Probing entropic repulsion through mesoscopic simulations

Following the publication of Freund's work on entropic pressure (Freund L., Proc. Natl. Acad. Sci. U.S.A., 110 (2013) 2047), which states that the undulation pressure for a biomembrane confined between two parallel rigid walls decays linearly with wall separation (d), different contradictory views on the pressure law evolved; some supporting Helfrich's prediction that the entropic pressure scales as $1/d^3$ . Attempts were made to resolve this stark contradiction by distinct groups of researchers. In this work, using dissipative particle dynamics simulations it has been shown for the first time that the height fluctuations are suppressed by wall confinement. An analysis of the fluctuation spectrum reveals that the entropic loss manifests as a membrane tension for a membrane that conserves its local area, and this fact is confirmed by the rise in stresses with an increase in wall confinement. Furthermore, we theorize a pressure law, which interestingly is congruous with Freund's prediction that the entropic pressure scales as $1/d$