New material that cleans decontaminated water

Scientists from the University of California San Diego have developed a 3D-printed material that could offer a sustainable and eco-friendly way to clean pollutants from water. The new ‘engineered living material’, made from a natural polymer combined with genetically engineered bacteria, was shown to decontaminate the dye-based pollutant indigo carmine, a dye widely used in textiles to color denim.

Engineered living materials, which can sense and respond to stimuli already present in the environment, involve an engineered microorganism integrated into a soft material. Such microorganisms are responsible for performing complex functions, here water decontamination, with the soft material providing a support system for the organism to grow.

As reported in Nature Communications [Datta et al. Nat. Commun. (2023) DOI: 10.1038/s41467-023-40265-2], the collaborative team of engineers, materials scientists and biologists used alginate, a seaweed-based polymer, before hydrating it to make a gel and combining it with bacteria genetically engineered to produce an enzyme, a water-dwelling, photosynthetic bacteria known as cyanobacteria. This can change many organic pollutants into benign molecules, and it was also engineered to self-destruct in the presence of a molecule called theophylline.

The mixture was fed into a 3D printer to fabricate a cyanobacterial biocomposite material able to produce multiple functional outputs in response to an external chemical stimulus. After assessing a range of 3D-printed geometries, a grid-like structure was found to be best for keeping the bacteria alive. This shape also offered a high surface area to volume ratio, allowing the majority of the cyanobacteria close to the material’s surface to access nutrients, gases and light.

As proof of concept, the cyanobacteria in the material were genetically engineered to continually produce a decontaminating enzyme called laccase. Laccase is known to neutralize many organic pollutants, such as bisphenol A (BPA), antibiotics, pharmaceutical drugs and dyes. The living material can thus act on pollutants of interest, before a small molecule is later added to kill the bacteria, which alleviate any concerns about genetically modified bacteria remaining in the environment.

The research helped develop scaffolding material that supports cyanobacterial growth. Cyanobacteria only need CO₂, water and light to grow, and are easy to program genetically to repurpose a known biological or biosynthetic pathway. As co-leader Jon Pokorski told Materials Today, “By embedding them into a material, it makes them easy to handle and deploy and easy to dispose of once their use is completed”. The team now hope to investigate engineering the bacteria for a wider range of pollutants.

“By embedding [cyanobacteria] into a material, it makes them easy to handle and deploy and easy to dispose of once their use is completed”Jon Pokorski