Biocoatings with Enhanced Bacterial Viability via Coagulant Dipping and Wet Sintering by Immersion

Biocoatings are typically colloidal polymer films confining metabolically active, nongrowing bacteria. Depending on the species of confined bacteria, biocoatings find applications in wastewater treatment, biofuel production, carbon fixation, environmental remediation, biosensing, and more. However, the successful use of biocoatings faces numerous challenges, including a low permeability to reactants and metabolized products, osmotic stress on bacteria during drying of the coatings, and cell dehydration leading to bacteria death. Here, we address these challenges through two interlinked processing methods. (1) Coagulant gelation of the colloidal polymer dispersion creates a porous microstructure with high permeability. (2) Wet sintering by immersion in a liquid medium reduces osmotic stress and avoids desiccation of the bacteria. In a model system of Escherichia coli in an acrylic copolymer latex biocoating, these two methods yielded a cell viability that is approximately 500 times greater than the conventional method of biocoating formation using dry sintering in air at an elevated temperature. We have discovered that when lysogeny broth is used as the medium for wet sintering, the cell viability is significantly higher than that for other liquids. Increasing the salt concentration for coagulant gelation leads to thicker coatings (and hence more cells per area of the coating). However, cell viability decreases when the salt concentration is increased, so a compromise is needed. Metabolic activity of E. coli in a wet-sintered biocoating was demonstrated through the production of ethanol as a biofuel. These results hold promise for the future exploitation of biocoatings using a broad range of bacterial, especially desiccation-intolerant species.