Thermodynamics of vesicle growth and instability.

We describe the growth of vesicles, due to the accretion of lipid molecules to their surface, in terms of linear irreversible thermodynamics. Our treatment differs from those previously put forward by consistently including the energy of the membrane in the thermodynamic description. We calculate the critical radius at which the spherical vesicle becomes unstable to a change of shape in terms of the parameters of the model. The analysis is carried out for the case both when the increase in volume is due to the absorption of water and when a solute is also absorbed through the walls of the vesicle.