title: Liposomes as lubricants: beyond drug delivery.
abstract: In this paper we review recent work (Goldberg et al., 2011a,b) on a new use for phosphatidylcholine liposomes: as ultra-efficient boundary lubricants at up to the highest physiological pressures. Using a surface force balance, we have measured the normal and shear interactions as a function of surface separation between layers of hydrogenated soy phophatidylcholine (HSPC) small unilamellar vesicles (SUVs) adsorbed from dispersion, at both pure water and physiologically high salt concentrations of 0.15 M NaNO(3). Cryo-Scanning Electron Microscopy shows each surface to be coated by a close-packed HSPC-SUV layer with an over-layer of liposomes on top. The shear forces reveal strikingly low friction coefficients down to 2×10(-5) in pure water system or 6×10(-4) in the 150 mM salt system, up to contact pressures of at least 12 MPa (pure water) or 6 MPa (high salt), comparable with those in the major joints. This low friction is attributed to the hydration lubrication mechanism arising from rubbing of the highly hydrated phosphocholine-headgroup layers exposed at the outer surface of each liposome, and provides support for the conjecture that phospholipids may play a significant role in biological lubrication.
authors: Dept. of Materials and Interfaces, Weizmann Institute, Rehovot 76100, Israel.
authors: Ronit
authors: R
authors: Goldberg
authors: Jacob
authors: J
authors: Klein
mesh_terms: D000818:Animals; D017276:Friction / Q000187:drug effects; D006801:Humans; D008081:Liposomes / Q000737:chemistry* / Q000494:pharmacology* / Q000648:ultrastructure; D054327:Lubricants / Q000737:chemistry* / Q000494:pharmacology*; D010713:Phosphatidylcholines / Q000737:chemistry* / Q000494:pharmacology*; D013582:Synovial Fluid / Q000737:chemistry / Q000187:drug effects
chemical_list: D008081:Liposomes; D054327:Lubricants; D010713:Phosphatidylcholines