Much of the short-range forces and structures of softly supported DMPC bila
yers has been described previously. However, one interesting feature of the
measured force-distance profile that remained unexplained is the presence
of a long-range exponentially decaying repulsive force that is not observed
between rigidly supported bilayers on solid mica substrate surfaces. This
observation is discussed in detail here based on recent static and dynamic
surface force experiments. The repulsive forces in the intermediate distanc
e regime (mica-mica separations from 15 to 40 nm) are shown to be due not t
o an electrostatic force between the bilayers but to compression (deswellin
g) of the underlying soft polyelectrolyte layer, which may be thought of as
a model cytoskeleton. The experimental data can be fit by simple theoretic
al models of polymer interactions from which the elastic properties of the
polymer layer can be deduced.