CHARACTERIZATION OF COLLAGEN FIBRIL DIAMETER DISTRIBUTION AND BIOMECHANICAL PROPERTIES OF HEALTHY AND INJURED RAT ANTERIOR CRUCIATE LIGAMENT

Abstract

With frequent leaping, colliding, turning, and cutting, women and men involved in sports-related activities are more vulnerable to anterior cruciate ligament (ACL) ruptures compared to the rest of the population. Researchers have shown that kinematics and neuromuscular control of the knee joint are affected inversely following ACL damage. Reconstructed ACLs cannot completely restore these adaptations, and it is critical to provide a physiologically viable environment for optimal biomaterial-cell interaction. Since ACL reconstruction procedures frequently result in failure or inferior scar tissue is formed, new strategies are needed to regenerate the torn/ruptured ACL tissue. In animal models of bovine and sheep, the ACL injuries were previously shown to lead to a change in the distribution of collagen fibrils diameter, with a shift from a bimodal distribution in the healthy ACL to a unimodal distribution after injury. In this study, it is hypothesized that the collagen fibril diameter distribution in rat ACL changes from a bimodal distribution in the healthy ACL to a unimodal distribution after injury and that this change can be mimicked in scaffolds fabricated using electrospinning. This hypothesis was tested by first creating an injured rat ACL model by applying a mechanical tensile force to the healthy ACL tissue until rupture. Secondly, transmission electron microscopy (TEM) evaluation of the healthy and injured ACL tissues was carried out to evaluate the collagen fibril diameter distributions in the tissues. Thirdly, using the electrospinning approach, polycaprolactone (PCL) scaffolds were created to imitate the bimodal and unimodal distributions of collagen fibrils seen in healthy and injured tissues, respectively. The mechanical properties of ACL and PCL electrospun nanofiber scaffolds were also tested at a crosshead speed of 5 mm/min under tension. Findings reveal that the bimodal distribution of ACL collagen fibril diameter changed to unimodal after injury, causing a decrease in the mean diameter. In healthy ACL, the fiber diameter distribution of PCL electrospun scaffolds were qualitatively and quantitatively similar. Native ACL tissue outperformed PCL scaffolds biomechanically. This study is significant because it addresses a major clinical issue that affects millions of people globally. The suggested bimodal fibrous scaffold design deviates from the usual unimodal scaffolds and may have a significant influence on the behavior of ACL cells and thus on ACL regeneration.