Fig. 1. Fluid pumping performance of MDCK-II epithelium.

a A schematic representation of the Micro-fluidic Kidney Pump (MFKP). b A DIC image of the MDCK-II monolayer. White dots indicate pores. Scale bar = 10 mm. c Longitudinal section of the device. Black arrows indicate fluid flux. d A schematic of a polarized epithelium. e Dashed rectangle shows zoomed schematic of fluid flow in the microcapillary (MC) and a mm scale (green). f A snapshot of the MFKP inside an incubator for time-lapsed videography. Scale bar = 1 cm. g The height of fluid in the MC is plotted as function of time for MDCK-II epithelium in MFKP. Compared to static condition (CT, red) (n = 11, N = 3, devices, biological replicates), the fluid pumping action changed when the apical medium is switched to 20% hypo-osmotic condition (OSMO, green) (n = 11, N = 3). Shaded area is the standard error of the mean (SEM). h Pump performance curve (PPC) of MDCK-II epithelium, showing the measured trans-epithelial fluid flux (J) (apical to basal) as a function of the hydrostatic pressure gradient (ΔP = P_basal − P_apical). J₀ is the fluid flux at zero pressure gradient (ΔP = 0) and ΔP* is the stall pressure when J = 0. Both J₀ and ΔP* change in the hypo-osmotic condition. Shaded area is the SEM. Comparison of J₀ (i) and ΔP* (j) for MDCK-II epithelium in the static condition (CT, red) (n = 11, N = 3, devices, biological replicates,) and 20% apical hypo-osmotic condition (OSMO, green) (n = 11, N = 3, devices, biological replicates, p = 0.0002). ****p < 0.0001 and ***p < 0.001 (two-tailed Mann–Whitney t-test). k Immunofluorescence (IF) images showing nuclei (blue), F-actin (green), NKA (red) and E-cadherin (purple) in MDCK-II epithelium in the MFKP. Scale bar = 25 mm. For the box plots, lower and upper box boundaries 25th and 75th percentiles, respectively, line inside box median, lower and upper error lines 10th and 90th percentiles, filled circles indicate data points, respectively.