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Multiscale Mechanics of Fibrin Polymer: Gel Stretching with Protein Unfolding and Loss of Water

Science  07 Aug 2009:
Vol. 325, Issue 5941, pp. 741-744
DOI: 10.1126/science.1172484

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<< Focusing on Fibrin

Vascular injury initiates biochemical reactions that cause the blood protein, fibrin, to polymerize and help to stop bleeding and support wound healing. Fibrin can also be a scaffold for thrombi that lead to cardiovascular diseases. To maintain homeostasis, fibrin clots must be stiff, plastic, and, so that the network can be decompsed, permeable. Brown et al. (p. 741) investigated the behavior of fibrin clots at the macroscopic, single-fiber, and molecular scale. At relatively low strains, fibers aligned and formed bundles, and at higher strains, protein unfolding occurred. An integrated model provides a molecular basis for fibrin elasticity and extensibility.

Abstract

Blood clots and thrombi consist primarily of a mesh of branched fibers made of the protein fibrin. We propose a molecular basis for the marked extensibility and negative compressibility of fibrin gels based on the structural and mechanical properties of clots at the network, fiber, and molecular levels. The force required to stretch a clot initially rises linearly and is accompanied by a dramatic decrease in clot volume and a peak in compressibility. These macroscopic transitions are accompanied by fiber alignment and bundling after forced protein unfolding. Constitutive models are developed to integrate observations at spatial scales that span six orders of magnitude and indicate that gel extensibility and expulsion of water are both manifestations of protein unfolding, which is not apparent in other matrix proteins such as collagen.

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