State of Utah Center of Excellence for Biomedical Microfluidics
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| Techniques for End Effect Reduction in FFF This work introduces a novel approach for the minimization of fluidic end effects, which give rise to band broadening and zone dispersion in FFF channels. In a typical FFF channel, due to the presence of the triangular end pieces, the sample entering at the same instance takes different paths in the channel as shown in Figure 1 and there is a considerable time lag between the samples that travel through center and along the edges. This phenomenon leads to a considerable zonal dispersion of the sample and subsequent increase in the plate height and in turn loss in separation efficiency of the device [1]. In this work, we have incorporated an array of constrictions in the path of fluid to optimize the fluid path and to obtain a more uniform particle distribution in the X-Y direction (Figure 1).
The flow simulation was done using FIDAP (Fluent Inc.), a CFD (computational fluid dynamics) analysis software. In this work, both two-dimensional and three-dimensional flow analysis were carried out. A variety of constrictions were employed to determine the optimum constriction geometry, which in turn were incorporated in the test channels. The distances traveled by the particles at a given time were simulated for the channels with obstructions and without obstructions. A plot of the standard deviation of the distances traveled by the particles at a given time (Figure 2) demonstrated that the standard deviation for the channel with obstruction was less in comparison to the channels without obstruction. This indicates the reduction in band broadening for the previous case.
A combination of photolithography, softlithography and micromolding was done to fabricate m-FFF channels from PDMS substrate. Colored dye sample was passed through the FFF channel and CCD camera was used to take the images at regular intervals of time and different locations along the length of channel. The results are encouraging and correlate well with modeling results. Related Papers: Jung Woo Kim, Himanshu J Sant and Bruce K Gale, "Reduction of Microfluidic End Effects In Micro-Field Flow Fractionation Channels," in Proc. of MicroTAS 2003, Squaw Valley, California, October 5-9, 2003. Sreenivas Rao, Himanshu Sant, and Bruce K. Gale, "Minimization of End Effects in Field Flow Fractionation," in Proc. Of the 10th International Symposium on Field Flow Fractionation, Amsterdam, Netherlands, July 2-5, 2002. |
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