Abstract
AbstractSteady-state and transient variations in frictional force observed in tribological experiments of mesothelial tissues sliding in lubricant were analyzed with a mathematical model to test the hypothesis that such phenomena are manifestations of elastohydrodynamic lubrication and, importantly, do not require physical contact between the sliding surfaces. The model incorporates three phenomena characteristic of elastohydrodynamic lubrication: thinning of the liquid layer between sliding surfaces under a normal load (“squeeze-out”), thickening of the liquid layer due to hydrodynamic pumping, and smoothing of the elastic surfaces caused by hydrodynamic pressure gradients. Observations in soft mesothelial tissues sliding in lubricant showed variations in steady state friction with velocity, load, and lubricant viscosity. In non-steady sliding, the decay rate of frictional transients at the start of rotation varied with velocity, the amplitudes of these transients varied with the preceding periods without rotation, and frictional force varied during sinusoidal sliding. Model simulations were qualitatively similar to experimental results, supporting these mechanisms. Higher lubricant viscosity increased lubricating layer thickness and lowered friction at low speeds and increased friction at high speeds, supporting hydrodynamic pumping. We conclude that the frictional variations seen with sliding mesothelial tissues are consistent with elastohydrodynamic lubrication without contact between the sliding surfaces.
Highlights
Throughout life, the mesothelial surfaces within the body slide against each other, lubricated by a thin layer of serous fluid
The bottom tissue surface was rotated at various rates in alternating directions with a square-wave pattern that allowed steady state coefficient of friction (CF) determinations after transients died out
We have interpreted steady state and transient behavior of tissues sliding in saline with a model that synthesizes physical principles and phenomena of elastohydrodynamic lubrication
Summary
Throughout life, the mesothelial surfaces within the body slide against each other, lubricated by a thin layer of serous fluid. Between sliding mesothelial tissues and a rotating glass plate and found that the thickness of the fluid layer beneath the tissue surface depended on sliding velocity. Soft materials sliding in lubricant are smoothed by hydrodynamic pressure gradients, making the lubricant layer more uniform in thickness [7]. Considered together, the latter three studies suggest that soft materials with statically uneven surfaces sliding in lubricants are smoothed and deformed so as to become load-bearing, maintaining a layer of lubricant between sliding surfaces [8, 9]
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