title: Influence of cross-link structure, density and mechanical properties in the mesoscale deformation mechanisms of collagen fibrils.
abstract: Collagen is a ubiquitous protein with remarkable mechanical properties. It is highly elastic, shows large fracture strength and enables substantial energy dissipation during deformation. Most of the connective tissue in humans consists of collagen fibrils composed of a staggered array of tropocollagen molecules, which are connected by intermolecular cross-links. In this study, we report a three-dimensional coarse-grained model of collagen and analyze the influence of enzymatic cross-links on the mechanics of collagen fibrils. Two representatives immature and mature cross-links are implemented in the mesoscale model using a bottom-up approach. By varying the number, type and mechanical properties of cross-links in the fibrils and performing tensile test on the models, we systematically investigate the deformation mechanisms of cross-linked collagen fibrils. We find that cross-linked fibrils exhibit a three phase behavior, which agrees closer with experimental results than what was obtained using previous models. The fibril mechanical response is characterized by: (i) an initial elastic deformation corresponding to the collagen molecule uncoiling, (ii) a linear regime dominated by molecule sliding and (iii) the second stiffer elastic regime related to the stretching of the backbone of the tropocollagen molecules until the fibril ruptures. Our results suggest that both cross-link density and type dictate the stiffness of large deformation regime by increasing the number of interconnected molecules while cross-links mechanical properties determine the failure strain and strength of the fibril. These findings reveal that cross-links play an essential role in creating an interconnected fibrillar material of tunable toughness and strength.
authors.affiliation: Laboratory for Atomistic and Molecular Mechanics (LAMM), Department of Civil and Environmental Engineering, Massachusetts Institute of Technology, 77 Massachusetts Ave., Room 1-290, Cambridge, 02139 MA, USA.
authors.forename: Baptiste
authors.initials: B
authors.lastname: Depalle
authors.affiliation: Laboratory for Atomistic and Molecular Mechanics (LAMM), Department of Civil and Environmental Engineering, Massachusetts Institute of Technology, 77 Massachusetts Ave., Room 1-290, Cambridge, 02139 MA, USA.
authors.forename: Zhao
authors.initials: Z
authors.lastname: Qin
authors.affiliation: Department of Mechanical and Industrial Engineering, Northeastern University, Boston, MA, USA.
authors.forename: Sandra J
authors.initials: SJ
authors.lastname: Shefelbine
authors.affiliation: Laboratory for Atomistic and Molecular Mechanics (LAMM), Department of Civil and Environmental Engineering, Massachusetts Institute of Technology, 77 Massachusetts Ave., Room 1-290, Cambridge, 02139 MA, USA; Center for Computational Engineering, Massachusetts Institute of Technology, 77 Massachusetts, Ave. Cambridge, MA 02139, USA; Center for Materials Science and Engineering, Massachusetts Institute of Technology, 77 Massachusetts Ave., Cambridge, MA 02139, USA. Electronic address: mbuehler@mit.edu.
authors.forename: Markus J
authors.initials: MJ
authors.lastname: Buehler
mesh_terms: D001696:Biomechanical Phenomena; D003094:Collagen / Q000737:chemistry*; D006801:Humans; D055595:Mechanical Phenomena; D056004:Molecular Dynamics Simulation; D011487:Protein Conformation
chemical_list: D003094:Collagen
keywords: Coarse-grained model; Collagen; Cross-links; Fibril; Fracture; Molecular dynamics; Nanomechanics