Mechanics of Microbial Granular Hydrogel Composites

To fabricate scalable engineered living materials (ELMs), researchers often embed living cells within artificial scaffolds and substrates. In hydrogel systems, this approach often results in the formation of fixed-sized microcolonies due to the confinement effect of the hydrogel matrix. These microcolonies can enhance the stiffness of the hydrogel by acting as reinforcing organic microparticles. Tuning the mechanical properties of these ELMs typically involves either increasing the cell density within the material before crosslinking or altering the crosslinking density of the hydrogel. Consequently, the final mechanical properties of these materials are fixed during the crosslinking process. In this study, we will overcome these challenges by fabricating microbial granular hydrogel composites by combining jammed microgel with photocrosslinkable methacrylate hyaluronic acid (MEHA) and Escherichia coli. The jammed microgels serve as a scaffold supporting cell growth before crosslinking, while MEHA immobilizes the cells post-crosslinking. We demonstrate how crosslinking after incubating the composites affects the final cell density and stiffness of the microbial hydrogel composites. Our findings provide fundamental insights into how cell growth in granular environments can influence the mechanical properties of microbial hydrogel composites.