Engineered biofilm-based living hydrogel for bioprinting.

Incorporating genetically modifiable microbial biomass with polymeric hydrogel matrices offers a simple strategy for both bottom-up and top-down approaches in functional living hydrogel materials design. In this work, we designed a two-part living hydrogel, consisting of a non-living hydrogel matrix and engineered living biofilms. We used polyvinylpyrrolidone (PVP), gelatin, and agar to make a composite polymeric hydrogel matrix. Then we incorporated genetically engineered functional Escherichia coli (E. coli) biofilms containing cells and curli fibers into the hydrogel matrix. We investigated the physical and mechanical properties of the living hydrogel material with various formulations. The results showed that this viscoelastic living hydrogel with shear-thinning properties and storage modulus in the range between a few hundred and thousand Pa was suitable for extrusion-base bioprinting. The living hydrogel can absorb water about 5 times its dry weight and disintegrate quickly by 50% within 8 h of water immersion. We also demonstrated that the incorporated cells maintained their viability and ability to express recombinant curli fusion proteins after printing. The incorporated genetically engineered biofilms also maintained their fluorescence and pH response. This work provides a promising foundation for the development of functional living materials and can serve as a useful reference for environmental sensing applications requiring responsive and biologically active hydrogel systems.