posted on 2020-07-28, 14:35authored byElizabeth
P. DeBenedictis, Yao Zhang, Sinan Keten
Fibrous
networks of semiflexible polymers are prevalent in biological
materials such as connective tissues, the cytoskeleton, and biofilm
extracellular matrices. While the mechanical behavior of permanently
cross-linked fibrous networks has been studied in detail, much less
is understood about how bundles and physical entanglements influence
the response of semiflexible polymer networks. Here we use coarse-grained
molecular dynamics simulations to ascertain how fiber bending rigidity,
interfiber cohesion, and network architecture influence the tensile
mechanical behavior of these systems. We find that the features of
self-assembled networks, namely mean bundle thicknesses, link lengths,
and number of links and nodes, depend strongly on fiber properties
as well as assembly conditions. Tensile tests show that high strength
networks have high densities arising from high cohesive energy and/or
low persistence lengths. Adjusting the cohesive potential has the
greatest impact on mechanical response, influencing bundle thickness
and therefore both network cohesive and bending energies. Changes
in network architecture such as fiber alignment, bundle thickening,
and link extension also contribute to stiffening. When stretched to
fracture, networks show a power law scaling for ultimate tensile strength
with both fiber persistence length and cohesive potential. Furthermore,
similar exponential scaling of the stress−strain relationship
is seen during stiffening of networks. These results shed light on
the competing influences of fiber stiffness, cohesion, architecture,
and structural evolution in entangled semiflexible polymer networks,
particularly underlining the significance of bundle formation and
thickening as an advantageous mechanism for generating mechanically
robust networks.