jp8b00238_si_001.pdf (106.66 kB)
The Effects of the Interplay between Motor and Brownian Forces on the Rheology of Active Gels
journal contribution
posted on 2018-03-26, 00:00 authored by Andrés CórdobaActive
gels perform key mechanical roles inside the cell, such
as cell division, motion, and force sensing. The unique mechanical
properties required to perform such functions arise from the interactions
between molecular motors and semiflexible polymeric filaments. Molecular
motors can convert the energy released in the hydrolysis of ATP into
forces of up to piconewton magnitudes. Moreover, the polymeric filaments
that form active gels are flexible enough to respond to Brownian forces
but also stiff enough to support the large tensions induced by the
motor-generated forces. Brownian forces are expected to have a significant
effect especially at motor activities at which stable noncontractile in vitro active gels are prepared for rheological measurements.
Here, a microscopic mean-field theory of active gels originally formulated
in the limit of motor-dominated dynamics is extended to include Brownian
forces. In the model presented here, Brownian forces are included
accurately, at real room temperature, even in systems with high motor
activity. It is shown that a subtle interplay, or competition, between
motor-generated forces and Brownian forces has an important impact
on the mass transport and rheological properties of active gels. The
model predictions show that at low frequencies the dynamic modulus
of active gels is determined mostly by motor protein dynamics. However,
Brownian forces significantly increase the breadth of the relaxation
spectrum and can affect the shape of the dynamic modulus over a wide
frequency range even for ratios of motor to Brownian forces of more
than a hundred. Since the ratio between motor and Brownian forces
is sensitive to ATP concentration, the results presented here shed
some light on how the transient mechanical response of active gels
changes with varying ATP concentration.