How do biofilms impact the mechanics of granular hydrogel composites?

To fabricate engineered living materials (ELMs), researchers often embed living cells within synthetic scaffolds and substrates. The majority of the work has focused on embedding planktonic cells in hydrogel, with less work using biofilm-forming cells, bacterial communities surrounded by a self-produced polymer matrix. Here, by mixing a biofilm former, Bacillus subtilis, a soil bacterium, within a synthetic granular hydrogel composite, we demonstrate how the mechanics of the composite can be modulated through biofilm phenotype and cell density. We observe matrix-producing cells form an interpenetrating polymer network within the granular hydrogel composites. These finding provides new insights into how cell phenotype and environmental cues affect the mechanical properties of granular hydrogel composites.