Ultrastructural comparison between the vessel make-up in Matrigel plugs injected with hMAPCs in arterial or standard media. Ultrastructural analysis of Matrigel plugs injected subcutaneously with hMAPCs combined with arterial (A-B) or standard media (C-D). Semithin sections of a Matrigel plug (A,C) and an ultrathin section of an artery-like tube (B) with a detail showing an SMC around an EC (inset) and a veinlike tube (D). “L” indicates the vessel lumen. Scale bars: 10 μm (A,C); 2.5 μm (B); 2 μm (D); 1 μm (B, inset).