Mechanical equilibrium of biological membranes.

The nature of mechanical and electrical forces on biological membranes in relation to mechanical equilibrium is examined. The presence of a double layer of electric charge is shown to give rise to an effective pressure drop across a curved membrane of finite thickness. For certain geometric shapes of a membrane, the magnitude of the pressure drop due to electrostatic forces may set a limit on the hydrostatic pressure drop that the membrane can support without buckling. The results are applied to the equilibrium shape of the red blood cell.