Ink containing engineered bacteria forms "living tattoo" for environmental sensing

The MIT team specialises in developing technologies based on responsive materials, gels and polymers, and has developed a variety of inks for 3D printing. They realised that genetically-engineered cells could form the responsive component of a hydrogel-based ink, but took a different route to realising this than previous researchers who have tried to use engineered mammalian cells.

"It turns out those cells were dying during the printing process, because mammalian cells are basically lipid bilayer balloons,” explained Hyunwoo Yuk, co-author of a paper on the research in Advanced Materials. “They are too weak, and they easily rupture.”

Rather than mammalian cells, the team decided to use bacteria, which have thicker cell walls, capable of surviving being squeezed through a printer niozzle, and are more compatible with hydrogels.

Researchers from MIT's mechanical engineering department, led by Prof Xuanhe Zhao, worked with bioengineers led by Timothy Lu, to determine the best hydrogel and nutrients to support bacteria engineered by Lu's team. To light up in the presence of certain chemicals Zhao’s engineers customised a 3D printer to work with an ink based on a hydrogel containing pluronic acid.