Inhomogenous Stiffness of Articular Chondrocytes Measured by Atomic Force Microscopy

Chondrocytes are responsible for the elaboration and maintenance of the extracellular matrix (ECM) in articular cartilage. Previous studies have demonstrated that mechanical loading modulates the biosynthetic response of chondrocytes in cartilage explants [1,2]. Therefore, the mechanical properties of chondrocytes play a pivotal role in regulating the interaction between the cell and ECM in situ [eg. 3–5]. The goal of this study is to investigate the indentation-dependent stiffness of chondrocytes using atomic force microscopy. Due to the composite nature of cellular organelles and the cytoskeleton, we hypothesize that chondrocytes exhibit a non-linear elastic modulus, requiring a non-Hertzian analysis of the contact and resulting stress-strain response [6,7]. The response of chondrocytes is investigated in a manner to probe the bulk stiffness of the cell (using 10 μm spherical probes), as well as the stiffness arising from composite subcellular structures (utilizing 3 μm spherical probes).