Droplet microfluidics driven by gradients of confinement (original) (raw)

Interfacial tension driven open droplet microfluidics

2021

We developed an open channel droplet microfluidic system that autonomously generates droplets at low Ca (~10-4-10-3) by leveraging competing hydrostatic and capillary pressure. With only our open channel polytetrafluoroethylene (PTFE) device, pipettes, and commercially available carrier fluid, we produce hundreds of microliter droplets; tubing, electronics, or pumps are not required, making droplet technology feasible for research labs without external flow generators. Furthermore, we demonstrated conceptual applications that showcase the process of droplet generation, splitting, transport, incubation, mixing, and sorting in our system. Unlike conventional droplet microfluidics, the open nature of the device enables the use of physical tools such as tweezers and styli to directly access the system; with this, we developed a new method of droplet sorting and transfer that capitalizes on the Cheerios effect, the aggregation of buoyant objects along a liquid interface. Our platform off...

Micro/Nanodroplets in Microfluidic Devices

Springer Handbook of Nanotechnology, 2007

Fluid is often transported in the form of droplets in nature. From the formation of clouds to the condensation of dew on leaves, droplets are formed spontaneously in air, on solids and in immiscible fluids. In biological systems, droplets with lipid bilayer membranes are used to transport subnanoliter amounts of reagents between organelles, between cells, and between organs, in processes that control our day-today metabolic activities. The precision of such systems is self-evident and proves that dropletbased systems provide intrinsically efficient ways to perform controlled transport, reactions and signaling. This precision and efficiency can be utilized in many lab-on-a-chip applications by manipulating individual droplets using microfabricated force gradients. Complex segmented flow processes involving generating, fusing, splitting and sorting droplets have been developed to digitally control fluid volumes and concentrations to nanoliter levels. In this chapter, microfluidic techniques for manipulating droplets are reviewed and analyzed.

Droplet generation in a microchannel with a controllable deformable wall

Microfluidics and Nanofluidics, 2016

cal analysis and precise mixing of reagents (Sarrazin et al. 2007) and as ultrasound agents (Reznik et al. 2011). The uniformity in the size distribution of droplets is an important criterion to determine the quality of emulsion (Link et al. 2006). Droplet emulsions have unique flow characteristics including the variation of viscosity with shear rate and increased elasticity due to the surface tension provided by droplets. Initially, microdroplets were produced in bulk media using conventional methods including spray drying (Vehring et al. 2007), membrane emulsification (Charcosset et al. 2004), agitation (Lignel et al. 2014), large-scale blenders (Huebner et al. 2008) and high speed mixing (Sugiura et al. 2001). Although the coefficient of variation in the size of droplets can be reduced by using a homogenizer with high frequency, microdroplets produced by the above methods have large polydispersity. Later, microfluidic devices, which use external electric fields (Link et al. 2006), microinjectors and needles (Yang et al. 2010; Meesters et al.1992) were used for the emulsification process. However, simple microfluidic devices, which produce microdroplets with low polydispersity (Christopher and Anna 2007; Sajeesh et al. 2014; Surya et al. 2014), by exploiting the flow instabilities of two laminar immiscible fluids, paid significant attention. High-throughput droplet generation and ability to carry out biological and chemical reactions in nanolitre-sized droplets make the emulsification process in microfluidic devices very attractive. Different configurations of microchannel including T-junction (Christopher and Anna 2007; Gupta and Kumar 2010), double T-junction (Surya et al. 2014), flow focusing (Adzima and Velankar 2006; Sajeesh et al. 2014) and co-flowing (Umbanhowar et al. 2000) were widely used for the emulsification process.

Microfluidic Droplet Manipulations and Their Applications

Droplet microfluidics" enables the manipulation of discrete fluid packets in the form of microdroplets that provide numerous benefits for conducting biological and chemical assays. Among these benefits are a large reduction in the volume of reagent required for assays, the size of sample required, and the size of the equipment itself. Such technology also enhances the speed of biological and chemical assays by reducing the volumes over which processes such as heating, diffusion, and convective mixing occur. Once the droplets are generated, carefully designed droplet operations allow for the multiplexing of a large number of droplets to enable large-scale complex biological and chemical assays. In this chapter, four major unit operations in droplets are discussed: droplet fusion, droplet fission, mixing in droplets, and droplet sorting. Combined, these operations allow for much complexity in executing chemical reactions and biological assays at the microscale. A broad overview of potential applications for such technology is provided throughout. While much research effort has been focused on the development of these individual devices, far fewer attempts to integrate these components have been undertaken. A review of many microfluidic unit operation devices is provided here, along with the advantages and disadvantages of each approach for various applications.

Drop formation in non-planar microfluidic devices

Lab on a Chip, 2012

Microfluidic devices can be used to produce single or multiple emulsions with remarkably precise control of both the contents and size of the drops. Since each level of a multiple emulsion is formed by a distinct fluid stream, very efficient encapsulation of materials can be achieved. To obtain high throughput, these devices can be fabricated lithographically, allowing many devices to operate in parallel. However, to form multiple emulsions using a planar microfluidic device, the wettability of its surface must switch from hydrophobic to hydrophilic on the scale of micrometers where the drops are formed; this makes the fabrication of the devices very difficult. To overcome this constraint, we introduce non-planar microfluidic devices with graduated thicknesses; these can make drops even when their wetting properties do not favor drop formation. Nevertheless, the dependence of drop formation on the device geometry, the flow rates and the properties of the fluids, particularly in the case of unfavorable wetting, is very complex, making the successful design of these devices more difficult. Here we show that there exists a critical value of flow of the continuous phase above which drop formation occurs; this value decreases by two orders of magnitude as the wetting to the device wall of the continuous phase improves. We demonstrate how this new understanding can be used to optimize device design for efficient production of double or multiple emulsions.

Droplet Microfluidics for Fabrication of Non-Spherical Particles

Macromolecular Rapid Communications, 2009

We describe new developments for controlled fabrication of monodisperse non-spherical particles using droplet microfluidics. The high degree of control afforded by microfluidic technologies enables generation of single and multiple emulsion droplets. We show that these droplets can be transformed to non-spherical particles through further simple, spontaneous processing steps, including arrested coalescence, asymmetric polymer solidification, polymerization in microfluidic flow, and evaporation-driven clustering. These versatile and scalable microfluidic approaches can be used for producing large quantities of non-spherical particles that are monodisperse in both size and shape; these have great potential for commercial applications. . He received his B.Sc. and M.Sc. in chemical engineering at Department of Chemical Engineering, Tsinghua University in 1987 and 1993, respectively, and obtained his Ph.D. from Tokyo University (Japan) in 2000. He studied on fuel cell and mass transport mechanism in dense membranes during 2001-2002 as JST oversea researcher at Tokyo University and Tsinghua University, and worked as a visiting fellow in Harvard University (USA) during 2007-2008. His current research focuses on polymeric membranes and the application of membrane technology, especially in Vanadium Redox Battery (VRB) for mass electricity transfer and storage. He is director of the R&D Center for flow battery, located in Tsinghua University. Wang's primary research interests are in membrane science and engineering applications.

Micropipette-powered droplet based microfluidics

Biomicrofluidics, 2018

Droplet-based microfluidics, using water-in-oil emulsion droplets as micro-reactors, is becoming a widespread method for performing assays and especially in the cell biology field. Making a simple and highly portable system for creating emulsion droplets would help to continue the popularization of such a technique. Also, the ability to emulsify all the samples would strengthen this compartimenlization technique to handle samples with limited volume. Here, we propose a strategy of droplet formation that combines a classical flow-focusing microfluidic chip, which could be commercially available, with a standard laboratory adjustable micropipette. The micropipette is used as a negative pressure generator for controlling liquid flows. In that way, emulsification does neither require any electrical power supply nor a cumbersome device and functions with small liquid volumes. Droplet formation can be easily and safely performed in places with limited space, opening a wide range of applic...