  The actin cytoskeleton in living cells has many types of crosslinkers. The
mechanical interplay between these different crosslinker types is an open issue
in cytoskeletal mechanics. We develop a framework to study the cooperativity
and redundancy in the mechanics of filamentous networks with two types of
crosslinkers: crosslinkers that allow free rotations of filaments and
crosslinkers that do not. The framework consists of numerical simulations and
an effective medium theory on a percolating triangular lattice. We find that
the introduction of angle-constraining crosslinkers significantly lowers the
filament concentrations required for these networks to attain mechanical
integrity. This cooperative effect also enhances the stiffness of the network
and suppresses non-affine deformations at a fixed filament concentration. We
further find that semiflexible networks with only freely-rotating crosslinks
are mechanically very similar to compositely crosslinked flexible networks with
both networks exhibiting the same scaling behavior. We show that the network
mechanics can either be redundant or cooperative depending on the relative
energy scale of filament bending to the energy stored in the angle-constraining
crosslinkers, and the relative concentration of crosslinkers. Our results may
have implications for understanding the role of multiple crosslinkers even in a
system without bundle formation or other structural motifs.
