Figure 7.

Illustrating the two mechanisms which are attributed to enable low friction hydration lubrication between PC-coated layers, even in the presence of HA. (a) In the case of the gel-phase lipid layers (HSPC) in HA-free water, the slip plane is the mid-plane between the vesicles. (b) When HA is added, it may adsorb on the vesicles’ surfaces to bridge the gap between them, leading to high friction at the mid-plane interface. As a result, the slip plane shifts, as shown, to the inner interfaces, where hydration lubrication is unhindered by the HA bridging. (c) In the case of the liquid-phase POPC, where the surfaces are immersed in a POPC dispersion (see text), the addition of HA leads to interactions between the lipids in solution and the polysaccharide, as indicated; this suppresses their adsorption on the surface-attached POPC bilayers and thus enables hydration lubrication between them, unhindered by any HA bridging.