title: Interactions between adsorbed hydrogenated soy phosphatidylcholine (HSPC) vesicles at physiologically high pressures and salt concentrations.
abstract: Using a surface force balance, we measured normal and shear interactions as a function of surface separation between layers of hydrogenated soy phosphatidylcholine (HSPC) small unilamellar vesicles (SUVs) adsorbed from dispersion at physiologically high salt concentrations (0.15 M NaNO₃). Cryo-scanning electron microscopy shows that each surface is coated by a close-packed HSPC-SUV layer with an overlayer of liposomes on top. A clear attractive interaction between the liposome layers is seen upon approach and separation, followed by a steric repulsion upon further compression. The shear forces reveal low friction coefficients (μ = 0.008-0.0006) up to contact pressures of at least 6 MPa, comparable to those observed in the major joints. The spread in μ-values may be qualitatively accounted for by different local liposome structure at different contact points, suggesting that the intrinsic friction of the HSPC-SUV layers at this salt concentration is closer to the lower limit (μ = ~0.0006). This low friction is attributed to the hydration lubrication mechanism arising from rubbing of the 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.affiliation: Department of Materials and Interfaces, Weizmann Institute, Rehovot, Israel.
authors.forename: Ronit
authors.initials: R
authors.lastname: Goldberg
authors.forename: Avi
authors.initials: A
authors.lastname: Schroeder
authors.forename: Yechezkel
authors.initials: Y
authors.lastname: Barenholz
authors.forename: Jacob
authors.initials: J
authors.lastname: Klein
mesh_terms: D000327:Adsorption / Q000187:drug effects; D001696:Biomechanical Phenomena / Q000187:drug effects; D020285:Cryoelectron Microscopy; D009566:Nitrates / Q000494:pharmacology*; D010713:Phosphatidylcholines / Q000737:chemistry*; D011312:Pressure; D013314:Stress, Mechanical; D013499:Surface Properties / Q000187:drug effects; D053835:Unilamellar Liposomes / Q000737:chemistry*
chemical_list: D009566:Nitrates; D010713:Phosphatidylcholines; D053835:Unilamellar Liposomes; C031618:sodium nitrate