Change in Collagen Fibril Diameter Distribution of Bovine Anterior Cruciate Ligament upon Injury Can Be Mimicked in a Nanostructured Scaffold

Abstract

More than 200,000 people are suffering from Anterior Cruciate Ligament (ACL) related injuries each year in the US. There is an unmet clinical demand for improving biological attachment between grafts and the host tissue in addition to providing mechanical support. For biological graft integration, it is important to provide a physiologically feasible environment for the host cells to enable them to perform their duties. However, behavior of cells during ACL healing and the mechanism of ACL healing is not fully understood partly due to the absence of appropriate environment to test cell behavior both in vitro and in vivo. This study aims at (i) investigating the change in fibril diameter of bovine ACL tissue upon injury and (ii) fabricating nanofiber-based scaffolds to represent the morphology and structure of healthy and injured ACL tissues. We hypothesized that distribution and mean diameter of ACL fibrils will be altered upon injury. Findings revealed that the collagen fibril diameter distribution of bovine ACL changed from bimodal to unimodal upon injury with subsequent decrease in mean diameter. Polycaprolactone (PCL) scaffold fiber diameter distribution exhibited similar bimodal and unimodal distribution behavior to qualitatively represent the cases of healthy and injured ACL, respectively. The native ACL tissue demonstrated comparable modulus values only with the aligned bimodal PCL scaffolds. There was significant difference between mechanical properties of aligned bimodal and unaligned unimodal PCL scaffolds. We believe that the results obtained from measurements of diameter of collagen fibrils of native bovine ACL tissue can serve as a benchmark for scaffold design.

A biomimetic synthetic nanofiber-based model for anterior cruciate ligament regeneration

“…Previous investigations on the collagen fibril diameter of healthy ACL tissue clearly demonstrate the presence of two peaks in the healthy human ( Zhu et al, 2012 ), rabbit ( Hart et al, 1999 ) and bovine ACL ( Beisbayeva et al, 2021 ) tissues. However, the distribution of the collagen fibril diameter in health and after injury has not been reported for these species except for bovine that was investigated by our group.…”

“…When the knee is stretched, the posterolateral bundle will get tight and the anteromedial bundle will relax depending on the viscoelastic and biomechanical properties of the ACL, which are controlled mainly by the collagen fibrils ( Petersen and Zantop, 2007 ). The ACL is positioned diagonally at the center of the knee and a tear or rupture of the collagen fibrils of the ACL results in structural and morphological changes mainly in the form of a variation in the diameter distribution of collagen fibrils and a reduction in the mean diameter ( Ochi et al, 1999 ; Beisbayeva et al, 2021 ). This can lead to a decrease in mechanical resistance to force, and instability in the joint, which can, then, be followed by tears to the meniscus as well as initiation of osteoarthritis ( Zantop et al, 2006 ).…”

“…However, the distribution of the collagen fibril diameter in health and after injury has not been reported for these species except for bovine that was investigated by our group. The collagen fibril diameter distribution of healthy bovine ACL demonstrated peaks at 73.3 ± 11.5 nm and 213 ± 11.5 nm which then disappeared, upon injury, to form a single peak at 100 ± 20 nm, with a decrease in the mean diameter ( Beisbayeva et al, 2021 ). For a broader aim at generating a generalizable behavior for the ACL fibril diameter distribution of other species in health and injury, this study reports the characterization of rat ACL collagen fibril diameter distribution before and after injury.…”

“…Given the nanometer scale of the collagen fibrils in ACL ( Neurath and Stofft, 1992 ; Beisbayeva et al, 2021 ), nanofiber-based synthetic grafts can add biomimicry to the regenerative engineering efforts of ACL reconstruction because of their architectural similarities to the extracellular matrix, as well as their adaptable chemical and physical properties for influencing cell response and behavior ( Ashammakhi et al, 2012 ; Han et al, 2021 ).…”

“…However, the challenge with the electrospinning is the creation of controlled ranges in both nanofiber and microfiber scales to mimic not only the diameter range but also the distribution of diameters in the desired range. In our previous efforts, we investigated the possibility of mimicking the range of collagen fibrils seen in bovine ACL tissue using polycaprolactone (PCL) as the material of construction of the synthetic models for ACL regeneration ( Beisbayeva et al, 2021 ). However, replicating the distribution of ACL collagen fibrils smaller than 100 nm has not been possible due to limitations related to the material properties in the process of electrospinning.…”