3D printed ‘living ink’ to deliver drugs or clean up the environment

A team of scientists used genetically engineered microbial cells from E. coli bacteria to print bioengineered fibres.

“The emerging field of living materials has leveraged microbial engineering to produce materials for various applications but building 3D structures in arbitrary patterns and shapes has been a major challenge,” they write.

They have overcome this challenge, printing out various shapes from E. coli bacteria by converting them into an ink that is ‘alive,’ calling the new product ‘microbial ink.

“Here we set out to develop a bioink, termed as ‘microbial ink’ that is produced entirely from genetically engineered microbial cells, programmed to perform a bottom-up, hierarchical self-assembly of protein monomers into nanofibers, and further into nanofiber networks that comprise extrudable hydrogels.”

As far as applications go, engineered bacterial cells turned into ‘microbial ink’ can be 3D printed into shapes and structures, which in turn “can sequester toxic moieties, release biologics, and regulate its own cell growth through the chemical induction of rationally designed genetic circuits,” the authors write. That means the printed material can capture toxins from the environment, deliver medication, and self-replicate as healing structures.

Sabrina Imbler notes “The material is still being developed, but the authors suggest that the ink could be a crucial renewable building material, able to grow and heal itself and ideal for constructing sustainable homes on Earth and in space.”

The researchers write in Nature Communications about previous efforts – efforts that have not been entirely satisfactory: “many bioink designs have already been explored, none so far have fully leveraged the genetic programmability of microbes to rationally control the mechanical properties of the bioink.”

This time, something is different from previous efforts: the new substance is “produced entirely from genetically engineered microbial cells,” the authors write. Containing no polymers, the gelatinous ink can be used in 3D printers to be turned into living structures that are stable and hold their form.

Bob Yirka, writing for Phys.org, notes that “The work began by bioengineering the bacteria to produce living nanofibers.” He goes on to say that the researchers later collected the fibres together and produced a type of what he calls “living ink” that could be used in a conventional 3D printer as material to be printed from.

The researchers say they have proven the microbial ink has integrity structurally and shape-wise; they add that it has many future application possibilities with the embedding of genetically programmed E. coli cells, such as “therapeutic living material, sequestration living material, and regulatable living material.”

What this means is that the bioengineered ink could be used to deliver medication or to keep the environment clean of toxins. The researchers, for example, “programmed E. coli to synthesize on demand an anticancer biologic drug, azurin, and secrete it into the extracellular milieu.” The successful detection of azurin 24 to 48 hours later proved that the microbial ink had done its work delivering the anticancer medication.

Likewise, the scientists tested the living material to sequester BPA, a toxic chemical commonly used to make plastics. They printed a 2D pattern with microbial ink, and tested it after grafting a BPA-binding peptide, finding out that it had been able to sequester eight to 27 percent of BPA after 12 and 24 hours of incubation. Thus the microbial ink also shows promise as sequestration material for dangerous chemicals.

The researchers don’t stop at drug delivery or environmental cleanup. They summarise their findings in Nature Communications, touting the living ink as a possible building block for homes on the Moon: “microbial bioink could also be particularly useful for structure building in space or extraterrestrial habitats, where raw material transport is difficult, making on-demand generation of building materials from very limited resources essential.”

Currently, microbial ink is at its infancy, and will require further testing and development to provide useful results to the public in the years to come. Yet its promise of one day delivering drugs biologically, sequestering dangerous chemicals which are linked to health hazards such as BPA, which is an endocrine disruptor – and can wreak havoc on human hormones, and becoming a self-healing building material suggests that it is worth further study.

THUMBNAIL IMAGE: The protocol to produce microbial ink from the engineered protein nanofibers involves standard bacterial culture, limited processing steps, and no addition of exogenous polymers. Microbial ink was 3D printed to obtain functional living materials. Credit: Nature Communications

HEADLINE IMAGE: 3D printed structures using the microbial ink CsgA-αγ i single-layer grid, j 10-layer square, k 10-layer circle, and l 21-layer solid cone. Insets in (j–l). are corresponding top views. Credit: Nature Communications