Friction and morphology of pleural mesothelia

Pleural Lubrication

“…Hence, even though hyaluronic acid acts as a good lubricant when applied to damaged mesothelium, its role as a lubricant of mesothelial surfaces under physiological conditions is not demonstrated. Recently Pecchiari et al [42] showed that interposition of hyaluronan between blotted or normal mesothelium during 2 min of reciprocating sliding, limited or prevented the damage of the normal surface, as well as the increase of µ. In this model, hyaluronic acid shows therefore very good protective properties.…”

“…When pleural surface is damaged to various extent by blotting or short treatment with pronase or phospholipase [26,38,42], with consequent substantial loss of part of the coat of macromolecules present at the mesothelial surface [11] and even of the mesothelial cells [42], µ increases markedly [8,26,42]. Moreover, this increase decreases with increasing velocity, suggesting that in damaged mesothelium lubrication regimen turns from boundary to mixed (boundary and elasto-hydrodynamic).…”

“…This finding indicates a regime of mixed lubrication in post-blotting Ringer, at variance with boundary lubrication occurring before blotting or postblotting with sufficient macromolecule addition. Actually, after mesothelial blotting the pleural surface appears damaged (see Section 4; [26,42]), consequently the mesothelial surface is likely much more rough than it was under control conditions and, after the addition of Ringer, the amount of liquid between the opposed mesothelial surfaces in several points should be greater than that before blotting. Therefore, when the visceral and parietal pleura are made to slide under physiological load, the shear induced hydrodynamic pressure, besides reducing the roughness of the mesothelial surface [5], generates some areas of elastohydrodynamic lubrication, which increase with the increase in sliding velocity, while those of boundary lubrication decrease [40].…”

“…Moreover, D'Angelo et al [8] and Bodega et al [26] by transmission electron microscopy (TEM) did not find differences between control specimens and specimens used to measure the coefficient of kinetic friction in physiological solution. Conversely, TEM micrographs show that, after mesothelial blotting with filter paper, pleural surface was damaged to various extent, showing areas where microvilli were partially or largely removed from the mesothelium surface [26] or even areas with substantial mesothelial damage with the disappearance of the cellular layer [42]. Anyway, the increase in µ after blotting should not be related to the removal of microvilli, because Pecchiari et al [42] showed that the superficial density of microvilli and their characteristics are not determinants of the frictional forces which oppose sliding of normal mesothelial surfaces under physiological conditions, nor of the lubricant effect of hyaluronic acid.…”

“…Conversely, TEM micrographs show that, after mesothelial blotting with filter paper, pleural surface was damaged to various extent, showing areas where microvilli were partially or largely removed from the mesothelium surface [26] or even areas with substantial mesothelial damage with the disappearance of the cellular layer [42]. Anyway, the increase in µ after blotting should not be related to the removal of microvilli, because Pecchiari et al [42] showed that the superficial density of microvilli and their characteristics are not determinants of the frictional forces which oppose sliding of normal mesothelial surfaces under physiological conditions, nor of the lubricant effect of hyaluronic acid. On the other hand, the mesothelium damage is consistent with a substantial loss of part of the coat of macromolecules normally entrapped among them at the mesothelial surface [11].…”