Mechanical and fatigue behaviour of artificial ligaments (ALs)

A flexible biologic band, ACL is the most injured and ruptured ligament in the knees of humans and animals. This research aims to produce synthetic anterior cruciate ligaments (ACLs) and compare these ligaments' mechanical and fatigue life properties with the natural ACL and commercial synthetic grafts. Artificial ligaments were designed as a core-sheath type structure. The core consisted of straight, parallel yarns and the sheath was a tubular fabric produced by weaving or braiding techniques from polyester or Vectran® yarns. The mechanical properties of the resulting artificial ligaments (AL) were tested before and after the fatigue test and compared to those of the natural ACL and commercial artificial ACLs in the market. Results showed that all ligaments had sufficient tensile strength, and they retained it after the fatigue test. If constructed sheath and core parts were from the same type of yarns, the breaking load of ligaments was higher. The breaking strain and stiffness of woven structures, particularly with Vectran cores, were better than braided ones. After the fatigue test, the breaking strain and stiffness of AL structures with a braided sheath or polyester core were improved. This finding suggests that to prevent the laxity of knee preconditioning of the ligament is necessary if the fabric structure or yarn inherently has high breaking strain and low stiffness. Overall, this study shows that a variety of suitable candidates for replacing ruptured anterior cruciate ligaments could be developed by carefully combining the fatigue-resistant yarns with leno, narrow, and braided structures.