Functionality of vascular networks. (A) A montage of low magnification images of mouse F4/80-stained sections. (B) Subpanels i through iii are high magnifications of correlated boxes in panel A showing that macrophages degrade most implanted AHA hydrogels within 2 weeks of implantation, replacing them with macrophages (in brown) and tissue and vessel ingrowth (unstained cells). (C) Subpanel i, isotype control and subpanel ii, mouse F4/80-stained sections after 2 weeks of AHA only (without cells) implantation. (D) A montage of low-magnification images of human CD31-stained sections. (E) Subpanels i through iii are high magnifications of correlated boxes in panel D showing that ECFCs form microvessels with a human endothelial lining (some indicated by arrows), some of which contain blood cells and participate in the host angiogenesis, as indicated by the microvasculature containing both human ECFCs (some indicated by arrows) and unstained mouse host ECs (some indicated by arrowheads), which contain blood cells. (F) In subpanel i, quantification shows size distribution of microvessels with CD31+ cells; in subpanel ii, quantification shows 40% of the vessels were solely human microvasculature, while the rest are vessels with both human ECFCs and host ECs. (G) Subpanel i indicates isotype control, and subpanel ii, human-CD31 -stained sections after 2 weeks of AHA only (without cells) implantation. Some microvessels found within the hydrogels, which contained blood cells, are positive for α-SMA, as demonstrated by panel H. A montage of low-magnification images of α-SMA–stained sections. (I) Subpanels i through iii are high magnifications of correlated boxes in panels H and J. (i) Isotype control; (ii) α-SMA–stained sections after 2 weeks of AHA only (without cells) implantation, suggesting that the vessels could recruit host SMCs to stabilize the engineered vessels. Significance levels were set at: *P < .05 and **P < .01. Dashed white lines indicate the periphery of the gels. H indicates hydrogels; M, muscle; and F, fat tissue. Scale bars are 100 μm.