Adjusting the Curvature of Supported Lipid Bilayers by Controlling Surface Interactions

Lipid membranes exert forces on their underlying substrates in order to obtain a certain equilibrium curvature. The properties of the substrate can affect many aspects of the lipid membrane structure. In order to further investigate the surface interactions governing the curvatures of lipid bilayers, we use microcantilever surfaces for measuring local mechanical forces applied by the membrane to the substrate. In particular, the surface interactions studied are changes in the electrostatic repulsions or the surface tension of palmitoyl- oleoyl- phosphatidylcholine (POPC) supported lipid bilayers. In one set of experiments, the ratio of positive to neutral charged lipids is adjusted while the curvature of the cantilever is monitored. We find that by increasing the number of positive charges in the lipid membrane, we can increase the curvature of the lipid membrane. Additionally, by introducing cholesterol into the lipid bilayer, we can also increase the curvature of the lipid membrane. This now leads us to create model membranes with a membrane stiffness that can be adjustable. To analyze the origin of microcantilever bending motion induced by a membrane formation, we report a quantitative free energy-based model to describe the artificial membrane system and its transduction into micromechanical motion.