Electronic inputs to cue the emergence of hydrogel structure and to confer function

Electrode-imposed electronic inputs can generate various cues that can control the emergence of hierarchical structure and confer function to hydrogel systems. Here we describe three such top-down cues. Electrolytic reactions can create pH cues that can induce the electrodeposition of pH-responsive self-assembling polymers (e.g., chitosan and alginate). The electric field provides a long-range cue that can induce polymer chains to migrate toward (or away from) the electrode and can align the polymer chains within the assembling hydrogel network (e.g., collagen). The electrochemical generation of diffusible oxidants provides a molecular cue that can induce oxidative assembly - typically through the formation of covalent bonds (e.g., disulfide bonds). Here, we review recent results on the use of these three cues for the electrofabrication of hydrogels and we illustrate how complementary capabilities from biotechnology allow the creation of functional hydrogel systems. Overall, we envision that electro-bio-fabrication could emerge as a scalable additive manufacturing method as well as a flexible approach for distributed manufacturing in public maker spaces.