Collagen Fibril Diameter Distribution of Sheep Anterior Cruciate Ligament

Abstract

The anterior cruciate ligament (ACL) tissue is a soft tissue connecting the femur and tibia at the knee joint and demonstrates a limited capacity for self-regeneration due to its low vascularity. The currently available clinical procedures are unable to fully restore damaged ACL tissue, and tissue engineering can offer options with a potential of restoring the torn/ruptured ACL by using biomimetic constructs that are similar to native tissue in terms of structure, composition, and functions. However, a model substrate to understand how the ACL cells regenerate the injured tissue is still not available. In this study, it is hypothesized that the nanofiber-based model substrate with bimodal and unimodal fiber diameter distributions will mimic the diameter distribution of collagen fibrils seen in healthy and injured sheep ACL, respectively. The aims were to (i) create an ACL injury in a sheep ACL by applying extensional force to rupture the healthy ACL tissue, (ii) measure the collagen fibril diameter distributions of healthy and injured ACL, (iii) fabricate polycaprolactone (PCL) nanofiber-based model constructs using electrospinning with diameter distributions similar to healthy and injured ACL tissue, and (iv) measure mechanical properties of ACL tissue and PCL electrospun constructs. The results showed that the fiber diameter distributions of PCL electrospun constructs and those of the healthy and injured ACL tissues were similar. The novelty in this investigation is that the collagen fibril diameter distribution of healthy and injured sheep ACL tissues was reported for the first time. The study is significant because it aims to create a model construct to solve an important orthopedic-related clinical problem affecting millions of people globally. The model construct fabricated in this work is expected to have an important impact on ACL regeneration efforts.

Braided biomimetic PCL grafts for anterior cruciate ligament repair and regeneration

“…The collagen diameter distribution of human ACL also showed a similar behavior, which decreased from 75 nm (20-185 nm) to 71 nm (20-290 nm) after injury. As also reported previously, the collagens of sheep and rat ACL showed two peaks of around 100 and 250 nm, and 60 and 160 nm, respectively, before the injury, which changed to one peak of around 100 nm when injured [18,25]. The diameter distribution of collagens of healthy and injured rabbit ACLs were investigated in this study.…”

“…Our findings have shown that the healthy rabbit ACL tissue exhibited a straight (aligned) pattern of collagens, which changed when the collagens were torn or ruptured. Similarly, the injured rat [18], bovine [3], sheep [25] and human [26] ACL also exhibited a disorientated collagen alignment.…”

“…Initially, in immature state of development, most ligaments exhibit unimodal aligned fibril structure, which, later changes to a more bimodal pattern [16]. Our research group measured diameter distribution of mature sheep [17], rat [18], and bovine [3], and found that they all possessed a bimodal fibril diameter distribution.…”

“…Previously cleaned joints were attached to the jaws of the device, and after the application of a preliminary load of approximately 5 N, the Tibia-ACL-Femur complex was strained uniaxially at a deformation rate of 5 mm min −1 until its total rupture (n = 4) [17,18]. After the mechanical test, ruptured ACLs were used as injured ACL tissues to measure the diameter distribution collagen fibrils.…”

“…Electrospinning is a convenient approach that can create continuous ultrathin polymeric random and aligned fibers [20,21]. In our previous studies, bovine, sheep, and rat ACL collagen fibrils were examined, and biomimetic scaffolds were fabricated using electrospinning [3,17,18]. As a material of construction for the grafts poly (ε-caprolactone) (PCL) was selected mainly because of its biocompatible and biodegradable nature.…”