Experimental and Computational Characterizations of Native Ligaments, Tendons, and Engineered 3-D Bone-Ligament-Bone Constructs in the Knee.

Abstract

Ligaments and tendons are soft tissues that support muscle and bone structures in the body. The incidence of ligament and tendon rupture in the US has increased drastically in recent years, with the incidence of knee ligament rupture among children becoming a more dire concern. A common approach to anterior cruciate ligament (ACL) reconstruction uses a portion of the patellar tendon (PT) from the patient or a cadaver as a graft to replace the torn ACL. The current approach has several limitations including graft availability, risk of rejection, increased morbidity and, more importantly, unmatched biomechanical properties of the native ACL. These limitations have led to an increased urgency for engineered replacement tissues for ACL reconstruction.

An engineered graft was developed by differentiating bone marrow stromal cells in vitro into bone and ligament and co-culturing their self-generated extracellular matrices to form a bone-ligament-bone (BLB) construct. The efficacy of this graft as an ACL replacement was evaluated at 6- and 9-months post surgery. ACL replacement was performed in sheep and morphological, biomechanical, and computational assessments were used to facilitate comparison of BLB constructs with the commonly used PT graft. A 6-month recovery showed that the BLB constructs adapted in vivo and based on histological and mechanical analysis, developed quickly to improve mechanical properties. By 9-months, the morphology of the BLB further developed. The geometric stiffness of the BLB constructs increased dramatically after 9-months of recovery and attained 60% of that of the contralateral ACL. More importantly, the analysis demonstrated the BLB also has inhomogeneous, non-linear viscoelastic properties that are characteristic of the native ACL. The engineered BLB developed a deformation pattern that was similar to the native ACL while the deformation of the PT autograft remained uniform even after 9-months of in vivo recovery. A computational model of these tissues was also constructed to examine the altered biomechanics of the knee as a result of PT autografts vs. tissue-engineered strategies.

From these analyses, the engineered BLB construct showed great potential for ACL reconstruction demonstrated by its similarity to the native ACL in terms of morphology and inhomogeneous and viscoelastic biomechanical properties.