Scientists have created a bacterial ink that can replicate itself and can be 3D printed into living buildings.

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The idea of ​​combining printers (the bane of office workers) with E. coli (the bane of romaine lettuce) may seem strange, if not an unpleasant collaboration.

But scientists have recently combined the advantages of this irritating tool with toxic microorganisms to produce a live ink made entirely of microorganisms. The microbial ink flows like toothpaste under pressure and can be 3D printed into a variety of tiny shapes-circles, squares and cones-all of which remain intact and sparkle like jelly.

The researchers described their programmable microbial ink formulation in a study published Tuesday in the journal Nature Communications. This material is still under development, but the author believes that this ink may be an important renewable building material, capable of self-growth and healing, and is an ideal choice for building sustainable homes on earth and space.

This new substance is not the first living ink. Scientists have previously created printable gels, which are a mixture of bacteria and polymers that help provide structure when printed. One such ink contains hyaluronic acid, seaweed extract and fumed silica-all of these substances can make the material thicker and more viscous.

But this new substance contains no additional polymers; it is produced entirely by genetically engineered E. coli. The researchers induced bacterial cultures to grow ink, which is also made from living bacterial cells. When the ink is harvested from the liquid culture, it becomes as strong as gelatin and can be inserted into a 3D printer and printed into living structures. These structures do not grow further and maintain their printed form.

"They developed this very good engineering platform in which microorganisms can secrete their own ink," said Sujit Datta, a chemical and biological engineer at Princeton University, who was not involved in the research. "Microbes are creating materials on their own-you just need to feed them and make them happy."

Bacteria seems to be an unconventional component. But microorganisms are an important part of products such as perfumes and vitamins, and scientists have designed microorganisms to produce biodegradable plastics.

Neel Joshi, a synthetic biologist at Tohoku University and author of this new paper, said that materials like microbial ink have greater ambitions. This ink is an expanding focus in the field of engineered biomaterials. Dr. Josh said that unlike concrete or plastic poured structures, living systems will be autonomous, able to adapt to environmental factors and be able to regenerate—at least, this is an ideal goal.

"Imagine building a self-repairing building," Dr. Datta said.

For Dr. Joshi, the best analogy may be that the seed becomes a tree. A seed has all the information needed to harvest solar energy and grow it and develop something as complex and magnificent as a tree. In an engineered life system, a single engineered cell can function like a seed.

Microorganisms are not good at forming well-defined shapes in three dimensions. "Think of the scum in the pond," Dr. Josh said. "In terms of shape, this is the degree of complexity that bacteria adapt to."

Generally, microbial ink relies on a polymer scaffold to harden its scum form. But polymers have their own limitations and can change the mechanical properties of the ink in undesirable ways, Dr. Datta said. In addition, the polymer must be biocompatible so that the microorganisms will not die. Synthetic polymers, such as polyethylene, are derived from petroleum and are not renewable.

R. Kōnane Bay, a soft matter physicist and incoming assistant professor at the University of Colorado Boulder who was not involved in the research, said that abandoning polymers and using only microorganisms “provides more possibilities for what you can print. Tonal".

Many engineered biological materials take the form of hydrogels, which can absorb large amounts of water, such as gelatin. In 2018, Dr. Joshi and Anna Duraj-Thatte, an engineer at Virginia Tech and author of this new paper, successfully created a hydrogel entirely derived from E. coli that can grow and regenerate.

Although the hydrogel can be squeezed through a syringe, it is not hard enough to stand on its own. "You can't make any structure," Dr. Duraj-Thatte said.

Researchers need to consolidate this substance. "We came up with this strategy. We use fibrin, a polymer used for blood clotting in humans and many other animals," said team member Avinash Manjula-Basavanna, who completed this work as a researcher at Harvard University.

Researchers genetically engineered Escherichia coli to produce a protein polymer from fibrin that is designed to connect into a network of networks—imagine a heavy cargo net. This makes the material hard enough for printing while still being able to flow out of the nozzle of the 3D printer.

The authors brought their microbial ink to the 3D printer in the laboratory of bioengineer Yu Shrike Zhang at Harvard Medical School, which often uses the printer for tissue engineering mammalian cells. This laboratory is one of the few laboratories that bravely introduced bacteria into its sanitary printing space.

"A laboratory whose bread and butter are just tissue engineering using mammalian cells would be a bit shy to bring bacteria anywhere near there," said Dr. Josh.

"This is a laboratory that will try many different things," said Dr. Duraj-Thatte.

Researchers printed microbial ink into a variety of shapes and patterns to test its ability to maintain shape: grids, boxes, rings, and cones that look almost like icicles. The ink was squeezed out of the printer like toothpaste, but it did not ooze or melt after printing and passed all the tests.

They also tested the fidelity of the ink to see how far the ink can stretch without breaking. In the test, the printer’s nozzle ejects a half-millimeter thick ink out of a row of continuous columns, each column is farther away from the last column-the purpose is to show that the ink column can stay on the column without breaking. How far to keep between.

The steel strand can support its own weight between the pillars 16 mm apart: success. They said that when Dr. Duraj-Thatte and Dr. Manjula-Basavanna were recording tests in the laboratory in real time, they started screaming with excitement to prove that the ink was effective. (Video accompanying published research does not include audio.)

To test whether the printed structure can perform functions, Dr. Duraj-Thatte and Dr. Manjula-Basavanna also remixed the ink with other microorganisms designed to perform specific tasks. In a treatment test, printing ink releases the anti-cancer drug azurin when exposed to chemicals. In another test, the printing ink successfully captured the toxic chemical BPA, which indicates that the material may remove harmful pollutants from the surrounding environment.

Ink still requires a lot of work. It cannot withstand dryness, and is currently not stable enough to become the only foundation for large-scale buildings, such as houses suitable for human habitation; researchers are studying ways to make stronger printed structures. But researchers believe that its possible future applications are almost unlimited.

Dr. Duraj-Thatte hopes to see this ink combined with tissue engineering because it can be customized for medical applications. Dr. Josh suggested that this ink could eventually provide a more environmentally friendly and renewable building construction method. Dr. Pei wants to know whether this ink can be made from other bacteria, such as Pseudomonas putida, which can remove the toxin phenol. "We can consider making them into biosensors," Dr. Pei suggested.

Dr. Manjula-Basavanna is photographing the Earth’s moon, where there is no forest to harvest wood, and there is no easy way to transport bulk construction materials. He said that there, ink may be used as a self-regenerating substance to help establish habitats on other planets and places on Earth.

"To make it scalable and economical, there is still a lot of work to be done," Dr. Datta admitted. However, he pointed out that just five years ago, it was unthinkable to use microorganisms to create solid structures. It is conceivable that self-repairing buildings may become a reality in our lifetime.

"It is difficult to predict the future," Dr. Datta said. "But given the pace of development in this field, the future looks very bright."