Salt mediated actuation of membranized coacervate droplets for regulation of enzymatic reactions

Regulation of transport is an essential design element for controlling biological networks within living cells. Its implementation within coacervate microdroplets, where reaction kinetics are modulated, would enable the design of adaptive cell-like compartments. Yet, the lack of a membrane limits the potential of coacervate microdroplets as artificial cells. Herein, we present a simple strategy to stabilize coacervate microdroplets via interfacial formation of solid polyelectrolyte complexes mediated by addition of a strong polyelectrolyte. Salt addition triggers network swelling within the membranized coacervate droplets, while salt removal induces deswelling. Several cycles of salt-mediated chemomechanical actuation can be achieved by alternating salt and water flows. The actuating droplets maintain a loosely cross-linked coacervate interior, allowing faster mass transport compared to non-actuating droplets, thereby doubling the rate of enzymatic reactions hosted within. Our work introduces an alternate mechanism for controlling reaction kinetics in coacervates and expands the toolbox for protometabolic regulation within artificial cells.