Articular cartilage functions as a smooth, wear-resistant bearing surface at the ends of long bones where joints are formed. Although it normally functions well for many years, disease and traumatic injury can cause degeneration in the tissue. leading to functional failure. Methods for repairing articular cartilage have been studied for many years, but functional results thus far have been somewhat disappointing. Improvements to these therapies may be possible with better understanding of the basic mechanical properties of articular cartilage and the cells that maintain it. This dissertation investigates the depth-varying compressive properties o f articular cartilage and the strength with which chondrocytes adhere to articular cartilage. The results of these studies are related to problems in cartilage repair.

A novel method for quantitating depth-varying strains within articular cartilage explants undergoing confined compression was developed and validated. With this method, it was found that articular cartilage is mechanically mhomogeneous. and estimates of the variation in the confined compression modulus were made.

Then, the depth-dependent confined compression modulus of full-thickness bovine articular cartilage explants was quantitated with a modification to the earlier apparatus. The tissue was modeled as a series of adjacent. 125 urn-thick layers, and it was found that there was a 15-fold variation in the modulus through the first nine such tissue layers. This information is relevant to the function of normal articular cartilage, provides parameters for mathematical models of tissue function, and may be relevant to tissue engineering using a biomimetic approach.

Finally, the strength with which isolated chondrooies adhere to articular cartilage surfaces was studied with a modified parallel-plate shear-tlow chamber. Cell detachment assays allowed measurement of the fraction of adherent chondrocytes that detached with exposure to precisely controlled shear stresses. If was found that chondrocyte detachment decreases with longer seeding times. This information may lead to improvements in cell-based methods for cartilage repair.

These studies provide a more detailed mechanical characterization of arucular cartilage. The information gathered in these studies prompts additional research which will aid in the understanding the tissue in normal, aging, and diseased states, and mav lead to improvements in methods for repairing articular cartilage.