Living materials—ones made from a scaffold embedded with live cells—can be used for applications such as sensing, chemical or material production, and bioelectronics. A challenge with such materials is keeping the cells alive over extended periods and under harsh conditions. Christopher A. Voigt, Lina M. González, and Nikita Mukhitov of the Massachusetts Institute of Technology have adapted a 3-D printer to make objects with embedded bacterial spores (Nat. Chem. Biol. 2019, DOI: 10.1038/s41589-019-0412-5). Instead of mixing the bioink ahead of time, the researchers combined separate streams of agarose and Bacillus subtilis spores in the printhead, which they maintained at 75 °C, a temperature high enough for the agarose to flow easily but not so high that the spores die. The spores survived even when the printed material was exposed to harsh conditions, including dehydration, ultraviolet light, X-rays, and short doses of γ-radiation. Genetically engineered bacterial spores were able to sense and respond to their environment, as well as to produce antibacterial compounds to kill Staphylococcus aureus. Spore-containing materials that were printed and dried were still active upon rehydration 1 month later, which suggests that these materials could be stored over extended periods.