Recent biological research has demonstrated that redox is an independent biological-signaling modality. [1-8] This redox signaling modality is best understood in host-pathogen immune interactions where an oxidative burst generates a set of reactive species (e.g., reactive oxygen species) that can sometimes be transduced into second messengers (i.e., reactive electrophiles) [4] and ultimately alters biological function through post-translational protein modification (e.g., conversion of protein cysteine residues into disulfide crosslinks). [6] The functions and the coding of information in this redox signaling modality [1] are distinctly different from the information coded in genes or in the action potentials of the ionic electrical modality. Since this redox modality involves the "flow" of electrons through oxidation-reduction reactions, it is accessible to appropriate electrochemical measurement, and this provides new opportunities for biodevice communication. [9-13] Redox has similarities to the ionic electrical modality, however electrons are the charged species moving in the redox modality. Interestingly, while water is a conductor of ionic currents, it can be considered an "insulator" for the flow of electrons since free electrons do not normally exist in aqueous

Reduction–oxidation (redox) reactions provide a distinct modality for biological communication that is fundamentally different from the more‐familiar ion‐based electrical modality. Biology uses these two modalities for communication through different systems (immune versus nervous), and uses different mechanisms to control the flow of the charge carriers: the flow of soluble ions is controlled using structural barriers (i.e., membranes) and gates (e.g., membrane‐spanning protein channels), while the flow of insoluble electrons is controlled using redox‐reaction networks. Here, a simple electrochemical approach to pattern catechols onto a flexible polysaccharide hydrogel is reported and it is demonstrated that the patterned catechol regions serve as nodes for the mediated flow of electrons through redox reactions. Electron flow through this node involves the switching of binary redox states (oxidized and reduced) and this node's redox state can be detected (i.e., “read”) by passively observing its optical absorbance, or actively switching its redox‐state electrochemically. Further, this catechol node can be switched through biological mechanisms, and this enables the fabricated catechol node to be embedded within biochemical redox reaction networks to facilitate the spanning of bio‐electronic communication. Thus, it is envisioned that catechols can emerge as a molecular equivalent to a transistor for miniaturize‐able, deployable and sustainable redox‐linked bioelectronics.

While conventional material fabrication methods focus on form and strength to achieve function, the fabrication of material systems for emerging life science applications will need to satisfy a more subtle set of requirements. A common goal for biofabrication is to recapitulate complex biological contexts (e.g. tissue) for applications that range from animal-on-a-chip to regenerative medicine. In these cases, the material systems will need to: (i) present appropriate surface functionalities over a hierarchy of length scales (e.g. molecular features that enable cell adhesion and topographical features that guide differentiation); (ii) provide a suite of mechanobiological cues that promote the emergence of native-like tissue form and function; and (iii) organize structure to control cellular ingress and molecular transport, to enable the development of an interconnected cellular community that is engaged in cell signaling. And these requirements are not likely to be static but will vary over time and space, which will require capabilities of the material systems to dynamically respond, adapt, heal and reconfigure. Here, we review recent advances in the use of electrically based fabrication methods to build material systems from biological macromolecules (e.g. chitosan, alginate, collagen and silk). Electrical signals are especially convenient for fabrication because they can be controllably imposed to promote the electrophoresis, alignment, self-assembly and functionalization of macromolecules to generate