Nature designs tough collagen: Explaining the nanostructure of collagen fibrils
- Department of Civil and Environmental Engineering, Massachusetts Institute of Technology, 77 Massachusetts Avenue, Room 1-272, Cambridge, MA 02139
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Edited by L. B. Freund, Brown University, Providence, RI, and approved June 23, 2006 (received for review April 22, 2006)
Abstract
Collagen is a protein material with superior mechanical properties. It consists of collagen fibrils composed of a staggered array of ultra-long tropocollagen (TC) molecules. Theoretical and molecular modeling suggests that this natural design of collagen fibrils maximizes the strength and provides large energy dissipation during deformation, thus creating a tough and robust material. We find that the mechanics of collagen fibrils can be understood quantitatively in terms of two critical molecular length scales χS and χR that characterize when (i) deformation changes from homogeneous intermolecular shear to propagation of slip pulses and when (ii) covalent bonds within TC molecules begin to fracture, leading to brittle-like failure. The ratio χS/χR indicates which mechanism dominates deformation. Our modeling rigorously links the chemical properties of individual TC molecules to the macroscopic mechanical response of fibrils. The results help to explain why collagen fibers found in nature consist of TC molecules with lengths in the proximity of 300 nm and advance the understanding how collagen diseases that change intermolecular adhesion properties influence mechanical properties.
Footnotes
- †E-mail: mbuehler{at}mit.edu
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Author contributions: M.J.B. designed research, performed research, contributed new analytic tools, analyzed data, and wrote the paper.
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Conflict of interest statement: No conflicts declared.
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This paper was submitted directly (Track II) to the PNAS office.
- Abbreviations:
- TC,
- tropocollagen;
- BM,
- bimolecular.
Abbreviations
- © 2006 by The National Academy of Sciences of the USA
