Studies on the transport pathway of PBCA nanoparticles in ocular tissues

The transport pathway of PBCA nanoparticles through the rabbit cornea and conjunctiva was studied using fluorescence microscopy. Nanoparticles were produced by an emulsion-polymerization process, purified by a GPC procedure, and labelled with rhodamine 6G or propidium iodide as fluorescent laser dyes. The stability of the dye label, particle diameter, and zeta potential of the nanoparticles were determined. Freshly excised rabbit cornea and conjunctiva were incubated with a suspension of labelled nanoparticles for about 30 min in standard perfusion cells. After incubation the particles were visualized, due to their fluorescent character, using laser scanning confocal microscopy. The results show a fluorescence signal inside the cells. In particular conjunctival cells showed an uptake of nanoparticles. Fluorescent particles were visually observed inside the cells, in what appeared to be vesicles or granules. Thus, either endocytosis of the nanoparticles by conjunctival tissue or lysis of the cell wall by nanoparticle metabolic degradation products, are possible explanations of the data. A fluorescence signal was also observed within corneal cells. Only a transcellular pathway was observed. A possible penetration through tight junctions was not noticed; moreover, penetration was observed only into the first two cell layers and no full tissue penetration occurred.