Biophysical Society Thematic Meeting | Riga 2026

Active and Responsive Soft Matter: From Biological to Engineered Systems

Poster Abstracts

7-POS Board 7 THREE-DIMENSIONAL DYNAMICS OF EPITHELIAL MONOLAYERS Silja Borring Låstad 1 ; Nigar Abbasova 1,2 ; Thomas Combriat 1,3 ; Dag Kristian Dysthe 1 ; 1 University of Oslo, Department of Physics, Oslo, Norway 2 University of Copenhagen, Niels Bohr Institute, Copenhagen, Denmark 3 University of Oslo, Department of Medicine, Oslo, Norway Collective migration and pulsatile flows in epithelial monolayers are commonly quantified using projected area, implicitly assuming constant cell volume and prism-shaped cells. These 2.5D assumptions ignore the other dynamics that must accompany every density fluctuation in confluent space-filling tissues, but have remained inaccessible to the labelling- and intensity based techniques used to date. Here, we use simultaneous time-lapse quantitative phase imaging (QPI) to obtain spatially and temporally resolved maps of height, volume, and dry mass in MDCK epithelial monolayers under physiological conditions. We find that: (i) Cellular dry mass concentration is uniform to within ~4.5 % cross the monolayer and over time, even during large amplitude pulsations, ruling out fluid transport as the dominant driver of height and area dynamics. (ii) Mean monolayer height rises from ~5.5 to ~9 µm and mean cell volume falls by ~20 % as cell density doubles, evidence of contact inhibition of cell size rather than constant cell volume, while cell heights vary up to 30 % oscillate with a ~5 h period and follow gamma shaped distributions. (iii) At cellular scales, both segmented-cell tracking and a continuum mass flux analysis show that projected cell volume is not conserved; mass conservation is recovered only after coarse-graining over ~ 2 cell diameters and ~0.6 h. Two non-exclusive mechanisms may explain this: non-prismatic cell geometry produces apparent volume fluctuations even at constant true volume, and a residual signal is consistent with periodic mass exchange between cells and the ECM. Each of these results requires simultaneous, time-resolved access to height and dry mass at the cellular scale and is therefore newly visible with QPI applied to epithelial monolayers. Together they question the common 2.5D assumptions of prism-shaped cells constant volume, plug-flow kinematics, and argue that quantitative continuum and cell-based models of epithelial dynamics must incorporate dry-mass-density regulation and 3D cell geometry.

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