Controlled stirring of tiny volumes of aqueous fluids is of particular importance in the life sciences, e.g. in the context of microfluidic and lab-on-chip applications. Local stirring not only accelerates fluid mixing and diffusion-limited processes, but it also allows for adding controlled active noise to the fluid. Here we report on the synthesis and characterization of magnetic nano-stir bars (MNBs) with which these features can be achieved in a straightforward fashion. We also demonstrate the applicability of MNBs to cell extract droplets in microfluidic channels and we show that they can introduce active noise to cell extracts as evidenced by altered fluctuations of ensembles of cytoskeletal filaments.

particles as well as the friction coefficient of BD particles. Integration of the methods shows little impact on the time-to-solution compared to a pure RDME simulation. A proof of principle is presented using the particle densities and geometry of a 500-nm diameter minimal cell. This minimal cell, named JCVI-syn3A, with a 543-kbp genome and 493 genes, provides a versatile platform to study the basics of life. This computational methodology will become a major component of the goal to simulate JCVI-syn3A at a spatially resolved, stochastic level.

Mixing of reactants in microdroplets predominantly relies on diffusional motion due to small Reynolds numbers and the resulting absence of turbulent flows. Enhancing diffusion in microdroplets by an auxiliary noise...

Self-organization of cells into higher-order structures is key for multicellular organisms, e.g. via repetitive replication of template-like founder cells or syncytial energids. Yet, very similar spatial arrangements of cell-like compartments (’protocells’) are also seen in a minimal model system of Xenopus egg extracts in the absence of template structures and chromatin, with dynamic microtubule assemblies driving the self-organization process. Quantifying geometrical features over time, we show here that protocell patterns are highly organized with a spatial arrangement and coarsening dynamics like two-dimensional foams but without the long-range ordering expected for hexagonal patterns. These features remain invariant when enforcing smaller protocells by adding taxol, i.e. patterns are dominated by a single, microtubule-derived length scale. Comparing our data to generic models, we conclude that protocell patterns emerge by simultaneous formation of randomly assembling protocells that grow at a uniform rate towards a frustrated arrangement before fusion of adjacent protocells eventually drives coarsening. The similarity of protocell patterns to arrays of energids and cells in developing organisms, but also to epithelial monolayers, suggests generic mechanical cues to drive self-organized space compartmentalization.

Self-organization of cells into higher-order structures is key for multicellular organisms, e.g. during embryonic epithelium formation via repetitive replication of template-like founder cells. Yet, very similar spatial arrangements of cell-like compartments ("protocells") are also seen in cell extracts in the absence of template structures and genetic material. Here we show that protocell patterns are highly organized, featuring a spatial arrangement and coarsening like two-dimensional foams but without signatures of disordered hyperuniformity. These features even remain unaffected when enforcing smaller protocells by stabilizing microtubule filaments. Comparing our data to generic models, we conclude that protocell patterns emerge by simultanous formation of randomly placed seeds that grow at a uniform rate until fusion of adjacent protocells drives coarsening. The strong similarity of our observations to the recently reported organization of epithelial monolayers suggests common generic principles for space allocation in living matter.