The microfluidic device. (a) In a PDMS-based microfluidic device three aqueous components are merged together, (b) while the flow rates of two of them are alternated in a periodic way. This way microfluidic drops with tunable content are produced in a flow focusing channel design. (c) The drops pass a serpentine channel that ensures fast mixing of the drop content which is due to the recirculating flow and chaotic advection within the moving drops. (d) In a drop basin, the drops are densified and excess drops are rejected to six outlet channels. At the bottom of the basin, there is a connection to a long channel which is called collecting channel. (e) At first, oil flows through this collecting channel into the basin so that no drop can enter. The inversion of the flow direction of the oil through the collecting channel triggers the collection of the drops in a controlled manner. (h) To determine the drop content afterwards, the drop collection process is recorded. (f) Thefirst part of the collecting channel is a delay line which ensures smooth drop collection. (g) Finally, the drops reach the drop storage which is a region with constrictions at the channel walls.8 Due to this confinement, the drops are immobilized when the overall flow rates in the device are stopped.
Determination of the fluorescein concentration in a drop series. (a) Comparison of the input and measured fluorescein concentration in drops as a function of time. Using triangular input pump profiles (violet stars), the measured concentration profile in the drops has the shape of a sine function (green circles). (b) The delay time is determined by a regression method. The measured (green circles) and calculated (blue triangles) concentrations in the drops agree well. (c)Measured fluorescein concentration (bins of 3 μM width) plotted over the calculated values. The straight line has a slope of 1. Error bars are not shown when smaller than symbols.
Vimentin networks in drops. Top: fluorescence micrographs (inverted gray scale, adjusted for displaying purposes) of vimentin networks at different magnesium concentrations . Bottom: intensity histograms of the fluorescence micrographs (total fluorescence intensity in each drop normalized to 105). Different network morphologies result in different standard deviations of the fluorescence intensity distribution: (a) Freely fluctuating networks show a narrow distribution, since the overall intensity is comparatively homogeneous. (b) The distribution of networks that have aggregated is broader leading to a higher value for . (c) Networks that are fully compacted to an intensely fluorescing aggregate show the largest standard deviation. The drop diameters are 40 μm.
Dependence of vimentin network morphology on the magnesium concentration. (a) For a vimentin-containing drop series, the standard deviation of the gray scale values is compared to the magnesium concentration for each drop. (b) Binning of the results (1 mM intervals) leads to an averaged standard deviation as a function of , shown here for two independent experiments. These curves show the ability of magnesium to induce network compaction of vimentin networks.
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