elasticity of flesh and blood.

by Michael Abrams
February 12, 2018

Any 3D printer can print out some version of a model heart, or a kidney, or a liver. But aside from their volumetric similarities, these printed organs have little in common with their flesh and blood counterparts. Made of filament extruded plastic that ends up rigid, they lack the essential squishiness and flexibility of the real thing.

But for surgeons hoping to practice on an organ stunt double before applying scalpel in the operating room, that squishiness is key. So Michael McAlpine, professor of mechanical engineering at the University of Minnesota, and his colleagues, have created a 3D printer that can print with a tunable elasticity.

To do so he needed a new material and a new machine with which to print it. “We still use extrusion,” says McAlpine, “but no filament. We have an ink that is mechanically extruded.” Though such an ink could in theory be made of a variety of materials, including soft polymers, McAlpine and his team found that silicon mixed with silicon grease and other softeners created the most realistic give. But their new ink would gum up a typical commercial 3D printer, so the team was forced to create their own, using a combination of off-the-shelf parts.

As a proof-of-concept, they set out to print one of the simpler organs, the prostate. Conveniently located a few buildings from the University of Minnesota Medical Center, McAlpine and his team were able to collect three cancerous prostates in a matter of weeks. After measuring their properties, scanning them, and creating a virtual model, he was able to tweak his inks to duplicate the flexibility of the prostates with incredible precision.

The result was an organ some 1,000 times softer than what a typical industrial-scale printer would be capable of making. Surgeons who tested the model prostates—with a little suturing and scalpel work—were amazed by how lifelike they were. And they’re not just generic prostates. They’re models of the specific organs of specific patients. Soon surgeons will be able to scan a living organ inside a body using MRI, and practice on printed models with the same dimensions as those of their patients.

The organ models aren’t just dummies waiting to be prodded. They are equipped to with sensors that allow surgeons and surgical students to know how hard they’re pressing. McAlpine has used soft electromechanical capacitors to provide this feedback. “It doesn’t change the mechanical properties of the organ model,” he says. “It blends right in.” Currently the sensors are printed separately, but McAlpine says they will eventually have a “one pot” solution.

There are other things to work on before the soft organ printer finds its way into med schools and surgeons’ quarters. At the moment, printing a prostate takes a good 10 to 12 hours. And, of course, not all organs are as simple as the prostate. Future models could include cartilage and tissues of varying density. They could also include cancer tissue if a surgeon wanted to practice removing a tumor with the same dimensions.

But however it ends up getting used, McAlpine is thrilled that it’s happened at all. “The thing that’s crazy for me is that it’s such an obvious idea: to match the mechanical properties of the model with the organ of a patient,” he says. “I was really surprised we were the first to do that.”

Michael Abrams is an independent technical writer based in Westfield, NJ.

Read more about 3D Bioprinting on