ADVANCED MATERIALS & PROCESSES | NOVEMBER 2026 64 3D PRINTSHOP BACTERIA ‘GLUES’ GRAINS OF SAND TOGETHER An innovation from ETH Zurich has produced two new methods of using bacteria to bond grains of sand together into solid architectural elements. The process is called microbiologically induced calcite precipitation (MICP), or simply biocementation. The bacteria used for this, Sporosarcina pasteurii, have been under research for many years for applications such as for stabilizing loose subsoil. They have also been used in concrete research for “self-healing” concrete, where the introduction of bacterial spores causes cracks to seal over on their own. Karen Antorveza Paez, a recent graduate of ETH Zurich, has looked at how the process is controlled: not as an addition to existing building materials, but as an architectural material in its own right. To achieve this, she combined two research fields that had until then been largely separate: bio- cementation and digital manufacturing. While it has long been known that bacteria can bond sand together into solid objects under certain conditions, Antorveza Paez explains, “What was missing were manufacturing processes whereby these biological processes can be controlled as required and used to make architectural elements.” For the first method, 3D biocement printing, the team developed a “bioink” made of a gel based on water and the natural substances alginate and xanthan, as well as sand and live bacteria. The bioink can be printed into a given desired structure, which is then immersed in a bath containing urea and calcium chloride. The bacteria break down the urea with an enzyme called urease. This reaction releases carbonate ions and, as a by-product, ammonium. The carbonate and calcium chloride in the solution bond together to form calcium carbonate, also known as limestone— the same mineral that makes up mussel shells and chalk. The limestone forms wherever the bacteria are located within the printed object. Microscopic crystals form between the grains of sand and “interlock” with each other. This is what gives the process its gluing property: rather than being glue in the traditional sense, it is made up of interlinked mineral crystals that mechanically hold the grains together. A second approach to applying biocement for architectural purposes is robotic spraying. In this technique, the researchers removed the intermediate stage of the immersion bath. A robotic arm applies bacteria, the mineralization substances for limestone formation, and sand to a surface repeatedly, building it up in height layer by layer. The two processes are complementary: “The printing is geared more toward architectural elements, while the spray process is more designed for surfaces,” says Antorveza Paez. www.ethz.ch/en. METAMATERIALS SENSE AND TRACK DAMAGE IN REAL TIME Research led by a team from the U.K. and Australia gives 3D-printed materials the ability to sense where they are being damaged and track how that damage develops. These “self-sensing” metamaterials are made with intricate lattice structures that are custom-designed to prioritize characteristics like weight, strength, impact resistance, or flexibility. The new approach is made possible by incorporating carbon nanotubes into plastic structures that are designed and 3D printed with precise arrangements of struts and spaces, giving them a lattice-like structure. By passing current through the carbon nanotubes via electrodes attached to the materials, the team can harness an imaging technique called electrical impedance tomography (EIT) to monitor the structural health of the material as it experiences external loads. The team believes its new research, published in the journal Advanced Functional Materials, is the first reported use of in situ EIT to monitor damage in 3D-printed architected metamaterials. These materials could find use in medical implants, aircraft parts, or car bodies in the years to come, allowing detailed feedback on the condition of the materials used in the parts as they degrade with age or suffer strains caused by impacts. doi.org/10.1002/ adfm.78620. This facade element was created by bacteria. Courtesy of Kai-Ksun Yeh/ETH Zurich. Real-time electrical imaging reveals where damage develops. Courtesy of University of Glasgow.
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