CHANGES IN PROTEOGLYCAN SYNTHESIS OF CHONDROCYTES IN ARTICULAR-CARTILAGE ARE ASSOCIATED WITH THE TIME-DEPENDENT CHANGES IN THEIR MECHANICALENVIRONMENT

Explant loading experiments were conducted to investigate the effect o f load duration on proteoglycan synthesis. A compressive load of 0.1 M Pa applied for 10 min was found to stimulate proteoglycan synthesis, w hile the same load applied for 20 h suppressed synthesis. This bimodal response suggests that the cells are responding to different mechanic al stimuli as time progresses. A theoretical model has therefore been developed to describe the mechanical environment perceived by cells wi thin soft hydrated tissues (e.g. articular cartilage) while the tissue is being loaded. The cells are modeled, using the biphasic theory, as fluid-solid inclusions embedded in and attached to a biphasic extrace llular matrix of distinct material properties. A method of solution is developed which is valid for any axisymmetric loading configuration, provided that the cell radius, a, is small relative to the tissue heig ht, h (i.e. h/a much greater than 1). A closed-form analytical solutio n for this inclusion problem is then presented for the confined compre ssion configuration. Results from this model show that the mechanical environment in and around the cells is time dependent and inhomogeneou s, and can be significantly influenced by differences in properties be tween the cell and the extracellular matrix.