This study proposes to establish a fundamental and theoretically consistent understanding of the load-bearing roles of the two major macromolecules (i.e., collagen and proteoglycans) of articular cartilage. For decades this had been a major goal in cartilage biology, biomechanics, biochemistry and osteoarthritis research. Progress over recent years has necessitated the development of a theory (i.e., the triphasic theory) capable of describing the extant mechano-electrochemical behaviors of articular cartilage in a consistent manner. Using the three apparatuses the investigators have constructed (for swelling-buoyancy, confined-compression-swelling and electrokinetic tests), and the theoretical models they have developed, they will attempt to determine a set of material properties to precisely characterize the mechano-electrochemical behaviors of the tissue. A fourth device, using the reverse-osmosis principle, will be developed during this granting period to extend the measurement of osmotic pressures of PG solutions to physiologic concentrations. To complete the full scope of required data, tensile and shear tests will also be performed. Data from all these tests, and results from predictions from relevant triphasic models, are necessary to validate the applicants' approach toward further understanding of the structure-function relationships of the tissue. The applicant indicates that from his instruments and theoretical models, his group can measure the true in situ volume fraction of collagen, the true density of collagen, extrafibrillar and intrafibrillar water volumes, effective fixed charge density, swelling pressure, Donnan osmotic pressure, and calculate the frictional coefficients between water and the solid matrix, between water and collagen, and between water and proteoglycan. Their ability to determine these properties has motivated a set of hypotheses on how collagen, proteoglycan, water and ions function to provide the compressive, tensile, shear, permeability, streaming potential properties of the tissue. Further, since there are three major morphologic zones in articular cartilage, each with its distinct distributions of collagen, proteoglycan, water and ionic contents, the proposed studies are aimed at determining the functional roles of each of these layers as well. All biochemical assays (S-GAG, hydroxyproline, collagen X-link density and enzymatic treatments) will be performed on the tested specimens, and on site- and depth-specific adjacent specimens. Skeletally-mature bovine knee joint articular cartilage will be used for the entire study.
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