title: Stress-strain experiments on individual collagen fibrils.
abstract: Collagen, a molecule consisting of three braided protein helices, is the primary building block of many biological tissues including bone, tendon, cartilage, and skin. Staggered arrays of collagen molecules form fibrils, which arrange into higher-ordered structures such as fibers and fascicles. Because collagen plays a crucial role in determining the mechanical properties of these tissues, significant theoretical research is directed toward developing models of the stiffness, strength, and toughness of collagen molecules and fibrils. Experimental data to guide the development of these models, however, are sparse and limited to small strain response. Using a microelectromechanical systems platform to test partially hydrated collagen fibrils under uniaxial tension, we obtained quantitative, reproducible mechanical measurements of the stress-strain curve of type I collagen fibrils, with diameters ranging from 150-470 nm. The fibrils showed a small strain (epsilon < 0.09) modulus of 0.86 +/- 0.45 GPa. Fibrils tested to strains as high as 100% demonstrated strain softening (sigma(yield) = 0.22 +/- 0.14 GPa; epsilon(yield) = 0.21 +/- 0.13) and strain hardening, time-dependent recoverable residual strain, dehydration-induced embrittlement, and susceptibility to cyclic fatigue. The results suggest that the stress-strain behavior of collagen fibrils is dictated by global characteristic dimensions as well as internal structure.
authors.affiliation: Department of Biomedical Engineering and Department of Materials Science and Engineering, Case Western Reserve University, Cleveland, Ohio 44106, USA.
authors.forename: Zhilei L
authors.initials: ZL
authors.lastname: Shen
authors.forename: Mohammad Reza
authors.initials: MR
authors.lastname: Dodge
authors.forename: Harold
authors.initials: H
authors.lastname: Kahn
authors.forename: Roberto
authors.initials: R
authors.lastname: Ballarini
authors.forename: Steven J
authors.initials: SJ
authors.lastname: Eppell
mesh_terms: D000818:Animals; D001696:Biomechanical Phenomena / Q000295:instrumentation; D024042:Collagen Type I / Q000737:chemistry* / Q000648:ultrastructure; D048016:Cucumaria / Q000737:chemistry*; D008855:Microscopy, Electron, Scanning
chemical_list: D024042:Collagen Type I