New 3D-printed 'living material' could purify water

For this innovation, the living material was made using alginate – a natural polymer extracted from seaweed. It was subsequently hydrated, resulting in the formation of a gel solution. Following this step, the gel was combined with engineered cyanobacteria, a photosynthetic bacteria that thrive in aquatic environments.

Finally, this meticulously crafted mixture was fed into a 3D printer to generate the novel material. 

After conducting a series of rigorous tests on different 3D-printed geometrics for their living material, the team opted for a grid-like structure. This geometry proved to be the most efficient for the survival of cyanobacteria. 

This distinct structure purposefully places the majority of the cyanobacteria toward the material's surface, facilitating their access to nutrients, gases, and light. As a result, they will continue to thrive within the material until the cleaning process is completely done. 

Furthermore, the grid-like design boasts another notable characteristic: "a high surface area to volume ratio." This expanded surface area considerably improves the new material's decontamination powers.

Self-destructive bacteria 

Notably, this genetically edited bacteria enables the production of a decontaminating enzyme known as laccase.

The production of this enzyme effectively “transforms various organic pollutants into benign molecules” in the material. 

Previous studies have demonstrated the efficacy of laccase to neutralize a wide range of organic contaminants, including bisphenol A (BPA), antibiotics, pharmaceutical drugs, and dyes. 

The team conducted a series of tests to demonstrate the use of this newly-created chemical cleaning material. 

The experiment showcased that the material could decolorize a water solution polluted with blue dye (indigo carmine), which is commonly used in the textile industry to make denim clothing. 

Another important aspect of this modified bacterium is its capacity to "self-destruct" after its task of purification is complete.  

This was accomplished by having genetically engineered bacteria respond to a molecule known as theophylline. The presence of these molecules triggers the bacteria to produce a protein that eventually starts to destroy their cells.

“The living material can act on the pollutant of interest, then a small molecule can be added afterward to kill the bacteria. This way, we can alleviate any concerns about having genetically modified bacteria lingering in the environment," said Pokorski. 

The material has been described in the journal Nature Communications.

Study abstract: 

The field of engineered living materials lies at the intersection of materials science and synthetic biology with the aim of developing materials that can sense and respond to the environment. In this study, we use 3D printing to fabricate a cyanobacterial biocomposite material capable of producing multiple functional outputs in response to an external chemical stimulus and demonstrate the advantages of utilizing additive manufacturing techniques in controlling the shape of the fabricated photosynthetic material. As an initial proof-of-concept, a synthetic riboswitch is used to regulate the expression of a yellow fluorescent protein reporter in Synechococcus elongatus PCC 7942 within a hydrogel matrix. Subsequently, a strain of S. elongatus is engineered to produce an oxidative laccase enzyme; when printed within a hydrogel matrix the responsive biomaterial can decolorize a common textile dye pollutant, indigo carmine, potentially serving as a tool in environmental bioremediation. Finally, cells are engineered for inducible cell death to eliminate their presence once their activity is no longer required, which is an important function for biocontainment and minimizing environmental impact. By integrating genetically engineered stimuli-responsive cyanobacteria in volumetric 3D-printed designs, we demonstrate programmable photosynthetic biocomposite materials capable of producing functional outputs including, but not limited to, bioremediation.