## Dynamics of initial cell spreading

###
With Alain Duperray

In [Biophys J 2011], we show
that the initial spreading of cells is governed by the rate at which gains of
adhesion energy can deform the actin cortex, e.g. by breakage of crosslinks.

Just after contact with a substrate, cells are found to spread at a
rate described by a sequence of power-laws, which is independent of the
spatial scale (that is, it scales with the cell size). Thus the
observed dynamics can only be explained by cell-scale phenomena, which
are of mechanical nature. This means that spreading rate can be used
to test apparent rheological properties of the live cell at a
time-scale of 10 to 100 seconds, which is the relevant time scale of a
large number of intriguing active dynamics of cells.

By testing a
number of simplified models, I have demonstrated that *the leading
order balance that governs this dynamics is between the adhesion force
and the dissipation incurred by the actin cortex during the shape
changes required by cell spreading.* This observed dissipation is
the trace of several dissipative phenomena, which include the energetic
cost of cross-linking and uncross-linking the actin bundles and viscous
drag.

Here is a poster presenting this for the conference *Cell Mechanics* in Amsterdam (October 2011).