Diffuse interface model of multicomponent vesicle adhesion and fusion.

Prefusion and postfusion states of the biological fusion process between lipid bilayer vesicle membranes are studied in this paper. Based on the Helfrich-type continuum theory, a diffuse interface model is developed which describes the phase changes on the deformable vesicles via a scalar phase field function, and incorporates the adhesion effect between the different phases of the vesicles through a nonlocal interaction potential. Various equilibrium configurations in the prefusion and postfusion states are examined. The effects of spontaneous curvatures, bending, and Gaussian rigidities on the fusion process are discussed. Instead of considering only the regions in close contact as in many previous studies, the present approach allows us to include the energetic contributions from all parts of the vesicles. By carrying out simulations based on the gradient flow of the associated energy functional, we are also able to elucidate the dynamic transitions between the prefusion and postfusion states.