Microbially Driven Reversible Actuation and Color Changing Materials

A common feature of natural living systems that is underexplored in the field of engineered living materials (ELMs) is macroscale mechanical actuation, as driven by active cellular processes. Here we demonstrate an ELM wherein Escherichia coli drives the reversible swelling and de-swelling actuation of a pH-responsive hydrogel by producing or consuming acidic metabolites. We covalently incorporated a novel synthetic pH indicator dye into the hydrogel network that complements the hydrogel actuation with coordinated color change. Acid production or consumption is controlled by media composition and multiple hydrogel form factors are explored. This approach represents a new form of biologically driven actuation that could be compatible with a range of responsive hydrogel applications. ### Competing Interest Statement The authors have declared no competing interest.