Hydrostatic Pressurization and Depletion of Trapped Lubricant Pool During Creep Contact of a Rippled Indenter Against a Biphasic Articular Cartilage Layer

Abstract

This study presents an analysis of the contact of a rippled rigid impermeable indenter against a cartilage layer, which represents a first simulation of the contact of rough cartilage surfaces with lubricant entrapment. Cartilage was modeled with the biphasic theory for hydrated soft tissues, to account for fluid flow into or out of the lubricant pool. The findings of this study demonstrate that under contact creep, the trapped lubricant pool gets depleted within a time period on the order of seconds or minutes as a result of lubricant flow into the articular cartilage. Prior to depletion, hydrostatic fluid load across the contact interface may be enhanced by the presence of the trapped lubricant pool, depending on the initial geometry of the lubricant pool. According to friction models based on the biphasic nature of the tissue, this enhancement in fluid load support produces a smaller minimum friction coefficient than would otherwise be predicted without a lubricant pool. The results of this study support the hypothesis that trapped lubricant decreases the initial friction coefficient following load application, independently of squeeze-film lubrication effects.

Lubrication of the Temporomandibular Joint

“…In addition, models have shown that the highly porous nature of cartilage at its surface is capable of maintaining effective lubrication even in the absence of weeping flow, as only about 1% of the total contact area of cartilage layer interactions consists of solid-solid contacts, where friction occurs. 151 Therefore, the initial friction coefficient following an applied load is decreased by trapped lubricant at the surface, independent of squeeze-film lubrication effects. 151 However, it has been suggested that although compressive stresses prevent the initiation of fissures in a healthy joint, that normal movements in a pathological joint with a thin synovial fluid layer can easily cause fissures.…”

“…151 Therefore, the initial friction coefficient following an applied load is decreased by trapped lubricant at the surface, independent of squeeze-film lubrication effects. 151 However, it has been suggested that although compressive stresses prevent the initiation of fissures in a healthy joint, that normal movements in a pathological joint with a thin synovial fluid layer can easily cause fissures. 82 A classic overview of surface characteristics of articular cartilage was presented in the mid 1970s.…”

The role of lubricant entrapment at biological interfaces: Reduction of friction and adhesion in articular cartilage

“…Articular cartilage is a multiphase material consisting of a fluid phase comprising 60-85% of the tissue wet weight (ww) Forster and Fisher, 1996) and a solid phase mainly composed of collagen ( 15-30% ww) and proteoglycans ( 4-7% ww) . Water and lubricant pools form between asperity microcontacts of loaded articular cartilage (Soltz et al, 2003). Various mechanisms responsible for the development of trapped lubricants have been proposed, including weeping (Lewis and McCutchen, 1959), boosted (Walker et al, 1968), and squeeze film mechanisms (Hou et al, 1992).…”

Reduced expression and proteolytic susceptibility of lubricin/superficial zone protein may explain early elevation in the coefficient of friction in the joints of rats with antigen‐induced arthritis

“…Although interstitial fluid pressurization contributes to joint lubrication in mammals (27), lubricin has been established as a very important factor in maintaining low values in diarthrodial joints. Previous research using Prg4-null mice indicated that joints from homozygotes had significantly higher values compared with those from either heterozygotes or normal mice (28).…”