Oscillatory Compressional Behavior of Articular Cartilage and Its Associated Electromechanical Properties

Abstract

The compressive stiffness of articular cartilage was examined in oscillatory confined compression over a wide frequency range including high frequencies relevant to impact loading. Nonlinear behavior was found when the imposed sinusoidal compression amplitude exceeded a threshold value that depended on frequency. Linear behavior was attained only by suitable control of the compression amplitude. This was enabled by real time Fourier analysis of data which provided an accurate assessment of the extent of nonlinearity. For linear viscoelastic behavior, a stiffness could be defined in the usual sense. The dependence of the stiffness on ionic strength and proteoglycan content showed that electrostatic forces between matrix charge groups contribute significantly to cartilage's compressive stiffness over the 0.001 to 20 Hz frequency range. Sinusoidal streaming potentials were also generated by oscillatory compression. A theory relating the streaming potential field to the fluid velocity field is derived and used to interpret the data. The observed magnitude of the streaming potential suggests that interstitial fluid flow is significant to cartilage behavior over the entire frequency range. The use of simultaneous streaming potential and stiffness data with an appropriate theory appears to be an important tool for assessing the relative contribution of fluid flow, intrinsic matrix viscoelasticity, or other molecular mechanisms to energy dissipation in cartilage. This method is applicable in general to hydrated, charged polymers.

Modeling the Matrix of Articular Cartilage Using a Continuous Fiber Angular Distribution Predicts Many Observed Phenomena

“…In particular, based on earlier experimental results [24], we propose to use a power-law relation (14) where ξ(n r ) (units of force per area) and α(n r ) (unitless) are material properties that may vary along the directions n r . (For inhomogeneous materials, it is also possible to vary ξ and α spatially.)…”

“…For example, the linear isotropic biphasic theory for soft hydrated tissues [13] can predict the transient response of cartilage deformation and interstitial fluid pressurization in confined compression creep, stress-relaxation, and dynamic loading [13][14][15][16], and indentation creep [17]. When accounting for the tension-compression nonlinearity arising from the fibrillar solid matrix, the biphasic theory can also predict the response of cartilage deformation and interstitial fluid pressurization in unconfined compression [3,4,7,11,18,19].…”

Influence of Structure and Composition on Dynamic Viscoelastic Property of Cartilaginous Tissue: Criteria for Classification between Hyaline Cartilage and Fibrocartilage Based on Mechanical Function

“…This finding reflects that the relative compressive energy dissipation of hyaline cartilage may be strongly dependent on the interstitial fluid flow at low frequencies. Lee et al examined the relationship between the compressive viscoelastic behavior and the streaming potential of articular cartilage (1) . They reported that the streaming potential of articular cartilage was induced by the flow of the electrolyte-containing interstitial fluid.…”

“…The specimen was loaded in unconfined compression geometry between impermeable platens (1), (2) . The stress σ of the specimen was defined as the load normalized to the initial disk area, and the strain rate ε was referenced to the initial thickness.…”

“…The ECM consists of a cross-linked network of collagen fibrils (mainly type II collagen) and large aggregating proteoglycans (PGs) that are negatively charged (aggrecans). The aggrecans exert a high swelling pressure on the collagen network due to their electrostatic osmotic pressure, to maintain the dynamic stiffness and relative energy dissipation of articular cartilage (1), (2) . On the other hand, articular cartilage has a poor healing capacity due to its avascular nature; furthermore, cartilage damage tends to lead to osteoarthritis (OA).…”