Structure of high density fibrin networks probed with neutron scattering and rheology

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The structural and mechanical properties of coarse fibrin networks formed in D2O solutions are investigated over a wide range of concentrations (1–40 mg mL−1). For the first time, this range includes concentrations that are relevant to those found in in vivo blood clots. Small angle neutron scattering (SANS) and ultra small angle neutron scattering (USANS) are used to seamlessly characterize the structure over length scales ranging from 1 nm to several micrometres. Using invariant and Guinier analyses the internal volume fraction of protein within the fiber and their bulk average radius are determined directly. The network properties of fibrin clots are also characterized using a model for fractal structures. The network scale features are shown to be highly dependent on the initial fibrinogen concentration while the average fiber radius is only weakly dependent on this parameter. These results demonstrate the usefulness of combining SANS and USANS as characterization tools for complex biopolymer systems such as fibrin. The linear viscoelastic modulus of fibrin gels is related to the concentration by a power law equation that is valid over the entire range. In contrast, the non-linear rheology of dense networks is altered from the monotonic strain hardening response that is found at lower concentrations. This demonstrates the need for thorough characterization of fibrin at concentrations relevant to those of thrombi formed in vivo.