Interactive Materials for Bidirectional Redox‐Based Communication

Abstract

Emerging research indicates that biology routinely uses diffusible redox‐active molecules to mediate communication that can span biological systems (e.g., nervous and immune) and even kingdoms (e.g., a microbiome and its plant/animal host). This redox modality also provides new opportunities to create interactive materials that can communicate with living systems. Here, it is reported that the fabrication of a redox‐active hydrogel film can autonomously synthesize a H2O2 signaling molecule for communication with a bacterial population. Specifically, a catechol‐conjugated/crosslinked 4‐armed thiolated poly(ethylene glycol) hydrogel film is electrochemically fabricated in which the added catechol moieties confer redox activity: the film can accept electrons from biological reductants (e.g., ascorbate) and donate electrons to O2 to generate H2O2. Electron‐transfer from an Escherichia coli culture poises this film to generate the H2O2 signaling molecule that can induce bacterial gene expression from a redox‐responsive operon. Overall, this work demonstrates that catecholic materials can participate in redox‐based interactions that elicit specific biological responses, and also suggests the possibility that natural phenolics may be a ubiquitous biological example of interactive materials.

Network-based redox communication between abiotic interactive materials

“…In general, phenazines have more reducing redox-potentials than catechols ( Wang et al., 2021 ) ( Figure 4 A), and we performed redox-probing studies to compare the relative redox-potentials of the PYO-PEG hydrogel reported here with previously reported catechol (CAT)-PEG hydrogels ( Li et al., 2021 ). To generate a CAT-PEG hydrogel that spanned the optical window of the honeycomb electrode of Figure 2 A, we first electro-assembled a PEG-hydrogel using PEG-SH (10 mM), Fc (5 mM) and applying an anodic potential (+0.5 V for 5 min).…”

“…A control was prepared by initially poising the hydrogel in its oxidized state (PYO Ox -PEG) by thorough rinsing with air-saturated water. A separate, smaller (diameter: 2 mm) CAT-PEG hydrogel was electro-assembled on a standard gold electrode by immersing the electrode in a solution containing PEG-SH (10 mM) and catechol (30 mM) and imposing a constant oxidative potential (+0.7 V for 1 min) ( Li et al., 2021 ). In our experiment, the CAT-PEG hydrogel is the sink for electrons and was poised in an oxidized state by gently shaking in air for at least 2 h. (Note: we were unable to provide a suitable CAT Red -PEG control because this reduced state was not sufficiently stable to allow a multi-hour sample handling and experimentation.)…”

“…The loss of electrons from the PYO Red -PEG hydrogel was observed optically by its change in absorbance at 750 nm. The gain of electrons by the CAT Ox -PEG was measured electrically by changes in the open circuit potential (OCP) for the underlying gold electrode ( Li et al., 2021 ).…”

“…This emerging understanding of redox-signaling also suggests opportunities to fabricate materials systems for redox-based communication ( De Luis et al., 2021a ; 2021b ). For instance, recent studies with synthetically-fabricated catechol-based materials have demonstrated their unique capabilities for bioelectronics ( Wu et al., 2020 ), wound dressings ( Liu et al., 2018 ), and interactive materials ( Li et al., 2021 ). Here, we report the fabrication of a polyethylene glycol (PEG) hydrogel modified with the phenazine, pyocyanin (PYO), which is a redox-active microbial metabolite reported to participate in molecular signaling in the rhizosphere ( Dar et al., 2020 ) and bacterial pathogenesis ( Gupte et al., 2021 ).…”

Simple, rapidly electroassembled thiolated PEG‐based sensor interfaces enable rapid interrogation of antibody titer and glycosylation

“…Fc near the surface of the electrode will become oxidized, diffuse away from the electrode surface, and oxidize the free thiol groups of PEG, converting them to sulfenic acid groups. Sulfenic acid groups will react with nearby thiol groups attached to PEG, thus establishing intermolecular bonds allowing a hydrogel to form Li et al, 2021;Raja et al, 2015;Sun & Huang, 2016). The thiolated PEG directly assembles onto gold through the sulfur-gold interactions commonly used for templated assembly on gold.…”