NON-LINEAR VISCOELASTIC MECHANICS OF NATIVE AND ENGINEERED LIGAMENTS AND TENDONS

Patellar tendon (PT) autografts and allografts are the most common methods currently used to replace a torn anterior cruciate ligament (ACL). The PT is not only much stiffer than the ACL it replaces it also exhibits qualitatively and quantitatively different non-linear viscoelastic behavior from those of the ACL. These mis-matched biomechanics may be contributing to the high incidence of early onset osteoarthritis suffered by patients who have had ACL surgeries. Thus there is a need for an ACL graft that can reproduce normal ligament biomechanics and knee function. This talk examines the inhomogeneous, non-linear viscoelastic response of native ACL and of a tissue engineered ACL graft designed to rapidly grow and remodel in vivo to restore the proper biomechanical properties of native ligament. The results using this graft as an ACL replacement are compared against those using a PT autograft for the ACL replacement. Uniaxial loading reveals that after nine months as an ACL replacement, the tissue-engineered graft develops a strain contour pattern closely resembling that of native ACL whereas the PT graft fails to similarly remodel in vivo.