  Endocytosis is a key cellular process involved in the uptake of nutrients,
pathogens or the diagnosis and therapy of diseases. Most studies have focused
on spherical objects, whereas biologically relevant shapes can be highly
anisotropic. In this letter, we use an experimental model system based on Giant
Unilamellar Vesicles (GUVs) and dumbbell-shaped colloidal particles to mimic
and investigate the first stage of the passive endocytic process: engulfment of
an anisotropic object by the membrane. Our model has specific ligand-receptor
interactions realized by mobile receptors on the vesicles and immobile ligands
on the particles. Through a series of experiments, theory and molecular
dynamics simulations, we quantify the wrapping process of anisotropic dumbbells
by GUVs and identify distinct stages of the wrapping pathway. We find that the
strong curvature variation in the neck of the dumbbell as well as membrane
tension are crucial in determining both the speed of wrapping and the final
states.
