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Exploring Giant Unilamellar Vesicle Production for Artificial Cells – Current Challenges and Future Directions
Get PDFCreating an artificial cell from the bottom up is a long-standing challenge and, while significant progress has been made, the full realization of this goal remains elusive. Arguably, one of the biggest hurdles that researchers are facing now is the assembly of different modules of cell function inside a single container. Giant unilamellar vesicles (GUVs) have emerged as a suitable container with many methods available for their production. Well-studied swelling-based methods offer a wide range of lipid compositions but at the expense of limited encapsulation efficiency. Emulsion-based methods, on the other hand, excel at encapsulation but are only effective with a limited set of membrane compositions and may entrap residual additives in the lipid bilayer. Since the ultimate artificial cell will need to comply with both specific membrane and encapsulation requirements, there is still no one-method-fits-all solution for GUV formation available today. This review discusses the state of the art in different GUV production methods and their compatibility with GUV requirements and operational requirements such as reproducibility and ease of use. It concludes by identifying the most pressing issues and proposes potential avenues for future research to bring us one step closer to turning artificial cells into a reality
Chiral Amplification through the Interplay of Racemizing Conditions and Asymmetric Crystal Growth
Get PDFAmplification of enantiomeric excesses (ee) is routinely observed during chiral crystallization of conglomerate crystals for which the enantiomers undergo racemization in solution. Although routes comprising a combination of crystal growth and dissolution are frequently used to obtain enantiopure molecules, crystal growth by itself has rather been considered as a source of enantiomeric erosion and discounted as a potential source of enantiomeric amplification. Counterintuitively, we here demonstrate striking enantiomeric amplification during crystal growth for clopidogrel and tert-leucine precursors. Based on a mechanistic framework, we identify that the interplay between racemization and crystal growth rates elicits this surprising effect. The asymmetric amplification of the solid-phase ee can be enhanced by increasing the mass of grown material relative to the product such that small amounts of seeds of only 60% ee already result in virtually exclusive growth of the majority phase. These results impact our understanding of asymmetric amplification mechanisms during crystallization and offer a tangible basis for practical production of enantiopure molecules
Organoid cell fate dynamics in space and time
Get PDFOrganoids are a major new tool to study tissue renewal. However, characterizing the underlying differentiation dynamics remains challenging. Here, we developed TypeTracker, which identifies cell fates by AI-enabled cell tracking and propagating end point fates back along the branched lineage trees. Cells that ultimately migrate to the villus commit to their new type early, when still deep inside the crypt, with important consequences: (i) Secretory cells commit before terminal division, with secretory fates emerging symmetrically in sister cells. (ii) Different secretory types descend from distinct stem cell lineages rather than an omnipotent secretory progenitor. (iii) The ratio between secretory and absorptive cells is strongly affected by proliferation after commitment. (iv) Spatial patterning occurs after commitment through type-dependent cell rearrangements. This "commit-then-sort" model contrasts with the conventional conveyor belt picture, where cells differentiate by moving up the crypt-villus axis and hence raises new questions about the underlying commitment and sorting mechanisms
Spectroscopic Analysis for the Identification of Loss Mechanisms in Back-Contact Perovskite Solar Cells
Get PDFBack-contact perovskite solar cells offer a significant potential to reach high efficiency due to reduced parasitic absorption from the top surface. However, the currently reported efficiencies are considerably lower (20%). Herein, back-contact perovskite solar cells are fabricated to study loss mechanisms that cause low device efficiency. This work spatially resolves the short-circuit current, open-circuit voltage, photoluminescence quantum yield, carrier lifetime, and external quantum efficiency of the devices. The results indicate that the front surface recombination, increased nonradiative recombination at hole contact layer/perovskite interface, and the extraction barriers are three main mechanisms limiting devices from achieving high efficiencies
Impact of Mobile Ions on Transient Capacitance Measurements of Perovskite Solar Cells
Get PDFMitigating the migration of mobile ions within perovskite solar cells is a crucial step on the way to improving their stability. In the past, transient capacitance measurements were applied to extract information about mobile ions, including their activation energy, diffusion coefficient, density, and polarity. However, in this work, we show that the interpretation of capacitance transients is more complex than originally proposed because of the intrinsic nature of the perovskite and the contributions of charge transport layers to the capacitance. Using drift-diffusion simulations and light-intensity-dependent capacitance transient measurements, we show that the direction of capacitance transients is not linked to the polarity of the migrating species. Instead, the direction of the transients is linked to the layer of the cell that dominates capacitance modulation. This work illustrates that transport layers can be crucial for the capacitance and impedance response of perovskite solar cells, and therefore, for characterizing mobile ions in perovskites
Light-driven nucleation, growth, and patterning of biorelevant crystals using resonant near-infrared laser heating
Get PDFSpatiotemporal control over crystal nucleation and growth is of fundamental interest for understanding how organisms assemble high-performance biominerals, and holds relevance for manufacturing of functional materials. Many methods have been developed towards static or global control, however gaining simultaneously dynamic and local control over crystallization remains challenging. Here, we show spatiotemporal control over crystallization of retrograde (inverse) soluble compounds induced by locally heating water using near-infrared (NIR) laser light. We modulate the NIR light intensity to start, steer, and stop crystallization of calcium carbonate and laser-write with micrometer precision. Tailoring the crystallization conditions overcomes the inherently stochastic crystallization behavior and enables positioning single crystals of vaterite, calcite, and aragonite. We demonstrate straightforward extension of these principles toward other biorelevant compounds by patterning barium-, strontium-, and calcium carbonate, as well as strontium sulfate and calcium phosphate. Since many important compounds exhibit retrograde solubility behavior, NIR-induced heating may enable light-controlled crystallization with precise spatiotemporal control
Influence of the crystallographic texture of ITO on the electrodeposition of silver nanoparticles
Get PDFThe electrochemical control over nucleation and growth of metal nanoparticles on foreign substrates is an active field of research, where the surface properties of the substrate have a key role in nucleation dynamics. Polycrystalline indium tin oxide (ITO) films are highly desired substrates for many optoelectronic applications, for which the only parameter that is often specified is the sheet resistance. As a result, growth on ITO is highly irreproducible. Here, we show that ITO substrates with same technical specifications (i.e. sheet resistance, light transmittance and roughness) and supplier may still have different crystalline texture, which we find it has a strong impact on the nucleation and growth of silver nanoparticles during electrodeposition. We find that the preferential presence of lower index surfaces leads to few orders of magnitude lower island density, which is strongly dependent on the nucleation pulse potential. By contrast, the island density on ITO with preferential 〈111〉 orientation is barely affected by the nucleation pulse potential. This work highlights the importance of reporting the surface properties of polycrystalline substrates when presenting nucleation studies and metal nanoparticle electrochemical growth
Molecular Orientation of Carboxylate Anions at the Water-Air Interface Studied with Heterodyne-Detected Vibrational Sum-Frequency Generation
Get PDFThe carboxylate anion group plays an important role in many (bio)chemical systems and polymeric materials. In this work, we study the orientation of carboxylate anions with various aliphatic and aromatic substituents at the water-air interface by probing the carboxylate stretch vibrations with heterodyne-detected vibrational sum-frequency generation spectroscopy in different polarization configurations. We find that carboxylate groups with small aliphatic substituents show a large tilt angle with respect to the surface normal and that this angle decreases with increasing size of the substituent. We further use the information about the orientation of the carboxylate group to determine the hyperpolarizability components of this group
Effective bet-hedging through growth rate dependent stability
Get PDFMicrobes in the wild face highly variable and unpredictable environments and are naturally selected for their average growth rate across environments. Apart from using sensory regulatory systems to adapt in a targeted manner to changing environments, microbes employ bet-hedging strategies where cells in an isogenic population switch stochastically between alternative phenotypes. Yet, bet-hedging suffers from a fundamental trade-off: Increasing the phenotype-switching rate increases the rate at which maladapted cells explore alternative phenotypes but also increases the rate at which cells switch out of a well-adapted state. Consequently, it is currently believed that bet-hedging strategies are effective only when the number of possible phenotypes is limited and when environments last for sufficiently many generations. However, recent experimental results show that gene expression noise generally decreases with growth rate, suggesting that phenotype-switching rates may systematically decrease with growth rate. Such growth rate dependent stability (GRDS) causes cells to be more explorative when maladapted and more phenotypically stable when well-adapted, and we show that GRDS can almost completely overcome the trade-off that limits bet-hedging, allowing for effective adaptation even when environments are diverse and change rapidly. We further show that even a small decrease in switching rates of faster-growing phenotypes can substantially increase long-term fitness of bet-hedging strategies. Together, our results suggest that stochastic strategies may play an even bigger role for microbial adaptation than hitherto appreciated
Shape Memory Soft Robotics with Yield Stress Fluids
Get PDFBiological movement is a source of inspiration for designing soft robots that use fluidic actuation for adaptive gripping and locomotion. While many biological systems use networks of non-Newtonian fluid for movement, to date, most soft robots use Newtonian fluids or pneumatics. Herein, yield stress fluids to manufacture and operate soft devices are exploited, particularly to create soft actuators that exhibit shape memory. Our soft robots are fabricated through embedded 3D printing where the suspension media is a yield stress fluid. Moreover, this complex fluid is encapsulated and used as the hydraulic transmission fluid. Diagnostic designs are developed to characterize the force and shape memory of the yield stress fluid, and the findings are used to create a gripper common in modern soft robotic applications. The diagnostic devices have deformable reservoirs that demonstrate force response, flow behavior, and deformation profiles dependent on the yield stress features of the transmission fluid. The actuation using the yield stress fluid from the retained suspension media creates avenues for partial shape retention and unconventional expansion from localized fluid flow. Looking toward the future of soft robotics, these fabrication and operational approaches using yield stress fluids can provide greater tunability for applications requiring nonlinear actuation and shape memory