Influence of Polylysine on the Rupture of Negatively Charged Membranes

We investigate the stability and rupture kinetics of planar lipid membranes covered with electrostatically adsorbed polyelectrolytes. After black lipid membranes were formed from negatively charged lipids, polylysines (PLs) of different molecular weights (MW) were added on one or on both sides of the membrane. The adsorption of PL was detected by recording changes of the transmembrane voltage. Rupture was induced by applying short voltage pulses across the membrane. The voltage causing breakdown of the membrane gives information on its mechanical stability. Adsorption of PL on one side of the membrane leads to an asymmetric transmembrane potential, which adds to the externally applied voltage. High MW PL decreases the critical breakdown voltage of the membrane significantly but also increases the delay time between the voltage pulse and pore formation. It is further shown that PL alters the time course of pore widening in a molecular weight-dependent manner. Low MW PL-decorated membranes and undecorated membranes show a fast rupture determined by inertia. In contrast, adsorption of high MW PLs causes a dramatic decrease of the rupture velocity. In this case, the rupture velocity is determined by viscosity. An analysis of the rupture kinetics allows an estimate of the 2D viscosity.