The latest 3D printer ink is alive, thanks to embedded bacteria. That means 3D printers can now make living materials capable of degrading toxins and facilitating organ transplants. Traditional 3D printers use powdery metals and plastics as their ink. These are great for making superstrong steel or even artificial bones, but not so great for making biocompatible materials that need more flexibility—such as skin grafts. That’s where the new functional living ink—or Flink—comes in. With Flink, researchers can print any number of bacteria-derived materials, including elastic ones. Researchers demonstrated this utility in a paper published today in Science Advances by printing materials embedded with the bacterium Acetobacter xylinum. This bacterium makes cellulose, which can be used as scaffolds for skin replacements and coatings for biomedical devices that help protect patients against organ rejection. What’s more, with Flink researchers can print these materials in any 3D shape in one step. Because any kind of bacterium or combination of bacteria can be infused in the ink, Flink expands the range of potential applications for 3D-printed materials—degrading environmental toxins, making vitamins, generating chemical energy through photosynthesis—that are not possible with nonliving inks.