Cell
cortices are responsible for the resilience and morphological
dynamics of cells. Measuring their mechanical properties is impeded
by contributions from other filament types, organelles, and the crowded
cytoplasm. We established a versatile concept for the precise assessment
of cortical viscoelasticity based on force cycle experiments paired
with continuum mechanics. Apical cell membranes of confluent MDCK
II cells were deposited on porous substrates and locally deformed.
Force cycles could be described with a time-dependent area compressibility
modulus obeying the same power law as employed for whole cells. The
reduced fluidity of apical cell membranes compared to living cells
could partially be restored by reactivating myosin motors. A comparison
with artificial minimal actin cortices (MACs) reveals lower stiffness
and higher fluidity attributed to missing cross-links in MACs.
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