Role of the Bilayer−Bilayer Interaction on the Ripple Structure of Supported Bilayers in Solution

We have developed a method to prepare supported double bilayers made of phospholipids to facilitate in-solution studies of the bilayer−bilayer interaction of biologically relevant model membranes. It is found that a ripple structure, with an average wavelength of 27 nm, appears at room temperature in the double-bilayer region only. Some large ripples, of an average wavelength of 53 nm, are also observed on the double-bilayer region and are extremely soft and flexible. These experimental observations demonstrate that the bilayer−bilayer interaction may play a role to induce the formation of the ripple structure in our system. We also found that the formation of the ripple structure takes a few minutes or less while cooling to room temperature, and the relaxation of the ripple structure takes over 10 h at room temperature or 4 °C.