Fascination With Technology Living Building Material Stores Carbon

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In our "Fascination with Technology" section, we present engineers with impressive projects from research and development every week. Today: a living material that actively extracts carbon dioxide from the atmosphere.

At ETH Zurich, researchers from various disciplines are working together to combine conventional materials with bacteria, algae, or fungi. The common goal is to create living materials that, thanks to the metabolism of microorganisms, acquire useful properties—"such as the ability to bind CO2 from the air through photosynthesis," says Mark Tibbitt, Professor of Macromolecular Engineering at ETH Zurich.

An interdisciplinary research team under Tibbitt's leadership has now turned this vision into reality: they have incorporated photosynthetic bacteria—known as cyanobacteria or blue-green algae—stably into a printable gel, creating a material that is living, grows internally, and actively removes carbon from the air. The researchers recently presented their "photosynthetic living material" in a study in the journal Nature Communications.

CO2, Sunlight, And Artificial Seawater for Growth

The living material can be shaped at will using 3D printing and requires only CO2, sunlight, and artificial seawater with readily available nutrients for its growth. "As a building material, it could help store CO2 directly in buildings in the future," says Tibbitt, who co-initiated the research on living materials at ETH Zurich. What is special about it: the living material absorbs much more CO2 than it binds through organic growth. "This is because the material can store carbon not only in biomass but also in the form of minerals—a special property of blue-green algae," reveals Tibbitt.

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Yifan Cui, one of the two lead authors of the study, explains: "Cyanobacteria are among the oldest life forms in the world. They perform photosynthesis very efficiently and can utilize even the weakest light to produce biomass from CO2 and water." At the same time, as a result of photosynthesis, blue-green algae alter their chemical environment outside the cell, causing solid carbonates (such as lime) to precipitate. These minerals represent an additional carbon sink and store CO2 permanently, unlike biomass.

Cyanobacteria as Builders

"We specifically exploit this ability in our material," says Cui, who is pursuing his doctorate in Tibbitt's research group. A practical side effect: the minerals deposit within the material and reinforce it mechanically. In this way, the cyanobacteria slowly harden the initially soft structures. Laboratory tests showed that the material continuously binds CO₂ over a period of 400 days, mostly in mineral form—about 26 milligrams of CO2 per gram of material. This is significantly more than many biological approaches and comparable to the chemical mineralization of recycled concrete (around 7 mg CO2 per gram).

The carrier material hosting the blue-green algae is a hydrogel—a gel made from cross-linked polymers with a high water content. Tibbitt's team selected the polymer network such that it can transport light, CO2, water, and nutrients, allowing the cells to spread evenly within without leaving the material. To ensure the cyanobacteria live as long and as efficiently as possible, the researchers also optimized the geometry of the structures using 3D printing methods to increase surface area, enhance light penetration, and promote nutrient flow.

Co-author Dalia Dranseike: "In this way, we created structures that stand with only a small part in the nutrient liquid and distribute it passively throughout the entire body using capillary forces." Thanks to this design, the encapsulated cyanobacteria lived productively for more than a year, the materials scientist in Tibbitts' team is pleased to report.

In the future, we want to explore how the material can be used as a coating for building facades to bind CO2 throughout the entire life cycle of a structure.

Mark Tibbitt

Material as A Coating for Building Facades

The researchers view their living material as an energy-efficient and environmentally friendly approach that can bind CO2 from the atmosphere and complement existing chemical processes. "In the future, we want to explore how the material can be used as a coating for building facades to bind CO2 throughout the entire life cycle of a structure," Tibbitt looks ahead.

There is still a long way to go, but colleagues from architecture have already adopted the concept and experimentally implemented initial interpretations. Thanks to ETH doctoral student Andrea Shin Ling, the foundational research from ETH labs has made it onto the big stage of the Venice Architecture Biennale. "The most challenging aspect was scaling the manufacturing process from the laboratory format to spatial dimensions," says the architect and biodesigner, who was also involved in the present study.

Picoplanktonics Bind Up to 39.7 lbs of CO2 per year

Ling is pursuing her doctorate at the Chair of Digital Building Technologies under ETH Professor Benjamin Dillenburger. In her dissertation, she developed a platform for biofabrication that can print living structures with embedded cyanobacteria at an architectural scale. For the installation Picoplanktonics in the Canada Pavilion, the project team used the printed structures as living building blocks to erect two tree trunk-like objects, each about three meters high. Thanks to the cyanobacteria, these can bind up to 39.7 lbs of CO2 per year—about the same amount as a 20-year-old pine tree in the temperate zone.

"The installation is an experiment—we have adapted the Canada Pavilion to provide enough light, moisture, and warmth to allow the cyanobacteria to thrive. Now we are observing how they behave," says Ling. This requires commitment: The team monitors and maintains the installation on-site—daily. Until November 23.

At the 24th Triennale di Milano, Dafne's Skin explores the potential of living materials for future building envelopes. On 3D-printed wooden shingles, microorganisms form a deep green patina that changes the wood over time: a sign of decay becomes an active design element that binds CO2 and emphasizes the aesthetics of microbial processes.

Dafne's Skin is a collaboration between Studio MAEID and Dalia Dranseike. The installation is part of the exhibition "We the Bacteria: Notes Toward Biotic Architecture" and runs until November 9.

The photosynthetic living material was created thanks to an interdisciplinary collaboration within the framework of ALIVE (Advanced Engineering with Living Materials). The initiative by ETH Zurich promotes the collaboration of researchers from various disciplines to develop new living materials for a variety of applications.

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