Rheology of giant vesicles: a micropipette study.

We develop a micropipette rheometer to study the effect of oscillatory shear flow on the spontaneous fluctuations of phospholipid bilayers. Our results on giant vesicles show that oscillatory shear flow leads to a suppression of membrane fluctuations. They also imply that the Helfrich equation is modified in the presence of the flow. This equation, a fundamental constitutive relation between the amount of area stored in the fluctuations and the membrane tension, must be supplemented under oscillatory shear by a flow excess function that we determine.