A Study of Chondrocyte Mechanics Using Digital Image Correlation

Faculty of Civil and Environmental Engineering, Technion-Israel Institute of Technology, Haifa, Israel

3.30pm, Friday 18 February 2005, Seminar Room AR103, Graduate Research Centre

Mechanical loading regulates chondrocyte metabolism and is essential for the health of articular cartilage. Consequently, it is important to understand the mechanical properties of these cells. In the past, a variety of methods such as micropipette aspiration and compression tests have employed for this purpose. However, these tests measure the deformation of the entire cell, and therefore they can't be used to resolve heterogeneity in the mechanical properties at a sub-cellular level.

In recent years several methods for the study of intracellular mechanics have emerged. These methods include microrheology, in which the viscoelastic properties of the cytoplasm are deduced by analyzing the random fluctuation of particles, and active tests in which the deformation of a sub-cellular structure in response to known boundary conditions is measured. These techniques have been applied to a variety of cells including, Smooth Muscle Cells, Endothelial cells and Fibroblasts.

In this talk I will report on a technique we have developed for studying the intracellular mechanics of Chondrocytes. Bovine articular chondrocytes are isolated and seeded in 3-D agarose constructs, and the mitochondria are flourescently labeled. Constructs are then placed on specially designed compression rig, which is mounted on a confocal microscope. This enables us to image intracellular features whilst subjecting the cell to increasing levels of strain. Digital Image Correlation (DIC) is then used to map intracellular deformation. Our results show that the strain fields in compressed chondrocytes are highly heterogeneous. This heterogeneity results from the combined effect of the mechanical compression, and the active transport of the mitochondria within the cell. Our results present a degree of complexity that is overlooked in most existing models for cell mechanics.

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