Abstract
The anterior cruciate ligament’s (ACL) mechanics is an important factor governing the ligament’s integrity and, hence, the knee joint’s response. Despite many investigations in this area, the cause and effect of injuries remain unclear or unknown. This may be due to the complexity of the direct link between macro- and micro-scale damage mechanisms. In the first part of this investigation, a three-dimensional coarse-grained model of collagen fibril (type I) was developed using a bottom-up approach to investigate deformation mechanisms under tensile testing. The output of this molecular level was used later to calibrate the parameters of a hierarchical multi-scale fibril-reinforced hyper-elastoplastic model of the ACL. Our model enabled us to determine the mechanical behavior of the ACL as a function of the basic response of the collagen molecules. Modeled elastic response and damage distribution were in good agreement with the reported measurements and computational investigations. Our results suggest that degradation of crosslink content dictates the loss of the stiffness of the fibrils and, hence, damage to the ACL. Therefore, the proposed computational frame is a promising tool that will allow new insights into the biomechanics of the ACL.
Highlights
Collagens type I that form fibrils are present as the main contributor to the integrity of the joint ligaments via a hierarchical extension over many length scales
Collagen is made up of amino-acid sequences organized in a polypeptide helix and combined into a set of three supercoils that produce a molecule of tropocollagen (TC) [1,2]
This paper presents a comprehensive work incorporating the degradation mechanism of the type I collagen on the nano-scale into a description of the mechanical behavior of the anterior cruciate ligament (ACL)
Summary
Collagens type I that form fibrils are present as the main contributor to the integrity of the joint ligaments via a hierarchical extension over many length scales. An X-ray diffraction experiment was employed to determine the topography of short peptide fragments representing the collagen molecules. This molecule was characterized by a weight of 300 KDa, length of 300 nm, and 1 to 2 nm diameter [3,4]. Most previous investigations were limited to nano- and micro-scales. The reasons behind this limitation were the intimate coupling between chemistry, biology, and mechanical deformation and their structural texture that involves specific implementation via different scales [20]
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