Abstract:
While the unusual tribological properties of cartilage are widely appreciated, its capacity for load support and distribution is comparatively under-rated. In-vivo measurements show that the most common contact stresses in joints (0.5 MPa-5 MPa) are about an order of magnitude higher than the compressive modulus (0.1-0.8 MPa) of cartilage regardless of species and weight-bearing status. Unprecedented large strains, anisotropy, through thickness heterogeneity, porosity, and water content are just the most important ways in which cartilage fails to represent traditional contact mechanics. Despite these well-known properties, there have been no studies relating load to contact area or the time dependent growth in contact area. Therefore, designing a controlled in-vitro tribology test that represents in-vivo contact conditions, specifically contact stresses, has proven difficult. In this study, we use a custom uniaxial compression device to image (in situ) and quantify contact areas of cartilage against an ideal flat over a wide range of experimentally relevant loads to help elucidate in-vivo contact mechanics. The results of this work will provide the empirical tools needed to support future experimental designs.