  Entry of micro- or nano-sized objects into cells or vesicles made of lipid
membranes occur in many processes such as entry of viruses in host cells,
microplastics pollution, drug delivery or biomedical imaging. Here, we
investigated the microparticle crossing of lipid membranes in giant unilamellar
vesicles in the absence of strong binding interactions (e.g.
streptavidin-biotin binding). In these conditions, we observed that organic and
inorganic particles can always penetrate inside the vesicles provided that an
external picoNewton force is applied and for relatively low membrane tensions.
In the limit of a vanishing adhesion, we pointed out the role of the membrane
area reservoir and show that a force minimum exists when the particle size is
comparable to the bendocapillary length.
