How Sliding and Hydrodynamics Contribute to Articular Cartilage Fluid and Lubrication Recovery

Abstract

The tribological functions of cartilage are governed primarily by its interstitial fluid content, but the means by which cartilage recovers and retains interstitial fluid during articulation following periods of static loading remain unclear. Recently, we demonstrated a phenomenon in which articular cartilage recovers fluid at the loaded contact interface; we refer to this as 'tribological rehydration'. Our findings were consistent with two competing hypotheses: (1) that hydrodynamic pressures exceeded local interstitial pressures; (2) that fluid from the trailing wedge squeezed into the porous surface during direction reversals (reciprocal wedging). In this paper, we use unidirectional sliding to eliminate the potential effects of reciprocal wedging on tribological rehydration. We observed the same tribological rehydration effects from speed as in our previous reciprocating studies; thus, any effects of reciprocation are secondary to those of sliding itself. Tribological rehydration was enhanced by increased speeds, decreased loads, increased lubricant viscosity, and increased sample diameter. Although our results are generally consistent with a hydrodynamic interpretation of tribological rehydration, our attempts to eliminate the convergence zone by systematically decreasing the sample diameter failed to extinguish tribological rehydration. This final observation reveals an extremely robust mechanism for preventing tissue collapse and highlights some of the remaining challenges in modeling cartilage as a mechanical and tribological material.

Tribological Rehydration and Its Role on Frictional Behavior of PVA/GO Hydrogels for Cartilage Replacement Under Migrating and Stationary Contact Conditions

“…Otherwise, the wedge effect on the friction behavior of PVA/GO hydrogel is considered for different counterface ball diameter. It has been reported that the friction coefficient of cartilage was mainly related to rehydration induced by the wedge effect and the compressing of liquid into the porous surface during sliding [22,48]. The larger diameter of counter ball results in lower angle of wedge (Fig.…”

“…Therefore, the factor of ( a/h) was introduced to modify the values of maximum contact pressure, P H , and contact depth, H , calculated from the Hertzian contact equations. For the model of elastic layer with a thickness of h on a rigid body, the modification to the load ( F ′ ) and contact depth ( ′ ) with respect to their Hertzian counterparts can be obtained as follows, where is equal to 0.15 for low friction (close to a frictionless boundary condition) at the indenter interface [48]. The correction reported in Eq.…”

Articular and Artificial Cartilage, Characteristics, Properties and Testing Approaches—A Review

“…Cartilage wear is because of PGs loss and alterations in the collagen network [ 63 ]. Cartilage wear could be initiated due to biochemical degradation and biomechanical factors such as knee misalignment, which induces higher pressure on either the medial or lateral side of the knee joint [ 64 ]. Most of the studies have fallen short of quantifying wear mechanism due to its complex nature; hence only frictional properties have been investigated.…”

Perspectives on Synthetic Materials to Guide Tissue Regeneration for Osteochondral Defect Repair

“…Cartilage is a highly hydrated, avascular tissue that displays remarkably complex biomechanical behavior characterized by high compressive stiffness, strength, and lubricity. , Such complexity can be attributed to its layered nature (Figure ), wherein horizontally aligned collagen at the surface progresses to vertically aligned deeper in the tissue, resulting in the tissue’s anisotropic feature. Furthermore, it has a remarkable ability to expel and regain its water content (up to 80% by weight) during loading and articulation. , Toward materials-driven regeneration of cartilage, synthetic materials should recapitulate an environment that drives chondrogenesis through chondroconductivity, chondroinductivity, and chondrointegration. Chondroconductive scaffolds provide a morphology similar to that of the confined chondrocytic environment (smaller interconnected pores (<300 μm) with low porosity) to facilitate cell–cell interactions for chondrogenesis.…”