Transmission electron micrographs of MDM. MDM were exposed for 24 h to MWCNTs (30 μg/ml) under different conditions (Curosurf pre-coating, functionalization) a.: Untreated control. b.-d.: MDM exposed to uncoated P-MWCNTs. P-MWCNT agglomerates are visible at low magnification (b); high magnification micrographs (c, d) reveal individual P-MWCNTs (black arrows). e.: MDM exposed to Curosurf pre-coated P-MWCNTs at low magnification; f, g: higher magnifications with black arrows indicating individual MWCNTs in “bird's-nest”-like arrangements. h.-j. MDM exposed to MWCNT-COOH (without Curosurf pre-coating); arrows indicate single MWCNT-COOH. Scalebar is 5 μm for a., 2 μm for b., e. and h., 500 nm for c., f. and i., and 200 nm for d., g. and j.