Lamellar phase refers generally to packing of
polar-headed long chain nonpolar-tail
molecules in an environment of bulk polar liquid, as sheets of bilayers separated by bulk liquid. In
biophysics, polar lipids (mostly,
phospholipids, and rarely,
glycolipids) pack as a
liquid crystalline bilayer, with
hydrophobic fatty
acyl long chains directed inwardly and polar headgroups of
lipids aligned on the outside in contact with water, as a 2-dimensional flat sheet surface. Under
transmission electron microscope (TEM), after staining with polar headgroup reactive chemical
osmium tetroxide, lamellar lipid phase appears as two thin parallel dark staining lines/sheets, constituted by aligned polar headgroups of lipids. 'Sandwiched' between these two parallel lines, there exists one thicker line/sheet of non-staining closely packed layer of long lipid fatty acyl chains. This TEM-appearance became famous as Robertson's unit membrane - the basis of all
biological membranes, and structure of
lipid bilayer in
unilamellar liposomes. In multilamellar
liposomes, many such lipid bilayer sheets are layered concentrically with water layers in between.