Development of mechanosensitive synthetic cells for biomedical applications

The ability of cells to sense and respond to their physical environment plays a fundamental role in a broad spectrum of biological processes. As one of the most essential molecular force sensors and transducers found in cell membranes, mechanosensitive (MS) ion channels can convert mechanical inputs into biochemical or electrical signals to mediate a variety of sensations. The bottom-up construction of cell-sized compartments displaying cell-like organization, behaviors, and complexity, also known as synthetic cells, has gained popularity as an experimental platform to characterize biological functions in isolation. By reconstituting MS channels in the synthetic lipid bilayers, we envision using mechanosensitive synthetic cells for several medical applications. Here, we describe three different concepts for using ultrasound, shear stress, and compressive stress as mechanical stimuli to activate drug release from mechanosensitive synthetic cells for disease treatments.

Recent advances of droplet-based microfluidics for engineering artificial cells

Artificial cells, synthetic cells, or minimal cells are microengineered cell-like structures that mimic the biological functions of cells. Artificial cells are typically biological or polymeric membranes where biologically active components, including proteins, genes, and enzymes, are encapsulated. The goal of engineering artificial cells is to build a living cell with the least amount of parts and complexity. Artificial cells hold great potential for several applications, including membrane protein interactions, gene expression, biomaterials, and drug development. It is critical to generate robust, stable artificial cells using high throughput, easy-to-control, and flexible techniques. Recently, droplet-based microfluidic techniques have shown great potential for the synthesis of vesicles and artificial cells. Here, we summarized the recent advances in droplet-based microfluidic techniques for the fabrication of vesicles and artificial cells. We first reviewed the different types of droplet-based microfluidic devices, including flow-focusing, T-junction, and coflowing. Next, we discussed the formation of multi-compartmental vesicles and artificial cells based on droplet-based microfluidics. The applications of artificial cells for studying gene expression dynamics, artificial cell-cell communications, and mechanobiology are highlighted and discussed. Finally, the current challenges and future outlook of droplet-based microfluidic methods for engineering artificial cells are discussed. This review will provide insights into scientific research in synthetic biology, microfluidic devices, membrane interactions, and mechanobiology.

Enzymatic control over coacervation

The discovery of membraneless organelles (MLOs) formed by liquid-liquid phase separation raised many questions about the spatial organization of biomolecular processes in cells, but also offered a new tool to mimic cellular media. Since disordered and charged protein domains are often necessary for phase separation, coacervates can be used as models both to understand MLO regulation and to develop dynamic cellular-like compartments. A versatile way to turn passive coacervate droplets into active and dynamic compartments is by introducing enzymatic reactions that affect parameters relevant for complex coacervation, such as the charge and length of the components. However, these reactions strictly take place in a heterogeneous medium, and the complexity thereof is hardly addressed, making it difficult to achieve true control. In this chapter we help close this gap by describing two coacervate systems in which enzymatic reactions endow coacervate droplets with a dynamic character. We further highlight the technical challenges posed by the two-phase systems and strategies to overcome them.

More from less - bottom-up reconstitution of cell biology

The ultimate goal of bottom-up synthetic biology is recreating life in its simplest form. However, in its quest to find the minimal functional units of life, this field contributes more than its main aim by also offering a range of tools for asking, and experimentally approaching, biological questions. This Review focusses on how bottom-up reconstitution has furthered our understanding of cell biology. Studying cell biological processes in vitro has a long tradition, but only recent technological advances have enabled researchers to reconstitute increasingly complex biomolecular systems by controlling their multi-component composition and their spatiotemporal arrangements. We illustrate this progress using the example of cytoskeletal processes. Our understanding of these has been greatly enhanced by reconstitution experiments, from the first in vitro experiments 70 years ago to recent work on minimal cytoskeleton systems (including this Special Issue of Journal of Cell Science). Importantly, reconstitution approaches are not limited to the cytoskeleton field. Thus, we also discuss progress in other areas, such as the shaping of biomembranes and cellular signalling, and prompt the reader to add their subfield of cell biology to this list in the future.

Self-organization of motors and microtubules in lipid-monolayered droplets

In living cells, the architecture of the microtubule cytoskeleton is intimately linked to its function. The principles determining how microtubules arrange in space are, however, still not fully understood. Biochemical activities controlling microtubule nucleation and dynamics as well as mechanochemical activities exerted by molecular motors and the dynamic microtubules themselves are known to be critical for the correct spatial organization of the microtubule cytoskeleton. In vitro reconstitution approaches have revealed the morphogenetic properties of these activities in minimal systems. In most cases, such in vitro experiments were performed in experimental chambers of spatial dimensions that exceeded typical cell sizes by orders of magnitude. Here, we describe a method for the fluorescence microscopic study of the effects of spatial confinement on the self-organization of purified motors and microtubules that are encapsulated in micrometer-sized lipid-monolayered droplets emulsified in oil. In the future, this experimental setup can be extended in several ways. Additional proteins can be added, either to the lumen or to the boundary of the microcontainers, and the droplets can be transformed into liposomes. Such more complex in vitro reconstitutions would be another step closer to mimicking intracellular cytoskeleton organization.