VISCOELASTIC SHEAR PROPERTIES OF ARTICULAR-CARTILAGE AND THE EFFECTS OF GLYCOSIDASE TREATMENTS

The objectives of this study were to determine the viscoelastic shear properties of articular cartilage and to investigate the effects of th e alteration of proteoglycan structure on these shear properties. Glyc osidase treatments (chondroitinase ABC and Streptomyces hyaluronidase) were used to alter the proteoglycan structure and content of the tiss ue. The dynamic viscoelastic shear properties of control and treated t issues were measured and statistically compared. Specifically, cylindr ical bovine cartilage specimens were subjected to oscillatory shear de formation of small amplitude (gamma(o) = 0.001 radian) over a physiolo gical range of frequencies (0.01-20 Hz) and at various compressive str ains (5,9,12, and 16%). The dynamic complex shear modulus was calculat ed from the measurements. The experimental results show that the solid matrix of normal articular cartilage exhibits intrinsic viscoelastic properties in shear over the range of frequencies tested. These viscoe lastic shear properties were found to be dependent on compressive stra ins. Our data also provide significant insights into the structure-fun ction relationships for articular cartilage. Significant correlations were found between the material properties (the magnitude of dynamic s hear modulus, the phase shift angle, and the equilibrium compressive m odulus), and the biochemical compositions of the cartilage (collagen, proteoglycan, and water contents). The shear modulus was greatly reduc ed when the proteoglycans were degraded by either chondroitinase ABC o r Streptomyces hyaluronidase. The results suggest that the ability of collagen to resist tension elastically provides the stiffness of the c artilage matrix in shear and its elastic energy storage capability. Pr oteoglycans enmeshed in the collagen matrix inflate the collagen netwo rk and induce a tensile prestress in the collagen fibrils. This intera ction of the collagen and proteoglycan within the cartilage matrix pro vides the complex mechanism that allows the tissue to resist shear def ormation.