A large German research consortium mainly within the Max Planck Society (“MaxSynBio”) was formed to investigate living systems from a fundamental perspective. The research program of MaxSynBio relies ...solely on the bottom‐up approach to synthetic biology. MaxSynBio focuses on the detailed analysis and understanding of essential processes of life through modular reconstitution in minimal synthetic systems. The ultimate goal is to construct a basic living unit entirely from non‐living components. The fundamental insights gained from the activities in MaxSynBio could eventually be utilized for establishing a new generation of biotechnological processes, which would be based on synthetic cell constructs that replace the natural cells currently used in conventional biotechnology.
To the Max: A research consortium associated with the Max Planck Society (“MaxSynBio”) was formed to investigate living systems from a fundamental perspective. The research program relies solely on the bottom‐up approach and focuses on the detailed analysis and understanding of essential processes of life through modular reconstitution in minimal synthetic systems. The ultimate goal is to construct a basic living unit entirely from non‐living components.
Electrowetting has become one of the most widely used tools for manipulating tiny amounts of liquids on surfaces. Applications range from 'lab-on-a-chip' devices to adjustable lenses and new kinds of ...electronic displays. In the present article, we review the recent progress in this rapidly growing field including both fundamental and applied aspects. We compare the various approaches used to derive the basic electrowetting equation, which has been shown to be very reliable as long as the applied voltage is not too high. We discuss in detail the origin of the electrostatic forces that induce both contact angle reduction and the motion of entire droplets. We examine the limitations of the electrowetting equation and present a variety of recent extensions to the theory that account for distortions of the liquid surface due to local electric fields, for the finite penetration depth of electric fields into the liquid, as well as for finite conductivity effects in the presence of AC voltage. The most prominent failure of the electrowetting equation, namely the saturation of the contact angle at high voltage, is discussed in a separate section. Recent work in this direction indicates that a variety of distinct physical effects-rather than a unique one-are responsible for the saturation phenomenon, depending on experimental details. In the presence of suitable electrode patterns or topographic structures on the substrate surface, variations of the contact angle can give rise not only to continuous changes of the droplet shape, but also to discontinuous morphological transitions between distinct liquid morphologies. The dynamics of electrowetting are discussed briefly. Finally, we give an overview of recent work aimed at commercial applications, in particular in the fields of adjustable lenses, display technology, fibre optics, and biotechnology-related microfluidic devices.
The assembly of adaptive hierarchical soft materials that resemble living tissues requires responsive building blocks of controlled dimensions. While DNA self‐assembly provides an exceptional tool ...for nanoscale architectural control, responsive DNA microstructures remain scarce. Here, two challenges controlling the size of DNA microstructures and embedding them with fast and ample structural response are addressed. For size‐control, arrested phase separation and microfluidic confinement are combined to produce monodisperse all‐DNA particles. For responsiveness, a light controlled coil‐globule transition of the microgel DNA network powered by an azobenzene cationic surfactant is implemented. The photoinduced trans‐cis isomerization of the azobenzene moiety reduces its affinity for DNA which results in fast, large amplitudes microgel swelling. Finally, the assembly of light responsive microgel superstructures is demonstrated as proof‐of‐concept hierarchical all‐DNA materials.
Phase transition is commonly used to synthesize and actuate synthetic hydrogels. This concept is brought into DNA materials to prepare monodisperse all‐DNA microgels and embed them with light responsive properties. Confined phase separation is used to control the size of the microgels and a photoresponsive surfactant to trigger tenfold swelling within seconds on isolated microgels and periodic superstructures.
Emulsions are metastable dispersions in which molecular transport is a major mechanism driving the system towards its state of minimal energy. Determining the underlying mechanisms of molecular ...transport between droplets is challenging due to the complexity of a typical emulsion system. Here we introduce the concept of 'minimal emulsions', which are controlled emulsions produced using microfluidic tools, simplifying an emulsion down to its minimal set of relevant parameters. We use these minimal emulsions to unravel the fundamentals of transport of small organic molecules in water-in-fluorinated-oil emulsions, a system of great interest for biotechnological applications. Our results are of practical relevance to guarantee a sustainable compartmentalization of compounds in droplet microreactors and to design new strategies for the dynamic control of droplet compositions.
Compartments for the spatially and temporally controlled assembly of biological processes are essential towards cellular life. Synthetic mimics of cellular compartments based on lipid-based ...protocells lack the mechanical and chemical stability to allow their manipulation into a complex and fully functional synthetic cell. Here, we present a high-throughput microfluidic method to generate stable, defined sized liposomes termed 'droplet-stabilized giant unilamellar vesicles (dsGUVs)'. The enhanced stability of dsGUVs enables the sequential loading of these compartments with biomolecules, namely purified transmembrane and cytoskeleton proteins by microfluidic pico-injection technology. This constitutes an experimental demonstration of a successful bottom-up assembly of a compartment with contents that would not self-assemble to full functionality when simply mixed together. Following assembly, the stabilizing oil phase and droplet shells are removed to release functional self-supporting protocells to an aqueous phase, enabling them to interact with physiologically relevant matrices.
We report on the formation of surfactant‐based complex catanionic coacervate droplets in mixtures of decanoic acid and cetylpyridinium chloride or cetyltrimethylammonium bromide. We show that ...coacervation occurs over a broad range of composition, pH, and ionic strength. The catanionic coacervates consist of elongated micelles, sequester a wide range of solutes including water‐soluble organic dyes, polysaccharides, proteins, enzymes, and DNA, and can be structurally stabilized by sodium alginate or gelatin‐based hydrogelation. These results suggest that catanionic coacervates could be exploited as a novel surfactant‐based membrane‐free protocell model.
Catanionic coacervates as protocells: Proteins, enzymes, and DNA are spontaneously sequestered within catanionic surfactant coacervates, thereby affording a novel protocell model.
The fabrication of stable colloidosomes derived from water‐in‐water Pickering‐like emulsions are described that were produced by addition of fluorescent amine‐modified polystyrene latex beads to an ...aqueous two‐phase system consisting of dextran‐enriched droplets dispersed in a PEG‐enriched continuous phase. Addition of polyacrylic acid followed by carbodiimide‐induced crosslinking with dextran produces hydrogelled droplets capable of reversible swelling and selective molecular uptake and exclusion. Colloidosomes produced specifically in all‐water systems could offer new opportunities in microencapsulation and the bottom‐up construction of synthetic protocells.
Ready to load: Hybrid hydrogel‐colloidosomes capable of swelling and spontaneous uptake of payloads have been fabricated from water‐in‐water emulsions.
A bimolecular synthetic reaction (imine synthesis) was performed compartmentalized in micrometer-diameter emulsion droplets. The apparent equilibrium constant (Keq) and apparent forward rate constant ...(k1) were both inversely proportional to the droplet radius. The results are explained by a noncatalytic reaction-adsorption model in which reactants adsorb to the droplet interface with relatively low binding energies of a few kBT, react and diffuse back to the bulk. Reaction thermodynamics is therefore modified by compartmentalization at the mesoscale--without confinement on the molecular scale--leading to a universal mechanism for improving unfavorable reactions.
The explosive growth in our knowledge of genomes, proteomes, and metabolomes is driving ever-increasing fundamental understanding of the biochemistry of life, enabling qualitatively new studies of ...complex biological systems and their evolution. This knowledge also drives modern biotechnologies, such as molecular engineering and synthetic biology, which have enormous potential to address urgent problems, including developing potent new drugs and providing environmentally friendly energy. Many of these studies, however, are ultimately limited by their need for even-higher-throughput measurements of biochemical reactions. We present a general ultrahigh-throughput screening platform using drop-based microfluidics that overcomes these limitations and revolutionizes both the scale and speed of screening. We use aqueous drops dispersed in oil as picoliter-volume reaction vessels and screen them at rates of thousands per second. To demonstrate its power, we apply the system to directed evolution, identifying new mutants of the enzyme horseradish peroxidase exhibiting catalytic rates more than 10 times faster than their parent, which is already a very efficient enzyme. We exploit the ultrahigh throughput to use an initial purifying selection that removes inactive mutants; we identify ~100 variants comparable in activity to the parent from an initial population of ~10⁷. After a second generation of mutagenesis and high-stringency screening, we identify several significantly improved mutants, some approaching diffusion-limited efficiency. In total, we screen ~10⁸ individual enzyme reactions in only 10 h, using < 150 μL of total reagent volume; compared to state-of-the-art robotic screening systems, we perform the entire assay with a 1,000-fold increase in speed and a 1-million-fold reduction in cost.
Surfactants are an essential part of the droplet-based microfluidic technology. They are involved in the stabilization of droplet interfaces, in the biocompatibility of the system and in the process ...of molecular exchange between droplets. The recent progress in the applications of droplet-based microfluidics has been made possible by the development of new molecules and their characterizations. In this review, the role of the surfactant in droplet-based microfluidics is discussed with an emphasis on the new molecules developed specifically to overcome the limitations of 'standard' surfactants. Emulsion properties and interfacial rheology of surfactant-laden layers strongly determine the overall capabilities of the technology. Dynamic properties of droplets, interfaces and emulsions are therefore very important to be characterized, understood and controlled. In this respect, microfluidic systems themselves appear to be very powerful tools for the study of surfactant dynamics at the time- and length-scale relevant to the corresponding microfluidic applications. More generally, microfluidic systems are becoming a new type of experimental platform for the study of the dynamics of interfaces in complex systems.
PDF
