Excitability and Oscillations of Active Droplets

In the field of biomolecular condensates and synthetic systems, it is an open question whether liquid droplets can undergo self-sustained oscillations of formation and dissolution. To unravel the minimal physicochemical prerequisite for such droplet oscillations, we present a simple model composed of only two independent chemical components with their diffusive and chemical fluxes governed by nonequilibrium thermodynamics. There is turnover of fuel that maintains a chemical reaction away from equilibrium, leading to active droplets. We find that a single active droplet undergoes a saddle-node bifurcation in the droplet volume upon increasing the fueling strength. Strikingly, the active droplet becomes excitable upon adding a further chemical reaction. For sufficient fueling, the system undergoes self-sustained oscillations.