Viscoelasticity of articular cartilage: Analysing the effect of induced stress and the restraint of bone in a dynamic environment.

Bernard M Lawless,David W.L Hukins,Daniel M Espino,Duncan K Temple,Hemeth Dhaliwal,Hamid Sadeghi

doi:10.1016/j.jmbbm.2017.07.040

Bernard M Lawless, David W.L Hukins + Show 4 more

Open Access

https://doi.org/10.1016/j.jmbbm.2017.07.040

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Abstract

The aim of this study was to determine the effect of the induced stress and restraint provided by the underlying bone on the frequency-dependent storage and loss stiffness (for bone restraint) or modulus (for induced stress) of articular cartilage, which characterise its viscoelasticity. Dynamic mechanical analysis has been used to determine the frequency-dependent viscoelastic properties of bovine femoral and humeral head articular cartilage. A sinusoidal load was applied to the specimens and out-of-phase displacement response was measured to determine the phase angle, the storage and loss stiffness or modulus. As induced stress increased, the storage modulus significantly increased (p < 0.05). The phase angle decreased significantly (p < 0.05) as the induced stress increased; reducing from 13.1° to 3.5°. The median storage stiffness ranged from 548 N/mm to 707 N/mm for cartilage tested on-bone and 544 N/mm to 732 N/mm for cartilage tested off-bone. On-bone articular cartilage loss stiffness was frequency independent (p > 0.05); however, off-bone, articular cartilage loss stiffness demonstrated a logarithmic frequency-dependency (p < 0.05). In conclusion, the frequency-dependent trends of storage and loss moduli of articular cartilage are dependent on the induced stress, while the restraint provided by the underlying bone removes the frequency-dependency of the loss stiffness.

Highlights

Articular cartilage is a load bearing material found at the articulating ends of bones within joints of the body
The viscoelastic response of articular cartilage varied with the induced stress (Fig. 2 and Fig. 3a)
The logarithmic trend of the frequency-dependency of E’ (p < 0.05; Table 4) did not change at low, walking or high stress; it was off-set between the groups

Summary

Introduction

Articular cartilage is a load bearing material found at the articulating ends of bones within joints of the body. Rapid heelstrike rise times, during gait, have been implicated in the onset of OA (Radin et al, 1991, 1986). These rapid heel-strike rise times were as low as 5–25 ms for the subset of the population potentially predisposed to OA (Radin et al, 1991, 1986). This is in contrast to estimated typical rise times of around 100–150 ms for otherwise healthy gait during walking (Fulcher et al, 2009). This rate of loading is important to the mechanical behaviour of cartilage, because its mechanical properties are rate dependent (Shepherd and Seedhom, 1997): cartilage is viscoelastic (Fulcher et al, 2009; Temple et al, 2016)

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