Fabrication of micro-spinbars with controllable aspect ratios using a simple fluidic device for fluid mixing

Micro-spinbars with uniform aspect ratios were fabricated from gelatin using a simple fluidic device based on water-in-oil emulsion for fluid mixing. Aqueous gelatin solution containing magnetic nanoparticles and toluene solution were used as the discontinuous and continuous phases, respectively. The gelatin droplets with uniform aspect ratios formed within the glass capillary tube of the fluidic device and flew into the cold collection phase (toluene). Due to the feature of sol-gel transition of the gelatin solution with respect to temperature, the gelatin droplets maintained their original shape in the cold collection phase during water evaporation. The aspect ratios of the micro-spinbars were finely controlled from 1 to 5 by simply changing the flow rate of the continuous phase. Their potential applications for active fluid mixing were demonstrated in a glass slide and Y-shaped small device.