The structures are imaged in red through confocal fluorescence, while the bacterial microcommunities are imaged in green.
Credit: Jason Shear
The technique can be used to mix small numbers of bacteria from the same or different species together under different conditions. The gelatin matrix used is also highly permeable to a variety of compounds, allowing the researchers to test how the bacteria react to all sorts of molecules. Of particular interest was how normally susceptible bacteria can be sheltered from antibiotic toxicity by the presence of resistant bacteria.
You can see one such experiment below:
Jodi L. Connell, Eric T. Ritschdorff, Marvin Whiteley, & Jason B. Shear (2013). 3D printing of microscopic bacterial communities Proceedings of the National Academy of Sciences of the United States of America DOI: 10.1073/pnas.1309729110.