Semi-living inks may revolutionise 3D printing

The distinction between living and non-living material is set to be significantly reset following the creation of inks made in part from active bacteria.

The inks, in which selected bacteria are supported physically and nutritionally within a specially formulated hydrogel, open the door to new types of hyper-functional 3D-printed materials.

To demonstrate proof-of-concept, a team led by André Studart, from the Laboratory for Complex Materials at science university ETH Zurich in Switzerland, created inks containing the species Pseudomonas putida and Acetobacter xylinum.

P. putida is already widely used in bioremediation technologies, because of its ability break down hydrocarbons. Indeed, it has been suggested that the only things it can’t break down are Teflon, Styrofoam and organic products containing hydrogen.

Studart’s team chose it because of its ability to break down phenol, a toxic by-product of many industrial chemical processes.

A. xylinum secretes nanocellulose, a compound noted for its painkilling ability. It also retains moisture, and is considered a potential therapeutic for burns treatments.

Studart’s team incorporate the bacteria in a hydrogel made of hyaluronic acid, long-chain sugar molecules and pyrogenic silica. Theoretically, it can then be put through a 3D-printing platform to create objects of any desired shape. The A. xylinum ink, for instance, could be formed into a dressing moulded precisely to an individual injury site, or the P. putida combination could be formed into objects that will capture and neutralise phenol.

Potentially, up to four bacteria-infused inks can be combined into a single structure, allowing it to perform multiple functions.

The team call their invention “Flink”, a portmanteau of “functionally living ink”. 

Team member Manuel Schaffner says one of the biggest hurdles in creating the inks was balancing the need for fluidity and strength. If the hydrogel was too stiff, then pushing it through a printer nozzle became difficult. The bacteria inside it, too, struggled to circulate.

Too loose, on the other hand, and it lacked structural integrity, making it impossible to build layer on layer as 3D-printing demands.

“The ink must be as viscous as toothpaste and have the consistency of Nivea hand cream,” he says.

At this early stage, the researchers have not yet tested the durability of the ink as a whole, or the microbes incorporated within it. However, they are optimistic.

“As bacteria require very little in the way of resources, we assume they can survive in printed structures for a very long time,” says team member Patrick Rühs.

Potential applications for Flink technology include not only medical and bioremediation tasks, but also bacteria-equipped sensors for detecting water or air pollution, and filters to warn of oil spills.

However, in a paper published in the journal Science Advances, the scientists admit there are still a few hurdles to overcome before microbial ink becomes widely available.

The first challenge involves scaling the process up from a lab bench to a factory floor, and the second concerns time. At present it takes several days for the A. xylinum ink to produce enough material for any medical application.

 The next print edition of Cosmos magazine includes an interview with scientist and artist Oron Catts, who uses semi-living tissue to create works that challenge the division between animate and inanimate matter. The magazine will be out in January subscribe today or, to request a pre-order, enter your details here.

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