Sheath flow forming by using twisted micro-channel

Abstract

Flow cytometers have been widely used to characterize biological cells statistically. Moreover, complicated sample pre- and post- processing methods such as separation, staining, and sorting of cells are combined with various analyzers have been demonstrated. In order to improve the usability, flow cytometer and pre- and post- function might be integrated into one micro-fluidic system. Soft-lithography with Polydimetylsiloxane (PDMS) is a powerful fabrication technique to make those complicated micro-fluidic structures. However the process has a substantial weak point. It is not available for making 3-dimensional focusing channel which is necessary to form smooth sheath flow. Then, we propose a new structure to generate 3-dimesional focusing flow by using the unique material property of PDMS; “easily bent and twisted”. We developed a twisted micro-channel in order to form a sheath flow in an integrated micro-fluidic system using PDMS. The new device has a central straight channel and two parts of 2-dimensional merging channel. It is twisted 90 degrees in between the first part and the second part. Sheath flow forming was predicted by using numerical simulation. The micro-channel configuration (width, length etc.) were designed to form an isotropic focusing flow. A unique evaluation method to predict sheath flow formation was proposed and used to characterize the sheath flow by distribution of particle velocity at the micro-channel junctions.