Within a few minutes following the addition of LCNPs to DOPC GUVs, the majority of vesicles developed lipid tubes protruding from the membrane. These tubes varied in size and direction (into the extra-vesicular medium or the interior lumen). Thin cylinder-like (Fig. ) and thick unduloid-like (Fig. ) external nanotubes were observed to protrude from the parent GUV toward the extra-vesicular medium. We also observed internal lipid nanotubes originating at the surfaces of the GUV and protruding into the vesicle lumen (Fig. ). Both external and internal tubes are undulating and wavy, while some of them form an undulatory pearling pattern. Dynamic fluctuations in all morphologies of both external and internal tubes were observed, suggesting that the incorporation of MO into the DOPC membrane facilitates the membrane to be highly flexible. In addition, the fluorescence of water-soluble membrane permeability probes in the internal nanotubes indicates that they have an open neck that connects to the extra-vesicular medium (Fig. ).