Revealing the molecular origins of fibrin’s elastomeric properties by in situ X-ray scattering

Abstract

Fibrin is an elastomeric protein forming highly extensible fiber networks that provide the scaffold of blood clots. Here we reveal the molecular mechanisms that explain the large extensibility of fibrin networks by performingin situsmall angle X-ray scattering measurements while applying a shear deformation. We simultaneously measure shear-induced alignment of the fibers and changes in their axially ordered molecular packing structure. We show that fibrin networks exhibit distinct structural responses that set in consecutively as the shear strain is increased. They exhibit an entropic response at small strains (<5%), followed by progressive fiber alignment (>25% strain) and finally changes in the fiber packing structure at high strain (>100%). Stretching reduces the fiber packing order and slightly increases the axial periodicity, indicative of molecular unfolding. However, the axial periodicity changes only by 0.7%, much less than the 80% length increase of the fibers, indicating that fiber elongation mainly stems from uncoiling of the natively disordered αC-peptide linkers that laterally bond the molecules. Upon removal of the load, the network structure returns to the original isotropic state, but the fiber structure becomes more ordered and adopts a smaller packing periodicity compared to the original state. We conclude that the hierarchical packing structure of fibrin fibers, with built-in disorder, makes the fibers extensible and allows for mechanical annealing. Our results provide a basis for interpreting the molecular basis of haemostatic and thrombotic disorders associated with clotting and provide inspiration to design resilient bio-mimicking materials.

A systematic review and comparison of automated tools for quantification of fibrous networks

“…Using synthetic images with known fiber dispersion confirmed that most of the tools, except for the Directionality plugin, performed well in the quantification of fiber alignment. We recommend a tool that returns a nematic order parameter, since this provides a sensitive measure between 0 and 1 that can be linked directly to theoretical models that connect fiber alignment to mechanical properties 34,58 . When also taking into account the ease of use of the tools and the possibility to adapt parameters, our preferences to quantify fiber alignment in fibrin networks go towards OrientationJ 27,59 (ImageJ plugin), CurveAlign 28 (MATLAB-based standalone application), or FiberFit 32 (Python-based standalone application).…”

“…Supplementary Figure V shows the 50 images with their corresponding nematic order parameter (S) as calculated by OrientationJ. OrientationJ was used as reference because of its proven sensitivity for fiber alignment 34 .…”

Modeling the extracellular matrix in cell migration and morphogenesis: a guide for the curious biologist

“…Common methods to investigate the mechanical properties of cells within the ECM are tensile testing (Yang et al, 2015), and rheometry (Vos et al, 2020). The former is more common when investigating tissues like skin and bone, and the latter is more convenient when studying reconstituted systems or samples that are particularly soft.…”