Influence of lubricant physicochemical properties on the tribological operation of fluide phase phospholipid biomimetic surfaces
Résumé
Phospholipid bilayers appear to play a key role in joint lubrication in controlling and reducing frictional forces between biological surfaces. We have investigated the mechanical and tribological properties of Dioleoyl phosphatidylcholine (DOPC) bilayers prepared by the micelle and vesicle method in different solutions (ultrapure water and Tris buffer pH 7.2 with or without 150 mM NaCl). Friction forces are measured using a homemade biotribometer. Mechanical resistance to indentation is measured by AFM and lipid bilayer degradation is controlled in-situ during friction testing using fluorescence microscopy. This study confirms that mechanical stability under shear or normal load is essential to obtain low and constant friction coefficients. The major result is that the Tris buffer pH 7.2 improves mechanical and tribological stability of the studied bilayers. In ultrapure water, bilayers obtained by the micelle method are not resistant and spontaneously adsorb to the other contacting surface. Bilayers prepared by the vesicle method show slightly better lubricant properties than those prepared by the micelle method. Additional salt (150 mM NaCl) has existing but secondary effects on the mechanical and tribological properties of the bilayers.