This article reviews the application of electric circuit methods for the analysis of pressure-driven microfluidic networks with an emphasis on concentration- and flow-dependent systems. The application of circuit methods to microfluidics is based on the analogous behaviour of hydraulic and electric circuits with correlations of pressure to voltage, volumetric flow rate to current, and hydraulic to electric resistance. Circuit analysis enables rapid predictions of pressure-driven laminar flow in microchannels and is very useful for designing complex microfluidic networks in advance of fabrication. This article provides a comprehensive overview of the physics of pressure-driven laminar flow, the formal analogy between electric and hydraulic circuits, applications of circuit theory to microfluidic network-based devices, recent development and applications of concentration- and flow-dependent microfluidic networks, and promising future applications. The lab-on-a-chip (LOC) and microfluidics community will gain insightful ideas and practical design strategies for developing unique microfluidic network-based devices to address a broad range of biological, chemical, pharmaceutical, and other scientific and technical challenges.

Design of pressure-driven microfluidic networks using electric circuit analogy

We develop a systematic coarse-graining procedure for modeling red blood cells (RBCs) using arguments based on mean-field theory. The three-dimensional RBC membrane model takes into account the bending energy, in-plane shear energy, and constraints of fixed surface area and fixed enclosed volume. The coarse-graining procedure is general, it can be used for arbitrary level of coarse-graining and does not employ any fitting parameters. The sensitivity of the coarse-grained model is investigated and its behavior is validated against available experimental data and in dissipative particle dynamics (DPD) simulations of RBCs in capillary and shear flows.

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Accurate coarse-grained modeling of red blood cells.

A Comprehensive Review on Emulsions and Emulsion Stability in Chemical and Energy Industries

Red blood cells (RBCs) possess a unique capacity for undergoing cellular deformation to navigate across various human microcirculation vessels, enabling them to pass through capillaries that are smaller than their diameter and to carry out their role as gas carriers between blood and tissues. Since there is growing evidence that red blood cell deformability is impaired in some pathological conditions, measurement of RBC deformability has been the focus of numerous studies over the past decades. Nevertheless, reports on healthy and pathological RBCs are currently limited and, in many cases, are not expressed in terms of well-defined cell membrane parameters such as elasticity and viscosity. Hence, it is often difficult to integrate these results into the basic understanding of RBC behaviour, as well as into clinical applications. The aim of this review is to summarize currently available reports on RBC deformability and to highlight its association with various human diseases such as hereditary disorders (e.g., spherocytosis, elliptocytosis, ovalocytosis, and stomatocytosis), metabolic disorders (e.g., diabetes, hypercholesterolemia, obesity), adenosine triphosphate-induced membrane changes, oxidative stress, and paroxysmal nocturnal hemoglobinuria. Microfluidic techniques have been identified as the key to develop state-of-the-art dynamic experimental models for elucidating the significance of RBC membrane alterations in pathological conditions and the role that such alterations play in the microvasculature flow dynamics.

Biomechanical properties of red blood cells in health and disease towards microfluidics.

Background The encapsulation and liberation technologies for bioactive food ingredients has opened the door to innovative and significant applications in food, nutrition, and pharmaceutical fields via the employment of nanotechnology. Coating materials in the formulation of nanocapsules are mostly lipid, carbohydrate or protein-based. The nanoencapsulation procedure in the food and nutraceutical areas involves the incorporation of natural ingredients, such as volatile additives, polyphenols, aromas, colors, vitamins, enzymes, oils and antimicrobial compounds in nano-sized capsules, providing the opportunities for higher stability and retention for the sensitive molecules against decomposition and loss of nutritional value during the production process or delivery along with offering a sustained release. Scope and approach This review highlights the most recent nanoencapsulation advancements along with the formulations mainly based on lipid components; i.e., nanoemulsions, nanoliposomes and nanostructured lipid carriers in terms of preparation strategies, their classes, composition, attributes, analysis techniques, worked examples, and implementation in functional foods along with their upcoming evolution and future trends. Key findings and conclusions Nanocapsules with lipid formulations are possible alternatives to micro-sized carriers owing to the enormous surface area and the following features which they offer, such as improved solubility, high bioavailability and establishment of sustained liberation of the nanoencapsulated food constituents and nutraceuticals.

Lipid nano scale cargos for the protection and delivery of food bioactive ingredients and nutraceuticals

Phase inversion emulsification: Current understanding and applications.

In this work, a microfluidic system to investigate the flow behavior of red blood cells in a microcirculation-mimicking network of PDMS microchannels with thickness comparable to cell size is presented. We provide the first quantitative description of cell velocity and shape as a function of the applied pressure drop in such devices. Based on these results, a novel methodology to measure cell membrane viscoelastic properties in converging/diverging flow is developed, and the results are in good agreement with data from the literature. In particular, in the diverging channel the effect of RBC surface viscosity is dominant with respect to shear elasticity. Possible applications include measurements of cell deformability in pathological samples, where reliable methods are still lacking.

Microfluidics analysis of red blood cell membrane viscoelasticity

Emulsions in porous media: From single droplet behavior to applications for oil recovery

Stable oil/water emulsions are usually obtained by using mixtures of different surfactants. Such systems display synergistic interface stabilizing effects, which have not been fully elucidated yet. Moreover, in many applications surfactants are added at concentrations well above their critical micellar concentration (CMC), and this regime has not been thoroughly explored in the literature as well. Here, we investigate oil/water emulsions through oil/water interfacial tension using two common non-ionic surfactants, Tween 80 and Span 20, in the concentration range C (0.3–1 wt%) well above their respective CMCs. Mesoscale molecular simulations coupled interfacial tensiometry experiments to characterise these interfaces at a molecular level. Interfacial tension γ was measured by a pendant drop technique. Coarse-grained calculations provided a microscopic view of the interface at the molecular level (i.e. surfactant arrangement, interface thickness), and were employed to extend the study to those surfactant concentrations where experiments could hardly provide reliable data, if any. We found a significant synergistic effect between Tween 80 and Span 20, with low molecular weight Span molecules occupying free spaces between the much larger, bulky Tween compounds. The surfactant intermolecular interactions could be associated to a striking decrease of interfacial tension in going from pure surfactants to a mixture at the same total weight concentration. Furthermore, the interface was found to exhibit a spatial inhomogeneity with a “patch-like” organisation, reminiscent of microphase separation. Our results show that the proposed, combined experimental/in silico approach provides relevant insights for several industrial applications, such as emulsion stability and oil spill remediation.

Valentina Preziosi

Papers

Phase inversion emulsification: Current understanding and applications.

Microfluidics analysis of red blood cell membrane viscoelasticity

Emulsions in porous media: From single droplet behavior to applications for oil recovery

Interfacial tension of oil/water emulsions with mixed non-ionic surfactants: comparison between experiments and molecular simulations

Droplet deformation under confined Poiseuille flow.