Researchers at Northeastern University in Boston have created a new 3D printing material composed entirely of a genetically modified version of E. coli bacteria. The material, its creators say, has myriad applications, but perhaps the most striking is that it can be used for the construction of self-repairing buildings - both here and on other planets.
E.coli is a bacterium that lives in the gut of warm-blooded animals and some of its variants can cause severe diarrhoea and vomiting if exposed to it. But a genetic modification of this bacterium, as demonstrated by the American research team, has proved ideal as an 'ink' for making all sorts of things with 3D printers.
This is not the first time microorganisms have been used in 3D printing, but they have always been mixed with some kind of polymer so that they can maintain their structure. The new material presented by the Northeastern University researchers does not need to be mixed with anything to achieve that firmness - once the print is made, the structure remains unchanged without the bacteria continuing to grow.
"It's not necessarily always growing," says Neel Joshi, associate professor of chemistry and chemical biology at Northeastern University and one of the lead authors of this discovery. "If you took the printed structure and immersed it in some glucose solution, the cells would eat that glucose and make more of that fibre, causing the structure to grow into something bigger. There is the option of taking advantage of the fact that there are living cells in there. But you can also just kill the cells and use it as an inert material.
For the team, this is the great advantage of their material, that it is alive. And that means it can heal itself just like our bodies do. As they describe in a paper published in the journal Nature Communcations, under the right conditions, the cells in this organic 'ink' could reproduce again and simply make more material to repair themselves.
"Just as a tree has cells embedded within it and grows from a seed to a tree by assimilating resources from its environment to build its structure, what we want to do is something similar, but using programmes in the form of DNA that we write ourselves and genetic engineering," says Prof Joshi.
The researchers say they see microbes as factories for building materials that are useful to us. The idea, they say, is to harness their unique properties for use in all kinds of applications, such as therapeutic or industrial applications. And they compare the way they approach this work to chemists dealing with polymers who have to decide whether a plastic should be hard and keep its shape or soft and elastic.
"Biology is capable of doing similar things," says Joshi. "Think about the difference between hair, which is flexible, and the horns of a deer or a rhino or something like that. They're made of similar materials, but they have very different functions. Biology has figured out how to fine-tune those mechanical properties using a limited set of building blocks."
In addition to this 'ink' made from 100% E. coli, the researchers have also tried mixing it with other genetically modified microbes. In this way, they say, they have been able to make a material that can carry an anti-cancer drug and release it when a particular chemical stimulus is applied to it. Or a material that can trap Bisphenol A, a highly toxic chemical, when it is in the air.
They also envisage its application in the colonisation of space, where, apart from regolith, it is difficult to find building materials. There, they say, the 'ink' could be used as a self-healing substance to help build habitats on other planets. Although they admit that this ability to fix itself could also be very useful here on Earth.
Although this material is very promising, we will have to wait and see if it makes the leap into the commercial world. For the team, this microbial 'ink' opens the door to building all sorts of things with biological materials.
"More sustainable manufacturing is going to involve the use of living cells," says Professor Joshi. "This discovery brings us closer to that kind of paradigm of building things with living cells.
