Abstract
The aim of this study was to determine the variation in viscoelastic properties of femoral head bovine articular cartilage, on-bone, over five orders of magnitude of loading frequency. These frequencies ranged from below, up to and above healthy gait-relevant frequencies, using<1, 1–5 and 10 Hz, respectively. Dynamic mechanical analysis was used to measure storage and loss stiffness. A maximum compressive force of 36 N was applied through a chamfered-end, 5.2-mm-diameter, indenter. This induced a maximum nominal stress of 1.7 MPa. The ratio of storage to loss stiffness increased from near parity (2.5) at low frequencies to 11.4 at 10 Hz. This was the result of a significant logarithmic increase (p < 0.05) in storage stiffness with frequency, from 367 N/mm (0.001 Hz) up to 1460 N/mm (10 Hz). In contrast, the loss stiffness remained approximately constant. In conclusion, viscoelastic properties of articular cartilage measured at frequencies below those of gait activities are poor predictors of its relevant dynamic mechanical behaviour.
Highlights
In this study, dynamic mechanical analysis (DMA) has been used to determine the variation in viscoelastic properties of bovine articular cartilage, on-bone, over five orders of magnitude of frequency
The storage stiffness was always greater than the loss stiffness
At lower frequencies, the storage-to-loss stiffness ratio tended towards parity
Summary
Dynamic mechanical analysis (DMA) has been used to determine the variation in viscoelastic properties of bovine articular cartilage, on-bone, over five orders of magnitude of frequency. Viscoelastic properties have been compared at loading frequencies associated with gait and at lower frequencies used experimentally. The findings highlight the limitations of extrapolating viscoelastic properties obtained at non-physiologically relevant frequencies for physiological function. Articular cartilage is a load-bearing structure,[1,2] which when undamaged contributes to smooth joint motion aided by a surface roughness of around 80– 170 nm.[3] osteoarthritis (OA) is associated with damaged cartilage and impaired or painful joint motion.[4] Rapid heel-strike rise times during gait have been implicated in the early onset of OA in lower limb joints.[5,6] heel-strike rise times not associated with OA are typically 100–150 ms[7] and correspond to loading frequencies of 3–5 Hz.[8]
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