Water pollution is becoming a growing problem worldwide, with the chemical industry dumping 300-400 megatons (600-800 billion pounds) of industrial waste into water bodies each year, according to research. As a team of material scientists, we are working to create a “living material” that could transform the chemical dyes that pollute the textile industry into harmless substances.

Water pollution is both an environmental and human problem that can affect both ecosystems and human health. We hope that the materials we have developed can be one of the available tools in combating this problem.

Living materials engineering

The “engineered living material” our team is working on involves programmed bacteria embedded in a soft hydrogel material. We first published an article about the potential effectiveness of this material. Nature Communication In August 2023.

The hydrogel that forms the basis of the material has the same properties as Jell-O; It is soft and consists mainly of water. Our custom hydrogel is made from a natural and biodegradable seaweed-based polymer called alginate, an ingredient found in some food products.

Alginate hydrogel provides strong physical support for bacterial cells, similar to how tissues support cells in the human body. We consciously chose this material so that the bacteria we placed could grow and develop. We chose seaweed-based alginate as the basis because it is porous and can retain water. It also allows bacterial cells to obtain nutrients from the environment.

After preparing the hydrogel, we placed photosynthetic or sunlight-harvesting bacteria called cyanobacteria into the gel. The cyanobacteria embedded in the material still needed light and carbon dioxide to carry out the photosynthesis that sustained them. The hydrogel was porous enough to allow this, but we 3D printed the gel into custom shapes (grids and honeycombs) to make the configuration as efficient as possible. These structures have a higher surface to volume ratio and allow more light, CO₂ and nutrients to enter the material.

The cells were happy with this geometry. We observed higher cell growth and density over time in alginate gels in mesh or honeycomb structures compared to the default disk shape.

paint cleaning

Cyanobacteria, like all other bacteria, have distinct genetic circuits that tell cells what results to produce. Our team genetically engineered bacterial DNA to enable cells to produce a specific enzyme called laccase. The laccase enzyme produced by cyanobacteria reacts chemically with the contaminant, converting it into a no longer functional form. It can turn a toxic pollutant into non-toxic by breaking chemical bonds. At the end of the reaction, the enzyme is renewed and goes to complete other reactions.

After placing these laccase-producing cyanobacteria into the alginate hydrogel, we placed them in a solution containing industrial dye contaminants to see if they could clear the dye. In this test, we wanted to see if our material could change the structure of the paint from colored to colorless. But in other cases, the material can potentially change its chemical structure from toxic to non-toxic.

The dye we used, indigo carmine, is a common industrial wastewater pollutant commonly found in water near textile mills, the main pigment in blue jeans. We found that our material completely removed most of the paint in about 10 days.

This is good news, but we wanted to make sure our material wasn’t adding waste to dirty water by washing away bacterial cells. So we engineered bacteria to produce a protein (a programmable switch) that could damage the bacterial cell membrane.

The genetic circuit is programmed to respond to a harmless chemical called theophylline, commonly found in caffeine, tea and chocolate. We can kill bacterial cells at any time by adding theophylline. The field of engineered living materials is still evolving, but this only means that there are many opportunities to develop new materials with both living and non-living components.