Entropy-driven tension and bending elasticity in condensed-fluid membranes

Sensitive micropipet methods have been used to measure the relation between tension and the projected surface area in fluid membranes of vesicles over a 4-order-of-magnitude range in tension (10^-3--10 dyn/cm). In the low-tension regime (0. 5 dyn/cm), the data confirm the prediction of equilibrium theory that the projected area should increase logarithmically with tension as shape fluctuations become progressively restricted. The slope of log (tension) versus area dilation yields and the elastic bending modulus of the membrane. In the high-tension regime, the projected area crosses over to vary linearly with tension due to direct expansion of area per molecule.