Chondrocytes in articular cartilage normally exhibit high expression of collagen II and aggrecan but rapidly dedifferentiate to a fibroblastic phenotype if passaged in culture. Previous studies have suggested that the loss of chondrocyte phenotype is associated with changes in the structure of the F-actin cytoskeleton, which also controls cell mechanical properties. In this study, we examined how dedifferentiation in monolayer influences the mechanical properties of chondrocytes isolated from different zones of articular cartilage. Atomic force microscopy was used to measure the mechanical properties of superficial and middle/deep zone chondrocytes as they underwent serial passaging and subsequent growth on fibronectin-coated, micropatterned self-assembled monolayers (MSAMs) that restored a rounded cell shape in 2D culture. Chondrocytes exhibited significant increases in elastic and viscoelastic moduli with dedifferentiation in culture. These changes were only partially ameliorated by the restoration of a rounded shape on micropatterned surfaces. Furthermore, intrinsic zonal differences in cell mechanical properties were rapidly lost with passage. These findings indicate that cell mechanical properties may provide additional measures of phenotypic expression of chondrocytes as they undergo dedifferentiation and possibly redifferentiation in culture.
