Life-like behaviors in programmable colloidal droplets

In biology, complex biochemical reactions on the molecular scale are coupled to the macroscopic behavior of the cell, governing cell division, adhesion, locomotion, and tissue formation. To reveal the minimal ingredients necessary for the emergence of these complex functions, here we use a reductionist approach employing interacting colloidal droplets to mimic cells [1,2]. The tunability, specificity, and programmability of droplet-droplet interactions are facilitated by DNA nanotechnologies, including strand displacement or enzyme-activated DNA circuits. The liquid membrane of the droplets allows them to freely rearrange after binding, optimizing their self-organization as cells do in tissues. Following design protocols, DNA-coated droplets can self-assemble into a variety of shapes, including clusters, chains, foldamers, and gel networks whose structure and connectivity can be finely tuned [3]. This designability relies on a thermodynamic theory for droplet-droplet adhesion, highlighting the importance of diffusivity and deformability at the interface. As a result, we show how, in analogy with proteins, colloidomer droplet chains can fold into well-defined 2D structures, which can further assemble into supracolloidal capsids in 3D [4]. Furthermore, we show that the use of enzyme-driven DNA reaction networks allows for an isothermal and autonomous control over the sequence and concentration of binding DNA strands over time and space. As a result, droplets assemble in clusters that can reorganize, resembling cell sorting and segregation in tissues where adhesion proteins are expressed at different levels. The spatiotemporal control of droplet self-organization opens the avenue for the design of functional colloidal materials with tunable dynamics.