Entropic forces generated by grafted semiflexible polymers

The entropic force exerted by the Brownian fluctuations of a
grafted semiflexible polymer upon a rigid smooth wall are
calculated both analytically and by Monte Carlo simulations. Such
forces are thought to play an important role for several cellular
phenomena, in particular, the physics of
actin-polymerization-driven cell motility and movement of bacteria
like Listeria. In the stiff limit, where the persistence length of
the polymer is larger than its contour length, we find that the
entropic force shows scaling behavior. We identify the
characteristic length scales and the explicit form of the scaling
functions. In certain asymptotic regimes, we give simple analytical
expressions which describe the full results to a very high
numerical accuracy. Depending on the constraints imposed on the
transverse fluctuations of the filament, there are characteristic
differences in the functional form of the entropic forces. In a
two-dimensional geometry, the entropic force exhibits a marked
peak.