title: Characterization via atomic force microscopy of discrete plasticity in collagen fibrils from mechanically overloaded tendons: Nano-scale structural changes mimic rope failure.
abstract: Tendons exposed to tensile overload show a structural alteration at the fibril scale termed discrete plasticity. Serial kinks appear along individual collagen fibrils that are susceptible to enzymatic digestion and are thermally unstable. Using atomic force microscopy we mapped the topography and mechanical properties in dehydrated and hydrated states of 25 control fibrils and 25 fibrils displaying periodic kinks, extracted from overloaded bovine tail tendons. Using the measured modulus of the hydrated fibrils as a probe of molecular density, we observed a non-linear negative correlation between molecular density and kink density of individual fibrils. This is accompanied by an increase in water uptake with kink density and a doubling of the coefficient of variation of the modulus between kinked, and control fibrils. The mechanical property maps of kinked collagen fibrils show radial heterogeneity that can be modeled as a high-density core surrounded by a low-density shell. The core of the fibril contains the kink structures characteristic of discrete plasticity; separated by inter-kink regions, which often retain the D-banding structure. We propose that the shell and kink structures mimic characteristic damage motifs observed in laid rope strands.
authors.affiliation: Department of Physics and Atmospheric Science, Dalhousie University, Halifax, NS, Canada.
authors.forename: Samuel J
authors.initials: SJ
authors.lastname: Baldwin
authors.affiliation: Department of Physics and Atmospheric Science, Dalhousie University, Halifax, NS, Canada; School of Biomedical Engineering and Department of Applied Oral Sciences, Dalhousie University, 5981 University Avenue, PO Box 15000, Halifax, NS, Canada B3H 4R2.
authors.forename: Laurent
authors.initials: L
authors.lastname: Kreplak
authors.affiliation: School of Biomedical Engineering and Department of Applied Oral Sciences, Dalhousie University, 5981 University Avenue, PO Box 15000, Halifax, NS, Canada B3H 4R2. Electronic address: michael.lee@dal.ca.
authors.forename: J Michael
authors.initials: JM
authors.lastname: Lee
mesh_terms: D000818:Animals; D001696:Biomechanical Phenomena; D002417:Cattle; D003094:Collagen / Q000648:ultrastructure*; D018625:Microscopy, Atomic Force; D013710:Tendons / Q000503:physiopathology*
chemical_list: D003094:Collagen
keywords: Atomic force microscopy; Collagen fibrils; Discrete plasticity; Molecular organization