The coordination of cell proliferation and migration in growing tissues is crucial in development and regeneration but remains poorly understood. Here, we find that, while expanding with an edge speed independent of initial conditions, millimeter-scale epithelial monolayers exhibit internal patterns of proliferation and migration that depend not on the current but on the initial tissue size, indicating memory effects. Specifically, the core of large tissues becomes very dense, almost quiescent, and ceases cell-cycle progression. In contrast, initially-smaller tissues develop a local minimum of cell density and a tissue-spanning vortex. To explain vortex formation, we propose an active polar fluid model with a feedback between cell polarization and tissue flow. Taken together, our findings suggest that expanding epithelia decouple their internal and edge regions, which enables robust expansion dynamics despite the presence of size and history-dependent patterns in the tissue interior.

Microbial electrochemical systems provide an environmentally-friendly means of energy conversion between chemical and electrical forms, with applications in wastewater treatment, bioelectronics, and biosensing. However, a major challenge to further development, miniaturization, and deployment of bioelectronics and biosensors is the limited thickness of biofilms, necessitating large anodes to achieve sufficient signal-to-noise ratios. Here we demonstrate a method for embedding an electroactive bacterium, Shewanella oneidensis MR-1, inside a conductive three-dimensional poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) matrix electropolymerized on a carbon felt substrate, which we call a multilayer conductive bacterial-composite film (MCBF). By mixing the bacteria with the PEDOT:PSS precursor in a flow-through method, we maintain over 90% viability of S. oneidensis during encapsulation. Microscopic analysis of the MCBFs reveal a tightly interleaved structure of bacteria and conductive PEDOT:PSS up to 80 µm thick. Electrochemical experiments indicate S. oneidensis in MCBFs can perform both direct and riboflavin-mediated electron transfer to PEDOT:PSS. When used in bioelectrochemical reactors, the MCBFs produce 20 times more steady-state current than native biofilms grown on unmodified carbon felt. This versatile approach to control the thickness of bacterial composite films and increase their current output has immediate applications in microbial electrochemical systems, including field-deployable environmental sensing and direct integration of microorganisms into miniaturized organic electronics.

Introducing an electronic interface into Escherichia coli will allow its enormous synthetic biology toolkit to be leveraged in bioelectrochemical applications. While E. coli expressing the Mtr pathway of Shewanella oneidensis MR‐1 transfer electrons to an anode, it has remained unclear if this current production alters the intracellular state of E. coli, which is a critical requirement for bioelectronic technologies. Here we address this by characterizing current production in Mtr‐expressing E. coli and its effects on cellular viability, substrate consumption, and product generation. We found that cymA‐mtr E. coli sustained ∼8‐fold higher current levels than a control strain. This increased current production did not change E. coli viability or substrate consumption, but it did alter metabolic fluxes. A shift to more oxidized products strongly suggests that the Mtr pathway improves redox balance in E. coli. By demonstrating the Mtr module couples current production to intracellular state, this work establishes Mtr‐expressing E. coli as a platform for accelerated development of bioelectronic technologies.

Highlights d SCHEEPDOG programs electrical cues to herd cell migration via ''electrotaxis'' d Programmable electrical control allows cellular groups to perform any 2D maneuver d Precise control is possible because cells time-average x-and y-electric fields d Electrotaxis occurs across many cell types and species and can be a powerful tool