Geometry of the microfluidic chips used in this study: (a) the large microfluidic chip; (b) the small microfluidic chip; and (c) the detailed geometry of the chips. Note that part (c) shows an enlarged image of the dotted square in part (a). (d) A schematic diagram of the microfluidic chip test set-up (drawn not to scale). DPT indicates the differential pressure transducer. A 1 mm thick lower PDMS without a pattern was attached to the slide glass, and a 3 mm thick upper PDMS with an etched channel pattern was then overlapped on the lower PDMS