## 1 Introduction  
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]. 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]. The TC molecules aggregate into fibrils via intermolecular adhesion and covalent crosslinks at their ends with respect to well-specified axial and center-to-center locations offset [5, 6, 7]. The mechanical behavior of the collagen structures has received significant attention from molecular to aggregate level, either experimentally [8, 9, 10, 11, 12, 13] or computationally via molecular dynamic (MD) simulation [14, 15, 16, 17, 18, 19, 20, 21]. A clear agreement has been reported that these superstructures lead to helpful mechanical behavior characterized by high strength and extensibility of up to 100% strain before breakage [22]. However, 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].  
On the larger scale (millimeter and upscale), the soft tissues' mechanical behavior was considered either elastic, basic hyperelastic, hyperelastic, or viscoelastic fiber-reinforcedcomposite materials [23]. Most of these constitutive models were limited to the elastic behavior and have been able to reproduce the mechanical response of the ligaments measured during experimental tensile testing [24; 25; 26; 27; 28; 29]. A very limited number of studies considered softening elasticity behavior yet restricted to the macro-mechanical scale [30; 31]. On the side of the model application, the anterior cruciate ligament (ACL) was the focus of most of the developed computational frames since it is more prone to injury than any other knee soft tissue. Recent investigations have shown that around 50% of lower limb ligament injuries involve the ACL [32]. ACL damage's pathogenesis and pathophysiological under-pinnings were well connected to the molecular level [33; 34]. This process of damage was described microscopically as collagen degradation [21]. Thereafter, exploring how molecular-level interactions combine, including micro-degradation mechanism, to create a tissue-level mechanical response of collagenous materials is a potential path for the advancement of ACL injury or trauma treatments.  
The principal aim of this work was to highlight the link between ACL molecular structure and its aggregate mechanical behavior. At one extreme, such a link uses molecular dynamic simulation to characterize the fibril structure properties as a function of crosslink degradation. At the other extreme, the link uses a multilevel hyper-elastoplastic fibril-reinforced model to simultaneously investigate how changes in the fibril structure are manifested at the ligament level. We hypothesized that the integrity of the fibril plays a remarkable role in the expression of ACL macro-damage.