Programable and Spatially Conforming Assembly of Engineered Living Materials Onto Electrodes via Redox

We developed an electrobiofabrication methodology that assembles well-defined cell/gel formations directly onto electrodes. For this, we oxidatively crosslinked terminal thiols of a 4-arm thiolated polyethylene glycol (PEG) by the purposeful addition of a ferrocene redox mediator to a PEG/cell assembly solution and the application of an oxidizing charge to an electrode. Because the resulting disulfide bonds are created near the electrode, the crosslinked hydrogel assembly is defined by the electrode dimensions and the time over which the oxidative potential is applied. Results indicate a strong positive correlation between the mediator concentration, the delivered oxidative charge, the number density of cells in the assembly solution and the subsequent gel thickness and density. In all cases tested, the viability of the assembled cells (E. coli bacteria) was near 100%. We further demonstrated a gravity-mediated layering methodology to create spatially defined interfaces, as well as electroassembly onto various conductive materials of nearly arbitrary shape. These results represent a means for electronic or "programed" assembly of cell laden hydrogels, enabling further study of cell-cell interactions, cell-device interactions, biosensing, device  ⇔ bio communication, and several applications such as electrogenetics wherein cell genetic circuits are actuated by application of electrical potentials using a redox-enabled communication modality.