The development and characterization of an in vitro system to study strain-induced cell deformation in isolated chondrocytes.

A model system has been developed to investigate cell deformation of chondrocytes in vitro. Chondrocytes were isolated from bovine articular cartilage by enzymatic digestion and seeded in agarose (type VII) at a final concentration of 2 x 10(6) cells.ml-1 in 3% agarose. Mechanical evaluation of the system showed no change in the tangent modulus of agarose/chondrocyte cultures over a 6-d culture period. The resulting agarose/chondrocyte cultures were subjected to compressive strains ranging from 5-20%. Cell shape was assessed by measuring the dimensions of the cell both perpendicular (x) and parallel (y) to the axis of compression and deformation indices (I = y/x) calculated. Cell deformation increased with the level of strain applied for freshly isolated chondrocytes. The cultures were maintained in medium that inhibits or stimulates matrix production (DMEM and DMEM + 20% FCS, respectively) in order to assess the effect of cartilaginous matrix on chondrocyte deformation. Matrix elaborated by the cells markedly influenced levels of cell deformation, an increase in matrix leading to a decrease in cell deformation. Freshly isolated deep zone chondrocytes were found to deform significantly more than surface zone chondrocytes, although this effect was lost after 6 d in culture. The elaborated matrix also altered the recovery characteristics of the chondrocytes following constant compressive strain of 15% for 24 h. Cells that had elaborated matrix took several hours to return to unloaded shape, while cells without matrix returned to the unloaded shape instantly.