Full length articleRevealing the molecular origins of fibrin's elastomeric properties by in situ X-ray scattering
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1. Introduction
In Nature, many examples are found of elastomeric materials made of protein fibers. Prominent elastomeric proteins in the human body are the intermediate filament cytoskeleton of cells [1], elastin and fibronectin in tissues [2,3], and fibrin networks in blood clots and wounds [4]. These proteins all form filaments that can reversibly stretch up to tensile strains of around 150% and resist strains of several hundred percent without breaking [5,6]. Two main molecular mechanisms have been
Fibrin network assembly
Human plasma fibrinogen (Plasminogen, von Willebrand Factor and Fibronectin depleted) and human α-thrombin were obtained in lyophilized form from Enzyme Research Laboratories (Swansea, United Kingdom). All chemicals were obtained from Sigma Aldrich (Zwijndrecht, The Netherlands). Fibrinogen (lyophilized in 20 mM sodium citrate-HCl buffer at pH 7.4) was dissolved in water at 37 °C for 15 min to its original concentration (ca. 13 mg/ml) and extensively dialysed against fibrin buffer containing
Shear-induced structural changes at the network and fiber level
In order to probe the effects of shear strain on fibrin network structure, we combined rheology experiments on fibrin networks in a Couette cell with in situ SAXS measurements (Fig. 1a,b). We subjected the networks to a stepwise increase in shear strain γ interspersed with intervals where the strain was brought back to zero to test for reversibility (Fig. 1c). Fig. 1d shows the background-subtracted scattering images of a 4 mg/ml fibrin gel at strains of 0%, 100% and 300%, and the same network
Discussion
The aim of our work was to elucidate how fibrin gels obtain their remarkable strain-stiffening behaviour, which spans a wide range of shear strains up to 250% (Fig. 3d). We therefore combined macroscopic measurements of the shear rheology of fibrin networks with in situ structural measurements by SAXS. We found that the networks exhibit multiple distinct mechanical regimes that are closely correlated with distinct changes in network structure on different length scales.
At low strains (γ < 25%),
Conclusion
We performed X-ray measurements coupled with shear rheology to reveal the structural mechanisms that mediate the nonlinear elastic response and large resilience of fibrin networks. We showed that increasing levels of shear strain induce distinct changes in elasticity that coincide with a sequence of structural responses. There were no observable changes in the fiber or network structure up to strains of around 25%, consistent with entropic elasticity. Above 25% strain the fibers progressively
Declaration of Competing Interest
The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
Acknowledgements
We gratefully acknowledge Paul Kouwer (Radboud University Nijmegen, the Netherlands) for kindly lending us his TA HR2-rheometer during beamtime BM26-02–797. We also acknowledge the beamline staff, in particular Daniel Hermida Merino, Giuseppe Portale and Wim Bras, of BM26 at the ESRF for their help with the experiments and data analysis. We thank Bela Mulder (AMOLF, Amsterdam, the Netherlands) for discussions on the calculation of the nematic order parameter, and Karin Jansen and Lucia Baldauf
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2021, Acta BiomaterialiaCitation Excerpt :Compared to shear loading, tensile deformation quickly aligns fibers in the XY plane – 20% tensile strain showed similar fiber alignment to 150% shear strain. Our findings are consistent with results from a previous study on fibrin structure under shear deformation (in the Couette geometry) using X-ray scattering by Vos et al[21]. In that study, the authors also found no clear evidence of secondary structural changes for shear deformation up to 300%.