How do growth conditions control the mechanics of biohybrid hydrogels?

To design scalable engineered living materials (ELMs), living cells are often embedded within hydrogel scaffolds and substrates. The mechanical properties of these hydrogels are fixed and set by the hydrogel matrix. In this work, we spatially patterned Esheriachia coli within a granular hydrogel composite composed of jammed acrylic acid/alkyl acrylate microgels and a photocrosslinkable methacrylaed hyaluronic acid (MeHA) interstitial matrix. We demonstrate that tuning the crosslinking and growth conditions modulates the mechanics and microstructure of the biohybrid composite. 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.