Scientists have printed three- dimensional (3D) 'living materials' using bacteria-loaded inks. The new printing material called "Flink", which stands for "functional living ink", has been developed by scientists at ETH Zurich in Switzerland. They developed a bacteria-containing ink that makes it possible to print mini biochemical factories with certain properties, depending on which species of bacteria the scientists put in the ink. The scientists, who published the technique in the journal Science Advances, used the bacteria Pseudomonas putida and Acetobacter xylinum. The former can break down the toxic chemical phenol, which is produced on a grand scale in the chemical industry, while the latter secretes high-purity nanocellulose. This bacterial cellulose relieves pain, retains moisture and is stable, opening up potential applications in the treatment of burns. The printing platform offers numerous potential combinations, according to researchers. 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 several properties. The ink is composed of a biocompatible hydrogel that provides structure. The hydrogel itself 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. 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, researchers said. 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.
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