The mechanical properties of cartilage strongly depend on the composition of the extracellular matrix, in which negatively charged proteoglycan (PG) molecules are enmeshed in a collagen network.  The collagen provides tensile strength while the highly charged anionic PGs create an osmotic swelling pressure.   The structure of the cartilage matrix and the distribution of the components are strongly depth-dependent.  The PG content is lowest in the superficial zone and highest in the middle zone.  The fixed charge density is highest in the deep zone.  We determined the depth dependence of the elastic and osmotic modulus of cartilage using a novel combination of atomic force microscopy (AFM) with osmotic swelling pressure measurements.  AFM indentations detect fine spatial variations in the mechanical properties of cartilage layers.  This study also reveals that the osmotic modulus of articular cartilage is highest in the superficial and deep zones, and lowest in the middle zone.

Nanomechanical properties of cartilage

243rd National Meeting (2012)

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