Biological lubrication of hydrated surface layer in small intestine

Frictional properties of the internal surface of small intestine (lamina epithelialis) were investigated. Friction between the internal surface of small intestine of porcine and silicon nitride ceramic was measured using an end-face friction test apparatus. The internal surface of small intestine was found to have a highly hydrated layer to protect tissue and transport food under digestion. Friction depends on water content of the surface layer because the water absorbed by the layer plays an important role in keeping friction low. The layer can recover low friction condition after water exudation by absorbing water again. At low sliding speed, friction is kept low and the tissue surface is protected from injury because the surface layer absorbs water. The mechanism of lubrication results from unique properties of water and is entirely different from industrial lubrication.