Abstract
Random fluctuations are inherent to all complex molecular systems. Although nature has evolved mechanisms to control stochastic events to achieve the desired biological output, reproducing this in synthetic systems represents a significant challenge. Here we present an artificial platform that enables us to exploit stochasticity to direct motile behavior. We found that enzymes, when confined to the fluidic polymer membrane of a core-shell coacervate, were distributed stochastically in time and space. This resulted in a transient, asymmetric configuration of propulsive units, which imparted motility to such coacervates in presence of substrate. This mechanism was confirmed by stochastic modelling and simulations in silico. Furthermore, we showed that a deeper understanding of the mechanism of stochasticity could be utilized to modulate the motion output. Conceptually, this work represents a leap in design philosophy in the construction of synthetic systems with life-like behaviors.
Highlights
Brownian motion 't (s)10 mM HO 0 mM HO Self- 4 propulsion
Asymmetry in the motor structure has been considered as a prerequisite for autonomous motion[6–10]. This has, for example, been achieved by the construction of Janus particles, which are hemi-spherically covered with active catalysts[11–15]
Our platform was composed of a complex coacervate droplet, which was formed by the spontaneous coacervation of two oppositely charged polyelectrolytes that associate when mixed in water, and which was further stabilized by the presence of a polymer membrane[23]
Summary
Asymmetry in the motor structure (e.g., shape, catalyst distribution) has been considered as a prerequisite for autonomous motion[6–10]. A random surface distribution of enzymes has been shown to propel micromotors in the presence of fuel[4,5] This inspired us to construct a system, in which asymmetry (i.e., heterogeneous distribution of enzymes) is transient and dynamic, enabled by the inherently fluidic polymer membrane (Fig. 1d, e). We set out to test the impact of enzyme density on motility by fabricating both mCAT- and mUR-coacervates with three different surface enzyme densities— low, medium, and high (for exact enzyme number and coverage, see “Methods” and Supplementary Tables 1 and 2). 10−4 were obtained for mCAT- and mUR-coacervates, respectively (for details, see “Methods—Estimation of Damköhler number”) In both cases, the Damköhler number is
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