Researchers at ETH Zurich have recently demonstrated an active material composed of hydrogel and embedded cyanobacteria, designed to help reduce the carbon footprint of future buildings and infrastructure.

At the Venice Biennale and Milan Triennale, two exhibitions explored the application of biomaterials in architecture. Researchers from various disciplines at ETH Zurich collaborated to combine traditional materials with bacteria, algae, and fungi, aiming to create active materials that acquire useful properties through microbial metabolism, such as the ability to absorb carbon dioxide from the air via photosynthesis.

Now, an interdisciplinary team led by Professor Mark Tibbitt from the Macromolecular Engineering Laboratory at ETH Zurich has turned this vision into reality. They have stably integrated photosynthetic bacteria (cyanobacteria) into a printable gel, developing a living, growing material that actively removes carbon from the air. The researchers recently published their findings in Nature Communications.

The material can be 3D-printed and grows with only sunlight, nutrient-rich artificial seawater, and carbon dioxide. Tibbitt stated that as a building material, it could in the future store carbon dioxide directly within buildings. The material's uniqueness lies in absorbing more CO₂ than is used for organic growth. This is because cyanobacteria not only store carbon as biomass but also as minerals: through photosynthesis, the bacteria alter the extracellular chemical environment, causing solid carbonates (like lime) to precipitate. These minerals form an additional carbon sink, storing CO₂ in a more stable form, while mineral deposition mechanically strengthens the material, gradually hardening the initially soft structure.

One of the study's lead authors, Yifan Cui, explained that cyanobacteria are among the oldest life forms on Earth, with highly efficient photosynthesis capable of converting CO₂ and water into biomass using minimal light. Lab tests showed the material continuously absorbed CO₂ over 400 days, mostly in mineral form, with each gram absorbing about 26mg of CO₂—surpassing many biological methods and comparable to chemical mineralization in recycled concrete (about 7mg per gram).

The carrier material for the living cells is a hydrogel. Tibbitt's team selected a polymer network that transports light, CO₂, water, and nutrients while evenly distributing cells throughout. To ensure cyanobacteria survive and remain efficient as long as possible, the researchers optimized structural geometry using 3D printing to increase surface area, light penetration, and nutrient flow. Co-first author Dalia Dranseike noted that this approach creates designs allowing light penetration and passive nutrient distribution throughout the structure via capillary forces, enabling encapsulated cyanobacteria to survive efficiently for over a year.

The researchers believe this active material offers a low-energy, environmentally friendly method for atmospheric CO₂ capture, complementing existing chemical carbon sequestration processes. Tibbitt envisions future research on using it as a building facade coating to absorb CO₂ throughout a structure's lifecycle.