Experimental Testing of Models to Determine Bending Modulus in Sperm Acrosomal Membrane Using Cell-Sized Vesicles of Controlled Mechanical Properties

. Abstract We propose to use a novel combination of atomic force microscopy (AFM) and micropipette chniques to study the mechanical properties of biological membranes, a materials problem that is of onsiderable interest to the biophysics community. The type of membrane vesicle to be studied is a ood model system for the membranes of living cells, but unlike living cells, such as the sperm cell, the embrane mechanical properties can be adjusted in a predictable way by the lipid, cholesterol and rotein content and the geometry is simpler. The sperm cell has been the subject of much research cluding an on-going Lawrence Livermore National Laboratory (LLNL) LDRD ERI Project as well as ther LLNL research at BBRP, and the findings of the vesicle experiments will be relevant. The use of e micropipette to position the vesicle and to adjust its tension will allow more cogent AFM forceisplacement measurements. The force-displacement measurements will not only serve as a proof-ofrinciple of a new technique for the characterization of biomembranes, but they will offer a means to alidate the membrane mechanics model developed in the LDRD ERI Project, "Probing the Properties f Cells and Cell Surfaces with the Atomic Force Microscope".