  Spherical cellular aggregates are in vitro systems to study the physical and
biophysical properties of tissues. We present a novel approach to characterize
the mechanical properties of cellular aggregates using micropipette aspiration
technique. We observe an aspiration in two distinct regimes, a fast elastic
deformation followed by a viscous flow. We develop a model based on this
viscoelastic behavior to deduce the surface tension, viscosity, and elastic
modulus. A major result is the increase of the surface tension with the applied
force, interpreted as an effect of cellular mechanosensing.
