Microchannel comparison with membrane

Figure 20.16 Influence of emulsification method on droplet size distribution (dispersed phase content 1 vol.%) [73]. MF high pressure homogenization (Microfluidizer) in comparison with SPG membrane, microchannel and a-Al203 membrane emulsification. The span value is a measure of the width of the droplet size distribution. It decreases when distributions become narrower.

The dispersion creation requites application of a pressure difference, AF, between the phase to be dispersed and the phase in which dispersion takes place through the pores. This AF has two contributions (1) capUlary pressure AFcr defined by Eq. (26.4) and (2) viscous flow pressure drop APflow through the capillary, which is the membrane pore (usually calculated from Hagen-PoiseuiUe law). The wetting characteristics of the pore material as well as the membrane channel are important for the emulsification process, especially, the nature of the emulsion produced. An earlier review of membrane-based emulsification is available in Joscelyne and Tragard (2000). A comparison of membrane emulsification with that through porous microchannel plate is provided in Lambrich and Schubert (2005). 

Due to the small volumes and feature sizes, reaction rates are found to be quite different in the microbiosensor system in comparison to their macro counter part. Most of this is due to the fact that diffusion is not the limiting factor in a reaction any longer. For example, the diffusion time of a particle with a diffusion coefficient = 10 m s is 15 min to travel a distance of 1 mm, but only 10 s to travel 100 /rm and only 0.1 s to travel 10/rm [37]. Therefore, DNA hybridization reactions, antibody-antigen binding events, and enzyme—substrate catalytic reactions take place in a fraction of the time required earlier. DNA hybridization can be accomplished in a matter of seconds in a microchannel system, while it takes in the order of an hour when employing standard Northern or Southern Blotting techniques with a piece of nylon membrane soaking in several milliliters of hybridization solution. 

LPC is known to cause hemolysis. This is because LPC incorporates very easily in the erythrocyte cell membrane and weakens the erythrocyte itself. However, this hemolysis depends on the level of LPC concentration. Under low-LPC concentration, hemolysis will not occur. We evaluated the deformability of the erythrocytes when treated with low-concentration DHA-LPC and the DHA-PC by measuring the flow speed of the erythrocytes going through a microchannel array called MC fan (Hosokawa et al. 1995, Nojima et al. 1995). As comparison, flow speed of soy PC-and LPC-incorporated erythrocytes was also measured. 

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