The ETH logo printed in 3D with bacterial printing ink. Photo: Laboratory for complex materials/ETH Zürich.
The ETH logo printed in 3D with bacterial printing ink. Photo: Laboratory for complex materials/ETH Zürich.

More and more objects and components can now be produced with 3D printing, but the materials used for this process are still ‘dead matter’ such as plastics or metals.

A group of researchers at ETH Zürich in Switzerland, led by André Studart, head of the Laboratory for Complex Materials, has now introduced a new 3D printing platform that works using living matter. The researchers developed a bacteria-containing ink that makes it possible to print mini biochemical factories with a range of properties, depending on which species of bacteria the scientists put in the ink. They report this work in a paper in Science Advances.

The ETH researchers’ new printing platform offers numerous potential combinations. In a single pass, the scientists can use up to four different inks containing different species of bacteria at different concentrations in order to produce objects exhibiting various properties.

As a first test, group members Patrick Rühs and Manuel Schaffner used two species of bacteria: Pseudomonas putida and Acetobacter xylinum. The former can break down the toxic chemical phenol, which is produced on a large scale in the chemical industry. The latter secretes high-purity nanocellulose, which can relieve pain, retain moisture and is stable, opening up potential applications in the treatment of burns.

The ink is composed of a biocompatible hydrogel that provides structure; the hydrogel is composed of hyaluronic acid, long-chain sugar molecules and pyrogenic silica. The culture medium for the bacteria is mixed into the ink so that the bacteria have everything they need to prosper. Using this hydrogel as a basis, the researchers can add bacteria with the desired ‘range of properties’ and then print any 3D structure they like.

During the development of the bacteria-containing hydrogel, the gel’s flow properties posed a particular challenge, as the ink must be fluid enough to be forced through the pressure nozzle. The consistency of the ink also affects the bacteria’s mobility: the stiffer the ink, the harder it is for them to move. What is more, if the hydrogel is too stiff, A. xylinum secretes less cellulose.

At the same time, the printed objects must be sturdy enough to support the weight of subsequent layers. If too fluid, the hydrogel can’t be used to print stable structures, as these collapse under the weight exerted on them. “The ink must be as viscous as toothpaste and have the consistency of Nivea hand cream,” is how Schaffner describes the successful formula.

The scientists have named their new printing material ‘flink’, which stands for ‘functional living ink’. As yet, the material scientists have not studied the lifespan of the printed minifactories. “As bacteria require very little in the way of resources, we assume they can survive in printed structures for a very long time,” says Rühs.

However, this research is still in its initial stages. “Printing using bacteria-containing hydrogels has enormous potential, as there is such a wide range of useful bacteria out there,” says Rühs. He blames the poor reputation of microorganisms for the almost total lack of existing research into additive methods using bacteria.

“Most people only associate bacteria with diseases, but we actually couldn’t survive without bacteria,” he says. However, the researchers believe their new ink is completely safe; the bacteria they use are all harmless and beneficial.

In addition to medical and biotechnology applications, the researchers envisage many other potential uses. For example, objects printed with flink could be used to study degradation processes or biofilm formation. One practical application might be a bacteria-containing 3D-printed sensor that could detect toxins in drinking water. Another idea would be to create bacteria-containing filters for cleaning-up oil spills.

First, it will be necessary to overcome the challenges of the slow printing time and difficult scalability: A. xylinum currently takes several days to produce cellulose for biomedical applications. However, the researchers are convinced they can further optimize and accelerate the process.

The development of special materials for 3D printing is a speciality of Studart’s research group. For example, he and his interdisciplinary team have also developed a printable high-porosity ink made of ceramic, which allows the printing of very lightweight bone-like structures used for energy production.

This story is adapted from material from ETH Zürich, with editorial changes made by Materials Today. The views expressed in this article do not necessarily represent those of Elsevier. Link to original source.