Figure 1.

(A) Schematic image of a custom-built dual extrusion gel printer³² used for bacteria printing. Two syringe pumps were hydraulically connected to a printhead holding two syringes, which were filled with bacteria-ink. The printhead was heated to 42 °C, and the gel quickly solidified upon cooling on the base plate. (B) Bacteria (E. coli DH5α) expressing either mRFP, mVenus, or mTurquoise were printed sequentially into hydrogel layers and incubated overnight to represent the painting “Blue Fox” by the Munich expressionist Franz Marc. The image demonstrates the resolution of ink deposition and the reproducibility of printing at specific locations. (C) Using dual extrusion with blank and bacteria-ink, three-dimensional gel objects were printed that contained single layers of bacteria. Images of the 3D structures (top and side view) were taken using a Canon 80D camera; fluorescence images were obtained with a Nikon Ti2-E microscope from the bottom and from slices of the structures.