Revisiting the entropic force between fluctuating biological membranes

The complex interplay between the various attractive and repulsive forces that mediate between biological membranes governs an astounding array of biological functions: cell adhesion, membrane fusion, self-assembly, binding-unbinding transition among others. In this work, the entropic repulsive force between membranes—which originates due to thermally excited fluctuations—is critically reexamined both analytically and through systematic Monte Carlo simulations. A recent work by Freund (2013) has questioned the validity of a well-accepted result derived by Helfrich (1978). We find that, in agreement with Freund, for small inter-membrane separations (d  ), the entropic pressure scales as p~1/dp~1/d, in contrast to Helfrich's result: p~1/d3p~1/d3. For intermediate separations, our calculations agree with that of Helfrich and finally, for large inter-membrane separations, we observe an exponentially decaying behavior.