“In microbial populations, there’s cooperation and there’s cheating and there’s competition, and so understanding how these very complicated things actually function is not something you can just do in a petri dish or a bulk broth,” said bioengineer Bryan Kaehr of Sandia National Laboratories in Albuquerque, NM. “In order for us to ever really understand cell communication in a meaningful way, you really have to organize populations like this—at this scale, the scale of cells.”

The work comes from Kaehr’s graduate advisor, chemist and bioengineer Jason Shear at the University of Texas at Austin, who has been working in 3-D fabrication using biological materials for about 10 years. Shear and his colleagues had previously used the cross-linking technique—which uses a laser to activate a photosensitizer that promotes bond formation between the molecules of the mold—to build molecular “houses” of bovine serum albumin (BSA), into which they seeded bacteria that could swim into the various “rooms.” The researchers could then warm the houses to 37°C, causing the “doors” of the house to swell shut, keeping the bacteria in place.