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Micrometer-scale monodisperse droplets are produced to generate nanowalled supramolecular microcapsules using microfluidics for high reproducibility and high-throughput manipulation, efficient material consumption, and control over hierarchical structure, shape, and size. In this study, an optimized microfluidic droplet generation technique and a unique liquid–liquid interfacial polymerization method were applied to fabricate the monodisperse polyrotaxane–based supramolecular microcapsules in a fast and simple way. To minimize the uncertainty due to droplet volume variation, the inlet pressures were supplied from the same source while lowering the interfacial tension and the main channel hydrodynamic resistance, which are critical for high monodispersity. The target polyrotaxane network (PN) was simply formed at the interface of the water and oil phases in ultra-monodisperse microdroplets via the cucurbit[6]uril (CB6)-catalyzed azide–alkyne cycloaddition (CB6-AAC) reaction between azido- and alkyne-functionalized tetraphenylporphyrin monomers (TPP-4AZ and TPP-4AL). The thickness of the interfacially assembled PN microcapsules was 20 nm as analyzed by cross-sectional TEM and TEM-EDX techniques. The resultant water-in-oil PN microcapsules were highly monodisperse in size and able to retain target molecules. Here, rhodamine 6G (Rh6G)-loaded PN microcapsules were fabricated, and the release rate of the Rh6G cargo was investigated over time for controlled drug release applications.

Despite the importance of droplet monodispersity, a universal methodology for high monodispersity droplet generation does not exist yet. We have recently demonstrated that unlike the conventional method of droplet generation, applying an identical pressure from a single source makes the microfluidic droplet system immune to the external fluctuations that originate from the imperfection of the flow source. In this work, we show that our method is universal and applicable to other common microfluidic devices and flow sources. We applied this method to flow-focusing and coflow devices that are commonly used for high-frequency microdroplet generation. In addition to the pressure pump, we used a syringe pump to show that our method is applicable to flow rate controllable systems as well. We compared the monodispersity of droplets formed by the conventional methods and the novel method explained in this work. © 2022 The Authors

In this article, we report a method to damp microfluidic hydrodynamic fluctuations caused by flow sources. We demonstrate that compliance of elastomeric off-chip tubings can be used to damp fluctuations and lead to steady flow rates. We analyze the whole microfluidic system using electrical circuit analogies, and demonstrate that off-chip compliances are significant, especially for displacement pump driven systems. We apply this hydrodynamic damping method to microfluidic droplet generation. Our results show that highly monodisperse microdroplets can be obtained by syringe pump driven systems utilizing this damping effect. We reached a coefficient of variation of 0.39% for the microdroplet area using a standard T-junction geometry. Additionally, we demonstrated that pressure pumps inherently use this effect, and have so far led the high performances reported in the literature in terms of droplet monodispersity. The presented off-chip hydrodynamic damping method is not only low-cost and practical, but can also be used in elastomeric and rigid microchannels without need to introduce additional components to the fluidic circuit. This project was supported by the Scientific and Technological Research Council of Turkey (TÜBİTAK, Project No. 215E086 ). Dr. Elnaz Alizadeh Haghighi is thankful to the support of TÜBİTAK BİDEB-2216 Postdoctoral Research Fellowship . The authors also thank Dr. Amar S. Basu for providing DMV software.

Droplet microfluidic systems are becoming routine in advanced biochemical studies such as single cell gene expression, immuno profiling, precise nucleic acid quantification (dPCR) and particle synthesis. For all these applications, ensuring droplet monodispersity is critical to minimize the uncertainty due to droplet volume variation. Despite the wide usage of droplet-based microfluidic systems, the limit of monodispersity for droplet generation systems is still unknown. Here, we present an analytical approach that takes into account all the system dynamics and internal/external factors that disturb monodisper-sity. Interestingly, we are able to model the dynamics of a segmented two-phase flow system using a single-phase flow analogy, electron flow, in electrical circuits. We offer a unique solution and design guidelines to ensure ultra-monodisperse droplet generation. Our analytical conclusions are experimentally verified using a T-junction droplet generator. Equally importantly, we show the limiting experimental factors for reaching the theoretical maximum of monodispersity. (C) 2020 Elsevier Ltd. All rights reserved.

In this paper, a magnetohydrodynamic micropump with side-walled electrodes has been studied. Micropump was fabricated using MEMS technology and applied Lorentz force induced as a result of interaction between an applied electric field and a perpendicular magnetic field to pump the continuous steady, incompressible and fully developed laminar conducting fluid. Since the micro-pump dimensions are comparable to that of the fluid molecules, the assumption of the continuum fluid theory is no longer justified. Hence, micropolar fluid theory is considered in this study. Application of the theory of fluid dynamics and electromagnetic led to derivation of governing equations of the corresponding momentum and angular momentum. The governing equations and their associated boundary conditions were first cast into dimensionless form. The resulting partial differential equations were solved numerically using finite difference technique and the profiles of the velocity and microrotations are obtained. The results for a special case were compared with the experimental ones and they showed a good agreement with each other. Furthermore, the effects of coupling number, Hartmann number and micropolar parameter on the velocity, microrotation and flow rate are discussed.

In this study the transformed theory is applied to derive the dielectric characteristics of cells, considering the electrorotation (ER) peak frequency. In current studies, estimations of low frequency, which are credible for the values less than 1 mS/m for medium conductivity, are used to obtain the corresponding permittivity and conductivity of cells. Unlike the presented works, the transformed theory applies the comprehensive statement for corresponding permittivity and conductivity of cells. In the transformed theory, the membrane and interior characteristics could be obtained from the high and the low frequencies of peak ER, for all values of conductivity of medium. Characteristics of cells are obtained via optimization of an equation for the conductivity of medium regarding the peak ER frequency. The optimization process is performed applying genetic algorithm due to its swift adaptation to the problem and faster convergence.

Viscous damping is a dominant source of energy dissipation in laterally oscillating micro-structures. In micro-resonators in which the characteristic dimensions are comparable to the dimensions of the fluid molecules, the assumption of the continuum fluid theory is no longer justified and the use of micro-polar fluid theory is indispensable. In this paper a mathematical model was presented in order to predict the viscous fluid damping in a laterally oscillating finger of a micro-resonator considering micro-polar fluid theory. The coupled governing partial differential equations of motion for the vibration of the finger and the micro-polar fluid field have been derived. Considering spin and no-spin boundary conditions, the related shape functions for the fluid field were presented. The obtained governing differential equations with time varying boundary conditions have been transformed to an enhanced form with homogenous boundary conditions and have been discretized using a Galerkin-based reduced order model. The effects of physical properties of the micro-polar fluid and geometrical parameters of the oscillating structure on the damping ratio of the system have been investigated.