European researchers have developed a biocompatible ink for 3D printing using living bacteria. This makes it possible to produce biological materials capable of breaking down toxic substances or producing high-purity cellulose for biomedical applications.
The team from the Swiss Federal Technical University (ETH) in Zurich have named their new printing material Flink, which stands for 'functional living ink'.
Its structure comes from a biocompatible hydrogel, which 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 all the prerequisites for life. Using this hydrogel as a basis, the researchers can add bacteria with the desired 'range of properties' and then print any three-dimensional structure they like.
In a single pass, the researchers can use up to four different inks containing different species of bacteria at different concentrations in order to produce objects exhibiting several properties. The ETH team chose the bacteria Pseudomonas putida, which can break down the toxic chemical phenol, and Acetobacter xylinumin, which secretes high-purity nanocellulose.
Phenol is produced on a grand scale in the chemical industry, while the bacterial cellulose relieves pain, retains moisture and is stable, opening up potential applications in the treatment of burns.
During the development of the bacteria-containing hydrogel, the gel’s flow properties posed a particular challenge: 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. If the hydrogel is too stiff, however, Acetobacter secretes less cellulose. At the same time, the printed objects must be sturdy enough to support the weight of subsequent layers. If they are too fluid, it is not possible 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,” said team leader Professor André Studart, Head of the ETH Laboratory for Complex Materials.
In addition to medical and biotechnology applications, Studart envisage many other potential uses. For example, objects of this kind can 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 use in disastrous oil spills.
First, it will be necessary to overcome the challenges of the slow printing time and difficult scalability. Acetobacter currently takes several days to produce cellulose for biomedical applications. However, the scientists are convinced that they can further optimise and accelerate the processes.
[A researcher inserts a syringe of biocompatible ink into the 3D printer. Image: ETH]