Sub-critical impact inhibits the lubricating mechanisms of articular cartilage

Abstract

Although post-traumatic osteoarthritis accounts for a significant proportion of all osteoarthritis, the understanding of both biological and mechanical phenomena that lead to cartilage degeneration in the years to decades after trauma is still lacking. In this study, we evaluate how cartilage lubrication is altered after a sub-critical impact (i.e., an impact to the cartilage surface that produces surface cracking but not full thickness fissuring). Through utilizing a Stribeck-like framework, the elastoviscous transition, we evaluated changes to both the innate boundary lubricating ability of cartilage after impact and also the effectiveness of high viscosity lubricants to lower friction after impact. Increases in boundary friction coincided with changes in lubricin localization after impact. However, larger increases in friction coefficient were observed in mixed-mode lubrication which can be predicted by increases in surface roughness due to cartilage fissuring. The data here reveal distinct mechanisms of cartilage lubrication that can fail after traumatic impact and may explain a key mechanical phenomenon that predisposes cartilage to development of osteoarthritis after injury.

Degradation alters the lubrication of articular cartilage by high viscosity, hyaluronic acid‐based lubricants

“…That is, higher viscosities are necessary to reduce friction when cartilage is rougher, softer, and more permeable. Specifically, we utilized a Stribeck‐like framework and examined mixed‐mode lubrication where HA is most effective at reducing cartilage friction . Using this framework, we analyzed the effectiveness of high viscosity lubricants by calculation of a transition number ( S t ) that represents the transition to mixed lubrication.…”

“…Similarly, sections were tested for localization of lubricin at the surface using a previously reported immunohistochemistry procedure . Briefly, after rehydration of mounted sections, antigen retrieval was conducted using citric acid (pH 6.0) for 20 min at 90°C.…”

“…To determine alterations of the surface roughness and topography, three samples were analyzed using a white light interferometer (ADE Phase Shift MicroXAM Optical interferometric profiler) as previously described . Four scans analyzing the height distribution in a 209 µm × 179 µm window were collected for each sample.…”

“…After collection of friction coefficients, they were presented as a function of the Sommerfeld number, S , given by: where V is sliding speed, η is lubricant viscosity, a is contact width, and F n is normal load. As described previously, data were fit to a model curve where friction coefficient, µ, transitioned from a boundary friction coefficient, µ B , to a minimum friction coefficient, µ min , and allowed the determination of a transition number, S t , that is representative of the Sommerfeld number at the midpoint of the transition. This equation was given by: where d is a fitting parameter controlling the slope of the transition.…”

“…C). Thus, the goal of this study was to analyze IL‐1β‐mediated changes in lubrication by clinically approved HAs using a recently developed framework of cartilage‐on‐glass to separate boundary and viscous effects on cartilage lubrication …”