Effect of the HIV-1 fusion peptide on the mechanical properties and leaflet coupling of lipid bilayers Supplementary material

The software for analysis of micropipette aspiration images is written in Python using the package wxPython for graphical user interface, PIL for image loading, matplotlib for outputs plotting and SciPy for numerical analysis. Since the studied system, vesicle aspirated in a cylindrical pipette, is axis-symmetric, the exact geometry is defined by a few parameters only and there is no need of finding the exact contour of the vesicle. The position of the pipette walls defining the internal diameter of the capillary is obtained from an intensity line profile perpendicular to the pipette axis; see blue line in Figure S1. The axis of the vesicle-pipette system is calculated and the brightness line profile along this axis is extracted; see yellow line in Figure S1. The latter provides the following characteristic features defining the system geometry: the position of the pipette tip, the position of the aspirated part of the vesicle and the position of the outside part of the vesicle. To exclude errors caused by possible flickering of the membrane several (usually 5) images were recorded for each pressure for further averaging during analysis. The waiting time between a pressure change and image acquisition is about 1 min, which for the soft membranes explored in this work is sufficient to establish equilibrium.