Structure of liposomes on different surfaces

Liposomes are soft lipid bilayer vesicles that are mostly explored and utilized as dispersion. However, liposomes tend to adsorb on surfaces, acting as surface-modifiers to reduce friction for example. This insofar puzzling since due to the zwitterionic choline lipid head-group, liposomes are neutral in principle. Therefore, the understanding of the adsorption and stability of PC-liposomes on various surfaces is a fundamental question. Liposomes are spherical in solution but our results demonstrate that their structure on the surface can be altered, depending on their composition and surface properties. We used the AFM technique to probe the morphology of various types of liposomes on to a hydrophilic or a hydrophobic surface under aqueous solution. The results demonstrate that liposomes adsorb in a closely-packed configuration onto hydrophilic mica surface, driven by attraction between their exposed dipolar phosphocholine groups and the negatively charged mica surface. More surprising, HSPC liposomes were found to attach on fluorinated, highly hydrophobic, surfaces. We attribute the attraction of the liposomes on the hydrophobic surface to the formation the net negative charged of the hydrophobic surface under water. The stable hydrated liposomes on such surfaces can serve as highly effective boundary lubricants, as was demonstrated using the surface force balance technique.

References:

1. Irit Rosenhek-Goldian, Nir Kampf, Jacob Klein. Trapped Aqueous Films Lubricate Highly Hydrophobic Surfaces, ACS Nano (2018), 12, 10075.
2. Raya Sorkin, Yael Dror, Nir Kampf, Jacob Klein. Mechanical Stability and Lubrication by Phosphatidylcholine Boundary Layers in the Vesicular and in the Extended Lamellar Phases, Langmuir (2014), 30, 5005.
3. Raya Sorkin, Nir Kampf, Yael Dror, Eyal Shimoni, Jacob Klein. Origins of Extreme Boundary Lubrication by Phosphatidylcholine Liposomes, Biomaterials (2013), 34, 5465.