Functional Tissue Engineering of Ligament and Tendon Injuries

This chapter reviews the properties of normal and healing ligaments and tendons and discusses the current functional tissue engineering (FTE) methods, which include the use of growth factors, gene delivery, stem cell therapy, and the use of scaffolding as well as external mechanical stimuli, aimed at enhancing tendon and ligament healing. The major function of ligaments and tendons include maintaining the proper anatomical alignment of the skeleton and guiding joint motions. They accomplish this by transmitting forces along their longitudinal axis but their biomechanical properties are measured in uniaxial tension. They demonstrate nonlinear behavior, which is governed by the recruitment of collagen. This allows ligaments to maintain normal joint laxity in response to low loads and also to stiffen dramatically in response to high loads, preventing excessive joint displacements. The events of healing of ligaments and tendons are divided into four overlapping phases: hemorrhage, inflammation, repair (proliferation), and remodeling. Following injury, the hemorrhagic and inflammatory phases occur over the first several days. Minutes after the ligament injury, blood collects and forms a platelet-rich fibrin clot at the injury site. The hemorrhage phase of the injury forms a lattice for many following cellular events. FTE has generated many significant developments; for example, there is a class of biodegradable metallic scaffolds, namely porous magnesium or magnesium oxide, that have the advantage of initial stiffness to provide the needed stability for the ligament to heal while performing its function. The degradation rate of these "smart" scaffolds could also be controlled as they are replaced by the neotissue. © 2011 Elsevier Inc. All rights reserved.