Alterations in the Young's modulus and volumetric properties of chondrocytes isolated from normal and osteoarthritic human cartilage

The mechanical environment of the chondrocyte is an important factor that i nfluences the maintenance of the articular cartilage extracellular matrix. Previous studies have utilized theoretical models of chondrocytes within ar ticular cartilage to predict the stress-strain and fluid flow environments around the cell, but little is currently known regarding the cellular prope rties which are required for implementation of these models. The objectives of this study were to characterize the mechanical behavior of primary huma n chondrocytes and to determine the Young's modulus of chondrocytes from no n-osteoarthritic ('normal') and osteoarthritic cartilage. A second goal was to quantify changes in the volume of isolated chondrocytes in response to mechanical deformation. The micropipette aspiration technique was used to m easure the deformation of a single chondrocyte into a glass micropipette in response to a prescribed pressure. The results of this study indicate that the human chondrocyte behaves as a viscoelastic solid. No differences were found between the Young's moduli of normal (0.65 +/- 0.63 kPa, n = 44) and osteoarthritic chondrocytes (0.67 +/- 0.86 kPa, n = 69, p = 0.93). A signi ficant difference in cell volume was observed immediately and 600 s after c omplete aspiration of the cell into the pipette (p < 0.001), and the magnit ude of this volume change between normal (11 +/- 11%, ir = 40) and osteoart hritic (20 +/- 11%, n = 41) chondroctyes was significantly different at bot h time points (p < 0.002). This finding suggests that chondrocytes from ost eoarthritic cartilage may have altered volume regulation capabilities in re sponse to mechanical deformation. The mechanical and volumetric properties determined in this study will be of use in analytical and finite element mo dels of chondrocyte-matrix interactions in order to better predict the mech anical environment of the cell in vivo. (C) 1999 Elsevier Science Ltd. All rights reserved.