Deformation of the equilibrium shape of a vesicle induced by enclosed flexible polymers

Using a field-theoretic approach, we study the equilibrium shape deformation of a vesicle induced by the presence of enclosed flexible polymers. Such a structure can commonly be found in drug delivery systems, endocytosis and polymer/surfactant solutions. To evaluate the total free energy of this system, we combine phase field theory for the membrane and self-consistent field theory for the polymers, and this combination allows us to calculate the bending elastic energy of the membrane, the conformation entropy of the polymers and their interactions simultaneously. Simulations on this coupled model system for axisymmetric shapes show a shape deformation of the vesicle induced by introducing polymers into it. We examined the dependence of the stability of the vesicle shape on the chain length of the polymers and the reduced volume of the vesicle. We present a simple model calculation that shows the relative stability of the prolate shape compared to the oblate shape.