Living organisms require constant energy supply and stimuli adaptation to maintain homeostasis which is regulated by out-of-equilibrium feedback loops. To achieve oscillations of metabolite concentrations, the feedback loops require integrated delayed enzymatic kinetics. One example is the control of metabolite concentrations modulated by the day and night cycle, i.e., the circadian rhythm. We took inspiration from this phenomenon with a ternary system of two polymersome enzymatic nanoreactors and a macroscopic hydrogel. One of the nanoreactor populations contained an acid generating enzyme and was functionalised with a Donor-Acceptor Stenhouse Adduct (DASA) acting as a light-sensitive catalytic activator. A second nanoreactor population was composed of a permanently semipermeable membrane and contained a base producing enzyme. The accumulation of acid protonated a pH-sensitive indicator dye which acted as a photomask. This process quenched the absorption of light by the light-responsive nanoreactor and inhibited its photocatalytic activity. Simultaneously, the production of acid activated the synthesis of base by the permeable base producing nanoreactor and deprotonated the photomask again. The variation of the pH states allowed the shape modulation of a macroscopic hydrogel with light, finding potential applications in soft robotics or microfluidics. Importantly, the system could be activated with light within the visible spectrum compared to enzyme-degrading UV-light and did not require continuous spiking of chemical fuel to achieve out-of-equilibrium states.

Out-of-equilibrium macroscopic shape modulation driven by DASA modified polymersome enzymatic nanoreactors

ACS Spring 2022

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