POLYCAPROLACTONE BASED NANOFIBER SCAFFOLDS CAN MIMIC COLLAGEN FIBRIL DIAMETER DISTRIBUTION OF HEALTHY AND INJURED SHEEP ANTERIOR CRUCIATE LIGAMENT

Abstract

A ligament is a soft connective tissue with a hierarchical structure that attaches bone to bone. The Anterior Cruciate Ligament (ACL) tissue connects femur and tibia, and possesses low potential for self-regeneration due to its hypovascularity and hypocellularity. ACL injuries in the knee joint are prevalent among the people actively involved in sports such as basketball, football and skiing. Unfortunately, currently available clinical treatments cannot fully restore the injured tissue as indicated by low success rates in clinical procedures. Tissue engineering strategies can provide alternative approaches with a potential of restoring the injured ligaments by employing biomimetic scaffolds that are similar to native tissue in terms of structure, composition and functions. Here, it is hypothesized that the electrospun fibers with bimodal and unimodal distributions will mimic the collagen fibril diameter distribution of healthy and injured sheep ACL, respectively. To test this hypothesis, it was aimed to, firstly, create an injured sheep ACL by applying mechanical loading to the healthy ACL tissue until rupture. Secondly, Transmission Electron Microscopy (TEM) characterization was performed on the healthy and injured ACL tissues to determine collagen fibril diameter distributions. Thirdly, Polycaprolactone (PCL) scaffolds were produced via electrospinning method to mimic the bimodal and unimodal distributions of collagen fibrils in the healthy and injured tissues. Finally, mechanical characteristics of ACL and PCL electrospun scaffolds were determined at a crosshead speed of 5 mm/min in tension. Findings of this study demonstrated that the bimodal distribution of collagen fibril diameter of ACL changes to unimodal upon injury, resulting in a reduction in mean diameter. The fiber diameter distributions of polycaprolactone electrospun scaffolds were shown to mimic the collagen fibril diameter distribution of healthy and damaged ACL. In terms of biomechanical characteristics, native ACL tissue outperformed PCL scaffolds. Aligned bimodal scaffolds exhibited improved mechanical properties as compared to unaligned unimodal PCL scaffolds. This study is novel because we demonstrated, for the first time, the collagen fibril diameter distribution of healthy and injured ACL tissues harvested from sheep. Additionally, we propose a method for fabrication of scaffolds that mimic the collagen fibril diameter distribution of healthy and injured ACL. The study’s significance relies on the fact that it addresses an important clinical problem related to orthopedics that concerns millions of patients worldwide. The fibrous scaffold design proposed here deviates from the traditional unimodal technique, and it is anticipated to have a substantial impact on ACL regeneration efforts. Keywords: ACL, PCL, tissue engineering, nanosized fibers, biomimicry, ligament scaffold, polymer fiber-based fibers, electrospinning, mesenchymal stem cells.