Wed. Jan 26th, 2022

We have seen how 3D printing can revolutionize certain manufacturing processes – whether on Earth or elsewhere – but there is a growing field of research looking at how this can also be used to produce living, biological structures.

In a new study, researchers have outlined a new type of ‘living ink’ or bio-ink made by programmed Escherichia coli bacterial cells that can be 3D-printed to create hydrogels in different forms that release different types of drugs or absorb toxins, depending on how they are engineered.

What sets this approach apart from previous bio-inks is how it uses genetic programming to control the mechanical properties of the ink itself – leading to better end results in the finished material and more practical uses for the ink (some existing bio-inks do not work properly at room temperature , e.g).

Examples of the printed bio-ink. (Joshi et al., Nature Communications, 2021)

“A tree has cells embedded in it, and it goes from a seed to a tree by assimilating resources from its surroundings to implement these structure-building programs,” says chemist Neel Joshi of Northeastern University in Massachusetts.

“What we want to do is a similar thing, but where we deliver the programs in the form of DNA that we write and genetic engineering.”

The way it works is by biomanipulating the bacterial cells to create living nanofibers. That E coli cells were combined with other substances to create the fibers using a chemical process inspired by fibrin – a protein that plays a central role in blood clots in mammals.

These protein-based nanofibers can then be fed into a 3D printer and manipulated into various shapes. Unlike previous bioinks, this one uses no artificial substances, and is instead completely biological. It is squeezed out like a toothpaste, but can then retain its shape if it does not dry out.

So far, the technique has been used to make very small objects: a circle, a square and a cone. But now that researchers have shown that microbial ink can be 3D-printed in this way, it opens up more possibilities for the future.

“If you were to take that whole cone and dip it in a glucose solution, the cells would eat that glucose, and they would make more of that fiber and grow the cone into something bigger,” Joshi says.

“There is an opportunity to take advantage of the fact that there are living cells there. But one can also just kill the cells and use it as an inert material.”

In experiments, the team was able to combine their bio-inks with other microbes to perform specific tasks: absorbing toxic chemicals, for example, or delivering an anti-cancer drug. In the future, the ink may also be designed to replicate itself, the researchers say.

This study builds on previous work from the same team, and looks at how E coli cells can be formed into a hydrogel that self-replicates when it comes in contact with a particular tissue – opening up a new and sustainable manufacturing method that can be used on the Moon and Mars as well as here on Earth.

Although the 3D-printable bio-ink has so far only been used on a small scale, further down the line it could eventually be used in everything from building self-healing structures to producing bottle caps capable of removing dangerous chemicals from water.

“Biology is capable of doing similar things,” Joshi says. “Think of the difference between flexible hair and the horns of a deer or a rhinoceros or something. They are made of similar materials, but they have very different functions. Biology has figured out how to tune the mechanical properties of using a limited set of building blocks. “

The research is published in Nature communication.

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