Viscoelastic properties of chondrocytes from normal and osteoarthritic human cartilage

The deformation behavior and mechanical properties of articular chondrocyte s are believed to play an important role in their response to mechanical lo ading of the extracellular matrix. This study utilized the micropipette asp iration test to measure the viscoelastic properties of chondrocytes isolate d from macroscopically normal or end-stage osteoarthritic cartilage. A thre e-parameter standard linear solid was used to model the viscoelastic behavi or of the cells. Significant differences were found between the mechanical properties of chondrocytes isolated from normal and osteoarthritic cartilag e. Specifically osteoarthritic chondrocytes exhibited a significantly highe r equilibrium modulus (0.33 +/- 0.23 compared with 0.24 +/- 0.11 kPa), inst antaneous modulus (0.63 +/- 0.51 compared with 0.41 +/- 0.17 kPa), and appa rent viscosity (5.8 +/- 6.5 compared with 3.0 +/- 1.8 kPa-s) compared with chondrocytes isolated from macroscopically normal, nonosteoarthritic cartil age. The elastic moduli and relaxation time constant determined experimenta lly in this study were used to estimate the apparent biphasic properties of the chondrocyte on the basis of the equation for the gel relaxation time o f a biphasic material. The differences in viscoelastic properties may refle ct alterations in the structure and composition of the chondrocyte cytoskel eton that have previously been associated with osteoarthritic cartilage. Co upled with earlier theoretical models of cell-matrix interactions in articu lar cartilage, the increased elastic and viscous properties suggest that th e mechanical environment of the chondrocyte may be altered in osteoarthriti c cartilage.