The Usual Suspects 2019: of Chips, Droplets, Synthesis, and Artificial Cells

Biocatalytic self-assembled synthetic vesicles and coacervates: From single compartment to artificial cells

Compartmentalization is an intrinsic feature of living cells that allows spatiotemporal control over the biochemical pathways expressed in them. Over the years, a library of compartmentalized systems has been generated, which includes nano to micrometer sized biomimetic vesicles derived from lipids, amphiphilic block copolymers, peptides, and nanoparticles. Biocatalytic vesicles have been developed using a simple bag containing enzyme design of liposomes to multienzymes immobilized multi-vesicular compartments for artificial cell generation. Additionally, enzymes were also entrapped in membrane-less coacervate droplets to mimic the cytoplasmic macromolecular crowding mechanisms. Here, we have discussed different types of single and multicompartment systems, emphasizing their recent developments as biocatalytic self-assembled structures using recent examples. Importantly, we have summarized the strategies in the development of the self-assembled structure to improvise their adaptivity and flexibility for enzyme immobilization. Finally, we have presented the use of biocatalytic assemblies in mimicking different aspects of living cells, which further carves the path for the engineering of a minimal cell.

Microcompartmentalized Cell-Free Protein Synthesis in Hydrogel μ-Channels

The rapid demand for protein-based molecules has stimulated much research on cell-free protein synthesis (CFPS); however, there are still many challenges in terms of cost-efficiency, process intensification, and sustainability. Herein, we describe the microcompartmentalization of CFPS of superfolded green fluorescent protein (sGFP) in alginate hydrogels, which were casted into a μ-channel device. CFPS was optimized for the microcompartmentalized environment and characterized in terms of synthesis yield. To extend the scope of this technology, the use of other biocompatible materials (collagen, laponite, and agarose) was explored. In addition, the diffusion of sGFP from the hydrogel microenvironment to the bulk was demonstrated, opening a promising opportunity for concurrent synthesis and delivery of proteins. Finally, we provide an application for this system: the CFPS of enzymes. The present design of the hydrogel μ-channel device may enhance the potential application of microcompartmentalized CFPS in biosensing, bioprototyping, and therapeutic development.

Microfluidics for Biosynthesizing: from Droplets and Vesicles to Artificial Cells

Fabrication of artificial biomimetic materials has attracted abundant attention. As one of the subcategories of biomimetic materials, artificial cells are highly significant for multiple disciplines and their synthesis has been intensively pursued. In order to manufacture robust "alive" artificial cells with high throughput, easy operation, and precise control, flexible microfluidic techniques are widely utilized. Herein, recent advances in microfluidic-based methods for the synthesis of droplets, vesicles, and artificial cells are summarized. First, the advances of droplet fabrication and manipulation on the T-junction, flow-focusing, and coflowing microfluidic devices are discussed. Then, the formation of unicompartmental and multicompartmental vesicles based on microfluidics are summarized. Furthermore, the engineering of droplet-based and vesicle-based artificial cells by microfluidics is also reviewed. Moreover, the artificial cells applied for imitating cell behavior and acting as bioreactors for synthetic biology are highlighted. Finally, the current challenges and future trends in microfluidic-based artificial cells are discussed. This review should be helpful for researchers in the fields of microfluidics, biomaterial fabrication, and synthetic biology.