Mechanisms of Lipid Spreading

Recently:   

    We are generally familiar with the phenomenon of a drop of water on a surface - if the surface is hydrophilic (e.g. clean glass) it spreads out, if it's hydrophobic (e.g. Teflon) the water beads up.  Here we show that lipids, the molecules that form our cells' membranes, spread on both hydrophobic and hydrophilic surfaces.  However, using ellipsometry and fluorescence microscopy we see that their spreading morphologies and kinetics are quite different.  On hydrophobic surfaces lipids spread as monolayers, on hydrophilic ones as bilayers, and monolayers spread about twice as quickly. 

    When we consider the amount of energy released by the modification of the hydrophobic surface we find that, all things being equal, monolayers should be spreading much, much faster than we observe - as much as a thousand times faster than bilayers.  We reconcile this by noting a recent study that indicates that it may be experiencing an increased drag of a surprisingly similar order. (Soft Matter, 2007)

Soon:

    – lipid collisions create composition gradients

    – spreading bilayers may have a rolling component