  The multiscale behavior of the individual fibrin fibers and fibrin clots is
modeled by coupling atomistic simulation data and microscopic experimental
data. We propose a protofibril element made up of nonlinear spring network,
constructed based on the molecular simulation and atomic force microscopy
results to simulate the force extension behavior of fibrin fibers. This new
network model also accounts for the complex interaction of protofibrils with
each other, effect of presence of solvent, Coulombic attraction and other
binding forces. The network model is applied to simulate the force extension
behavior of single fibrin fiber from atomic force microscopy experiments and
shows good agreement. Thus validated fibrin fiber network model is then
combined with a modified version of Arruda-Boyce eight chain model to estimate
the force extension behavior of continuum level fibrin clot, which shows very
good correlation. The results show that this network model is able to predict
the behavior of fibrin fibers as well as fibrin clot at small strains, large
strains and even closer to the break strain. We use the network model to
explain why the fibrin clots and fibers doesn't behave like a worm like chain,
instead behaves like a nonlinear spring.
