基礎講座 電気泳動(Electrophoresis)

Intermolecular And Surface Forces

Fundamental and applied research in chemistry and biology benefits from opportunities provided by droplet-based microfluidic systems. These systems enable the miniaturization of reactions by compartmentalizing reactions in droplets of femoliter to microliter volumes. Compartmentalization in droplets provides rapid mixing of reagents, control of the timing of reactions on timescales from milliseconds to months, control of interfacial properties, and the ability to synthesize and transport solid reagents and products. Droplet-based microfluidics can help to enhance and accelerate chemical and biochemical screening, protein crystallization, enzymatic kinetics, and assays. Moreover, the control provided by droplets in microfluidic devices can lead to new scientific methods and insights.

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Reactions in Droplets in Microfluidic Channels

Droplet microfluidics generates and manipulates discrete droplets through immiscible multiphase flows inside microchannels Due to its remarkable advantages, droplet microfluidics bears significant value in an extremely wide range of area In this review, we provide a comprehensive and in-depth insight into droplet microfluidics, covering fundamental research from microfluidic chip fabrication and droplet generation to the applications of droplets in bio(chemical) analysis and materials generation The purpose of this review is to convey the fundamentals of droplet microfluidics, a critical analysis on its current status and challenges, and opinions on its future development We believe this review will promote communications among biology, chemistry, physics, and materials science

Emerging Droplet Microfluidics

Microdroplets in microfluidics offer a great number of opportunities in chemical and biological research. They provide a compartment in which species or reactions can be isolated, they are monodisperse and therefore suitable for quantitative studies, they offer the possibility to work with extremely small volumes, single cells, or single molecules, and are suitable for high-throughput experiments. The aim of this Review is to show the importance of these features in enabling new experiments in biology and chemistry. The recent advances in device fabrication are highlighted as are the remaining technological challenges. Examples are presented to show how compartmentalization, monodispersity, single-molecule sensitivity, and high throughput have been exploited in experiments that would have been extremely difficult outside the microfluidics platform.

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Microdroplets in microfluidics: an evolving platform for discoveries in chemistry and biology

In this work, we have systematically analyzed the scaling law of droplet formation by cross-flow shear method in T-junction microfluidic devices The droplet formation mechanisms can be distinguished by the capillary number for the continuous phase (Cac), which are the squeezing regime (Cac < 0002), dripping regime (001 < Cac < 03), and the transient regime (0002 < Cac< 001) Three corresponding correlations have been suggested in the different range of Cac In the dripping regime, we developed a modified capillary number for the continuous phase (Cac′) by considering the influence of growing droplet size on the continuous phase flow rate And the modified model could predict droplet diameter more accurately In the squeezing regime, the final plug length was contributed by the growth and ‘squeeze’ stages based on the observation of dynamic break-up process In the transient regime, we firstly suggested a mathematical model by considering the influences of the above two mechanisms The correlations should be very useful for the application of controlling droplet size in T-junction microfluidic devices

Correlations of droplet formation in T-junction microfluidic devices: from squeezing to dripping

Droplet microfluidics offers exquisite control over the flows of multiple fluids in microscale, enabling fabrication of advanced microparticles with precisely tunable structures and compositions in a high throughput manner The combination of these remarkable features with proper materials and fabrication methods has enabled high efficiency, direct encapsulation of actives in microparticles whose features and functionalities can be well controlled These microparticles have great potential in a wide range of bio-related applications including drug delivery, cell-laden matrices, biosensors and even as artificial cells In this review, we briefly summarize the materials, fabrication methods, and microparticle structures produced with droplet microfluidics We also provide a comprehensive overview of their recent uses in biomedical applications Finally, we discuss the existing challenges and perspectives to promote the future development of these engineered microparticles

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Microfluidic fabrication of microparticles for biomedical applications

In our previous work, a new flow route was developed—a so-called perpendicular shear force–induced droplet formation—in a self-designed simple T-junction microchannel device. In this work, the crossflowing rupture technique was used to prepare monodisperse droplets in a similar device and successfully prepared monodisperse droplets ranging from 50 to 500 μm with polydispersity index (σ) values of <2%. Two kinds of flow patterns of plug flow and drop flow in the T-junction microchannels could be formed. By changes in the surfactant concentration, the interfacial tension and the wetting ability varied, and the disordered or ordered two-phase flow patterns could be controlled. Evolutions of the contact angle of the oil in contact with the wall surface were explained by the adsorption of surfactant molecules to the solid–liquid interface. The increase of continuous phase flow rate and viscosity resulted in the decrease of the droplet size, and the droplet size was correlated with capillary number Ca. By comparing the variation range of drop size using the two methods, it was found that the method of perpendicular flow-induced droplet formation can control the drop size over a much wider range. © 2006 American Institute of Chemical Engineers AIChE J, 2006

Preparation of highly monodisperse droplet in a T-junction microfluidic device

Perpendicular flow is used to induce oil droplet breakup by using a capillary as water phase flow channel. It is a new route to produce monodisperse emulsions. The wetting properties of the fluids on the walls are exceedingly important parameters. Depending on the oil and water flow rates, different spatial distributions of the two phases as laminar, plugs, cobbles and drops, are obtained. The effects of two-phase flow rates on plugs and drop size are studied, and the different droplet formation mechanisms of plug flow and drop flow are discussed. Two quantitative equations utilized to predict the droplet size are developed.

Shear force induced monodisperse droplet formation in a microfluidic device by controlling wetting properties

This letter presents a simple way to prepare monodisperse O/W and W/O emulsions in the same T-junction microfluidic device just by changing the wetting properties of the microchannel wall with different surfactants Highly uniform droplets ranging from 50 to 400 μm with a polydispersity index (σ) value of less than 2% were successfully prepared With the change in surfactants and surfactant concentrations, the interfacial tension and the wetting properties varied, and disordered or ordered two-phase flow patterns could be controllable Monodisperse O/W and W/O emulsions were prepared under the action of a cross-flowing shear force or a perpendicular shear force by using an oil solution with 01−20 wt % Span 80 and an aqueous solution with 01−20 wt % Tween 20 as a continuous-phase flow, respectively It gives a controllable method of preparing O/W and W/O emulsions in the same microfluidic device

Jianhong Xu

Papers

Correlations of droplet formation in T-junction microfluidic devices: from squeezing to dripping

Microfluidic fabrication of microparticles for biomedical applications

Preparation of highly monodisperse droplet in a T-junction microfluidic device

Shear force induced monodisperse droplet formation in a microfluidic device by controlling wetting properties

Controllable preparation of monodisperse O/W and W/O emulsions in the same microfluidic device.