Intermolecular Slip Mechanism in Tropocollagen Nanofibrils

摘要

Collagen is the most important structural protein in the animal kingdom and is responsible for the strength and integrity of many tissues like bone, teeth, cartilage and tendons. The mechanical properties of these tissues are determined by their hierarchical structure. However, how each level contributes to the overall properties of collagenous tissues, and how individual hierarchical levels interact, remains poorly understood. Furthermore, despite extensive experimental and computational studies including both the single molecule and macro-scale levels, few studies have focused on the level of collagen fibrils. Here we report a detailed study of the shear interaction between two tropocollagen molecules, a major mechanism that contributes to the fibril mechanical behavior. Using steered molecular dynamics (SMD) simulations in explicit solvent, we model the slip of two tropocollagen molecules at varying pulling rates. We find that the adhesion strength is highly sensitive to the pulling rate, and that it converges to a value of 10.12 pN/Angstrom for vanishing loading rates. We find that intermolecular H-bonds play a key role in determining the resistance against slip. Our results provide quantitative details on this mechanism of load transmission inside collagen fibrils and fibers, which is crucial for the development of constitutive models of collagenous tissues at larger hierarchical levels. Such constitutive models of collagenous tissue mechanics have many applications, ranging from development of bio-inspired materials to studies in tissue engineering. By incorporating pathological collagen mutations, these studies could advance our knowledge of mechanisms underlying important collagen-related diseases like Osteogenesis Imperfecta or Ehlers-Danlos Syndrome.