Energy and Matter Supply for Active Droplets

Abstract

Chemically active droplets provide simple models for cell‐like systems that can grow and divide. Such active droplet systems are driven away from thermodynamic equilibrium and turn over chemically, which corresponds to a simple metabolism. Two scenarios of nonequilibrium driving are considered. First, droplets are driven via the system boundaries by external reservoirs that supply nutrient and remove waste (boundary‐driven). Second, droplets are driven by a chemical energy provided by a fuel in the bulk (bulk‐driven). For both scenarios, the conservation of energy and matter as well as the balance of entropy are discussed. Conserved and nonconserved fields are used to analyse the nonequilibrium steady states of active droplets. Using an effective droplet model, droplet stability and instabilities leading to droplet division are explored. This work reveals that droplet division occurs quite generally in active droplet systems. The results suggest that life‐like processes such as metabolism and division can emerge in simple nonequilibrium systems that combine the physics of phase separation and chemical reactions.

Nonequilibrium Wet–Dry Cycling Acts as a Catalyst for Chemical Reactions

“…When considering chemical reactions occurring with rates around min –1 , the condition for phase equilibrium (A ) is satisfied for system sizes of 0.1 mm or smaller. For larger system sizes, gradients in the system should be taken into account by using a sharp interface model to calculate diffusive fluxes driven spatial inhomogeneities ) during the wet–dry cycles and the reaction kinetics.…”

On Non-ideal Chemical-Reaction Networks and Phase Separation

“…Then, reactions that involve both chemostatted and non-chemostatted species are driven in one direction by the work done by the chemostats inserting and removing particles from the system (in order to keep their chemical potentials constant). Given that the mechanism of reaction remains the same, in line with the previous section the rates of these driven chemical transitions are taken to be [22,23,25,26]…”

“…Early progress in reconciling the spatial patterns predicted by these models with a thermodynamically consistent description was limited to a linear-stability analysis of binary systems [21]. More recently, some works aimed at establishing a deterministic theory for non-ideal CRNs [22], the relation between phase coexistence and chemical kinetics [23], and exploring minimal examples for pattern formation with non-ideal CRNs [24][25][26]. Nevertheless, the link between non-equilibrium CRNs and phase separation has not yet been elucidated in full generality.…”

Reaction-driven assembly: controlling changes in membrane topology by reaction cycles

“…20,21 Already the simplest of such systems, an immiscible reactant-product system exhibits a variety of effects that differ from immiscible binary mixtures such as an arrest of droplet coalescence [22][23][24] or a shape instability for emerging droplets, leading to fission. [25][26][27] It has remained a challenge to reproduce these predicted effects experimentally for which high reaction rates are necessary.…”

“…20,21 Already the simplest of such systems, an immiscible reactant-product system exhibits a variety of effects that differ from immiscible binary mixtures such as an arrest of droplet coalescence 22–24 or a shape instability for emerging droplets, leading to fission. 25–27…”