Final answer:
Cartilage exhibits creep as it deforms gradually under a constant load and stress relaxation as the stress decreases under constant strain. The cytoskeleton responds dynamically to stress, altering cell stiffness and viscoelastic properties, including the reorientation of stress fibers in response to mechanical forces.
Step-by-step explanation:
Creep and stress relaxation are characteristics that describe how cartilage responds to mechanical load over time. Creep refers to the gradual deformation of cartilage under a constant load, while stress relaxation describes the decrease in stress within the cartilage when it is held at a constant strain.
Experiments reveal that the cytoskeleton (CSK) of cells displays a dynamic response to applied stress. When stretched, cells exhibit a reduction in contractility, suggesting a fluidization process which then leads to a reassembly that alters cell stiffness. Moreover, viscoelastic properties change, with the complex shear modulus (G*) experiencing increases and the ratio of G"/G' decreasing during stepwise stretch. This indicates a non-linear elastic response and a rise in elastic rigidity due to cytoskeletal reorganization. In contrast, a transient stretch causes a sharp drop in both G' and G", implying cell softening and fluidization. The response also includes the reorientation of cytoskeletal stress fibers, particularly under uniaxial stretching where repeated cycles lead to perpendicular realignment to the stretching force.