Polyethylene glycol hydrogel coatings for protection of electroactive bacteria against chemical shocks

Loss of bioelectrochemical activity in low resource environments or from chemical toxin exposure is a significant limitation in microbial electrochemical cells (MxCs), necessitating the development of materials that can stabilize and protect electroactive biofilms. Here, polyethylene glycol (PEG) hydrogels were designed as protective coatings over anodic biofilms, and the effect of the hydrogel coatings on biofilm viability under oligotrophic conditions and ammonia-N (NH₄⁺-N) shocks was investigated. Hydrogel deposition occurred through polymerization of PEG divinyl sulfone and PEG tetrathiol precursor molecules, generating crosslinked PEG coatings with long-term hydrolytic stability between pH values of 3 and 10. Simultaneous monitoring of coated and uncoated electrodes co-located within the same MxC anode chamber confirmed that the hydrogel did not compromise biofilm viability, while the coated anode sustained nearly a 4 × higher current density (0.44 A/m²) compared to the uncoated anode (0.12 A/m²) under oligotrophic conditions. Chemical interactions between NH₄⁺-N and PEG hydrogels revealed that the hydrogels provided a diffusive barrier to NH₄⁺-N transport. This enabled PEG-coated biofilms to generate higher current densities during NH₄⁺-N shocks and faster recovery afterwards. These results indicate that PEG-based coatings can expand the non-ideal chemical environments that electroactive biofilms can reliably operate in.