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Interactions between a macrophage cell line (J774A1) and surface-modified poly (D,L-lactide) nanocapsules bearing poly(ethylene glycol).

The interactions of naked and surface-modified poly(D,L-lactic acid) (PLA) nanocapsules (NC), where polyethyleneglycol (PEG) was adsorbed or covalently attached, have been studied with a macrophage-like cell line. The fluorescent oil marker, DiD, was successfully encapsulated in NCs in order to follow their interactions with cells. The cell-associated fluorescence obtained with PEG-PLA NC was about 3- to 13-fold lower than that obtained with naked-PLA NC. The effects of PEG chain length, its content as a percentage of total polymer and NC concentration in the culture medium were evaluated. PEG-PLA NC showed dramatically reduced fluorescence association with cells during an 18 h incubation compared with naked-PLA NC, showing that covalent attachment of PEG is important for the persistence of low uptake. The best results in reducing cell-associated fluorescence were obtained with a surface-modified PEG-PLA NC bearing a chain with 20000 MW. Increasing the percentage of PEG produced a reduction in marker association for a given PEG chain length. Moreover, when the PEG-containing poloxamer was simply adsorbed, marker association was dependent on the extent of dilution and the type of serum in the culture medium. Serum proteins, especially immunoglobulins, increased cell-associated fluorescence for PEG-adsorbed NC, but had very little effect on PEG-PLA NC. Marker association was only partially inhibited in the presence of cytochalasin B. The mechanisms of cell-NC interaction depended on the characteristics of the NC surface in each formulation. When the NC was physically separated from cells no diffusion of fluorescent marker in aqueous medium occurred. Nevertheless, collision-mediated transfer of DiD from NC to J774 cells was a non-negligible route of marker transfer, mainly for naked NC. However, this collision-mediated transfer was reduced for the PEG-PLA NC probably due to the restricted contact between NC and cells afforded by PEG steric hindrance at the surface.