Recurrent catalase targeting by anti-ICAM nanocarriers provides prolonged antioxidant protection of EC. HUVECs were treated with first-dose “empty” anti-ICAM/NCs (gray bars) or anti-ICAM/NC/catalase (hatched and black bars) and 170 minutes later with a second-dose anti-ICAM/NC/catalase (black and gray bars). As determined by a cell viability assay, the first-dose anti-ICAM/NC/catalase protected cells from H₂O₂-induced injury for 2 hours, while double-dose treated cells remained protected for at least 8 hours. Data were quantified by fluorescence microscopy from at least 500 cells per condition and represent M ± SD as percent of cell survival.