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Science 7 August 2009:
Vol. 325. no. 5941, pp. 741 - 744
DOI: 10.1126/science.1172484
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Reports

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

André E. X. Brown,1,2 Rustem I. Litvinov,3 Dennis E. Discher,2,4 Prashant K. Purohit,5 John W. Weisel3,*

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.

1 Department of Physics and Astronomy, University of Pennsylvania, Philadelphia, PA 19104, USA.
2 Nano/Bio Interface Center, University of Pennsylvania, Philadelphia, PA 19104, USA.
3 Department of Cell and Developmental Biology, University of Pennsylvania School of Medicine, Philadelphia, PA 19104, USA.
4 Graduate Groups in Physics and Cell Biology and Physiology, University of Pennsylvania, Philadelphia, PA 19104, USA.
5 Department of Mechanical Engineering and Applied Mechanics, University of Pennsylvania, Philadelphia, PA 19104, USA.

* To whom correspondence should be addressed. E-mail: weisel{at}mail.med.upenn.edu

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