Bacteria turn 3D-printed sand into solid building elements
Cement manufacturing is one of the largest sources of CO₂ emissions in the construction industry. At the Department of Architecture, Karen Antorveza Paez, who has just completed her doctorate at ETH Zurich, is researching an alternative that works in a different way: instead of firing rocks at over 1,000°C, she is getting bacteria to bond grains of sand together into solid architectural elements.
A researcher at ETH Zurich has discovered a way to turn 3D-printed sand into solid building elements by using bacteria to create a mineral glue. This process, known as microbiologically induced calcite precipitation (MICP), involves the use of a specific type of bacteria called Sporosarcina pasteurii, which has been previously studied for stabilizing loose subsoil and self-healing concrete.
Antorveza Paez, the researcher, developed two methods for this innovative technique. The first method, 3D biocement printing, involves creating a bio-ink made of a gel based on water and natural substances, along with sand and live bacteria. This bio-ink is then printed into the desired structure. Following the printing, the object is immersed in a urea and calcium chloride solution, where the bacteria break down the urea and form limestone—a mineral found in mussel shells and chalk—through a reaction that releases carbonate ions and ammonium.
The limestone forms between the sand grains and interlocks with them, creating a solid structure without using heat sources.
The second method, robotic spraying, eliminates the intermediate immersion bath step. Instead, a robotic arm applies bacteria, mineralization substances, and sand repeatedly to build up the structure layer by layer, inspired by natural stromatolites. This method has been demonstrated at the 2025 Biennale Architettura in Venice, where it was left running for six months to showcase the process.
Antorveza Paez highlights that the printing process focuses on materials science and bio-ink while the spraying process concentrates on the machine and its control. Both methods are currently in different stages of development, with the spraying process requiring further research into its mechanical properties. Overall, this research offers a more sustainable and eco-friendly approach to construction materials, providing architects with a new relationship to building materials and the potential to create unique architectural elements.
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