Figure 3.

Particle coatings that prevent nonspecific binding of proteins such as PEG, also provide particles with protection against nonspecific cellular internalization. Opsonized particles on the other hand are highly likely to be nonspecifically internalized by cells. Affinity ligands on the surface of particles aid in the internalization of particles within specific cells having surface receptors complimentary to the ligand. Particles that are smaller than 10 nm do not have efficient cellular internalization due to the membrane having to adopt a shape with high curvature which is not energetically favored. Particles within the 10–100 nm size range are at sizes that the cellular membrane can accommodate and wrap around in a short period. Internalization is not kinetically favored for particles that are larger than 100 nm due to the long wrapping times required to cover the significantly larger surface areas. When increasing the aspect ratio of a particle, internalization becomes less efficient as the membrane must adopt configurations with greater surface area to volume ratios which are not energetically favored