The Inhomogeneous Mechanical Properties of the Pericellular Matrix of Articular Cartilage Measured In Situ by Atomic Force Microscopy

Articular cartilage is the connective tissue that lines the articulating surfaces of diarthrodial joints, providing a low-friction, load-bearing surface during joint motion. Articular cartilage comprises of a single cell type, the chondrocyte, embedded within an extensive extracellular matrix (ECM). Each chondrocyte is surrounded by a narrow region called the pericellular matrix (PCM) that is distinct from the ECM in both its biochemical composition [1] and biomechanical properties [2]. While multiple techniques have been used to measure the mechanical properties of the PCM, including micropipette aspiration of isolated chondrons [2], these studies required mechanical or enzymatic extraction of the chondrocyte and surrounding PCM (i.e., the “chondron” [1]) from the cartilage, and the influence of this isolation process on PCM properties is unknown. Atomic force microscopy (AFM) provides a high resolution form of nano- and microindentation approaches that can be used to measure local mechanical properties in situ [3,4]. The objective of this study was to use AFM to quantify the biomechanical properties of the ECM and PCM of human articular cartilage in situ.