How to Hack a 3D Printer to Print a Human Heart

Engineers convert a regular desktop 3D printer into a bioprinter for a fraction of the cost

by Lina Zeldovich
July 20, 2018

From plastic devices to metal parts to artificial coral reefs, 3D printing has revolutionized design and manufacturing in many industries. It also has great potential in the printing of tissues and cells, promising to transform the medical world. Patients wouldn’t have to wait for organ transplants, with their new body parts printed on demand. The 4,000 people in America who are waiting for heart transplants today could receive new hearts within months if the technology was market-ready. 

But advances in bioprinting have been slow, says Adam Feinberg, associate professor of materials science and biomedical engineering at Carnegie Mellon University. The problem is that printing tissues and living cells is a more complex endeavor, and the traditional 3D printers aren’t built to do it. A typical desktop 3D printer works by pushing its plastic feed through a heated extruder head. The heat melts the plastic, which then flows through a metal nozzle, gets deposited onto the growing workpiece, and then cools off, becoming solid. But printing biomolecules and tissues must be done at very specific temperatures, and with additional support so that the soft squishy structure of an organ being built wouldn’t collapse under its own weight. Commercial bioprinters capable of these complex tasks do exist, but they cost around $100,000 and perform mediocre at best.  

“A lot of innovation is happening in the bioprinting space but there’s been a lack of machines that people have access to,” Feinberg says. “They are expensive, but they don't have to be.” 

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So Feinberg’s team developed a way to convert any desktop 3D printer into a bioprinter for a fraction of that cost. They did it by replacing the traditional 3D printer extruder with an instrument more appropriate for a medical job: a syringe.

In Feinberg’s syringe extruder design, the biomaterials are loaded into the syringe and the printers’ gears push the plunger to pump it out. Instead of the metal nozzle, the materials flow out of a needle. All you need to buy is the syringe and the needle, plus a few screws, and the same printer can start producing biological structures at room temperature, Feinberg says. The rest of the printer hardware or software doesn’t change, so the entire set up costs about $50, compared to $100,000.

“One of the beauties of our approach is that the printer is still printing the same way with the same software,” Feinberg says. “It’s almost like the printer doesn't know you made it into a bioprinter. It still thinks it is the normal plastic printer so people don't have to do anything new.”

Feinberg says that his set-up allows printing tissues with high precision. With traditional 3D printers, it’s not unusual to see little strings of plastic strewn around while the part is being built. While this drawback often isn’t significant for plastic parts, it is a problem for soft tissues, where the extra material can catch onto or pull at the delicate structure, or just simply weigh it down too much. With some mechanical tweaks to the gears’ inner workings, Feinberg’s syringe extruder solves this problem by reversing the material flow after each deposition, basically by drawing some extra material back in. Currently, the printer can print up to three different materials, but that limitation can be expanded.

The weight of biostructures is also an issue. Because cells and tissues are soft and squishy, the structures often collapse under their own weight. Once they are completed and have their normal biological form, they retain their natural structural integrity, but getting them to that point requires additional support. To solve that challenge, the team began printing biostructures inside a gel. To explain the concept, Feinberg cites hair gel jars where air bubbles hang suspended within the gel, which acts as a supporting scaffold, keeping them in place. In Feinberg’s approach, the syringe’s needle deposits cells inside a gelatin-based slurry. The printing is done at room temperature, but once the piece is printed, the structure is warmed up to body temperature. The gel melts but the resulting structure remains intact. The team named the method FRESH (Freeform Reversible Embedding of Suspended Hydrogels), and has already experimented with printing coronary arteries, and even a small embryonic heart.

The bioprinted structures must undergo one more critical step before they become viable transplants. When they are first printed, they are really just “organ frameworks” that still need to mature and grow into real body parts. They must be placed into bioreactors, which are chambers that maintain the environment necessary to support the cells’ metabolism by providing the right temperature, pH levels, and nutrient supply. Bioreactors perfuse the organs with nutrient-rich solutions and can potentially provide mechanical resistance and electrical stimulation to tissues in order to grow them into full-functioning muscles or hearts.

All of the team’s bioprinting hacks are open-source, and the shared files and instructions can be found on the National Institute of Heath’s 3D printing exchange website. The instructions for the bioprinter conversion are simple enough that they don't require an advanced degree. Even a high school student can do it.

 “In fact we already have heard from several different schools,” Feinberg says, “We got emails from people all over the world, from South America, Asia, and even Africa.”

Lina Zeldovich is an independent technical writer.

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