Designing Synthetic Microcapsules That Undergo Biomimetic Communication and Autonomous Motion

Abstract

Inspired by the collective behavior of slime molds and amoebas, we designed synthetic cell-like objects that move and self-organize in response to self-generated chemical gradients, thereby exhibiting autochemotaxis. Using computational modeling, we specifically focused on microcapsules that encompass a permeable shell and are localized on an adhesive surface in solution. Lacking any internal machinery, these spherical, fluid-filled shells might resemble the earliest protocells. Our microcapsules do, however, encase particles that can diffuse through the outer shell and into the surrounding fluid. The released particles play two important, physically realizable roles: (1) they affect the permeability of neighboring capsules and (2) they generate adhesion gradients on the underlying surface. Due to feedback mechanisms provided by the released particles, the self-generated adhesion gradients, and hydrodynamic interactions, the capsules undergo collective, self-sustained motion and even exhibit antlike tracking behavior. With the introduction of a chemically patterned stripe on the surface, a triad of capsules can be driven to pick up four-capsule cargo, transport this cargo, and drop off this payload at a designated site. We also modeled a system where the released particles give rise to a particular cycle of negative feedback loops (mimicking the "repressilator" network), which regulates the production of chemicals within the capsules and hence their release into the solution. By altering the system parameters, three capsules could be controllably driven to self-organize into a stable, close-packed triad that would either translate as a group or remain stationary. Moreover, the stationary triads could be made to switch off after assembly and thus produce minimal quantities of chemicals. Taken together, our models allow us to design a rich variety of self-propelled structures that achieve complex, cooperative behavior through fundamental physicochemical phenomena. The studies can also shed light on factors that enable individual protocells to communicate and self-assemble into larger communities.

Microscopic agents programmed by DNA circuits

“…Our strategy based on template-decorated particles provides the basic set of tools required to build and study artificial microscopic communities 19 . It uses a hierarchical approach that maintains a rational link from molecular pairwise interactions all the way to multiparticles dynamics.…”

“…These building blocks enable the rational molecular programming of population-scale phenomena 19,20 . We generate spatially random arrays containing thousands of particles in which we observed the propagation of bistable travelling fronts, or the generation of stationary symbiotic activation patterns, depending on the molecular instructions carried by the microscopic agents.…”

Chemotaxis and autochemotaxis of self-propelling droplet swimmers

“…To untangle these effects, there have been some design proposals for artificial systems, such as in ref. 25, and simulations on the dynamics of simple autochemotactic microswimmers (26)(27)(28)(29)(30). Studies exist on collective effects like autochemotaxis-induced clustering (31)(32)(33), but generally, there is still a lack of well-controllable and quantifiable experimental realizations of autochemotactic artificial swimmers.…”

Communication between hydrogel beadsviachemical signalling

“…11,12 Furthermore, simple microorganisms such as the amoeba release chemical signals to induce self--assembly of individuals into multi--cellular colonies, allowing for collective motion. 13,14 It is theorised that protocells (the earliest versions of modern day cells) 14 Man--made materials have been proposed and designed in an effort to mimic communication in and between organisms. The ability to exchanges information by means of chemical signal transduction has been demonstrated computationally, for example gels and microcapsules that undergo communication and auto--chemotaxis, 14,[16][17][18][19] vesicles that communicate through nanotubes, 20 and microcapsules that self--assemble.…”

“…13,14 It is theorised that protocells (the earliest versions of modern day cells) 14 Man--made materials have been proposed and designed in an effort to mimic communication in and between organisms. The ability to exchanges information by means of chemical signal transduction has been demonstrated computationally, for example gels and microcapsules that undergo communication and auto--chemotaxis, 14,[16][17][18][19] vesicles that communicate through nanotubes, 20 and microcapsules that self--assemble. 21 A number of interesting studies have demonstrated that this kind of communication between synthetic objects is indeed realistic.…”