Effect of dynamic loading on the frictional response of bovine articular cartilage
Introduction
Articular cartilage functions as the bearing material between the opposing articular surfaces of diarthrodial joints. Previous frictional studies have found that articular cartilage can have very low friction coefficients upon loading (0.002–0.02) (Jones, 1934, Jones, 1936; Charnley, 1959, Charnely, 1960; McCutchen, 1959; Barnett and Cobbold, 1962; Linn, 1967; Linn and Radin, 1968; Unsworth et al., 1975; Malcom, 1976; Forster and Fisher, 1996; Krishnan et al., 2003). But with a step load of constant magnitude (static load) applied for several hours, the coefficient becomes quite elevated (0.1–0.6) (McCutchen, 1962; Malcom, 1976; Forster and Fisher, 1996, Forster and Fisher, 1999; Ateshian et al., 1998; Krishnan et al., 2004). It has been proposed by McCutchen, 1959, McCutchen, 1962) and supported by others (Malcom, 1976; Macirowski et al., 1994; Forster and Fisher, 1996; Ateshian et al., 1998) that this transient frictional behavior is related to the fluid pressurization in the tissue. Under this hypothesis, by load transfer from the solid to the fluid phase, the interstitial fluid is able to substantially reduce the friction coefficient. When the interstitial fluid pressure within the tissue subsides to zero, the frictional coefficient reaches an equilibrium value.
Experimental measurements of the interstitial fluid pressurization of articular cartilage (Oloyede and Broom, 1991; Soltz and Ateshian, 1998, Soltz and Ateshian, 2000a; Park et al., 2003) have confirmed theoretical predictions (Ateshian et al., 1994; Macirowski et al., 1994; Ateshian and Wang, 1995; Kelkar and Ateshian, 1999) that the load supported by interstitial fluid can be in excess of 90% of the total applied load immediately upon loading, though it subsides to zero under prolonged static loading. In our recent study where measurements of cartilage interstitial fluid pressurization were performed simultaneously with frictional measurements against glass under a constant applied load (Krishnan et al., 2004), a linear correlation with a negative slope was observed between the friction coefficient and interstitial fluid load support, strongly supporting the hypothesis that interstitial fluid pressurization is a primary regulator of the frictional response of cartilage.
Under static loading, in laboratory conditions, the equilibrium cartilage friction coefficient achieved when fluid pressurization has subsided () is typically too high to provide functionally effective lubrication. For example, if the peak load transmitted across the hip joint during gait is approximately five times normal body weight (∼5×750 N=3750 N), this would result in friction forces ranging between 375 and 2250 N. Such elevated friction forces can lead to rapid wear and degeneration of the surfaces (Forster and Fisher, 1996). It is therefore expected that the normal environment in diarthrodial joints would maintain the friction coefficient in a low range (e.g., ∼0.02 or less) over the range of activities of daily living. This study begins to address the question of what makes the friction coefficient stay sufficiently low under physiological loading conditions in vivo.
Under physiological activities such as walking and running, the loading environment in the lower extremities is cyclical (Dillman, 1975; Paul and McGrouther, 1975), yet few studies have investigated the frictional characteristics of articular cartilage under such conditions. Malcom observed that the effect of dynamic loading, compared to static loading, was to reduce the friction coefficient of cartilage and keep it lower over a wider range of normal stresses (Malcom, 1976). Results from our previous measurements of interstitial fluid load support under dynamic confined compression loading (Soltz and Ateshian, 2000a) indicate that substantial interstitial fluid pressurization persists at frequencies as low as 10−4 Hz. Based on these observations, the hypothesis of the current study is that under cyclical loading rates and physiological stresses, normal articular cartilage always maintains high interstitial fluid load support and low friction coefficient, never achieving the zero-pressure/high friction equilibrium conditions typical of prolonged static loading under laboratory conditions. More specifically, (1) the steady-state friction coefficient is significantly smaller under cyclical compressive loading than the equilibrium friction coefficient under static loading, and decreases as a function of loading frequency; (2) the steady-state interstitial fluid load support remains significantly greater than zero under cyclical compressive loading and increases as a function of loading frequency. These hypotheses are tested using a combination of experimental and theoretical studies.
Section snippets
Materials and methods
In the experimental study, friction measurements between bovine articular cartilage and glass were performed in unconfined compression under three dynamic loading frequencies representative of physiological conditions (0.05, 0.5 and 1 Hz), and under a static load. In the theoretical study, cartilage interstitial fluid load support was predicted under similar conditions of static and dynamic loading, using the previously described biphasic-conewise linear elasticity (CLE) mixture model of
Statistical analyses
A one-way analysis of variance (ANOVA) with repeated measures was performed to detect differences in the experimentally measured values of in all four friction tests. Similarly, ANOVA with repeated measures was used to detect differences between from the static loading test and and from the three dynamic loading tests. Statistical significance was accepted for , with . Post-hoc testing of the means was performed using Bonferroni correction.
Results
Representative experimental results for the applied load W and measured frictional force F are shown in Fig. 2a–d under static loading and dynamic loading at 0.05 Hz. The friction force is observed to increase with time, both for static and dynamic loading configurations. The corresponding effective friction coefficient is shown in Fig. 2e,f along with a trace of the corresponding lower bound and upper bound responses under dynamic loading. For this specimen, the rise in occurs at a
Discussion
Cyclical compressive loading is an important testing configuration as it is frequently encountered in our joints during activities of daily living such as walking or running. The experimental results presented in Fig. 2 and Table 1 demonstrate that the friction coefficient under cyclical compressive loading oscillates above and below the response to static loading, with the upper bound steady-state friction coefficient considerably higher than the equilibrium friction coefficient, .
Acknowledgements
This study was supported by funds from the National Institute of Arthritis and Musculoskeletal and Skin Diseases of the National Institutes of Health (AR43628).
References (32)
- et al.
A theoretical solution for the frictionless rolling contact of cylindrical biphasic articular cartilage layers
Journal of Biomechanics
(1995) - et al.
An asymptotic solution for the contact of two biphasic cartilage layers
Journal of Biomechanics
(1994) Joint lubrication
Lancet
(1934)- et al.
Experimental verification of the role of interstitial fluid pressurization in cartilage lubrication
Journal of Orthopaedic Research
(2004) - et al.
Is classical consolidation theory applicable to articular cartilage deformation?
Clinical Biomechanics
(1991) - et al.
Cartilage interstitial fluid load support in unconfined compression
Journal of Biomechanics
(2003) - et al.
Experimental verification and theoretical prediction of cartilage interstitial fluid pressurization at an impermeable contact interface in confined compression
Journal of Biomechanics
(1998) Dynamic unconfined compression of articular cartilage under a cyclic compressive load
Biorheology
(1996)- et al.
An analysis of the unconfined compression of articular cartilage
Journal of Biomechanical Engineering
(1984) - et al.
The role of interstitial fluid pressurization and surface porosities on the boundary friction of articular cartilage
Journal of Tribology
(1998)
Lubrication within living joints
Journal of Bone and Joint Surgery British Volume
The lubrication of animal joints in relation to surgical reconstruction by arthroplasty
Annals of the Rheumatic Diseases
Conewise linear elastic materials
Journal of Elasticity
Kinematic analysis of running
The influence of loading time and lubricant on the friction of articular cartilage
Proceedings of the Institute of Mechanical Engineers [H]
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2021, Journal of BiomechanicsCitation Excerpt :As the main load-bearing tissue, articular cartilage can withstand compressive forces while also maintaining low friction properties, allowing the repeated sliding contact between opposing surfaces during locomotion to occur with minimal tissue wear. These friction properties of cartilage have been characterized at the tissue level with loading devices for both intact joints (Unsworth et al., 1975) and explanted cartilage tissues (Wang and Ateshian, 1997; Krishnan et al., 2004; Basalo et al., 2005; Krishnan et al., 2005; Basalo et al., 2006; Basalo et al., 2007; Carter et al., 2007; Caligaris and Ateshian, 2008; Oungoulian et al., 2014), and at the molecular scale utilizing atomic force microscopy (Park et al., 2004; Kienle et al., 2015). Further work has identified mechanisms that dictate the frictional interactions between articular surfaces such as lubrication by fluid film, boundary, and interstitial fluid pressurization phenomena (Ateshian and Mow, 2005).