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While shear emulsification is a well understood industrial process, geometrical confinement in microfluidic systems introduces fascinating complexity, so far prohibiting complete understanding of droplet formation. The size of confined droplets is controlled by the ratio between shear and capillary forces when both are of the same order, in a regime known as jetting, while being surprisingly insensitive to this ratio when shear is orders of magnitude smaller than capillary forces, in a regime known as squeezing. Here, we reveal that further reduction of—already negligibly small—shear unexpectedly re-introduces the dependence of droplet size on shear/capillary-force ratio. For the first time we formally account for the flow around forming droplets, to predict and discover experimentally an additional regime—leaking. Our model predicts droplet size and characterizes the transitions from leaking into squeezing and from squeezing into jetting, unifying the description for confined droplet generation, and offering a practical guide for applications. T-junctions are a tool for droplet generation; they are well-described by models that distinguish for squeezing and jetting regimes for different capillary numbers. By considering the usually neglected corner flow, the authors identify an additional leaking regime for very low capillary numbers.

Sticking of particles has a tremendous impact on powder-processing industries, especially for hygroscopic amorphous powders. A wide variety of experimental methods has been developed to measure at what combinations of temperature and moisture content material becomes sticky. This review describes, for each method, how so-called stickiness curves are determined. As particle velocity also plays a key role, we classify the methods into static and dynamic stickiness tests. Static stickiness tests have limited particle motion during the conditioning step prior to the measurement. Thus, the obtained information is particularly useful in predicting the long-term behavior of powder during storage or in packaging. Dynamic stickiness tests involve significant particle motion during conditioning and measurement. Stickiness curves strongly depend on particle velocity, and the obtained information is highly relevant to the design and operation of powder production and processing equipment. Virtually all methods determine the onset of stickiness using powder as a starting point. Given the many industrial processes like spray drying that start from a liquid that may become sticky upon drying, future effort should focus on developing test methods that determine the onset of stickiness using a liquid droplet as a starting point.

Extracellular vesicles (EVs) are a family of small membrane vesicles that carry information about cells by which they are secreted. Growing interest in the role of EVs in intercellular communication, but also in using their diagnostic, prognostic and therapeutic potential in (bio) medical applications, demands for accurate assessment of their biochemical and physical properties. In this review, we provide an overview of available technologies for EV analysis by describing their working principles, assessing their utility in EV research and summarising their potential and limitations. To emphasise the innovations in EV analysis, we also highlight the unique possibilities of emerging technologies with high potential for further development.

Concentrated emulsions flowing through channels of varying widths are omnipresent in daily life, from dispensing mayonnaise in our kitchens to large-scale industrial processing of food, pharmaceuticals, etc. Local changes in channel geometry affect the stability of emulsions over length scales far beyond the droplet magnitude, for example through propagation of coalescence events called a coalescence avalanche. The underlying mechanisms are not well understood. In this work, we investigated the stability of concentrated emulsions flowing through microchannels featuring a constriction. We found that in this model geometry, the acceleration of the droplets induced near the entrance of the constriction triggers a coalescence event between the leading and the trailing droplet, but only above a critical droplet velocity. This separation-induced coalescence event, in turn, was found to trigger a coalescence avalanche in the upstream direction. Analysis of the flow behavior through particle image velocimetry and particle tracking velocimetry revealed that the propagation also follows a separation-induced coalescence mechanism, due to the retraction of the interface of the trailing droplet upon coalescence and the corresponding acceleration of the liquid inside the coalesced fluid thread. The constriction ratio was found to enhance the coalescence occurrence but did not affect the speed of coalescence propagation.

Self-assembly provides access to a variety of molecular materials, yet spatial control over structure formation remains difficult to achieve. Here we show how reaction–diffusion (RD) can be coupled to a molecular self-assembly process to generate macroscopic free-standing objects with control over shape, size, and functionality. In RD, two or more reactants diffuse from different positions to give rise to spatially defined structures on reaction. We demonstrate that RD can be used to locally control formation and self-assembly of hydrazone molecular gelators from their non-assembling precursors, leading to soft, free-standing hydrogel objects with sizes ranging from several hundred micrometres up to centimeters. Different chemical functionalities and gradients can easily be integrated in the hydrogel objects by using different reactants. Our methodology, together with the vast range of organic reactions and self-assembling building blocks, provides a general approach towards the programmed fabrication of soft microscale objects with controlled functionality and shape. Reaction-diffusion controls the spatial formation of many natural structures but is rarely applied to organic materials. Here, the authors couple reaction-diffusion to the self-assembly of a supramolecular gelator, introducing a strategy to forming soft, free-standing objects with controlled shape and functionality.

Thermal fluctuations have been shown to influence the thinning dynamics of planar thin liquid films, bringing predicted rupture times closer to experiments. Most liquid films in nature and industry are, however, non-planar. Thinning of such films not just results from the interplay between stabilizing surface tension forces and destabilizing van der Waals forces, but also from drainage due to curvature differences. This work explores the influence of thermal fluctuations on the dynamics of thin non-planar films subjected to drainage, with their dynamics governed by two parameters: the strength of thermal fluctuations, $\\unicode[STIX]{x1D703}$ , and the strength of drainage, $\\unicode[STIX]{x1D705}$ . For strong drainage ( $\\unicode[STIX]{x1D705}\\gg \\unicode[STIX]{x1D705}_{tr}$ ), we find that the film ruptures due to the formation of a local depression called a dimple that appears at the connection between the curved and flat parts of the film. For this dimple-dominated regime, the rupture time, $t_{r}$ , solely depends on $\\unicode[STIX]{x1D705}$ , according to the earlier reported scaling, $t_{r}\\sim \\unicode[STIX]{x1D705}^{-10/7}$ . By contrast, for weak drainage ( $\\unicode[STIX]{x1D705}\\ll \\unicode[STIX]{x1D705}_{tr}$ ), the film ruptures at a random location due to the spontaneous growth of fluctuations originating from thermal fluctuations. In this fluctuations-dominated regime, the rupture time solely depends on $\\unicode[STIX]{x1D703}$ as $t_{r}\\sim -(1/\\unicode[STIX]{x1D714}_{max})\\ln (\\sqrt{2\\unicode[STIX]{x1D703}})^{\\unicode[STIX]{x1D6FC}}$ , with $\\unicode[STIX]{x1D6FC}=1.15$ . This scaling is rationalized using linear stability theory, which yields $\\unicode[STIX]{x1D714}_{max}$ as the growth rate of the fastest-growing wave and $\\unicode[STIX]{x1D6FC}=1$ . These insights on if, when and how thermal fluctuations play a role are instrumental in predicting the dynamics and rupture time of non-flat draining thin films.

Separating medical radionuclides from their targets is one of the most critical steps in radiopharmaceutical production. Among many separation methods, solvent extraction has a lot of potential due to its simplicity, high selectivity, and high efficiency. Especially with the rise of polydimethylsiloxane (PDMS) microfluidic chips, this extraction process can take place in a simple and reproducible chip platform continuously and automatically. Furthermore, the microfluidic chips can be coated with metal-oxide nano-layers, increasing their resistance against the employed organic solvents. We fabricated such chips and demonstrated a parallel flow at a considerably large range of flow rates using the aqueous and organic solutions commonly used in medical radionuclide extraction. In our following case study for the separation of Ac-225 from radium with the chelator di(2-ethylhexyl)phosphoric acid (D2EHPA), a remarkable extraction efficiency of 97.1 % ± 1.5 % was reached within 1.8 seconds of contact time, while maintaining a near perfect phase separation of the aqueous and organic solutions. This method has the potential to enable automation of solvent extraction and faster target recycling, and serves, therefore, as a proof-of-concept for the applicability of microfluidic chip solvent extraction of (medical) radionuclides.

Safety and efficacy of coronary drug-eluting stents (DES) are often preclinically tested using healthy or minimally diseased swine. These generally show significant fibrotic neointima at follow-up, while in patients, incomplete healing is often observed. The aim of this study was to investigate neointima responses to DES in swine with significant coronary atherosclerosis. Adult familial hypercholesterolemic swine (n = 6) received a high fat diet to develop atherosclerosis. Serial OCT was performed before, directly after, and 28 days after DES implantation (n = 14 stents). Lumen, stent and plaque area, uncovered struts, neointima thickness and neointima type were analyzed for each frame and averaged per stent. Histology was performed to show differences in coronary atherosclerosis. A range of plaque size and severity was found, from healthy segments to lipid-rich plaques. Accordingly, neointima responses ranged from uncovered struts, to minimal neointima, to fibrotic neointima. Lower plaque burden resulted in a fibrotic neointima at follow-up, reminiscent of minimally diseased swine coronary models. In contrast, higher plaque burden resulted in minimal neointima and more uncovered struts at follow-up, similarly to patients’ responses. The presence of lipid-rich plaques resulted in more uncovered struts, which underscores the importance of advanced disease when performing safety and efficacy testing of DES.

Nature Communications 8: Article number:15137 (2017); Published: 5 June 2017; Updated 30 June 2017 In the original HTML version of this Article, which was published on 5 June 2017, the publication date was incorrectly given as 5 July 2017. This has now been corrected in the HTML; the PDF version of the paper was correct from the time of publication.

Sticking of particles has a tremendous impact on powder-processing industries, especially for hygroscopic amorphous powders. A wide variety of experimental methods has been developed to measure at what combinations of temperature and moisture content material becomes sticky. This review describes, for each method, how so-called stickiness curves are determined. As particle velocity also plays a key role, we classify the methods into static and dynamic stickiness tests. Static stickiness tests have limited particle motion during the conditioning step prior to the measurement. Thus, the obtained information is particularly useful in predicting the long-term behavior of powder during storage or in packaging. Dynamic stickiness tests involve significant particle motion during conditioning and measurement. Stickiness curves strongly depend on particle velocity, and the obtained information is highly relevant to the design and operation of powder production and processing equipment. Virtually all methods determine the onset of stickiness using powder as a starting point. Given the many industrial processes like spray drying that start from a liquid that may become sticky upon drying, future effort should focus on developing test methods that determine the onset of stickiness using a liquid droplet as a starting point.