| Chondrocytes are responsible for the maintenance of articular cartilage. This regulation is controlled in part by physical factors generated by mechanical loading of the joint. Previous studies have used theoretical models of chondrocytes within articular cartilage to predict the mechanical environment around the cell, but cellular material properties are necessary to provide more quantitative information from these analyses. The objective of this dissertation, therefore, was to use the micropipette technique, along with analytical and numerical models of the experimental configurations, to determine the mechanical properties of chondrocytes and how they are altered with osteoarthritis.;An elastic test was performed and no differences were found between the Young's moduli of normal and osteoarthritic chondrocytes. When modeled as viscoelastic solids, osteoarthritic chondrocytes exhibited a significantly higher equilibrium modulus, instantaneous modulus, and viscosity as compared to normal chondrocytes. Additionally, the viscoelastic test was performed on cells exposed to cytoskeletal disruptors, which showed that microfilaments and intermediate filaments play a major role in the mechanical properties of the chondrocyte.;A significant difference in cell volume was observed after complete aspiration of the cell into the micropipette, and the percent volume decrease of normal chondrocytes was significantly less than that of osteoarthritic chondroctyes. Using a finite element model to simulate these experiments, the Poisson's ratio of normal and osteoarthritic chondrocytes was also determined.;The recovery properties of the chondrocyte after release from complete aspiration into the micropipette were determined. The ratio of the equilibrium modulus to the instantaneous modulus was found to be similar in both normal and osteoarthritic chondrocytes, but the time constant changed with osteoarthritis.;The viscoelastic properties, the volume change with compression, and the time constant for recovery from compression were found to change with osteoarthritis. These alterations in chondrocyte properties, along with differences in cartilage material properties with osteoarthritis, imply that the environment of the chondrocyte may be altered with disease. The material parameters measured in this study can be used to more accurately characterize the mechanical environment of the chondrocyte in situ, which will lead to a better understanding of the alterations in chondrocyte physiology with osteoarthritis. |
