Transcriptional Regulation of Synthetic Polymer Networks

Abstract

Individual cells direct non-equilibrium processes through coordinated signal transduction and gene expression, allowing for dynamic control over multicellular, system-wide behavior. This behavior extends to remodeling the extracellular polymer matrix that encases biofilms and tissues, where constituent cells dictate spatiotemporal network properties including stiffness, pattern formation, and transport properties. The majority of synthetic polymer networks cannot recreate these phenomena due to their lack of autonomous centralized actuators (i.e., cells). In addition, non-living polymer networks that perform computation are generally restricted to a few inputs (e.g., light, pH, enzymes), limiting the logical complexity available to a single network chemistry. Toward synergizing the advantages of living and synthetic systems, engineered living materials leverage genetic and metabolic programming to establish control over material-wide properties. Here we demonstrate that a bacterial metal respiration mechanism, extracellular electron transfer (EET), can control metal-catalyzed radical cross-linking of polymer networks. Linking metabolic electron flux to a synthetic redox catalyst allows dynamic, tunable, and predictable control over material formation and bulk polymer network mechanics using genetic circuits. By programming key EET genes with transcriptional Boolean logic, we rationally design computational networks that sense-and-respond to multiple inputs in biological contexts. Finally, we capitalize on the wide reactivity of EET and redox catalyses to predictably control another class of living synthetic materials using copper(I) alkyne-azide cycloaddition click chemistry. Our results demonstrate the utility of EET as a bridge for controlling abiotic materials and how the design rules of synthetic biology can be applied to emulate physiological behavior in polymer networks.

Extracellular Electron Transfer Enables Cellular Control of Cu(I)-Catalyzed Alkyne–Azide Cycloaddition

“…These results indicate that there are likely cytotoxic effects due to either the cosolvents or the CalFluor488 and alkyne-PEG 4 -acid (Figure S6). However, we note that significantly higher concentrations of substrates such as 4-arm-PEG polymers (3.3 mM) can successfully undergo CuAAC when water solubility and cell viability are maintained . In contrast to traditional chemical reductants, adherent S. oneidensis performed aerobic CuAAC over multiple cycles.…”

“…However, we note that significantly higher concentrations of substrates such as 4-arm-PEG polymers (3.3 mM) can successfully undergo CuAAC when water solubility and cell viability are maintained. 67 In contrast to traditional chemical reductants, adherent S. oneidensis performed aerobic CuAAC over multiple cycles. In these experiments, the bacteria did not require regeneration, replenishment, or intervention even after several repeated oxygen exposures.…”

Engineered Living Materials For Sustainability

“…Some living organisms have also been shown to be capable of controlling the polymerization of chemical monomers. − For example, S. oneidensis can transfer electrons generated by metabolic processes to exogenous metal catalysts, which triggers the chemical process of atom transfer radical polymerization. , Thus, making living hydrogels with controlled molecular weight and mechanical strength is feasible using in situ polymerization mediated by living cells. , …”

“…368,369 Thus, making living hydrogels with controlled molecular weight and mechanical strength is feasible using in situ polymerization mediated by living cells. 370,371 Hydrogels are frequently used as an important nonliving component in the fabrication of hybrid living materials. Going beyond the use of gels merely to support and protect free bacteria or cells, current research is gradually beginning to explore the effects of gels on the physiological activities of living organisms.…”

A hybrid transistor with transcriptionally controlled computation and plasticity

“…To facilitate this transition, we, and others, have created genetic circuits that tightly regulate the expression of EET-relevant genes, allowing EET flux to be turned on and off in response to specific combinations of chemical, biological, and physical stimuli 25,26 . Thus, genetic regulation over electron transport via EET has the potential to serve as a universal interface between bacteria and electronic devices, including OECTs.…”