Uptake of CNT by macrophages. Light micrographs (A-G) of THP-1 cells untreated (D) or treated with the CNT panel. NPCB (A), NTshort (E), NTtang1 (B) and NTtang2 (F) appear as aggregates within the cells (white arrows). However NTlong1 (C) and NTlong2 (G) appear to be protruding from the cells (white arrows). Scale bar indicates 20 μm. SEM images (H-K) show an untreated THP-1 cell (H) and THP-1 cells treated with NPCB (I), NTshort (J) and NTlong2 (K). No particles can be seen associated with the cell surface or protruding from the cells in I or J however the fibre from the NTlong2 (K) sample appear on the surface of the cells and also protruding from the cell. Scale bar indicates 10 μm.