This application proposes to study the mechanical behavior of normal articular cartilage to different dynamic load conditions and to determine any changes that occur after the tissue has been physically changed. Recent evidence suggests that ultrastructural alterations in the dense collagenous surface layer causes mechanical softening of the tissue due to increased fluid transport across the articular surface. This could lead to proteoglycan depletion and further tissue softening. The specific aim of this proposal is to test this hypothesis by studying the mechanical behavior of the tissue to different mechanical factors, including the type, magnitude and frequency of load application (dead weight creep, cyclic creep, unloaded recovery and cyclic recovery), and different morphological factors, including surface removal and proteoglycan removal. One-dimensional confined compression tests will be performed on whole plugs of adult bovine articular cartilage. A specific sequence of mechanical tests will be performed on each intact specimen and repeated after tissue alteration. The biphasic creep model of Mow and coworkers will be used (when applicable) to determine the intrinsic aggregate elastic modulus and average permeability for each specimen and test. In addition, the amount of fluid exuded and imbibed during each phase of the cyclic experiments will be determined as a function of loading time. After each test is completed the plug will be serially sliced on a microtome and the aggregate modulus, permeability and fluid content determined as a function of depth. A layered mathematical model and a multivariate regression model will be developed to predict overall tissue behavior. The results from this study will yield vital information concerning the dynamic mechanical behavior of healthy (normal) articular cartilage, the factors controlling this behavior and how their interaction contributes in producing an altered mechanical behavior in pathological tissue. Since the mechanical and morphological configurations proposed in this research application are similar to those experienced and exhibited in diarthrodial joints, this information will provide useful insight into the physiology of the degenerative joint disease process.