Hydrodynamically focused channels

Mixer type Hydrodynamic focusing crossinjection micro Channel width 10 pm... 

Transverse IEF was also conducted in a pressure-driven flow for BSA and soybean lectin separation on-chip [1040], Here, Pd electrodes were used (in preference to Au) because of the non-gassing character of Pd. In addition, the protein sample was sandwiched between two buffer streams and was prevented from direct contact with the channel wall (and hence the electrode), a process akin to hydrodynamic focusing [1040],... 

The laminar flow restriction and small dimensions of microfluidic devices have been exploited to expose different portions of a single cell to different chemical environments. A method developed by Whitesides and coworkers utilized hydrodynamic focusing on a microfluidic platform to selectively label portions of a cell with different dyes (Figure 32.15). Laminar fluid flow confined the dye solution to particular regions of the channel despite being in contact with streams containing... 

FIGURE 44.24 Channel structure with the sample inlet, S, and the hydrodynamically focusing buffer inlet, B, together with with the valve-less switching inputs G1 and G2. 

The efficiency of mixing in microfluidic devices is another important feature to consider, as in hydrodynamic focusing, the fluid stream to be mixed globally described as dispersed phase, flowing along the central microfluidics channel, is confined into a narrow stream delimited by the two adjacent streams at higher flow rates. 

A. Jahn, W. Vreeland, M. Gaitan, and L. Locascio, Controlled vesicle self-assembly in microfluidic channels with hydrodynamic focusing, Journal of the American Chemical Society, 126, 2674-2675, 2004. 

Hydrodynamic focusing A process in which a fluid stream is first surrounded by a second fluid and then narrowed to a thin stream by a narrowing of the channel. 

Droplets are formed by shear stress or a pressure drop in an in-channel continuous platform. The two basic configurations for droplet formation are shown in Fig. 4. The cross-junction configuration is similar to that for hydrodynamic focusing. The carrier fluid enters the channel from the middle inlet, while the droplet liquids join from both sides (Fig. 4a). The T-junction configuration lets the droplet liquids join perpendicular to the carrier flow (Fig. 4b). The formation behavior of droplets depends on the capillary number, which represents the ratio between the friction force and the surface tension in a two-phase system ... 

Figure 5 Scanning small-angle X-ray scattering and diffraction in a hydrodynamic focusing device. A solution of negatively charged double-stranded DNA molecules is hydrodynamically focused by solutions of positively charged dendrimers. Different spatial positions in the outlet channel correspond to different concentration ratios of the reaction partners, which can be seen by the position dependant SAXS 2D-pattern.

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