In situ neutron scattering study of structural transitions in fibrin networks under shear deformation

Abstract

Small angle neutron scattering (SANS) is used to decipher the origin of the strain hardening in biopolymer networks by directly measuring the structural response of a fibrin gel to simple shear deformation. A special Couette shear cell is used to systematically probe the structural properties of a fibrin clot over strain values in the range of γ = 1–170%. The SANS results indicate that the strain hardening response of coarse fibrin gels occurs in two distinct regions having different structural and mechanical signatures that are separated by an intermediate strain softening regime. At low strains (γ < 10%) there is a measurable increase in the shear modulus upon the application of shear strain but there are no significant changes to the clot structure. At higher strain values (γ > 30%), a second strain-hardening regime is directly correlated to significant fiber alignment. The mean diameter of the fibers determined directly from two-dimensional fits to the anisotropic scattering data is found to decrease monotonically in the high-strain regime. The results suggest that the non-linear mechanical properties of fibrin clots are the result of a reduction of lateral entropic fluctuations at low strains and a transition between bending and stretching at higher strain values.