3D printing has become a ubiquitous phenomenon. However, "dead matter" such as metals or plastics are still being used for this process.
A team of ETH researchers headed by Professor André Studart, Head of the Laboratory for Complex Materials, has now launched an innovative 3D printing platform that functions using living matter. A bacteria-containing ink developed by these researchers makes it possible to print mini biochemical factories with certain properties, depending on which species of bacteria the researchers put in the ink.
"Flink" harnesses the range of bacterial products
Studart's team and First Authors Manuel Schaffner and Patrick Rühs used the bacteria Acetobacter xylinum and Pseudomonas putida in their work. The first secretes high-purity nanocellulose, whereas the second can break down the toxic chemical phenol, which is produced on a large scale in the chemical industry. This bacterial cellulose retains moisture, relieves pain, and is stable, opening up unrealized applications in the treatment of burns.
The new printing platform developed by the ETH researchers offers a number of possible combinations. In a single pass, the researchers can use up to four different inks containing different species of bacteria at different concentrations to produce objects exhibiting various properties.
The ink is composed of a biocompatible hydrogel that gives structure. The hydrogel itself is composed of pyrogenic silica and hyaluronic acid, long-chain sugar molecules. The bacteria’s culture medium is mixed into the ink so that the bacteria have all the preconditions for life. The scientists can add bacteria with the desired "range of properties" and then print any three-dimensional structure they envision using this hydrogel as a basis.
As viscous as toothpaste
A specific challenge faced during the development of the bacteria-containing hydrogel was the flow properties of the gel: the ink should be so fluid that it can be easily forced through the pressure nozzle. The bacteria's mobility is also affected by the ink’s consistency. The stiffer the ink, the harder it is for them to move. However, Acetobacter secretes less cellulose if the hydrogel is too stiff. Additionally, the printed objects must be sturdy enough to support the weight of subsequent layers.
If they are too fluid, it is not feasible to print stable structures, as these structures collapse under the weight applied on them.
The ink must be as viscous as toothpaste and have the consistency of Nivea hand cream.
Professor André Studart, Head of the Laboratory for Complex Materials
The researchers have recently presented this technique in the journal Science Advances and named their new printing material "Flink", which stands for "functional living ink."
Until now, 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.
Patrick Rühs, First Author
Nevertheless, the research is still in its nascent stages. "Printing using bacteria-containing hydrogels has enormous potential, as there is such a wide range of useful bacteria out there," said Rühs. He accuses the bad reputation attached to microorganisms for the virtually total lack of existing research into additive methods using bacteria. He says, "Most people only associate bacteria with diseases, but we actually couldn't survive without bacteria." The bacteria that the scientists use are all beneficial and harmless. Hence, they believe that their new ink is absolutely safe.
Sensors for toxic substances and filters for oil spills
Besides biotechnology and medical uses, the scientists consider many other likely applications. For instance, objects of this nature can be used to study biofilm formation or degradation processes. One of the feasible applications might be a bacteria-containing 3D-printed sensor that could discover toxins in drinking water. Yet another idea would be to develop bacteria-containing filters for use in catastrophic oil spills. First, it will be essential to surpass the challenges of difficult scalability and the slow printing time. Acetobacter presently takes numerous days to produce cellulose for biomedical applications, but the researchers are certain that they can further accelerate and optimize the processes.
One of the specialties of ETH Professor André Studart's research team is the development of special materials for 3D printing. For instance, he and his interdisciplinary team have also developed a printable high-porosity ink made of ceramic. This ink allows the printing of highly lightweight bone-like structures used for production of energy.